Key for Electrical Safety 2013

8/22/2019 Key for Electrical Safety 2013

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K.S.RANGASAMY COLLEGE OF TECHNOLOGY, TIRUCHENGODE-637215

Branch: M.E. - Industrial Safety Engineering Semester: 2/May 2013

Subject: ELECTRICAL SAFETY Subject Code: 10 PIS 203

KEY

1. a) Electrical equipment and wiring methods appropriate for the environments found in

factory premises are designed in accordance with the Indian Electricity Act and Rules.

Proper grounding of systems and equipment and selection of over current devices to

facilitate fail-safe electrical systems are presented. 3

Methods to limit voltage drop to 5% from the facility power source to the end-use

equipment are offered. There are recommendations for location of equipment and wiring

and additional safety switches for protection of equipment and facilitating service. 2

b) bonding and grounding humidification static collectors 3

Additives ** Controlling static electricity on people 2

c) Electromagnetism is magnetism caused by the flow of electricity. 2

Referred to as EMF, the fields of energy surrounding electric power wires and other current-

carrying devices. Electric power lines, household wiring, and appliances all carry electric current.

Electromagnetism is the branch of science concerned with the forces that occurs

between charged particles. 3

d) a. Inspection and examination of any place;

b. Carrying out testing and examination of electrical apparatus as required by the Act;2

c. Serving an order to the consumer for complying any Law;

d. Impose prescribed time for complying the provisions of Law; and

e. Suspend the electrical operation if the conditions are not complied within the time.3

2. a) Some rotating machines, because of electrical or mechanical characteristics, induce an

electrical potential (voltage) on their rotating shafts. If this voltage is not managed, or if the voltage

mitigation system (often a shaft-grounding brush) is not maintained and fails, the voltage seeks an

alternate path to ground. 2

That path is the metal component typically a bearing or seal closest to the shaft, and electric arcing

to that component is termed electrostatic discharge. Arcing erodes metal surfaces and opens the tight

clearances that these components depend upon for proper operation. Voltages between the shaft and

ground, due to a static charge or DC voltage ripple, can be mitigated by the installation of grounding

brushes that ride on the shaft near the uninsulated generator bearing. The brushes keep the shaft-to-

ground voltage at a safe level by bleeding off current and causing the weak source voltage to decay. 3b) Must guard live parts of electric equipment operating at 230 volts or more against accidental contact

by:

Approved cabinets/enclosures, or

Location or permanent partitions making them accessible only to qualified persons, or

Elevation of 8 ft. or more above the floor or working surface. 2

Mark entrances to guarded locations with conspicuous warning signs. 1
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Must enclose or guard electric equipment in locations where it would be exposed to physical damage.

Junction boxes pull boxes and fittings must have approved covers. 2

c) An electrical machine is the apparatus that converts energy in three categories: generators which

convert mechanical energy to electrical, motors which convert electrical energy to mechanical energy,

and transformers which changes the voltage level of an alternating. 3

The amount of flux lines that do not follow the core and are lost to the surrounding air. The magnetic

circuit's flux that does not interlink both windings is the leakage flux. 2

d) The fundamental force associated with electric and magnetic fields. 2

The electromagnetic force is carried by the photon and is responsible for atomic structure, chemical

reactions, the attractive and repulsive forces associated with electrical charge and magnetism, and all

other electromagnetic phenomena. 3

3. a)Corona is a phenomenon associated with all energized transmission lines. Under certain conditions,

the localized electric field near an energized conductor can be sufficiently concentrated to produce atiny electric discharge that can ionize air close to the conductors. 3

This partial discharge of electrical energy is called corona discharge, or corona. An electric current can

flow when an object has an induced charge and a path to ground is presented. 2

b) 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 suns surface. 3

The air and gases surrounding the arc are instantly heated and the conductors are vaporized causing apressure wave called an Arc Blast. 2

c) Low Voltage - up to 250 V: Medium Voltage - up to 650 V; High Voltage - up to 30 KV: Extra-

