SAFETY MONITORING SYSTEM
Safety monitoring is concerned with the measurement and evaluation of safety performance. It may take the following forms:
1. Safety surveys: This is a detailed examination of a number of critical areas of operation or, perhaps, an in-depth study of all health and safety related activities in a workplace.
2. Safety tours: These are an unscheduled examination of a working area, frequently undertaken as a group exercise (eg foreman, safety representative and safety committee member), to assess general compliance with safety requirements (eg fire protection measures and use of machinery safety devices).
3. Safety audits: A safety audit fundamentally subjects each area of an organisation’s activities to a systematic critical examination with the object of minimising injury and loss. It generally takes the form of a series of questions directed to examining factors such as the operation of safe systems of work, compliance with the Statement of Health and Safety Policy and the operation of hazard reporting systems.
4. Safety inspections: A scheduled inspection of a premises or working area to assess levels of legal compliance and observation of company safety procedures. Safety inspections are frequently undertaken by company safety specialists and trade union safety representatives.
5. Safety sampling: A system designed to measure by random sampling the accident potential in a workplace or process by identifying defects in safety performance or omissions. Observers follow a prescribed route through the working area noting deficiencies in performance, eg concerning the wearing of personal protective equipment or the use of correct manual handling techniques.
In some cases, individual topics in the safety sampling exercise are ranked according to importance with a maximum number of points achievable. At the end of the exercise a total score is identified which gives an indication of the performance level at that point in time.
6. Hazard and operability studies: Such studies incorporate the application of formal critical examination to the process and engineering intentions regarding new facilities. The principal aim of such a study is to assess the hazard potential arising from the incorrect operation of equipment and the consequential effects on the facility. Such an operation enables remedial action to be taken at a very early stage.
7. Damage control: Levels of damage are an indication of future accident potential. Damage control operates on the philosophy that non-injury accidents are just as important as injury accidents. The elimination of the causes of accidents resulting in damage to property, plant and products frequently results in a reduction in injury accidents.
Showing posts with label Safety. Show all posts
Showing posts with label Safety. Show all posts
ACCIDENT PREVENTION STRATEGIES FOR AND BY MANAGERS AND SUPERVISORS
MEANS OF ACCIDENT PREVENTION THAT CAN BE INITIATED BY MANAGERS
As a Manager, there are means and ways that can prevent accidents that you may initiate.
Means of preventing accidents
Strategies for preventing accidents take many forms. These include:
1. Prohibition: Some processes and practices may be so inherently dangerous that the only way to prevent accidents is by management placing a total prohibition on that activity. This may take the form of a prohibition on the use of a particular substance, such as an identified toxic substance, or of prohibiting people from carrying out unsafe practices, such as riding on the tines of a fork-lift truck, climbing over moving conveyors or working on roofs without crawlboards.
2. Substitution: The substitution of a less dangerous material or system of work will, in many cases, reduce accident potential. Typical examples are the introduction of remote control handling facilities for direct manual handling operations, the substitution of toluene, a much safer substance, for benzene, and the use of non-asbestos substitutes for boiler and pipe lagging.
3. Change of process: Design or process engineering can usually change a process to ensure better operator protection. Safety aspects of new systems should be considered in the early stages of projects.
4. Process control: This can be achieved through the isolation of a particular process, the use of ‘permit to work’ systems, mechanical or remote control handling systems, restriction of certain operations to highly trained and competent operators, and the introduction of dust and fume arrestment plant.
5. Safe systems of work: Formally designated safe systems of work, with high levels of training, supervision and control, are an important strategy in accident prevention (see below).
6. Personal protective equipment: This entails the provision of items such as safety boots, goggles, aprons, gloves, etc, but is limited in its application as a safety strategy
Safe systems of work
A safe system of work is defined as ‘the integration of men, machinery and materials in the correct environment to provide the safest possible working conditions in a particular working area’.
A safe system of work should incorporate the following features:
(a) a correct sequence of operations;
(b) a safe working area layout;
(c) a controlled environment in terms of temperature, lighting, ventilation, dust control, humidity control, sound pressure levels and radiation hazards; and
(d) clear specification of safe practices and procedures for the task in question.
Safe systems of work are generally designed through the technique of ‘job safety analysis’.
HEALTH EFFECTS TO EXPOSURE OF INDUSTRIAL CHEMICALS BASIC INFORMATION AND TUTORIALS
WHAT ARE EFFECTS TO EXPOSURE OF CHEMICALS?
Toxicology and Health Information
The consequences of exposure, if any, by inhalation, skin or eye contact, or ingestion are outlined in this section. The signs, symptoms and effects that the exposure could produce are described so that any exposure would be recognized as quickly as possible and the appropriate action taken.
The organs that are more susceptible to attack are referred to as target organs. The effects and damage that exposure could produce on these organs are given together with the symptoms. Some of the terms used that may be less familiar or which may have a specific inference in MSDS are defined below:
• Acute Effect: An adverse effect on a human or animal resulting from a single exposure with symptoms developing almost immediately after exposure. The effect is often of short duration.
• Chronic Effect: An adverse effect on a human or animal body resulting from repeated low level exposure, with symptoms that develop slowly over a long period of time or that reoccur frequently.
• Corrosive: A liquid or solid that causes visible destruction or irreversible alterations in human or animal tissue.
• Irritation: An inflammatory response or reaction of the eye, skin or respiratory system.
• Allergic Sensitization: A process whereby on first exposure a substance causes little or no reaction in humans or test animals, but which on repeated exposure may cause a marked response not necessarily limited to the contact site.
Skin sensitization is the most common form of sensitization in the industrial setting, although respiratory sensitization is also known to occur.
• Teratogen: A substance or agent to which exposure of a pregnant female can result in malformations (birth defects) to the skeleton and or soft tissue of the fetus.
• Mutagen: A substance or agent capable of altering the genetic material in a living organism.
• Carcinogen: A substance or agent capable of causing or producing cancer in humans or animals. Authorities/ organizations that have evaluated whether or not a substance is a carcinogen are the International Agency for Research on Cancer (IARC), the U.S. National Toxicology Program (NTP) and OSHA.
• Target Organ Effects: Chemically-caused effects upon organs and systems such as the liver, kidneys, nervous system, lungs, skin, and eyes from exposure to a material.
Toxicology and Health Information
The consequences of exposure, if any, by inhalation, skin or eye contact, or ingestion are outlined in this section. The signs, symptoms and effects that the exposure could produce are described so that any exposure would be recognized as quickly as possible and the appropriate action taken.
The organs that are more susceptible to attack are referred to as target organs. The effects and damage that exposure could produce on these organs are given together with the symptoms. Some of the terms used that may be less familiar or which may have a specific inference in MSDS are defined below:
• Acute Effect: An adverse effect on a human or animal resulting from a single exposure with symptoms developing almost immediately after exposure. The effect is often of short duration.
• Chronic Effect: An adverse effect on a human or animal body resulting from repeated low level exposure, with symptoms that develop slowly over a long period of time or that reoccur frequently.
• Corrosive: A liquid or solid that causes visible destruction or irreversible alterations in human or animal tissue.
• Irritation: An inflammatory response or reaction of the eye, skin or respiratory system.
• Allergic Sensitization: A process whereby on first exposure a substance causes little or no reaction in humans or test animals, but which on repeated exposure may cause a marked response not necessarily limited to the contact site.
Skin sensitization is the most common form of sensitization in the industrial setting, although respiratory sensitization is also known to occur.
• Teratogen: A substance or agent to which exposure of a pregnant female can result in malformations (birth defects) to the skeleton and or soft tissue of the fetus.
• Mutagen: A substance or agent capable of altering the genetic material in a living organism.
• Carcinogen: A substance or agent capable of causing or producing cancer in humans or animals. Authorities/ organizations that have evaluated whether or not a substance is a carcinogen are the International Agency for Research on Cancer (IARC), the U.S. National Toxicology Program (NTP) and OSHA.
• Target Organ Effects: Chemically-caused effects upon organs and systems such as the liver, kidneys, nervous system, lungs, skin, and eyes from exposure to a material.
PORTABLE FIRE EXTINGUISHER SAFETY TIPS BASIC INFORMATION AND TUTORIALS
SAFETY TIPS ON THE USE OF PORTABLE FIRE EXTINGUISHERS
A portable fire extinguisher can save lives and property by putting out a small fire or containing it until the fire department arrives; but portable extinguishers have limitations. Because fire grows and spreads so rapidly, the number one priority for residents is to get out safely.
