elecrical equipment maintenance in pipelines

8/10/2019 Elecrical Equipment Maintenance in Pipelines

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ELECTRICAL EQUIPMENT MAINTENANCE IN PIPELINES

1submitted by Anirban Das

ELECRICAL EQUIPMENT MAINTENANCE IN PIPELINES

1. INTRODUCTION:

The most economical way of transporting petroleum products from one place to

another is through the pipelines. The pipeline offers low operating cost and high reliability of

transportation of fluids.

Generally pipeline consists of the following major systems:

Tank farms

Pumping stations

Metering stations

Valve manifolds

Pigging stations

SCADA systems

Corrosion control systems

Figure-1: Product pipe line system


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The major electrical equipments that are used in pipelines are:

POWER SUPPLY AND DISTRIBUTION

SUB STATIONS

TRANSFORMERS

SWITCH GEAR

ELECTRIC MOTORS

MOV ACTUATORS

CATHODIC PROTECTION SYSTEMS

EMERGENCY GENERATORS

2. POWER SUPPLY AND DISTRIBUTION

The power supply and distribution depend on the electrical power requirements (or

maximum demand load) for the installation.

2.1 LOAD ESTIMATION:

Load estimation requires analysis of load characteristics and will take into account

the demand factor relationship between connected loads and the actual demand imposed on the

system. For load estimation the following factors are used.

2.1.1 Preliminary loads:

The minimum loads which are connected to power system.

2.1.2 Demand Factor:

It is defined as ratio of maximum demand (largest demand during a specified time) to

the total connected load.


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By this demand factor we can know the capacity of transformer and the conductor

size, and all equipment associated with distribution of electrical power to utilization equipment.

2.1.3 Diversity Factor:

Diversity factor is defined as the ratio of the sum of the individual maximum

demands of various subsystems within a system to the maximum demand of the system.

2.1.4 Load Factor:

Load factor is defined as the ratio of the average load over a designated period of

time to the peak load occurring in that period.

A low load factor indicates short-time demand peaks which can result in heavy

charges to the Using Agency. Low load factor will be corrected by shedding loads or by peak-

shaving generation during periods of peak demand.

2.2 Voltage Requirement:

The voltage requirement is based on the type of distribution. That means

primary distribution and secondary distribution.

Primary distribution means distribution from main substations to local substations.

Secondary distribution means local substations to domestic users.

The voltage requirement is also based the type of equipment we are using.

3. SUBSTATIONS

Substations mainly consist of:

Power transformers

Underground cables

Air circuit breakers or Oil circuit breakers

Buses


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Protective relays

Current transformers and Voltage transformers

LT/HT control panels

Lightening or Surge arrestor

Grounding

Figure-2: An 11 KV substation (single line diagram)

4. TRANSFORMERS

4.1 BASIC PRINCIPLE:

The transformer is based on two principles:

An electric current can produce a magnetic field (electromagnetism)

A changing magnetic field within a coil of wire induces a voltage across the ends of the

coil (electromagnetic induction).


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Figure -3: An ideal step-down Transformer

4.2 SWITCHING ON AND OPERATION:

4.2.1 HV Energisation:

When the installation has been fully checked, the HV side can first be switched-on and

following this, the LV side. It is recommended that the transformer is left energized for a few

hours before switching-on the LV side and applying load. During this time the transformer should

be closely supervised paying attention to both coolant oil level and temperature. Verify the voltage

between the low voltage phases and phase to neutral if used.

4.2.2 Re-adjusting the tap switch:

The tap switch enables sections of the HV winding to be in or out of the turns ratio

thus affecting the secondary low voltage side. When the voltage measured at the low voltage side

deviates from the required value this usually indicates that the incoming HV voltage is too high or

too low. Normally the supply voltage is held within limits of plus or minus 6%. The tapping switch

can compensate for variations of plus or minus 5% in 2.5% steps. If adjustment is desired then the

following procedure should be followed.


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Disconnect the transformer from both the HV systems and the LV systems.

Unlock and remove the padlock, if fitted. Release the tapping switch mechanism by lifting

the operating handle.

Turn the handle to the desired position to increase LV volts - turn to a higher tap position

number, which will decrease the HV, turns in circuit and proportionally increase the output

voltage.

4.3 MAINTENANCE:

4.3.1 ONLINE MAINTENANCE:

Frequency of routine maintenance is quarterly for distribution transformers and daily

for grid transformers.

Check load current: If more than rated, reduce non priority loads

Check voltage: control the appropriate voltage H.V voltage and L.V voltage variations. If

online tap changer (O.L.T.C) is provided change the tap positions as required.

Check OTI&WTI readings:

Check the temperature does not increase beyond rated temperature.

Check oil level in Transformer and O.L.T.C: check the oil level in respective conservators.

Ensure that they are not beyond rated temperature. If not top up with dry transformer oil.

Check transformer for oil leaks.

Check breather on transformer and O.L.T.C: check color of silica gel. It should be blue. If

it is pink replace it by spare charge.