High voltage - > 30 KV. 3

Internal causes: (i) Switching surges (ii) Insulation failure (iii) Arcing ground (iv) Resonance and

External causes i.e. lightning 2

d) High frequency electromagnetic fields are absorbed by biological systems and lead, above all, to a

warming of the tissue. 2

Although the exposure to high frequency electromagnetic fields is relatively low for the general public,

there are certain working environments where exposure is high, for example, applications in medicine,

equipment for warming and connecting of materials in industry, as well as repair or maintenance of

technical installations during operation. 3

4. a) when we are working around electric circuits capable of delivering high power to loads, electric

shock becomes a much more serious issue, and pain is the least significant result of shock. 2
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As electric current is conducted through a material, any opposition to that flow of electrons (resistance)

results in a dissipation of energy, usually in the form of heat. This is the most basic and easy-to-

understand effect of electricity on living tissue: current makes it heat up. If the amount of heat

generated is sufficient, the tissue may be burnt. The effect is physiologically the same as damage caused

by an open flame or other high-temperature source of heat, except that electricity has the ability to

burn tissue well beneath the skin of a victim, even burning internal organs. 3

b) Normally, under voltage faults occur because the voltage supplying the drive is too low. The obvious

cause of this fault is that the incoming mains supply is low or not the correct voltage. 2

For example, a 440 volt drive powered by 230 volts will display an under volt fault. Also, if the 440 volt

mains supplying the drive are low, for example due to transformer overload or supply brown-out this

fault will be displayed. 3

c) Ground fault that occurs when the "hot" wire comes into contact with the ground wire or a grounded

portion of a junction box or grounded part of an appliance or device. 2

Similar to a short circuit, large amounts of current are forced to flow through the fuse or circuit

breaker, causing a fuse to blow or acircuit breakerto trip. Co-ordination of over current devices uses a

combination of current settings and time delayed operation. Where fault current can flow in both

directions then directional over current and or earth fault relays can be applied. 3

d) Transformers that are operated properly (not overloaded) are not as likely to suffer the kind of

insulation damage that can lead to fires. 2

It is recommended that transformer fire suppression systems be activated automatically by fire and/or

detectors even in facilities staffed full time. As described under Control and Protection Systems, false

activation can be eliminated assuring the operator that if the suppression system has activated, a fire isvery likely. Recent developments and experience with ester-based insulating fluids show great promise

for reducing the likelihood of transformer fires, and thus the need for suppression and containment

while minimizing environmental effects from the insulating medium. 3

5. a) To protect a circuit against overload and short circuit destructive currents, a protective device

automatically disconnects the electrical equipment from the power source when a fault condition

occurs. Interlocks prevent someone from inadvertently opening the cover while the switch is in the "on"

position or inadvertently turning on the switch while the cover is open. Interlock devices are commonly

used in opening electrical panels; trapped key interlock switches and non-trapped key interlock switches

are the two main types. 3

The electronic timed delay unit provides an ideal solution by tripping the key within the unit for a preset

time after a stop signal has been made. When this time has elapsed the previously trapped key can be

withdrawn and used in the next sequence of operation. 2

b) An over current protective device with a circuit-opening fusible part that is heated and severed by the

passage of over current through it. Fuses are inherently single-pole devices (i.e., an individual fuse can
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only operate to open one phase of a multi-phase circuit), but two or three individual fuses can be

applied together in a disconnect to protect a multi-phase system. 3

Fuses shall reduce the current flowing in the faulted circuit to a magnitude substantially less than that

obtainable in the same circuit if the device were replaced with a solid conductor having comparable

impedance. In other words, the current-limiting fuses open very quickly (within 1/2 cycle) in thepresence of a high-level fault, allowing them to provide excellent protection for distribution system

components or load equipment. 2

c) FRLS = Flame Retardant Low Smoke; LSOH = Low Smoke Zero Halogen; 2

A watertight metallic outer covering used to protect a conductor's insulating material. A lead sheath is a