Safety tips
Use a portable fire extinguisher when the fire is confined to a small area, such as a wastebasket, and is not growing; everyone has exited the building; the fire department has been called or is being called; and the room is not filled with smoke.
To operate a fire extinguisher, remember the word PASS:
- Pull the pin. Hold the extinguisher with the nozzle pointing away from you, and release the locking mechanism.
- Aim low. Point the extinguisher at the base of the fire.
- Squeeze the lever slowly and evenly.
- Sweep the nozzle from side-to-side.
For the home, select a multi-purpose extinguisher (can be used on all types of home fires) that is large enough to put out a small fire, but not so heavy as to be difficult to handle.
Choose a fire extinguisher that carries the label of an independent testing laboratory.
Read the instructions that come with the fire extinguisher and become familiar with its parts and operation before a fire breaks out.
Install fire extinguishers close to an exit and keep your back to a clear exit when you use the
device so you can make an easy escape if the fire cannot be controlled. If the room fills with smoke, leave immediately.
Know when to go.
Fire extinguishers are one element of a fire response plan, but the primary element is safe escape. Every household should have a home fire escape plan and working smoke alarms.
A portable fire extinguisher can save lives and property by putting out a small fire or containing it until the fire department arrives; but portable extinguishers have limitations. Because fire grows and spreads so rapidly, the number one priority for residents is to get out safely.
Safety tips
Use a portable fire extinguisher when the fire is confined to a small area, such as a wastebasket, and is not growing; everyone has exited the building; the fire department has been called or is being called; and the room is not filled with smoke.
To operate a fire extinguisher, remember the word PASS:
- Pull the pin. Hold the extinguisher with the nozzle pointing away from you, and release the locking mechanism.
- Aim low. Point the extinguisher at the base of the fire.
- Squeeze the lever slowly and evenly.
- Sweep the nozzle from side-to-side.
For the home, select a multi-purpose extinguisher (can be used on all types of home fires) that is large enough to put out a small fire, but not so heavy as to be difficult to handle.
Choose a fire extinguisher that carries the label of an independent testing laboratory.
Read the instructions that come with the fire extinguisher and become familiar with its parts and operation before a fire breaks out.
Install fire extinguishers close to an exit and keep your back to a clear exit when you use the
device so you can make an easy escape if the fire cannot be controlled. If the room fills with smoke, leave immediately.
Know when to go.
Fire extinguishers are one element of a fire response plan, but the primary element is safe escape. Every household should have a home fire escape plan and working smoke alarms.
WORKING ON OR NEAR DE-ENERGIZED EQUIPMENT AS SUGGESTED BY IEEE STD 902-1998
WHY WE SHOULD WORK ON NEAR OR DE-ENERGIZED EQUIPMENT?
Working on or near de-energized equipment.
The definition of the term de-energized can be found in IEEE Std 100-1996 and in several other documents. It is defined as "free from any electrical connection to a source of potential difference and from electric charge; not having a potential different from that of the earth".
At first thought, some people might think that they are safe if the electrical equipment on which they are going to work is de-energized. However, things are not always as they appear.
The unexpected happens. A person should think, "What if...?." What if the wrong disconnect switch was opened? Or, since you can't watch the switch and work at the same time, what if someone turns the switch back on while you are busy working?
What if a source of voltage from another circuit somehow gets accidentally connected onto the conductors on which you are going to work? What if a very large induced voltage is present? The point is that there are several things to consider to ensure a person's safety while working. De energizing is only one part of creating an electrically safe work condition.
Establishing an electrically safe work condition
In the past, the methods that electrical personnel followed to protect themselves were lumped into a term called clearance procedures. In some cases, clearance simply meant permission to work on a particular system, whether it was energized or not.
In other cases, clearance meant taking measures to ensure that equipment is de-energized, and to reinforce those measures with formal safeguards against altering that de-energized status for as long as clearance is required. The latter use of the word clearance is closer to the hazardous energy control requirements in place today.
The term clearance is falling out of use in modern electrical safety terminology because it does not mean safety. Clearance (for work) is defined in 29 CFR 1910.269 as "authorization to perform specified work or permission to enter a restricted area."
Today, for safety purposes, the phrase "establish an electrically safe work condition" is preferred. An electrically safe work condition is defined in Part II of NFPA 70E- 1995. Section 2-3.1.3 of that document states
An electrically safe work condition shall be achieved and verified by the following process:
a) Determine all possible sources of electrical supply to the specifc equipment. Check applicable up-to-date drawings, diagrams, and identifcation tags.
b) After properly interrupting the load current, open the disconnecting device(s) for each source.
c) Where it is possible, visually verify that all blades of the disconnecting devices are fully open, or that drawout type circuit breakers are withdrawn to the fully disconnected position.
d) Apply lockout/tagout devices in accordance with a documented and established policy.
e) Use an adequately rated voltage detector to test each phase conductor or circuit part to verify that it is de-energized. Before and after each test, determine that the voltage detector is operating satisfactorily.
f) Where the possibility of induced voltages or stored electrical energy exists, ground the phase conductors or circuit parts before touching them. Where it could be reasonably anticipated that the conductors or circuit parts being de-energized could contact other exposed energized conductors or circuit parts, apply ground connecting devices rated for the available fault duty.
When nondrawout, molded-case circuit breakers are being used as the disconnecting device mentioned in item b), visual verification of an open circuit, as suggested in item c), cannot be made.
One technique that could be used to verify true opening is to have a voltmeter, or other voltage indicating device, safely applied somewhere away from the breaker enclosure itself on the load side of the breaker before the breaker is opened.
Always try to place the voltmeter at a point where exposure to energized conductors is minimized. Then, have someone watch the meter as the breaker is being opened. Simultaneous opening of the breaker and disappearance of voltage is generally a good indicator of disconnection.
If that can't be done, the next best way is to measure load-side voltage (using safe practices and appropriate protective and test equipment), remove the meter, open the breaker, and measure again immediately. With multiple pole systems, all load-side poles should be verified to have voltage prior to disconnection.
Again, apply a voltmeter to one of the poles. After the breaker is opened and the first pole is verified, move the meter, as safely and quickly as possible, to verify deenergization of the other poles.
Working on or near de-energized equipment.
The definition of the term de-energized can be found in IEEE Std 100-1996 and in several other documents. It is defined as "free from any electrical connection to a source of potential difference and from electric charge; not having a potential different from that of the earth".
At first thought, some people might think that they are safe if the electrical equipment on which they are going to work is de-energized. However, things are not always as they appear.
The unexpected happens. A person should think, "What if...?." What if the wrong disconnect switch was opened? Or, since you can't watch the switch and work at the same time, what if someone turns the switch back on while you are busy working?
What if a source of voltage from another circuit somehow gets accidentally connected onto the conductors on which you are going to work? What if a very large induced voltage is present? The point is that there are several things to consider to ensure a person's safety while working. De energizing is only one part of creating an electrically safe work condition.
Establishing an electrically safe work condition
In the past, the methods that electrical personnel followed to protect themselves were lumped into a term called clearance procedures. In some cases, clearance simply meant permission to work on a particular system, whether it was energized or not.
In other cases, clearance meant taking measures to ensure that equipment is de-energized, and to reinforce those measures with formal safeguards against altering that de-energized status for as long as clearance is required. The latter use of the word clearance is closer to the hazardous energy control requirements in place today.
The term clearance is falling out of use in modern electrical safety terminology because it does not mean safety. Clearance (for work) is defined in 29 CFR 1910.269 as "authorization to perform specified work or permission to enter a restricted area."
Today, for safety purposes, the phrase "establish an electrically safe work condition" is preferred. An electrically safe work condition is defined in Part II of NFPA 70E- 1995. Section 2-3.1.3 of that document states
An electrically safe work condition shall be achieved and verified by the following process:
a) Determine all possible sources of electrical supply to the specifc equipment. Check applicable up-to-date drawings, diagrams, and identifcation tags.
b) After properly interrupting the load current, open the disconnecting device(s) for each source.
c) Where it is possible, visually verify that all blades of the disconnecting devices are fully open, or that drawout type circuit breakers are withdrawn to the fully disconnected position.
d) Apply lockout/tagout devices in accordance with a documented and established policy.
e) Use an adequately rated voltage detector to test each phase conductor or circuit part to verify that it is de-energized. Before and after each test, determine that the voltage detector is operating satisfactorily.
f) Where the possibility of induced voltages or stored electrical energy exists, ground the phase conductors or circuit parts before touching them. Where it could be reasonably anticipated that the conductors or circuit parts being de-energized could contact other exposed energized conductors or circuit parts, apply ground connecting devices rated for the available fault duty.