Check sound level: Certified sound levels determined in accordance with NEMA, shall not

exceed the following:


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Transformer Rating

Sound Level Rating

0 - 9 KVA 40 dB

10 - 50 KVA 45 dB

51 - 150 KVA 50 dB

151 - 300 KVA 55 dB

301 - 500 KVA 60 dB

TABLE-01

4.3.2 ANNUAL SHUTDOWN MAINTENANCE:

Visual inspection of transformers for oil leakage, oil level, and silica gel conditions should

be done.

Clean the transformer body and paint it if necessary.

Check the oil level and top-up in necessary.

Remove the silica gel and reactivate if necessary.

Open H.T terminal box and check for loose connections, heating and oil leakage from

bushings.

Open L.T terminal box and check for the same.

Check the body and neutral earthing joints.

Check the tap changer for pitting and overheating etc;

Examine Bucholzs relay, OTI (oil temperature indicator) and WTI (winding temperature

indicator) relays operation and check for accuracy.


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4.3.3 CAPITAL OVERHAUL:

Capital over haul shall include overhaul inspection, lifting of core and coils, cleaning

of transformer tank. Frequency of overhaul will be normally in between 7 to 8 years.

TRANSFORMER OIL: Properties

S.N Description New oil Old oil

1

2

3

4

Electrical strength

Moisture, Mechanicalimpurities

Flash Point

Viscosity at 270C

40kv

None

140

0

C

27 cst

25kv/40kv

25/35 ppm

Max. 5

0

C lower

27 cst

TABLE-02

After one year any changes in the oil properties above said, the oil should be changed. The old

mineral oil should be reconditioned.


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The following table depicts the transformer trouble shooting

SYMPTOM CAUSE CORRECTIVE

MAINTENANCE

High Temperature.

Fractured metal or

porcelain parts of thebushings.

Badly discolored oil.

DRY_TYPE

TRASNFORMERS:

High temperatures

Moisture

Over voltage.

Over current.

High ambient temperatures.

Insufficient cooling.

Unusual strains place on

terminal connections.

Contaminated by varnishes.

Carbonized oil due to

switching.

Winding or core failure.

Insufficient air flow

Transformer in moisture

atmosphere or accidental

wetting

Change the circuit voltage or

transformer connections to avoid

over excitation.

If possible reduce the load.

Heating can often be reduced by

improving power factor of load.

Check parallel circuits for

circulating currents which may be

caused by improper ratios of their

impedances.

Either improve ventilation or

relocate transformer in lower

ambient temperature.

Make sure cooling is adequate.

Cables and bus bars attached to

the transformers should beadequately supported. In the case

of heavy leads, flexible

connections should be provided to

remove strain on the terminal and

bushing porcelain.

Retain oil if di-electric strength is

satisfactory.

Filter/ reclaim/ replace oil.

Repair transformer.

Check that in take is not

obstructed. If unit is fan cooled

check fan speed.

Transformers dry out to be done.

TABLE-03


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5. ELECTRICAL POWER CABLES

5.1 INTRODUCTION:

A power cable is an assembly of two or more electrical conductors, usually held

together with an overall sheath. The assembly is used for transmission of electrical power.

Power cables may be installed as permanent wiring buried in the ground, run overhead, or

exposed. Flexible power cables are used for portable devices, mobile tools and machinery.

For constructional details of power cables see ANNEXURE- A

For cable selection criterion see ANNEXURE-B

For cable laying details see ANNEXURE-C

For testing of cables see ANNEXURE-D

For NETA insulation standards see ANNEXURE-E

5.2 CABLE FAULTS:

The problems occurs in the cables due to

Environmental changes.

Changes in the thermal resistivity of the soil.

Defects in the earthing and bonding.

Excavation by other utilities.

The most frequent faults are short circuit faults and earth leakage faults and

insulation breakdown. Due to these, some part of the cable (specifically, underground) get

heated up and burst.

5.3 LOCATING CABLE FAULT:

There are two basic methods of locating an underground cable fault.


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5.3.1 Sectionalizing:

In this procedure, we divide the cable into smaller sections and examine the insulation

resistance or continuity.

5.3.2 Thumping:

When we supply a high voltage to a faulted cable, the resulting high-current arc

makes a noise loud enough for us to hear above ground. While this method eliminates the

sectionalizing method's cutting and splicing, it has its own drawback. Thumping requires a

current on the order of tens of thousands of amps at voltages as high as 25kV to make an

underground noise loud enough for you to hear above ground.

The heating from this high current often causes some degradation of the cable insulation.

There are some relatively new methods of locating cable faults that use rather

sophisticated technology.

5.3.3 Time Domain Reflectometry (TDR):

The TDR sends a low-energy signal through the cable, causing no insulation

degradation. A theoretically perfect cable returns the signal in a known time and in a known

profile. Impedance variations in a "real-world" cable alter both the time and profile, which

the TDR screen or printout graphically represents. This graph (called a "trace") gives the user

approximate distances to "landmarks" such as opens, splices, Y-taps, transformers, and water

ingression.

One weakness of TDR is that it does not pinpoint faults. TDR is accurate to

within about 1% of testing range.


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Another weakness of TDR is that reflectometers cannot see faults-to-ground with

resistances much greater than 200 ohms. So, in the case of a "bleeding fault" rather than a

short or near-short, TDR is blind.