continuous jacket molded around the wire to seal it from any moisture damage. Lead sheathed power

control and auxiliary cables are used as underground cables in oil, gas and petrochemical industries. 3

d) The oil in Oil Circuit Breakers serves two purposes. It insulates between the phases and between the

phases and the ground, and it provides the medium for the extinguishing of the arc. When electric arc is

drawn under oil, the arc vaporizes the oil and creates a large bubble that surrounds the arc. The gasinside the bubble is around 80% hydrogen, which impairs ionization. The decomposition of oil into gas

requires energy that comes from the heat generated by the arc. The oil surrounding the bubble

conducts the heat away from the arc and thus also contributes to deionization of the arc. 3

Main disadvantage of the oil circuit breakers is the flammability of the oil, and the maintenance

necessary to keep the oil in good condition (i.e. changing and purifying the oil). 2

6. a) Steel wire armored cable, commonly abbreviated as SWA, is a hard-wearing cable designed for the

supply of mains electricity. It is one of a number of armored electrical cables which include 11kV Cable

and 33kV Cable and is found in underground systems, power networks and cable ducting. 3

Armoring is done for a cable to save the cable Conductor from damage by mechanical injury. SWA cable

can be referred to more generally as mains cable, armored cable, power cable and booklet armoredcable. 2

b) A Fuse, in its simplest form, is a piece of thin metal wire, which opens the circuit in which it is

inserted, by melting when the current through it exceed a certain value for a sufficient period of time.

Melting or blowing of the fuse is caused by the heat generated by the current. 2

Fusing Current is the minimum current at which a fuse element melt in such a time interval as shall be

necessary for the fuse-element to attain steady temperature. 3

c) A circuit breaker is an automatically operatedelectricalswitchdesigned to protect an electrical

circuitfrom damage caused byoverloadorshort circuit. Its basic function is to detect a fault condition

and interrupt current flow. 2Unlike afuse, which operates once and then must be replaced, a circuit breaker can be reset (either

manually or automatically) to resume normal operation. Circuit breakers are made in varying sizes, from

small devices that protect an individual household appliance up to largeswitchgeardesigned to protect

high-voltage circuits feeding an entire city. 3

d) The major difference between the over current and short circuit current is the magnitude and

duration of the fault current. In a short circuit, an extremely large current is experienced by the circuit in
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a short duration (fault magnitude will depend on the supply situation, but fifty kA would not be an

unreasonable figure in a 440 V system. In an overload, the normal load current is greater than the

circuits rating. 2

For example a circuit rated at two hundred amps, is loaded to 250A.

The type of fault changes how it is dealt with. Most circuit breaker devices will have a response curve

with a thermal portion, and a magnetic portion. Under a short circuit condition, the circuit breaker and

circuit experiences a massive current leading to a large induced magnetic force in the device. This will

trip the circuit breaker in it's magnetic setting, clearing the fault. Under an overload condition, the cable

and circuit breaker will experience excessive heating due to the overload; this will trip the circuit breaker

in its thermal trip settings. 3

7. a) * Never carry a power tool by the cord or hose.

Never yank the cord or the hose to disconnect it from the receptacle.

Keep cords and hoses away from heat, oil and sharp edges that could damage them. 3

Disconnect tools when not in use, before servicing and when changing accessories such as

blades, bits and cutters.

Remove portable electric tools from the workplace if they are damaged, and attach a Do

Not Use tag. 2b) Lockout-tagout (LOTO) or lockand tag is a safety procedure which is used in industry and research

settings to ensure that dangerous machines are properly shut off and not started up again prior to the

completion of maintenance or servicing work. It requires that hazardous power sources be "isolated and

rendered inoperative" before any repair procedure is started. 3

"Lock and tag" works in conjunction with a lockusually locking the device or the power source with

the hasp, and placing it in such a position that no hazardous power sources can be turned on. The

procedure requires that a tag be affixed to the locked device indicating that it shouldnt be turned on.2

c) At the heart of the process of locating the thermal power plant, an environmental audit shall be

conducted. It should review all the major aspects of the plants equipment and operating procedures in

order to identify the environmental problems so as to improve the environmental performance. The

ambient environmental quality in the air shed or water basin together with approximate estimates of

the contribution of the thermal power plant to total emissions loads of the main pollutants shall be

arrived. 3

The impact of the plant, under the normal operating conditions and abnormal scenarios on ambient air

and water quality affecting neighboring populations and sensitive ecosystems shall also be ascertained.