When nondrawout, molded-case circuit breakers are being used as the disconnecting device mentioned in item b), visual verification of an open circuit, as suggested in item c), cannot be made.
One technique that could be used to verify true opening is to have a voltmeter, or other voltage indicating device, safely applied somewhere away from the breaker enclosure itself on the load side of the breaker before the breaker is opened.
Always try to place the voltmeter at a point where exposure to energized conductors is minimized. Then, have someone watch the meter as the breaker is being opened. Simultaneous opening of the breaker and disappearance of voltage is generally a good indicator of disconnection.
If that can't be done, the next best way is to measure load-side voltage (using safe practices and appropriate protective and test equipment), remove the meter, open the breaker, and measure again immediately. With multiple pole systems, all load-side poles should be verified to have voltage prior to disconnection.
Again, apply a voltmeter to one of the poles. After the breaker is opened and the first pole is verified, move the meter, as safely and quickly as possible, to verify deenergization of the other poles.
ELECTRICAL SAFETY HAZARDS THAT NEEDS TO BE IDENTIFIED ON ELECTRICAL SAFETY WORKS
WHAT ARE THE DIFFERENT ELECTRICAL SAFETY HAZARDS?
Identifying electrical safety hazards.
When electrical systems break down what are the primary hazards and what are the consequences to personnel? Electric shock Exposure to Arc-Flash Exposure to Arc-Blast Exposure to excessive light and sound energies
Secondary hazards may include burns, the release of toxic gases, molten metal, airborne debris and shrapnel. Unexpected events can cause startled workers to lose their balance and fall from ladders or jerk their muscles possibly causing whiplash or other injuries.
Electric Shock
When personnel come in contact with energized conductors they receive a shock with current flowing through their skin, muscles and vital organs. The severity of the shock depends on the current’s path through the body, the current intensity, and the duration of the contact.
They may only experience a mild tingling sensation or it could result in serious injury or death. As voltage levels increase, the effects of electric shock escalate. Current may also cause an erratic heartbeat known as ventricular fibrillation.
If fibrillation occurs even briefly and goes untreated, the effects are usually fatal. A clear understanding of how electric current travels through the body can help minimize injury if such contact occurs. The table below outlines the effects that various values of electrical current have on the human body.
There are three basic pathways electric current travels through the body;
1) Touch Potential (hand/hand path)
2) Step Potential (foot/foot path)
3) Touch/Step Potential (hand/foot path)
1) In a touch potential contact, current travels from one hand through the heart and out through the other hand. Because the heart and lungs are in the path of current, ventricular fibrillation, difficulty in breathing, unconsciousness, or death may occur.
2) In a step potential contact, current travels from one foot through the legs, and out of the other foot. The heart is not in the direct path of current but the leg muscles may contract, causing the victim to collapse or be momentarily paralyzed.
3) In a touch/step potential contact, current travels from one hand, through the heart, down the leg, and out of the foot. The heart and lungs are in the direct path of current so ventricular fibrillation, difficulty in breathing, collapse, unconsciousness, or death may occur.
Even though there may be no external signs from the electrical shock, internal tissue or organ damage may have occurred. Signs of internal damage may not surface immediately; and when it does, it may be too late.
Any person experiencing any kind of electrical shock should seek immediate medical attention. Using the correct personal protective equipment (PPE) and following safe work practices will minimize risk of electrical shock hazards.
Arc-Flash and Arc Blasts
An Arc-Flash is an unexpected sudden release of heat and light energy produced by electricity traveling through air, usually caused by accidental contact between live conductors. Temperatures at the arc terminals can reach or exceed 35,000 degrees Fahrenheit (F), or four times the temperature of the sun’s surface.
The air and gases surrounding the arc are instantly heated and the conductors are vaporized causing a pressure wave called an Arc Blast. Personnel directly exposed to an Arc-Flash and Arc-Blast events are subject to third degree burns, possible blindness, shock, blast effects and hearing loss. Even relatively small arcs can cause severe injury.
The secondary effect of arcs includes toxic gases, airborne debris, and potential damage to electrical equipment, enclosures and raceways. The high temperatures of the arc and the molten and vaporized metals quickly ignite any flammable materials.
While these fires may cause extensive property damage and loss of production, the hazards to personnel are even greater. Any energized electrical conductor that makes accidental contact with another conductor or with ground will produce an Arc-Flash.
The arcing current will continue to flow until the overcurrent protective device used upstream opens the circuit or until something else causes the current to stop flowing. The arc current can vary up to the maximum available bolted fault current
Identifying electrical safety hazards.
When electrical systems break down what are the primary hazards and what are the consequences to personnel? Electric shock Exposure to Arc-Flash Exposure to Arc-Blast Exposure to excessive light and sound energies
Secondary hazards may include burns, the release of toxic gases, molten metal, airborne debris and shrapnel. Unexpected events can cause startled workers to lose their balance and fall from ladders or jerk their muscles possibly causing whiplash or other injuries.
Electric Shock
When personnel come in contact with energized conductors they receive a shock with current flowing through their skin, muscles and vital organs. The severity of the shock depends on the current’s path through the body, the current intensity, and the duration of the contact.
They may only experience a mild tingling sensation or it could result in serious injury or death. As voltage levels increase, the effects of electric shock escalate. Current may also cause an erratic heartbeat known as ventricular fibrillation.
If fibrillation occurs even briefly and goes untreated, the effects are usually fatal. A clear understanding of how electric current travels through the body can help minimize injury if such contact occurs. The table below outlines the effects that various values of electrical current have on the human body.
There are three basic pathways electric current travels through the body;
1) Touch Potential (hand/hand path)
2) Step Potential (foot/foot path)
3) Touch/Step Potential (hand/foot path)
1) In a touch potential contact, current travels from one hand through the heart and out through the other hand. Because the heart and lungs are in the path of current, ventricular fibrillation, difficulty in breathing, unconsciousness, or death may occur.
2) In a step potential contact, current travels from one foot through the legs, and out of the other foot. The heart is not in the direct path of current but the leg muscles may contract, causing the victim to collapse or be momentarily paralyzed.
3) In a touch/step potential contact, current travels from one hand, through the heart, down the leg, and out of the foot. The heart and lungs are in the direct path of current so ventricular fibrillation, difficulty in breathing, collapse, unconsciousness, or death may occur.
Even though there may be no external signs from the electrical shock, internal tissue or organ damage may have occurred. Signs of internal damage may not surface immediately; and when it does, it may be too late.
Any person experiencing any kind of electrical shock should seek immediate medical attention. Using the correct personal protective equipment (PPE) and following safe work practices will minimize risk of electrical shock hazards.
Arc-Flash and Arc Blasts
An Arc-Flash is an unexpected sudden release of heat and light energy produced by electricity traveling through air, usually caused by accidental contact between live conductors. Temperatures at the arc terminals can reach or exceed 35,000 degrees Fahrenheit (F), or four times the temperature of the sun’s surface.
The air and gases surrounding the arc are instantly heated and the conductors are vaporized causing a pressure wave called an Arc Blast. Personnel directly exposed to an Arc-Flash and Arc-Blast events are subject to third degree burns, possible blindness, shock, blast effects and hearing loss. Even relatively small arcs can cause severe injury.
The secondary effect of arcs includes toxic gases, airborne debris, and potential damage to electrical equipment, enclosures and raceways. The high temperatures of the arc and the molten and vaporized metals quickly ignite any flammable materials.
While these fires may cause extensive property damage and loss of production, the hazards to personnel are even greater. Any energized electrical conductor that makes accidental contact with another conductor or with ground will produce an Arc-Flash.
The arcing current will continue to flow until the overcurrent protective device used upstream opens the circuit or until something else causes the current to stop flowing. The arc current can vary up to the maximum available bolted fault current
SAFETY ON WORKING OVER OVERHEAD POWER LINES BASIC INFORMATION
Statistics on accidental electrocution show that quite a few of them involve work on or near overhead electric lines. Work on overhead lines is only to be done by qualified electrical lineworkers.
Many times, due to the need to maintain service continuity, the lines are kept energized while work is being performed on them. Lineworkers must be well trained to perform such tasks using safe practices, appropriate personal protective equipment, and insulated tools.
When planning for work on overhead lines, however, one should always try to make the safest choice, which is to put the lines in an electrically safe work condition. Grounding the lines to create an equipotential zone within which a lineworker can be safe is advisable while working on overhead lines.
Work on or near overhead lines requires unique safety analysis because
a) The overhead lines can change position due to wind or other disturbances.
b) A person working on the lines is not usually in the most stable position.
c) The voltages and energy levels involved with overhead lines are often large.