5.3.4 High-voltage radar method:

There are three basic methods for high-voltage radar, they are

Arc reflection

Surge pulse reflection

Voltage pulse reflection

The arc reflection method uses a TDR with a filter and thumper. The filter limits both

the surge current and voltage that can reach the cable under test, thus allowing

minimal stress to the cable. Arc reflection provides an approximate distance to the

fault (when there is an ionizing, clean arc produced at the fault and the TDR in use is

powerful enough to sense and display a reflected pulse).

The surge pulse reflection method uses a current coupler and a storage oscilloscope

with a thumper. The advantage of this method is its superior ability to ionize difficult

and distant faults. Its disadvantages are that its high output surge can damage the

cable, and interpreting the trace requires more skill than with the other methods.

The voltage pulse reflection method uses a voltage coupler and an analyzer with a

dielectric test set or proof tester. This method provides a way to find faults that occur

at voltages above the maximum thumper voltage of 25kV.

One test to detect an open neutral requires shorting a known good conductor to a

suspect neutral, then measuring the resistance with an ohmmeter. If the reading is 10

ohms or higher, we can suspect an open neutral. Remember, other objects can

complete the circuit.


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5.4 REPAIRING OF CABLES:

The repairing is nothing but locating the cable fault and cut the cable and re-joint

the cables. There are two methods presently used in jointing of the cable, they are

Polyurethane Cable Jointing.

Heat shrinkable Cable Jointing.

5.4.1 POLYURETHANE CABLE JOINT:

Underground cable joints in electricity distribution networks must remain

moisture free to prevent arc failure of any joint. Because the joints are created on-site, the

quality of the jointing technique is critical.

The quality of the joint is such that it does not add any resistant to the circuit. The

materials and technique so designed to give adequate mechanical and electrical protection to

the joints under all service conditions.

Polyurethane kit consists of

Adequate number of mechanical conductors.

PTFE (Polytetrafluoroethylene) tube set to provide primary electrical insulation and

correct cable positioning.

Cast metal conducting tubes to make the electrical cable connection with snap -off

bolt heads to ensure that perfect compression torque is applied.

Armour bonding system in case of armoured cables (Earth continuity).

A pair of white Glassfibre-Reinforced-Polyester (GRP) mating shell moulds which

completely enclose and seal the joint, forming the inner shell.

A container of liquid silicone, which is poured into the polyester mould, completely

encasing the cable joint.


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Figure-4: Cutaway view of straight water resistance medium voltage underground joint

Figure-5: Cable jointing Kit

Figure-6: Conductor joints in the cable


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Figure-7: POLYURETHANE JOINTING PROCESS

The above figure shows us how the polyurethane jointing process is going. The

third from right connector is having its white, inner shell mould filled with liquid silicone.

Note the temporarily placed funnel, mounted in the white inner shell, towards the foreground,

which ensures the correct level of the silicone fill and zero air entrapment, and the support

frame holding the container, as the filling is carried out. The liquid silicone container has two

outlets, and the flow rate into the white, inner shell, is controlled by the gentle release of the

seal on the second, (red) cap. As soon as the silicon pour is completed, the entry holes into

this white mould are sealed. The whole process is cold, ideal for hazardous zoned areas.

5.4.2 HEAT SHRINKABLE CABLE JOINT:

Heat shrinksplices are available as a series of heat shrinkable tubes. Some may

be preassembled by the manufacturer to reduce the number that must be handled in the field.

The tubes must be slipped over the cable prior to connecting the conductors. After

positioning each tubeover the connected cables, heat is applied to shrinkthe tube snugly over

the underlying surface and soften anymastic material used in the assembly. Stress relief is


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generally provided by stresscontrol tubesthat arealso shrunkinto place sothat endsof the

stress control tubeoverlap both cable insulation shields. The joint is finished in thenormal

manner.

Figure-8: Heat shrinkable cable jointing Kit

During the heat shrink installation process, the stored recovery force of the tube

is released in addition to the recovery force of the heat shrinkable outer layer. A pre-designed

screen and thick layer of insulation is installed in one simple process. This allows extremely

tight electrical interfaces due to the shrink force generated. The elastomeric (tube) insulation

characteristic combined with the rigid outer heat shrinkable screen layer enables the joint to

follow the thermally induced dimensional changes of the cable insulation.


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5.5 MAINTENANCE:

SCHEDULE EQUIPMENT TASK

Annually Cable Terminations Check connections for security

(Except switchgear connections)

Cable above ground Check for outer sheath damageCheck attachment to poleWhere fitted, ensure protectivepipe is secure.

Cable loading Where fitted, check and recordDemand indicator readings(MV cable loadings are normallyestablished by load flow studies).

Earthing Check all earth connections forsecurity.

5 yearly Earthing Test all earth connections at MVand LV substations and compareto standards.

TABLE-04

6. SWITCH GEARS AND PROTECTIVE RELAYS

6.1 INTRODUCTION:

Switch gears are available in many forms, from single simple isolator to

sophisticated vacuum breakers.