An analysis of the feasibility including benefits of switching to a cleaner fuel shall be preferred. Gas is

preferred where its supply can be assured at or below world average prices. Coal with high heat content

and low sulfur content is preferred over coal with high heat content and high sulfur content. 2

d) Ironically, more than two-thirds of electrical system failures can be prevented by a routine preventive

maintenance program. Studies show that the failure rate of electrical equipment is three times higher

for components that are not part of a scheduled preventive maintenance program as compared with

those that are. In addition, a planned EPM program allows the equipment owner to schedule the system

outage at a time of their choosing rather than having to correct major problems resulting from an

always untimely failure. 2
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It is recognized that individual locations may require more frequent maintenance due to the physical

environment or operational nature of the equipment. For example, harsh environments where excessive

moisture or dust may be present should have a more frequent EPM program. Similarly, equipment that

is used intermittently or equipment critical to a key process should be considered for a more frequent

program. Sound engineering judgment should be used in determining if more frequent maintenance is

appropriate. 3

8. a) Before issuing the Work Permit for work on a power line, the foremost step is-

* isolating the power supply by effective LOTO procedure;

determining a distance to avoid electrical flashover; and

providing additional allowance for inadvertent movements of the person, crane or plant relative to the

overhead power lines, or the movement of the overhead power lines relative to the person, crane or

Plant. 3

Operators and other workers are provided with information and instruction about the safety

precautions needed and the requirements of the electrical code, as well as appropriate training,

supervision and safe work practices and procedures.

An essential requirement of a safe system of work is that workers are competent to carry out the work

concerned. 2

b) As a primary grounding electrode, the ground rod must be driven into the earth to a depth of at least

8 feet (2.4 m). Angles of no more than 45 degrees away from vertical are allowed where the ground is

rocky. Best performance will be achieved if the second electrode is more than six feet (1.8 m) away. 3

Proper grounding rods will enhance safety (both user and equipment), improve performance, and may

even reduce costs. 2

c) The cable system must prevent contact of the high-voltage conductor with other objects or persons,

and must contain and control leakage current. Cable joints and terminals must be designed to control

the high-voltage stress to prevent breakdown of the insulation. Often a high-voltage cable will have a

metallic shield layer over the insulation, connected to earth ground and designed to equalize the

dielectric stress on the insulation layer. 3

Before laying a cable, proper locations for the proposed cable joints, if any, shall be decided, so that

when the cable is actually laid, the joints are made in the most suitable places. As far as possible, water

logged locations, carriage ways, pavements, proximity to telephone cables, gas or water mains,

inaccessible places, ducts, pipes, racks etc. shall be avoided for locating the cable joints. 2

d) 1. Excavation on earth for a normal earth Pit size is 1.5M X 1.5M X 3.0 M

2. Use 500 mm X 500 mm X 10 mm GI Plate (Plate may be use as big as possible to contact more and

more area of Earth for low resistance & best result)


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3. Make a mixture of Wood Coal Powder Salt & Sand all in equal part: (a) Wood Coal Powder use as good

conductor of electricity, anti corrosive, rust prove for GI Plate for long life: (b) Salt use as electrolyte to

form conductivity between GI Plate Coal and Earth with humidity: (c) Sand has used to form porosity to

cycle water & humidity around the mixture

4. Put GI Plate (EARTH PLATE) of size 500 mm X 500 mm X 10 mm in the mid of mixture

5. Use Double GI Strip size 30 mm X 10 mm to connect GI Plate to System Earthling 3

6. It will be better to use GI Pipe of size 2.5" diameter with a Flange on the top of GI Pipe to cover GI

Strip from EARTH PLATE to Top Flange

7. Cover Top of GI pipe with a T joint to avoid jamming of pipe with dust & mud and also use water time

to time through this pipe to bottom of earth plate

8. Maintain less than one Ohm Resistance from EARTH PIT conductor to a distance of 15 Meters around

the EARTH PIT with an other conductor dip on the Earth at least 500 mm deep.