Working near overhead lines, or near vehicles and equipment that could contact overhead lines, requires electrical safety training even for nonelectrical personnel.
The National Electrical Safety Code¨ (NESC¨) (Accredited Standards Committee C2-1997) is a key document that gives significant detail regarding the safety rules for the installation and maintenance of overhead electric supply and communication lines. NFPA 70E-1995 also mentions safety around overhead lines in Part II.
The OSHA regulations that cover work on and near overhead electric lines are 29 CFR 1910.269 and 29 CFR 1910.333 for general industry, and 29 CFR 1926.955 for the construction industry.
Many times, due to the need to maintain service continuity, the lines are kept energized while work is being performed on them. Lineworkers must be well trained to perform such tasks using safe practices, appropriate personal protective equipment, and insulated tools.
When planning for work on overhead lines, however, one should always try to make the safest choice, which is to put the lines in an electrically safe work condition. Grounding the lines to create an equipotential zone within which a lineworker can be safe is advisable while working on overhead lines.
Work on or near overhead lines requires unique safety analysis because
a) The overhead lines can change position due to wind or other disturbances.
b) A person working on the lines is not usually in the most stable position.
c) The voltages and energy levels involved with overhead lines are often large.
Working near overhead lines, or near vehicles and equipment that could contact overhead lines, requires electrical safety training even for nonelectrical personnel.
The National Electrical Safety Code¨ (NESC¨) (Accredited Standards Committee C2-1997) is a key document that gives significant detail regarding the safety rules for the installation and maintenance of overhead electric supply and communication lines. NFPA 70E-1995 also mentions safety around overhead lines in Part II.
The OSHA regulations that cover work on and near overhead electric lines are 29 CFR 1910.269 and 29 CFR 1910.333 for general industry, and 29 CFR 1926.955 for the construction industry.
TEMPORARY PERSONAL PROTECTIVE GROUNDING BASICS
What is temporary personal protective grounding?
Sometimes, additional measures are desirable to provide an extra margin of safety assurance. Temporary personal protective grounds are used when working on de-energized electrical conductors to minimize the possibility of accidental re-energization from unexpected sources. Sometimes these are called safety grounds or equipotential grounding.
Induced voltages, capacitive recharging, and accidental contact with other circuits can occur. Depending on the electrical energy available, these occurrences could cause injury or death.
More often, however, they only cause reßexive actions. For example, although most induced voltages will not normally cause serious injury themselves, they could cause a person to jump backward suddenly, possibly tripping against something or falling to the floor.
Temporary protective grounding devices should be applied where such conditions might occur. Temporary personal protective grounds should be applied at possible points of re-energization. They can also be applied in such a way as to establish a zone of equipotential around a person.
When these grounds are used, they shall be connected tightly, since they establish a deliberate fault point in the circuit. If current does somehow get onto the circuit, the grounds shall stay connected securely until a protective device clears the circuit.
It is difficult to set firm criteria for when temporary personal protective grounds are needed. Blanket requirements are usually established. Many times, it is a decision made in the field by the person performing the work.
When there is uncertainty about exposure, it is wise to add this extra protection. Many industrial facilities and utilities require temporary personal protective grounding for all aerial power line work and for all work on power systems over 600 V because of the increased exposure these systems often have due to their length and location.
Temporary personal protective grounding can also be used as the additional safety measure required when hazardous electrical energy control must be performed using a tag only. Temporary personal protective grounding devices should meet the specifications in ASTM F855-96 and should be sized for the maximum available current of any possible event.
Temporary personal protective grounds should only be installed after all other conditions of an electrically safe work condition have been established. Because the unexpected can happen at any time, however, the installation and removal of temporary grounding devices should be performed, by procedure, as the conductors are energized.
When installed inside equipment enclosures, temporary grounds should be lengthy enough to extend outside of the equipment so that they can be easily seen. If they cannot extend out, they should be made highly visible. Brightly colored tapes are helpful identifiers. Once they are installed, bare-hand work could be permitted.
It should be quite obvious that all personal protective grounds must be removed prior to reenergization. Identification and accountability controls may be necessary on large construction or maintenance jobs. The installation and removal of these grounding devices can be controlled by permit in order to avoid re-energizing equipment into a faulted condition.
The integrity of personal protective grounds should be maintained through the use of periodic inspection and testing. It is a good idea to document this inspection and testing.
Sometimes, additional measures are desirable to provide an extra margin of safety assurance. Temporary personal protective grounds are used when working on de-energized electrical conductors to minimize the possibility of accidental re-energization from unexpected sources. Sometimes these are called safety grounds or equipotential grounding.
Induced voltages, capacitive recharging, and accidental contact with other circuits can occur. Depending on the electrical energy available, these occurrences could cause injury or death.
More often, however, they only cause reßexive actions. For example, although most induced voltages will not normally cause serious injury themselves, they could cause a person to jump backward suddenly, possibly tripping against something or falling to the floor.
Temporary protective grounding devices should be applied where such conditions might occur. Temporary personal protective grounds should be applied at possible points of re-energization. They can also be applied in such a way as to establish a zone of equipotential around a person.
When these grounds are used, they shall be connected tightly, since they establish a deliberate fault point in the circuit. If current does somehow get onto the circuit, the grounds shall stay connected securely until a protective device clears the circuit.
It is difficult to set firm criteria for when temporary personal protective grounds are needed. Blanket requirements are usually established. Many times, it is a decision made in the field by the person performing the work.
When there is uncertainty about exposure, it is wise to add this extra protection. Many industrial facilities and utilities require temporary personal protective grounding for all aerial power line work and for all work on power systems over 600 V because of the increased exposure these systems often have due to their length and location.
Temporary personal protective grounding can also be used as the additional safety measure required when hazardous electrical energy control must be performed using a tag only. Temporary personal protective grounding devices should meet the specifications in ASTM F855-96 and should be sized for the maximum available current of any possible event.
Temporary personal protective grounds should only be installed after all other conditions of an electrically safe work condition have been established. Because the unexpected can happen at any time, however, the installation and removal of temporary grounding devices should be performed, by procedure, as the conductors are energized.
When installed inside equipment enclosures, temporary grounds should be lengthy enough to extend outside of the equipment so that they can be easily seen. If they cannot extend out, they should be made highly visible. Brightly colored tapes are helpful identifiers. Once they are installed, bare-hand work could be permitted.
It should be quite obvious that all personal protective grounds must be removed prior to reenergization. Identification and accountability controls may be necessary on large construction or maintenance jobs. The installation and removal of these grounding devices can be controlled by permit in order to avoid re-energizing equipment into a faulted condition.
The integrity of personal protective grounds should be maintained through the use of periodic inspection and testing. It is a good idea to document this inspection and testing.
POOR HAZARDOUS ELECTRICAL ENERGY CONTROL PRACTICES
What are the examples of poor hazardous energy control practices.
The following items discuss some practices that were used in the past for safety control. These practices are not truly safe practices and should not be used today.
a) Locking out a push-button, control switch, or other pilot device does not ensure that the circuit will remain de-energized. A short circuit or ground in the control circuit can bypass the pilot device.
Another employee might even engage the contactor or starter by hand. Unless the disconnecting means is opened and locked out, an employee should not place himself in a position where unexpected equipment startup or energization might cause injury.
b) Turning the handle of a disconnect switch to the "off' position does not ensure safety. The switch linkage might be broken, leaving the switchblades engaged.
Switchblades in the open position should be confirmed by visual inspection. The load side of the switch should also be checked with a voltage tester to ensure that the outgoing circuit is de-energized, and that there is no backfeed.
c) Removing and tagging fuses does not constitute a lockout/tagout. A lockout/tagout device should be attached to the fuse clips in a manner such that no fuses can be inserted without removing the device.
If fuses are contained in a drawout fuse block, the tag should be attached to the fuse panel, not to the drawout block. Special precautions shall be taken to prevent shock whenever energized fuse clips that are accessible to the touch must be tagged.
d) Simply opening a power circuit breaker does not ensure safety. Even if the control fuses are removed, the breaker can still be engaged with the manual operating mechanism.
The switchgear must be racked away from the bus contacts and into the "fully disconnected" position, and the racking mechanism shall be locked and tagged.
The following items discuss some practices that were used in the past for safety control. These practices are not truly safe practices and should not be used today.
a) Locking out a push-button, control switch, or other pilot device does not ensure that the circuit will remain de-energized. A short circuit or ground in the control circuit can bypass the pilot device.