The term switchgear, used in association with the electric power system, or grid,

refers to the combination of electrical disconnects, fuses and/or circuit breakers used to isolate

electrical equipment. Switchgear is used both to de-energize equipment to allow work to be done

and to clear faults downstream.


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6.2 TYPES OF CIRCUIT BREAKERS:

The circuit breakers are classified on the basis of insulating medium present in it.

They are

Air circuit breaker

Vacuum circuit breaker

SF6 circuit breaker

Oil circuit breaker


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Figure-9: A 25 kv Single phase Air Circuit Breaker

For the circuit breaker it is necessary to beak the circuit immediately when the fault

occurs and isolates the fault position from healthy position.

To ensure the equipment remains safe and reliable, regular examination is essential.

6.3 MAINTENANCE:

Essential areas requirements for inspection and testing:

6.3.1 INSULATION:

Insulation systems must be closely inspected for sings of over heating, cracking and

other defects.

6.3.2 CONTACTS:

Inspect the contacts for signs of excessive wear and over heating. Free movement of

the contactors also examined.

6.3.3 TERMINALS:

All terminals must be checked for firmness and signs of over heat.

6.3.4 CABLES:

Power and control cables must be examined with the connecting equipment.

6.3.5 BUS BARS:

Bus bars shall subject to periodic inspection.

6.4 MAINTENANCE OF POWER AIR CIRCUIRT BREAKER:

Power air circuit breaker should be maintained annually.

To perform maintenance, withdraw the circuit breaker from its enclosure and do the following:


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Inspect alignment of movable and stationary contacts. Make adjustments as

recommended in manufacturers manual.

Wipe bushings, barriers, and insulating parts. Remove the dust, smoke, and any foreign

deposits. Replace the damaged parts.

Check control devices and replace if needed.

Check breaker control wiring and ensure that the connections will be tight.

Operating breaker in fully opened and closed position after service. Check for any

binding before going to put in the circuit.

6.5 MAINTENANCE OF CONTACTOR:

The duty of the contactor is very often in a day. Such duty reflected in mechanical wear and tear

and also electrical contact wear. The maintenance process:

Cleaning

Dressing or renewal of main and auxiliary contacts.

Checking contact alignment.

Trip mechanism inspection.

Check tightness and conditions of all connections.

Arc chute inspection.

Lubrication.


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6.6 MAINTENANCE OF ISOLATOR:

The maintenance of isolator mainly consists of:

Cleaning, checking contact conditions and tightness of connections and confirming the

tightness and continuity of the fuses, if fitted.

6.7 PROTECTIVE RELAY MAINTENANCE:

The maintenance of protective relays should include general inspection of physical condition of

all parts at regular intervals. Maintenance as follows:

Relays are provided with dust proof covers and before a cover is removed, the cases

should be carefully dusted.

Relay interior should be free from dust, iron particles etc.

Dust and dirt should be carefully wiped off by a soft squirrel hair brush. Mechanical

blowers or blowing by mouth is not recommended.

The internal wiring, ICs, printed circuits should be examined for corrosion. Excessive

heat may damage the insulation.

Relay flags/targets should operate freely without friction and also reset freely.

Perform complete tripping and operational tests to verify all control and protective

functions and alarms and tripping mechanism.


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TROUBLE SHOOTING:


MAINTENANCE

Over heating

Breaker is not closing.

Improper alignment and

adjustment of contactor.

Burnt and pitted due to

lack of attention after

many heavy operations,

or too frequent

operations.

Breaker kept closed (oropen) for a too long

period.

Transmission of heat to

the breaker from

overheated or inadequate

cables or connection bars.

Failure of latching device.

Damaged trip coil

Damaged or dirty

contacts of tripping

circuit

Faulty connections in trip

circuit (loose or broken)

Insufficient voltage

caused by too much drop

in leads.

Poor voltage regulation

Loose connections

Contacts should be aligned and

adjusted properly. Contacts to be

repaired or replaced properly.

Burnt and pitted contacts should

be dressed up if possible or

replace with new parts. Dressing

up to be done carefully.

Contacts to be wiped out forcleaning and if possible silver-to-

silver contacts to be arranged.

If heat is due to excess current,

fault should be corrected. If

cable size is in adequate, cable

should be replaced.

Examine surface of the latch, if

worn or corroded, check latch,wipe, and adjust according to

instruction book.

Replace it.

Dress or replace damaged

contacts. Clean the dirty

contacts.

Replace faulty wires. All

connections are to be tightened.

Replace with oversize wires.

Improve contact at connections.

Check up voltage, if less correct

it.

Tighten the connections.


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Frequent damage of

moving and fixing

contacts

Bushing problems

Inadequate current

carrying capacity

Improper replacement of

switch gear during

maintenance.

Misalignment of controls

or inadequate pressure

between moving and

fixed contacts

Accumulation of dirt or

other deposits

Flash over due to foreign

deposits like salt, cement

dust etc.

Capacity of contactors as well as

breakers should be examined.

Capacity of original switch gear

should be matched with new one.

Contacts to be dressed up. Spring

etc. to be checked for proper

pressure.

Clean external surface.

Frequency of cleaning to be

increased. Carbon tetra chloride

or liquid ammonia or any other

suitable agent may be used to

clean porcelain.