9. Check Voltage between EARTH PIT conductors to Neutral of Mains Supply 230V AC 50 Hz it should be

less than 2.0 Volts. 2

9. a) Intrinsic safety is intended for products in which the level of electrical energy circulating or stored

in the product is insufficient to ignite a surrounding explosive atmosphere even under fault conditions.

Because of the method by which intrinsic safety is achieved, it is necessary to ensure that not only theelectrical apparatus exposed to the potentially explosive atmosphere but also other electrical apparatus

with which it is interconnected is suitably constructed. 3

The equipment is designed according to EN 50020 and is suitable for gas groups I and II, categories 1G or

M1 (ia) and 2G or M2 (ib). Typical areas of use are control and instrumentation circuits with low voltage

and current. 2

b) The likelihood of the hazard being present in flammable concentrations will vary from place to place.

A location very close to an open source of hazard will have a high likelihood of a flammable

atmosphere. On the other hand, outside a flanged pipe containing a flammable liquid, the likelihood of

a flammable atmosphere being present is much lower since it will only occur if the flange leaks. 3

Rather than work with an infinite range of possibilities, three zones are defined: Zone 0, Zone 1 andZone 2. 2

c) Zone 0: Flammable atmosphere highly likely to be present - may be present for long periods or even

continuously

Zone 1: Flammable atmosphere possible but unlikely to be present for long periods 3

Zone 2: Flammable atmosphere unlikely to be present except for short periods of time - typically as a

result of a process fault condition. 2

d) Ex e: Increased Safety: Ex ia: Intrinsic Safety ia; Ex ib: Intrinsic Safety ib 3Ex p: Pressurized Protection; Ex m: Encapsulation 2

10. a)A circuit breaker in which the current carrying contacts operate in Sulphur Hexafluoride or SF6 gasis known as an SF6. SF6 has excellent insulating property. SF6 has high electro-negativity. That means it

has high affinity of absorbing free electron. Whenever a free electron collides with the SF6 gas molecule,

it is absorbed by that gas molecule and forms a negative ion. 2

The attachment of electron with SF6 gas molecules may occur in tow different ways,


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1) SF6 +e=SF6

2) SF6 + e = SF5+ F

These negative ions obviously much heavier than a free electron and therefore over all mobility

of the charged particle in the SF6 gas is much less as compared other common gases. We know

that mobility of charged particle is majorly responsible for conducting current through a gas. 3

b) Zone 1: A place in which an explosive atmosphere consisting of a mixture with air of dangerous

substances in the form of gas, vapor or mist is likely to occur in normal operation occasionally. 2

Zone 2: A place in which an explosive atmosphere consisting of a mixture with air of dangerous

substances in the form of gas, vapor or mist is not likely to occur in normal operation but, if it

does occur, will persist for a short period only. 3

c) There are varying types of equipment that can be used within the hazardous zones to

ensure that the potential for an explosion is removed or greatly reduced. This equipment

must be designed and manufactured in accordance with particular construction

parameters known as protection concepts. Essentially these concepts fall under four

main methods. 2

Intended to prevent an ignition from escaping outside the equipment= Type Exd= Encapsulation

Intended to prevent the explosive atmosphere contacting the ignition source= Ex m=

Encapsulation. 3

d). i. Bureau of Indian Standards ii. ATEX: (ATmospheres EXplosibles) iii. CSA: CanadianStandards Association 3

iv. UL: Underwriters Laboratories Inc. v. Factory Mutual vi. CE: Conformance European 2

Key for Electrical Safety 2013

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