Another employee might even engage the contactor or starter by hand. Unless the disconnecting means is opened and locked out, an employee should not place himself in a position where unexpected equipment startup or energization might cause injury.
b) Turning the handle of a disconnect switch to the "off' position does not ensure safety. The switch linkage might be broken, leaving the switchblades engaged.
Switchblades in the open position should be confirmed by visual inspection. The load side of the switch should also be checked with a voltage tester to ensure that the outgoing circuit is de-energized, and that there is no backfeed.
c) Removing and tagging fuses does not constitute a lockout/tagout. A lockout/tagout device should be attached to the fuse clips in a manner such that no fuses can be inserted without removing the device.
If fuses are contained in a drawout fuse block, the tag should be attached to the fuse panel, not to the drawout block. Special precautions shall be taken to prevent shock whenever energized fuse clips that are accessible to the touch must be tagged.
d) Simply opening a power circuit breaker does not ensure safety. Even if the control fuses are removed, the breaker can still be engaged with the manual operating mechanism.
The switchgear must be racked away from the bus contacts and into the "fully disconnected" position, and the racking mechanism shall be locked and tagged.
LOCK OUT AND TAG OUT PERMIT BASIC INFORMATION
Some work requires rigid lockout/tagout control of the type that should not be the responsibility of the employee alone. Lockout/tagouts of this nature should be secured by a formal permit.
This more formal approach is called a documented lockout/tagout. Typically, this type of lockout/tagout would be used on those types of jobs that are not simple and easily understood.
Electrical work performed on medium- and high-voltage circuits is a good example. It would also include work on equipment that requires a complex lockout/tagout due to multiple sources of electrical energy.
Also included would be jobs that require work inside of grinding mills, choppers, fan housings, ovens, storage tanks and silos, and similar situations in which personnel are in a position that unexpected equipment start-up would, without question, result in serious injury or death.
In general, the documented lockout/tagout shall be used except when the conditions given in 29 CFR 1910.147 for a nondocumented lockout/tagout allow an exception.
No specific permit system can be recommended as good practice in all circumstances. A workable permit system can be developed only on an individual basis at the plant level by personnel intimately familiar with plant operations. Certain requirements that represent good practice in one plant might be inadequate or unworkable in another plant with different problems and a different personnel structure.
One fundamental feature, however, should be incorporated into any permit system. It should be designed with checks and balances.
Specific responsibility for a particular operation should be assigned to an individual without relieving others of the obligation to double-check the status of the lockout/tagout before proceeding with their own assigned steps in the process. The permit system, then, should be developed to duplicate and reinforce, rather than dilute, responsibility.
Every step in processing a lockout/tagout permit, from the initial request to the official closing, should be confirmed in writing on an official form. The permit form should include spaces for every person involved to indicate the times and dates when the paperwork was received and when the action was taken.
Completion of each step should be acknowledged by the signature of the person responsible for taking the appropriate action. Every person involved in processing the permit should be held responsible for checking the paperwork referred to them to see that everything is in order before proceeding with their own step.
This more formal approach is called a documented lockout/tagout. Typically, this type of lockout/tagout would be used on those types of jobs that are not simple and easily understood.
Electrical work performed on medium- and high-voltage circuits is a good example. It would also include work on equipment that requires a complex lockout/tagout due to multiple sources of electrical energy.
Also included would be jobs that require work inside of grinding mills, choppers, fan housings, ovens, storage tanks and silos, and similar situations in which personnel are in a position that unexpected equipment start-up would, without question, result in serious injury or death.
In general, the documented lockout/tagout shall be used except when the conditions given in 29 CFR 1910.147 for a nondocumented lockout/tagout allow an exception.
No specific permit system can be recommended as good practice in all circumstances. A workable permit system can be developed only on an individual basis at the plant level by personnel intimately familiar with plant operations. Certain requirements that represent good practice in one plant might be inadequate or unworkable in another plant with different problems and a different personnel structure.
One fundamental feature, however, should be incorporated into any permit system. It should be designed with checks and balances.
Specific responsibility for a particular operation should be assigned to an individual without relieving others of the obligation to double-check the status of the lockout/tagout before proceeding with their own assigned steps in the process. The permit system, then, should be developed to duplicate and reinforce, rather than dilute, responsibility.
Every step in processing a lockout/tagout permit, from the initial request to the official closing, should be confirmed in writing on an official form. The permit form should include spaces for every person involved to indicate the times and dates when the paperwork was received and when the action was taken.
Completion of each step should be acknowledged by the signature of the person responsible for taking the appropriate action. Every person involved in processing the permit should be held responsible for checking the paperwork referred to them to see that everything is in order before proceeding with their own step.
BURNS FROM ELECTRICAL ARCS OT ARC FLASH BASIC INFORMATION
Almost everyone is aware that electrical shock can be a hazard to life. Many people, however, have experienced minor shocks with no dire consequences. This tends to make people somewhat complacent around electricity.
What most people don't know is that approximately half of the serious electrical injuries involve burns. Electrical burns include not only burns from contact, but also radiation burns from the fierce fire of electric arcs that result from short circuits due to poor electrical contact or insulation failure.
The electric arc between metals is, next to the laser, the hottest thing on earth. It is about four times as hot as the sun's surface.
Where high arc currents are involved, burns from such arcs can be fatal, even when the victim is some distance from the arc. Serious or fatal burns can occur at distances of more than 304 cm (10 ft) from the source of a flash.
In addition to burns from the flash itself, clothing is often ignited. Fatal burns can result because the clothing cannot be removed or extinguished quickly enough to prevent serious burns over much of the body.
Thus, even at what a person thinks to be a large distance, serious or fatal injuries can occur to a person's bare skin or skin covered with flammable clothing as a result of a severe power arc. Electrical workers are frequently in the vicinity of energized parts.
It is only the relative infrequency of such arcs that has limited the number of injuries. Examples of exposure are working on open panelboards or switchboards, hook stick operation of medium-voltage fuses, testing of cable terminals, grounding before testing, or working in manholes near still-energized cables.
Several studies, tests, and technical papers are being written on the subject of the flash hazard. Safety standards and procedures are being developed to recognize the fact that arcs can cause serious injuries at significant distances from energized sources.
Equally important in these new safety standards is the fact that, in many cases, only trained people with arc protective equipment should approach exposed energized electrical equipment. Spectators should stay away because, even though they think they are far enough away, they generally don't have an understanding of what is a safe approach distance.
Depending upon the fault energy available, spectators can be seriously hurt at large distances from the point of an arc.
What most people don't know is that approximately half of the serious electrical injuries involve burns. Electrical burns include not only burns from contact, but also radiation burns from the fierce fire of electric arcs that result from short circuits due to poor electrical contact or insulation failure.
The electric arc between metals is, next to the laser, the hottest thing on earth. It is about four times as hot as the sun's surface.
Where high arc currents are involved, burns from such arcs can be fatal, even when the victim is some distance from the arc. Serious or fatal burns can occur at distances of more than 304 cm (10 ft) from the source of a flash.
In addition to burns from the flash itself, clothing is often ignited. Fatal burns can result because the clothing cannot be removed or extinguished quickly enough to prevent serious burns over much of the body.
Thus, even at what a person thinks to be a large distance, serious or fatal injuries can occur to a person's bare skin or skin covered with flammable clothing as a result of a severe power arc. Electrical workers are frequently in the vicinity of energized parts.
It is only the relative infrequency of such arcs that has limited the number of injuries. Examples of exposure are working on open panelboards or switchboards, hook stick operation of medium-voltage fuses, testing of cable terminals, grounding before testing, or working in manholes near still-energized cables.
Several studies, tests, and technical papers are being written on the subject of the flash hazard. Safety standards and procedures are being developed to recognize the fact that arcs can cause serious injuries at significant distances from energized sources.
Equally important in these new safety standards is the fact that, in many cases, only trained people with arc protective equipment should approach exposed energized electrical equipment. Spectators should stay away because, even though they think they are far enough away, they generally don't have an understanding of what is a safe approach distance.
Depending upon the fault energy available, spectators can be seriously hurt at large distances from the point of an arc.
NATURE OF ELECTRICAL ARCS BASIC INFORMATION AND TUTORIALS
What are arcing? What is the effect of electrical arcing?
Electrical arcing is the term that is applied to the passage of substantial electrical currents through what had previously been air. It is initiated by flashover or the introduction of some conductive material.
Current passage is through ionized air and the vapor of the arc terminal material, which is usually a conductive metal or carbon. In contrast to current flow through low-pressure gases such as neon, arcing involves high temperatures of up to, or beyond, 20 000 °K (35 000 °F) at the arc terminals.