TABLE-05

7. ELECTRIC MOTOR

7.1 INTRODUCTION:

Motors covert electrical energy into mechanical energy. Mainly motors are classified

into two types:

D.C motors

A.C motors

D.C. motors are mainly used in traction works and cranes where constant speed

characteristics are necessary. These are not used in domestic and industrial purposes because the

cost of the D.C motor is high and also the supply of D.C power also costly one.


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So the best alternative is using A.C motors. In general most of industries are using 3-

phase motors. Hence we here consider 3-phase motors only.

The motors are classified into two types:

Induction motors

Synchronous motors

Let us briefly discuss about induction motors because many industries using

induction motors only.

7.2 CONSTRUCTION:

Motor mainly consists of two basic parts know as

Stator

Rotor

Figure-10: cut way view of squirrel cage induction motor


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Figure-11: Rotor of the squirrel cage induction motor

The stator winding and rotor windings are insulated. The primary purpose of

insulation is to withstand turn-to-turn, phase to-phase and phase-to-ground voltage such that to

direct the stator phase currents through the desired paths of stator windings.

The insulations are classified as:

Class A: 105C

Class B: 130C

Class F: 155C

Class G: 180C

For motors having high temperature rise class F insulation is uses.

7.3 MAINTENANCE OF MOTOR:

Motors are designed to give many years of reliable service with less attention. A

definite schedule of preventive/inspection/predictive maintenance should be established to avoid

breakdown. The schedule depends on the operating conditions and experience with the similar

equipment.


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7.3.1 PREDECTIVE MAINTENACE:

The main goal of the predictive maintenance is to predict and fix the faults by using

following techniques before they occur.

The techniques are:

Vibration analysis:

This technique involves measuring machinery vibration to identify ongoing

conditions through vibrometer. This tells us the bearing damages.

Motor circuit analysis:

This technology monitors the conditions of complete motor circuit parameters like phase

resistance, inductance and capacitance.

7.3.2 PREVENTIVE MAINTENANCE:

7.3.2.1 A schedule for LT&HT motors (Half yearly):

Counter check that equipment is isolated positively.

Check the terminal box for loose connection in the cable termination.

Perform regreasing.

Remove front and rear grease cups if regreasing system is not healthy.

Check the condition of the grease. Top up grease if condition is not o.k.

Put back grease cups.

Connect the terminal box.

Check the earthing and return the clearance.

Perform the visual inspection of the stator module, cable terminals.

7.3.2.2 B schedule for LT&HT motors(Predictive):


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Counter check that equipment is isolated positively by means of LT/HT tester.

Get the motor decoupled.

Open the terminal cover and remove the cable connections.

Open the foundation bolts and take out the motor from foundation and send to electrical

workshop for schedule.

Inspect the motor for visible damages and rotor freeness.

Open the fan cover and remove the fan from the shaft.

Remove the grease cups on both sides. Inspect the condition of grease.

Take out both rear and front end shields.

Check the bearing housing for correct measurement of the bearing with sufficient

tolerances.

Remove both front and rear bearing from the shaft.

Clean all the grease using suitable solvent. Then wash the bearing with diesel and dry air.

Remove the rotor from stator.

Inspect rotor thoroughly for the loose bars and cage/shorting rings.

Inspect the bearing seat. If it is worn out and loose metalize the bearing.

Check the rotor trueness. If the shaft is bent send it for reshafting.

Replace the studs and nuts of the grease cups if worn out.

Inspect the stator winding for loose coils, loose connections, heating effect, deterioration

of insulation etc.

Clean the stator winding with clean dry cloth and blower.

Heat the winding in heating chamber up to 100C for 8 hours.

Again clean the winding.

Heat the stator for 6 hours.


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Apply protective coat of varnish.

Heat the windings (80C) till the varnish is dried.

Clean the stator and make ready for the assembly.

Clean the rotor also and insert the rotor in position.

Put the bearings on the shaft.

Assemble the motor with end shields in position.

Put back the fan on shaft.

Put back coupling on the shaft.

Run the motor and monitor the performance for four hours.

TROUBLE SHOOTING:


MAINTENANCE

Motor will not start Overload control trip

Power not connected to motor

Faulty (open) fuses

Low voltage

Wrong control connections

Loose terminal lead connections

Open circuit in stator or rotor

winding

Short circuit in stator winding

Wait for overload to cool. Try

starting again. If motor still

doesnt start, check all thecauses shown below.

Connect power to motor.

Test fuses and circuit breakers.

Check motor name plate values

with power supply. Check

voltage at motor terminals with

motor under load to be sure wire

size is adequate.

Check connection with control

wiring diagram.

Tight connections.

Check for open circuits.

Check for shorted coil.


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Motor noisy

Motor vibrates

At higher than normal

temperature or

smoking

Bearings stiff

Over load

Motor running in single phase

Electrical load unbalance

Vibration due to unbalance or

misalignment

Mechanical system resonance

Air gap is non uniform

Noisy ball bearings

Loose punching or loose rotor

on shaft

Objects caught between fan and

end shields

Motor loose on foundation

Coupling loose

Overload

Electrical load unbalance

Restricted ventilation

Incorrect voltage and frequency.

Stator winding shorted

Rotor winding with loose

Free bearings or replace.

Reduce the load.

Stop motor and then try to start

motor, it will not start in singlephase.

Check current balance.

Balance or align the machine.

Remove motor from load. If

motor is still noisy, rebalance

the rotor.

Centre the rotor and if necessary

replace the bearings.

Check the lubrication. Replace

bearings if noise is excessive.

Tighten all holding bolts.

Disassemble motor and clean it.

Tighten holding-down bolts.

Check coupling joint, check

alignment. Tighten coupling.

Measure the motor load with

ammeter and reduce the load.

Check for voltage un balance orsingle phasing.

Clean air passages and

windings.

Check motor name plate values

with power supply.

Use insulation testing

procedures.

Tighten if possible or replace


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Bearings hot

Sleeve bearings

connections

Motor used for rapid reversing

service

Bent shaft

Insufficient oil

Foreign materials in oil or poor

grade of oil

Oil rings rotating slowly or not

rotating at all

Defective bearings or roughshaft

with another rotor.

Replace with motor designed for

reversing service.

Straighten the bent shaft atservice shop.

Add oil if oil is very low.

Drain, oil flush, and re lubricate

using industrial lubricant.

Oil too heavy, drain and replace.

Replace bearings. Resurface

shaft.

TABLE-06

8. MOV ACTUATORS

8.1 DESCRIPTION:

Electrically operated motor operated valves are widely used in power plant/process

units and play a critical role. A typical actuator consists of

3-phase induction motor

Control gear

Travel limit switches and torque switches

Local controls


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Electronics circuit consists of power supply unit, remote operating unit, and logic cords.

Figure-12: Sectional View of Motor operated valve


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Figure-13: Motor Operated Valve

8.2 MAINTENANCE:

Schedule:

Based on the plant run length and application, a routine maintenance program is to

be developed. The maintenance period will be 1 year.

Check for evidence of oil leakage and rectify

Check the condition of gear case oil and replace if necessary.

Check the security of actuator mounting bolts.

Check cable connections to the actuator.

Check motor winding insulation resistance and check winding resistance is balance.

Check engagement of the clutch.

Energize the actuator and check direction of rotation.

Check electrical operation to limits.

In intelligent units check the healthiness from the diagnostic codes as per the vendors

manual.


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TROUBLE SHOOTING:

TABLE-07

9. CATHODIC PROTECTION

9.1 INTRODUCTION:

Cathodic protection is an electrochemical method used to prevent or control

corrosion of buried or submerged metallic structures.

After a CP system is installed and adjusted to provide adequate protection, currents

and potentials should remain relatively stable; changes in currents or potentials indicate a

problem.

SYMPTOM CORRECTIVE MAINTENANCE

MOV not operating

MOV not operating

although 3 phase

supply is healthy

MOV not operatingfor intelligent type

MOV

Check healthiness of 3 phase supply.

Check mechanism for freeness.

Check control gear/contactor.

Check PCBs.

Check control circuit.

Check limit switch.

Check internal battery.

Check PCBs.


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9.2 CATHODIC PROTECTION METHODS:

Sacrificial (Galvanic) Cathodic protection.

Impressed current Cathodic protection.

Out of these two methods impressed current protection is the most economical one

for the long pipelines. The disadvantages of the Galvanic protection is small driving voltage is

available, and small current available in higher resistivity electrolytes. Here we discuss briefly

about impressed current CP protection.

In an impressed current system, the protective current is supplied by a rectifier (or

other DC power source) to the structure.

Figure-14: Impressed Current Cathodic Protection System

Impressed current Cathodic protection systems use alternating current or solar

powered rectifiers as a power source.

Rectifiers used for Cathodic protection commonly use an

Adjustable step down transformer,

Rectifier stacks,


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A shunt to measure output current,

Meters to indicate output current and voltage.

The function of the rectifier is to convert alternating current into controlled direct current.

Figure-15: Impressed current Cathodic protection system Rectifier

9.3 RECTIFIERS USED IN CATHODIC PROTECTION:

Silicon diodes

Thyristors

Switch mode

9.4 ANODE MATERIAL:

The anodes of an impressed current system provide the means for the protective

current to enter the electrolyte. Since the anodes form the corroding part of the system, the best

material is one that has a low rate of weight loss per ampere-year. The most commonly used

materials for impressed current anodes are graphite and high-silicon cast iron.

9.5 MAINTENANCE:

9.5.1 RECTIFIER OPERATIONAL INSPECTION:


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The purpose of the rectifier operational inspection is to determine the serviceability

of all components required to impress current to the anodes of the impressed current system.

Maintenance Schedule:

Thirty days after cathodic protection system is installed and properly adjusted.

One to two years after that.

Procedure:

Visually check all rectifier components, shunt box components, safety switches.

Tighten all accessible connections and check temperature of all the components.

For rectifiers with more than one circuit, measure the output voltage and current for each

circuit using a dependable hand-held meter, and calibrate the rectifier meters, if present.