No materials on earth can withstand these temperatures; all materials are not only melted, but vaporized. Actually, 20 000 °K (35 000 °F) is about four times as hot as the surface temperature of the sun.
The vapor of the terminal material has substantially higher resistance than solid metal, to the extent that the voltage drop in the arc ranges from 29.53 V/cm (75 V/in) to 39.37 V/cm (100 V/in), which is several thousand times the voltage drop in a solid conductor.
Since the inductance of the arc path is not appreciably different from that of a solid conductor of the same length, the arc current path is substantially resistive in nature, thus yielding unity power factor. Voltage drop in a faulted large solid or stranded conductor is about 0.016-0.033 V/cm (0.5-1 V/ft).
For low-voltage circuits, an arc length of 29.53-39.37 V/cm (75-100 V/in) consumes a substantial portion of the available voltage, leaving only the difference between source voltage and arc voltage to force the fault current through the total system impedance, including that of the arc. This is the reason for the "stabilization" of arc current on 480 Y/277 V circuits when the arc length is of the order of 10.16 cm (4 in), such as with bus spacing.
For higher voltages, the arc lengths can be substantially greater, e.g., 2.54 cm (1 in) per 100 V of supply, before the system impedance starts to regulate or limit the fault current. Note that the arc voltage drop and the source voltage drop add in quadrature, the former resistive, the latter substantially reactive.
The length or size of arcs in the higher voltage systems thus can be greater and can readily bridge the gap from energized parts to ground or other polarities with little drop in fault current.
The hazard of the arc is not only due to the level of voltage. Under some cases it is possible to generate a higher energy arc from a lower voltage than from a higher voltage.
The amount of arc energy generated is dependent upon the amount of short-circuit current available and the amount of time before the fault causing the arc is cleared (removed from the power source) by a circuit breaker or fuse.
Electrical arcing is the term that is applied to the passage of substantial electrical currents through what had previously been air. It is initiated by flashover or the introduction of some conductive material.
Current passage is through ionized air and the vapor of the arc terminal material, which is usually a conductive metal or carbon. In contrast to current flow through low-pressure gases such as neon, arcing involves high temperatures of up to, or beyond, 20 000 °K (35 000 °F) at the arc terminals.
No materials on earth can withstand these temperatures; all materials are not only melted, but vaporized. Actually, 20 000 °K (35 000 °F) is about four times as hot as the surface temperature of the sun.
The vapor of the terminal material has substantially higher resistance than solid metal, to the extent that the voltage drop in the arc ranges from 29.53 V/cm (75 V/in) to 39.37 V/cm (100 V/in), which is several thousand times the voltage drop in a solid conductor.
Since the inductance of the arc path is not appreciably different from that of a solid conductor of the same length, the arc current path is substantially resistive in nature, thus yielding unity power factor. Voltage drop in a faulted large solid or stranded conductor is about 0.016-0.033 V/cm (0.5-1 V/ft).
For low-voltage circuits, an arc length of 29.53-39.37 V/cm (75-100 V/in) consumes a substantial portion of the available voltage, leaving only the difference between source voltage and arc voltage to force the fault current through the total system impedance, including that of the arc. This is the reason for the "stabilization" of arc current on 480 Y/277 V circuits when the arc length is of the order of 10.16 cm (4 in), such as with bus spacing.
For higher voltages, the arc lengths can be substantially greater, e.g., 2.54 cm (1 in) per 100 V of supply, before the system impedance starts to regulate or limit the fault current. Note that the arc voltage drop and the source voltage drop add in quadrature, the former resistive, the latter substantially reactive.
The length or size of arcs in the higher voltage systems thus can be greater and can readily bridge the gap from energized parts to ground or other polarities with little drop in fault current.
The hazard of the arc is not only due to the level of voltage. Under some cases it is possible to generate a higher energy arc from a lower voltage than from a higher voltage.
The amount of arc energy generated is dependent upon the amount of short-circuit current available and the amount of time before the fault causing the arc is cleared (removed from the power source) by a circuit breaker or fuse.
ELECTRICAL SAFE PRACTICES PROCEDURE OUTLINE BASIC INFORMATION
Typical outline of an electrical safe practices procedure
-Title. The title identifies the specific equipment where the procedure applies.
-Purpose. The purpose is to identify the task to be performed.
-Qualification. The training and knowledge that qualified personnel shall possess in order to perform particular tasks are identified.
-Hazard identification. The hazards that were identified during development of the procedure are highlighted. These are the hazards that may not appear obvious to personnel performing work on or near the energized equipment.
-Hazard classification. The degree of risk, as deÞned by the hazard/risk analysis, is identified for the particular task to be performed.
-Limits of approach. The approach distances and restrictions are identified for personnel access around energized electrical equipment.
-Safe work practices. The controls that shall be in place prior to, and during the performance of, work on or near energized equipment are emphasized.
-Personnel protective clothing and equipment. The minimum types and amounts of protective clothing and equipment that are required by personnel to perform the tasks described in the procedures are listed. Personnel performing the work shall wear the protective clothing at all times while performing the tasks identified in the procedure.
-Test equipment and tools. All the test equipment and tools that are required to perform the work described in this procedure are listed. The test equipment and tools shall be maintained and operated in accordance with the manufacturer's instructions.
-Reference data. The reference material used in the development of the procedure is listed. It includes the appropriate electrical single-line diagrams, equipment rating (voltage level), and manufacturer's operating instructions.
-Procedure steps. The steps required by qualified personnel wearing personal protective clothing and using the approved test equipment to perform specific tasks in a specified manner are identified.
-Sketches. Sketches are used, where necessary, to properly illustrate and elaborate specific tasks.
-Title. The title identifies the specific equipment where the procedure applies.
-Purpose. The purpose is to identify the task to be performed.
-Qualification. The training and knowledge that qualified personnel shall possess in order to perform particular tasks are identified.
-Hazard identification. The hazards that were identified during development of the procedure are highlighted. These are the hazards that may not appear obvious to personnel performing work on or near the energized equipment.
-Hazard classification. The degree of risk, as deÞned by the hazard/risk analysis, is identified for the particular task to be performed.
-Limits of approach. The approach distances and restrictions are identified for personnel access around energized electrical equipment.
-Safe work practices. The controls that shall be in place prior to, and during the performance of, work on or near energized equipment are emphasized.
-Personnel protective clothing and equipment. The minimum types and amounts of protective clothing and equipment that are required by personnel to perform the tasks described in the procedures are listed. Personnel performing the work shall wear the protective clothing at all times while performing the tasks identified in the procedure.
-Test equipment and tools. All the test equipment and tools that are required to perform the work described in this procedure are listed. The test equipment and tools shall be maintained and operated in accordance with the manufacturer's instructions.
-Reference data. The reference material used in the development of the procedure is listed. It includes the appropriate electrical single-line diagrams, equipment rating (voltage level), and manufacturer's operating instructions.
-Procedure steps. The steps required by qualified personnel wearing personal protective clothing and using the approved test equipment to perform specific tasks in a specified manner are identified.
-Sketches. Sketches are used, where necessary, to properly illustrate and elaborate specific tasks.
PROTECTIVE RELAY TESTING BASIC INFORMATION AND TUTORIALS
What is protective relay testing? How to do protective relay testing?
Protective relaying is a very broad subject. Only a brief overview can be given here. There are two major objectives in protective relaying.
First, a protective relay serves to provide equipment protection (i.e., locate and isolate overloads, short circuits, undervoltages, and other types of electrical problems quickly in order to minimize damage).
Second, the protective device that is closest to the problem should operate first to clear the problem, and no other device should operate unless the closest one fails. This concept, known as "selective tripping" or "selectivity", maintains service to as much of the electrical system as possible by isolating only the problem area.
In order to achieve these objectives, each relay must function as it was designed, and the relays must function in conjunction with the other protective devices in the system. Having all the protective devices function as one overall protective system is called "coordination".
Each protective device has specific parameters within which it has been designed to operate. For example, a single element fuse has a value of current above which it opens.
It takes a specific amount of time for a given current to melt the link away and open the fuse. Manufacturers of fuses publish "time-current" curves that show how long it takes a fuse to operate for varying current values.
Generally, the higher the current, the shorter the time.
This same inverse current-vs.-time concept is used for overcurrent relays and for low-voltage circuit breakers. Relays and low-voltage circuit breakers (with internal trip units) have a range of "pickup" operating current that causes them to operate.
In many cases, this value of current is adjustable. By properly selecting the type, characteristic, and/or setting of fuses, relays, or circuit breakers, the system can be coordinated so that the device that is closest to the problem opens before any device upstream of it. It is necessary to select compatible time current characteristics of the devices for the entire system, in addition to selecting the proper settings for the devices.