Calculate the cathodic protection system circuit resistance of each circuit by dividing the

rectifier DC voltage output of each circuit by the rectifier DC ampere output for that

circuit.

9.5.2 IMPRESSED CURRENT CHECK:

Maintenance schedule:

Sixty days after rectifier inspection, more frequent checks may be required by local

conditions.

Procedure:

Measure output D.C voltage and current from the rectifier.

Ensure the DC ampere output of the rectifier meets the current (ampere) requirement of

the system.


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Calculate the cathodic protection system circuit resistance of each circuit by dividing the

rectifier DC voltage output of each circuit by the rectifier DC ampere output for that

circuit.

Calculate the D.C out put voltage of the rectifier and check that it is rated or not.

TROUBLE SHOOTING:

Figure-16: Wiring diagram of a Rectifier


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.

TABLE-08

10. EMERGENCY GENERATOR

10.1 INTRODUCTION:

Generator is the alternate energy source for emergency power needs in the pumping

station. There are many names for generator such as A.C generator and alternator. Alternator is

the commonly used name.

A typical pump station consists of diesel engine driven alternator to cater to

emergency power requirements like,


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Radiator motors of mainline engines

Air compressors

Centrifuges

UPS system

Lighting in the pump shed and control room etc.

10.2 GENERATOR CONSTRUCTION:

The stationary field

The rotating dc magnetic field.

The armature, normally containing a three-phase winding, is mounted on the shaft.

The armature winding is fed through three slip rings (collectors) and a set of brushes

sliding on them.

The rectifier-bridge is fed from a shaft-mounted alternator, which is itself excited by

the pilot exciter.

The core is slotted (normally open slots), and the coils making the winding are placed

in the slots.

.


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Figure-17: The figure shows Silent type Generator

10.3 MACHINE RATINGS:

A generator is usually described by giving it a rating. This rating is given at the generators

capability point of maximum continuous power output. The terms generally used to provide

the rating are as follows:

Apparent power MVA Mega volt amperes

Real power MW Mega watts

Reactive power MVARs Mega volt amps reactance

Power factor pf A dimensionless quantity

Stator terminal- Voltage Vt Alternating voltage

Stator current Ia Alternating current amperes

Field voltage Vf Direct voltage

Field current If Direct current amperes

Frequency Hz Hertz

Speed rpm Revolutions per minute


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Figure-21: Name plate details of A Generator

10.4 GENERATOR MAINTENANCE:

10.4.1 Weekly Maintenance: Before starting engine

Check oil level (add oil as needed).

Check coolant level.

Walk around inspection.

Check air cleaner indication (change filter as needed).

Fuel system- check for leaks.

Inspect belts, adjust or repair as needed.

Check generator for moisture, dust, &debris and clean it.

10.4.2 Weekly Maintenance: With engine running

Check for proper oil pressure.

Check for proper jacket water temperature.


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Check for proper fuel pressure.

Check frequency and voltage.

Record engine run hours.

10.4.3 Weekly Maintenance: After stopping engine

Automatic switches- check switches in proper position for automatic start.

Check fuel level; refill the tank if below 3/4 full.

10.4.4 Yearly Maintenance: Before starting the engine

Perform all weekly before starting engine maintenance first.

Add coolant conditioner as needed.

Drain water and sediment from fuel tank.

Change fuel filter.

Inspect and clean or replace air filter element if needed.

Check and adjust all linkages.

Test all engine protective devices.

Check generator winding with mega ohm meter.

Check generator bearing. Lubricate as required.

10.4.5 Yearly Maintenance: With engine running

Perform all weeklywith running engine maintenance first.

Inspect engine mounts. Check for proper torque.

Load test to minimum 30% its rated load for minimum 2 hours. Record all the gauge

readings.

Jacket water temperature will be higher compared to weekly no-load tests.


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10.4.6 Yearly Maintenance: After stopping engine

Perform all weekly after stopping engine maintenance first.

Obtain oil sample for analysis of chemical and physical test.

Change engine oil.

Replace oil filter. Cut filter and inspect for foreign material.

10.4.7 Three years maintenance: Before starting engine

Perform all weekly & yearly before starting engine first.

Cooling system

Drain, clean and flush.

Replace thermostats.

Refill with coolant solution and conditioner.

Inspect radiator cap and replace if needed.

Replace all hoses and belts.

Inspect turbo charger for proper operation.

Perform engine adjustment & tune up.

10.4.8 Three years maintenance: With engine running

Perform all weekly & yearly before starting engine first.

Check engine mounts. Check for proper torque.

Check exhaust system for leaks. Repair as needed.

10.4.9 Three years maintenance: After stopping engine

Perform all weekly & yearly after stopping engine first.

Obtain oil samples for analysis.


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10.4.10 Grounding Cables:

Schedule: Monthly:

All generator frames and casings are grounded to the power plant grounding system.

This is usually done at one location only to allow control over the ground current flow, and to

ensure that there are no circulating currents in the generator frame structure that will cause arcing

between components inside the machine.

Figure-19: Grounding of a Generator

The ground cables should be inspected to ensure they are tight and in generally good condition.

Signs of damage would be corrosion, overheating, fraying, or cracking.