Prior to performing protective relay testing, a coordination study should be completed to determine the proper settings for the relays to be calibrated. This is usually done by the design engineer when the system is first installed. If there have been revisions or additions to the system, a new study may be necessary.
Once the coordination study has been completed, the relays need to be calibrated to the proper settings. There are special test sets available for this purpose that inject currents and voltages, as necessary, and time the various operations of the relays.
This type of testing is usually performed by a technician who specializes in this area. Depending upon the relay to be calibrated, quite complex test equipment may be required and in-depth training in protective relaying may be needed to properly set the relay.
Protective relaying is a very broad subject. Only a brief overview can be given here. There are two major objectives in protective relaying.
First, a protective relay serves to provide equipment protection (i.e., locate and isolate overloads, short circuits, undervoltages, and other types of electrical problems quickly in order to minimize damage).
Second, the protective device that is closest to the problem should operate first to clear the problem, and no other device should operate unless the closest one fails. This concept, known as "selective tripping" or "selectivity", maintains service to as much of the electrical system as possible by isolating only the problem area.
In order to achieve these objectives, each relay must function as it was designed, and the relays must function in conjunction with the other protective devices in the system. Having all the protective devices function as one overall protective system is called "coordination".
Each protective device has specific parameters within which it has been designed to operate. For example, a single element fuse has a value of current above which it opens.
It takes a specific amount of time for a given current to melt the link away and open the fuse. Manufacturers of fuses publish "time-current" curves that show how long it takes a fuse to operate for varying current values.
Generally, the higher the current, the shorter the time.
This same inverse current-vs.-time concept is used for overcurrent relays and for low-voltage circuit breakers. Relays and low-voltage circuit breakers (with internal trip units) have a range of "pickup" operating current that causes them to operate.
In many cases, this value of current is adjustable. By properly selecting the type, characteristic, and/or setting of fuses, relays, or circuit breakers, the system can be coordinated so that the device that is closest to the problem opens before any device upstream of it. It is necessary to select compatible time current characteristics of the devices for the entire system, in addition to selecting the proper settings for the devices.
Prior to performing protective relay testing, a coordination study should be completed to determine the proper settings for the relays to be calibrated. This is usually done by the design engineer when the system is first installed. If there have been revisions or additions to the system, a new study may be necessary.
Once the coordination study has been completed, the relays need to be calibrated to the proper settings. There are special test sets available for this purpose that inject currents and voltages, as necessary, and time the various operations of the relays.
This type of testing is usually performed by a technician who specializes in this area. Depending upon the relay to be calibrated, quite complex test equipment may be required and in-depth training in protective relaying may be needed to properly set the relay.
MEDIUM AND HIGH VOLTAGE CABLE TESTING BASIC INFORMATION AND TUTORIALS
Most cables that are rated for use at voltage levels above 600 V are shielded cables. A shielded cable has a conductor in the center, a semiconducting layer over the strands that is surrounded by insulation, a semiconducting layer, and then a metal foil or wire mesh that surrounds the whole assembly.
There is usually another layer over the shield that makes up the outer jacket of the cable. It is a common practice to hi-pot test the cables on initial installation in order to verify that the cables were not damaged when they were pulled into place and that all the splices and/or terminations were installed properly.
The voltage level that is selected usually is lower than factory test levels, frequently 80% of the dc equivalent of the factory test level.
There are normally two considerations that are given to hi-pot testing of cables as a routine maintenance practice. One is a function of the chosen maintenance philosophy [i.e., breakdown maintenance, preventive maintenance, predictive maintenance, or reliability-centered maintenance (RCM)].
The other depends upon the type of operation and how critical it is to have continuous power without interruption.
The debate on whether or not to perform maintenance hi-pot testing centers around the fact that a cable in marginal condition can be caused to fail by the hi-pot test itself. A cable that is in good condition should not be harmed.
People who subscribe to maintenance testing feel that it is much better to have the cable fail under test. Cable maintenance testing frequently is performed at 50-65% of the factory test voltage.
Problems can then be corrected while the circuit is intentionally shut down, thus avoiding an in-service failure that could interrupt production.
It is important to remember that the necessary material, such as splice kits or cable terminations, should be available to facilitate repairs should the cable fail during testing.
There is usually another layer over the shield that makes up the outer jacket of the cable. It is a common practice to hi-pot test the cables on initial installation in order to verify that the cables were not damaged when they were pulled into place and that all the splices and/or terminations were installed properly.
The voltage level that is selected usually is lower than factory test levels, frequently 80% of the dc equivalent of the factory test level.
There are normally two considerations that are given to hi-pot testing of cables as a routine maintenance practice. One is a function of the chosen maintenance philosophy [i.e., breakdown maintenance, preventive maintenance, predictive maintenance, or reliability-centered maintenance (RCM)].
The other depends upon the type of operation and how critical it is to have continuous power without interruption.
The debate on whether or not to perform maintenance hi-pot testing centers around the fact that a cable in marginal condition can be caused to fail by the hi-pot test itself. A cable that is in good condition should not be harmed.
People who subscribe to maintenance testing feel that it is much better to have the cable fail under test. Cable maintenance testing frequently is performed at 50-65% of the factory test voltage.
Problems can then be corrected while the circuit is intentionally shut down, thus avoiding an in-service failure that could interrupt production.
It is important to remember that the necessary material, such as splice kits or cable terminations, should be available to facilitate repairs should the cable fail during testing.
POWER SYSTEM PROTECTION COORDINATION FOR SAFETY
When an electrical distribution system is designed and constructed, a fault-current coordination study should be conducted, and circuit protective devices should be sized and set according to the results of the study. In time, however, the electrical system configurations are often changed due to the changing needs of the end users.
If the coordination and capability of the electrical equipment are not reviewed at the time of the changes, faults could result in unnecessary tripping of a main breaker or, even worse, an explosion of equipment that was thought to be in good condition.
When system conditions change, the results that were obtained in the original fault-current coordination study may no longer apply to the current system. Unnecessary tripping, known as lack of selectivity, could be caused by poor coordination.
An equipment explosion could result from the interrupting capability of the circuit breaker being exceeded. Both indicate a clear need for an updated fault-current coordination study.
Utility systems delivering higher fault currents
The demand for electricity, particularly in the industrial and commercial environment, has been steadily increasing. Consequently, utility systems have grown much larger and have become capable of delivering much higher fault-currents at service points than in the past.
Therefore, protective devices that were properly applied at the time they were installed may have become inadequate after system changes, and the protective system may no longer be coordinated. When available fault current increases to the point at which it exceeds protective device interrupting and withstand ratings, violent failure is possible, regardless of how well the devices are maintained.
Protection in an electrical distribution system
System and equipment protective devices are a form of insurance. This insurance pays nothing as long as there is no fault or other emergency.
When a fault occurs, however, properly applied protective devices reduce the extent and duration of the interruption, thereby reducing the exposure to personal injury and property damage. If, however, the protective system does not match system needs, just as an insurance policy should keep up with inflation, it is no help at all. It is the responsibility of the system operator to ensure proper system protection and coordination.
Protective equipment set to sense and remove short circuits
In medium-voltage systems, the protective equipment for feeder conductors is often set to sense and remove short circuits, but not necessarily to provide overload protection of circuits. Device settings sometimes are purposely chosen low enough to sense and provide a degree of overload protection.
Operators should be aware of this so that a protective device that is set lower than necessary for coordination does not cause a false tripping action during system switching procedures. System protection coordination is an important consideration in switching systems with loop feeds and alternate sources. To avoid false tripping action, operators should be aware of the settings and any probable temporary overloads or circulating currents during switching.
If the coordination and capability of the electrical equipment are not reviewed at the time of the changes, faults could result in unnecessary tripping of a main breaker or, even worse, an explosion of equipment that was thought to be in good condition.
When system conditions change, the results that were obtained in the original fault-current coordination study may no longer apply to the current system. Unnecessary tripping, known as lack of selectivity, could be caused by poor coordination.
An equipment explosion could result from the interrupting capability of the circuit breaker being exceeded. Both indicate a clear need for an updated fault-current coordination study.
Utility systems delivering higher fault currents
The demand for electricity, particularly in the industrial and commercial environment, has been steadily increasing. Consequently, utility systems have grown much larger and have become capable of delivering much higher fault-currents at service points than in the past.
Therefore, protective devices that were properly applied at the time they were installed may have become inadequate after system changes, and the protective system may no longer be coordinated. When available fault current increases to the point at which it exceeds protective device interrupting and withstand ratings, violent failure is possible, regardless of how well the devices are maintained.
Protection in an electrical distribution system
System and equipment protective devices are a form of insurance. This insurance pays nothing as long as there is no fault or other emergency.
When a fault occurs, however, properly applied protective devices reduce the extent and duration of the interruption, thereby reducing the exposure to personal injury and property damage. If, however, the protective system does not match system needs, just as an insurance policy should keep up with inflation, it is no help at all. It is the responsibility of the system operator to ensure proper system protection and coordination.
Protective equipment set to sense and remove short circuits
In medium-voltage systems, the protective equipment for feeder conductors is often set to sense and remove short circuits, but not necessarily to provide overload protection of circuits. Device settings sometimes are purposely chosen low enough to sense and provide a degree of overload protection.
Operators should be aware of this so that a protective device that is set lower than necessary for coordination does not cause a false tripping action during system switching procedures. System protection coordination is an important consideration in switching systems with loop feeds and alternate sources. To avoid false tripping action, operators should be aware of the settings and any probable temporary overloads or circulating currents during switching.
SAFETY AND POWER SYSTEM MANAGEMENT BASIC INFORMATION AND TUTORIALS
A well designed and constructed power system will not provide a safe and reliable operation unless it is properly managed. Any electrical power distribution system, from the smallest system to the largest and most complex system, needs to be managed. As systems become larger in size and complexity, the problems of system management increase, thereby requiring more time and attention from the system-operating personnel.
Good design, proper installation, quality assurance, and sound operating and maintenance programs provide the basic foundation for the safe and reliable operation of industrial electric power systems. A plant engineer who is faced with the task of improving the plant's electric power system performance, however, will likely find that programs to reduce human error are more cost-effective than system modifications or additional preventive maintenance. In fact, given good design and a sound maintenance program, the inherent system reliability can only be achieved by the reduction of operating error.
The operation of an electric power system should also address the problem of human errors. The following examples should be considered:
Following a severe thunderstorm, a plant shift supervisor made a walk-through inspection of the plant's primary distribution switchgear. Upon seeing a red light for each circuit breaker, he immediately tripped each circuit breaker in order to obtain a green-light indication. Because he incorrectly thought that the red light meant "open," he shut down the entire plant.
One of a plant's two steam boilers was down for annual inspection and maintenance. An electrician who was assigned to make a modification to the boiler control circuit erroneously began working on the operating boiler control circuit and shut down the operating boiler.
An investigation of a 15 kV outdoor bus duct fault revealed that production personnel routinely turned off outside lighting at the beginning of the day shift by switching off circuit breakers in a 120 V distribution panel. The bus duct heater circuit was incorrectly identified, and was being switched off with the lighting circuits.
It is a natural tendency to blame equipment for failures, rather than human error. The bus duct fault in the last example could have been classified as an equipment failure; however, the prime cause was improper operation (human error) of the bus duct heaters.
Most plant electrical outages that clearly are not due to equipment failure, lightning, or utility disturbances can be prevented by making an objective investigation of the potential for outages and by following these guidelines:
a) Document the system and identify the equipment.
b) Plan switching operations in detail.
c) Secure equipment from unintentional operation.
d) Clearly define operating responsibility and adhere to it rigidly. System operation can and should be managed.
Effective managers of a power system will consider load distribution, system integrity, power factor, system protection coordination, and operating economics. Each of these areas is discussed in this chapter, thus showing how all of these considerations relate to each other. No area of industrial and commercial power system management is independent of the other.
Good design, proper installation, quality assurance, and sound operating and maintenance programs provide the basic foundation for the safe and reliable operation of industrial electric power systems. A plant engineer who is faced with the task of improving the plant's electric power system performance, however, will likely find that programs to reduce human error are more cost-effective than system modifications or additional preventive maintenance. In fact, given good design and a sound maintenance program, the inherent system reliability can only be achieved by the reduction of operating error.
The operation of an electric power system should also address the problem of human errors. The following examples should be considered:
Following a severe thunderstorm, a plant shift supervisor made a walk-through inspection of the plant's primary distribution switchgear. Upon seeing a red light for each circuit breaker, he immediately tripped each circuit breaker in order to obtain a green-light indication. Because he incorrectly thought that the red light meant "open," he shut down the entire plant.
One of a plant's two steam boilers was down for annual inspection and maintenance. An electrician who was assigned to make a modification to the boiler control circuit erroneously began working on the operating boiler control circuit and shut down the operating boiler.
An investigation of a 15 kV outdoor bus duct fault revealed that production personnel routinely turned off outside lighting at the beginning of the day shift by switching off circuit breakers in a 120 V distribution panel. The bus duct heater circuit was incorrectly identified, and was being switched off with the lighting circuits.
It is a natural tendency to blame equipment for failures, rather than human error. The bus duct fault in the last example could have been classified as an equipment failure; however, the prime cause was improper operation (human error) of the bus duct heaters.
Most plant electrical outages that clearly are not due to equipment failure, lightning, or utility disturbances can be prevented by making an objective investigation of the potential for outages and by following these guidelines:
a) Document the system and identify the equipment.
b) Plan switching operations in detail.
c) Secure equipment from unintentional operation.
d) Clearly define operating responsibility and adhere to it rigidly. System operation can and should be managed.
Effective managers of a power system will consider load distribution, system integrity, power factor, system protection coordination, and operating economics. Each of these areas is discussed in this chapter, thus showing how all of these considerations relate to each other. No area of industrial and commercial power system management is independent of the other.
SELECTION OF LINEMAN ELECTRICAL PROTECTIVE EQUIPMENT BASIC INFORMATION AND TUTORIALS
How to select electrical protective equipment for lineman safety engineering?
The requirements for the hazard analysis and selection of protective clothing must first be defined.
Assess the workplace to determine if hazards are present, or are likely to be present, which require the use of personal protective equipment. If such hazards are determined, the employer should select and have each employee use, the type of personal productive equipment that will protect the affected employee from the hazards identified in the hazard assessment.
Train the employee to be knowledgeable with the following issues and scenarios:
• When personal productive equipment is necessary;
• What personal productive equipment is necessary;
• How to properly don, doff, adjust, and wear personal productive equipment;
• The limitations of the personal productive equipment;
and
• The proper care, maintenance, useful life, and disposal of personal productive equipment.
Include shock, arc, and blast assessments in the hazard analyses. Identify the selection, inspection, and use requirements for electrical personal productive equipment. Specify the type of clothing that is prohibited.
Utilize protective shields, protective barriers, or insulating materials to protect each employee from shock, burns, or other electrically related injuries while that employee is working near exposed energized parts which might be accidentally contacted or where dangerous electric heating or arcing might occur.
Protective clothing, including a complete multilayered flash suit with hood and face shield, may be required for the operation, insertion, or removal of a circuit breaker.
Calculate the incident energy (in cal/cm2) available at the work site in order to determine and the protective clothing required for the specific task. Additionally, determine a "Flash protection boundary" for all energized work.
At this boundary, exposed flesh must not receive a second-degree burn or worse. After determining the type, purchase the necessary protective
clothing and train employees on how to properly wear the gear.
The requirements for the hazard analysis and selection of protective clothing must first be defined.
Assess the workplace to determine if hazards are present, or are likely to be present, which require the use of personal protective equipment. If such hazards are determined, the employer should select and have each employee use, the type of personal productive equipment that will protect the affected employee from the hazards identified in the hazard assessment.
Train the employee to be knowledgeable with the following issues and scenarios:
• When personal productive equipment is necessary;
• What personal productive equipment is necessary;
• How to properly don, doff, adjust, and wear personal productive equipment;
• The limitations of the personal productive equipment;
and
• The proper care, maintenance, useful life, and disposal of personal productive equipment.
Include shock, arc, and blast assessments in the hazard analyses. Identify the selection, inspection, and use requirements for electrical personal productive equipment. Specify the type of clothing that is prohibited.
Utilize protective shields, protective barriers, or insulating materials to protect each employee from shock, burns, or other electrically related injuries while that employee is working near exposed energized parts which might be accidentally contacted or where dangerous electric heating or arcing might occur.
Protective clothing, including a complete multilayered flash suit with hood and face shield, may be required for the operation, insertion, or removal of a circuit breaker.
Calculate the incident energy (in cal/cm2) available at the work site in order to determine and the protective clothing required for the specific task. Additionally, determine a "Flash protection boundary" for all energized work.
At this boundary, exposed flesh must not receive a second-degree burn or worse. After determining the type, purchase the necessary protective
clothing and train employees on how to properly wear the gear.
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