11. SAFETY WHILE DOING ELECTRICAL MAINTENANCE

While doing maintenance works every one should follow the safety procedures.

A routine task can easily become a hazard if the required procedure is not followed or if

attention to detail is not applied.

Do not assume that the hazards in your work area are always at your eye/foot level. Be

aware of ALL your surroundings.


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A complete review of all systems should be conducted prior to any maintenance work.

All electrical equipment connected to line voltage must be bonded to ground

Necessary electrical repairs should be made by a qualified electrician.

ALWAYS de-energize electrical power source before making any adjustments

Discharge capacitors (if present) to prevent electrical shock.

Beware of moving parts.

Remove and replace any safety guards.

Figure-20: Protective Equipment

Wear Common Protective or Safety Equipment such as Safety Shoes, Glasses, Gloves,

Hearing Protection, Hard Hats, or Life Jackets.

When working on cables that are close to energized cables, particularly if they are

running in parallel, precautions shall be taken to minimize the risk of injury to personnel.

Similar precautions are required when working within 100 meters of a Zone.

Jointing of high voltage cables shall only be carried out by personnel trained and

accredited for a particular joint type.


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Jointing of high voltage cables is not permitted if it is raining.

Make sure that system is properly earthed.

Tag out the devices.

ANNEXURE-A:


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CONSTRUCTION:

Cables consist of three major components: conductors, insulation, and protective jacket. The

makeup of individual cables varies according to application. The construction and material

are determined by three main factors:

Working voltage, determining the thickness of the insulation

Current-carrying capacity, determining the cross-sectional size

Environmental conditions such as temperature, water, chemical or sunlight exposure,

and mechanical impact, determining the form and composition of the outer cable

jacket.

Fig:Cut way view of the cable

TYPES OF CABLES USED FOR DISTRIBUTION NETWORK

MAJOR TYPES MAJOR SIZES

(Sq mm)

33kv underground

22kv underground

11kv underground

LT cables underground

XLPE

PILC

PILC

XLPE

400,300

300

240,120,70

240,120,50


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XLPE- CROSS LINKED POLY ETHYLENE CONDUCTOR

PILC- PAPRE INSULATED LEAD SHEATHED CONDUCTOR

HT CABLES:

FIG: CROSS SECTIONAL DRAWING FOR 33KV 3CX400 sq.mm-A2XWY CABLE

HT cable components:

Conductors:

H4 grade Aluminum conductor of electrolytic grade stranded of circular cross section

complying with IS-8130/1984.


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Size

mm2

Min. Number of

strands/wires per conductor

Min. Diameter of each strand/

Wire (mm)

1000

400

300

150

89

59

36

36

3.93

3.04

3.4

2.4

Conductor Screening:

Either non-metallic semi-conducting tape or a layer of extruded semi-conducting compound

or a combination of two.

Insulation:

XLPE extruded insulation

Insulation Screening:

Extruded Semi-conducting screening with water swellable tapes and metallic screening.

Inner Sheath:

Pressure extruded inner sheathing of Black PVC.

Armour:

The Armour shall be of galvanized steel round wires with fault level of 1500 MVA at 33kV

& 500 MVA at 11 kV. Duration of fault level is one (1) second.

Outer Sheath:


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An extruded outer sheathing of Blue PVC.

LT CABLES:

LT cables Standardized Ratings are:

2 core 25 sq. mm

4 core 25 sq. mm

4 core 50 sq. mm

3.5 core 120 /240 sq. mm

3.5 core 150 / 300 sq. mm

SECTOR SHAPED

CROSS SECTIONAL DRAWING FOR3.5 C X 240 sqmm (A2 X FY) L.T. CABLE

ALLUMINUM CONDUCTOR

XLPE INSULATION EXTRUDED PVCOUTER SHEATH

INNER SHEATHEXTRUDED PVC

FLAT G.S.STRIP

D:\\ OLDHDD\MISC\cross sectional view of 3.5 c x 240 sqmm cable


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Insulation:

XLPE extruded insulation

Inner Sheath:

An extruded inner sheathing of Black PVC conforming to the requirement of type

ST-2.

Armour:

The dimension of galvanized steel Strips shall be as specified and shall conform to IS:

7098/Pt-1

Outer Sheath:

An extruded outer sheathing of Yellow PVC.


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ANNEXURE-B:

Cable Selection Criterion:

Cable Types- XLPE, PILC & PVC.

XLPE cables are most popular because of its better electrical and thermal properties like

higher continuous operating temperature, Short Circuit temperature, Break Down strength

etc.

Main Consideration:

For 11 kV,22 kV and 33 kV cables, the cable size is determined by continuous current

rating and short circuit rating.

For 1.1 kV cable, the selection of size is determined by continuous current rating, the

maximum permissible voltage drop and short circuit rating.

In addition to above, following are some factors for deciding the type and size of

cable.

1. Earth fault current carrying capacity.

2. Voltage drop (For low voltage system)

3. Power loss

ANNEXURE- C:

METHODS OF CABLE LAYING:

Laying direct in ground

Drawing in Ducts

Horizontal drilling


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The cables are laid directly in the ground with a depth of 1 meter. Cables are also pulled in

ducts. The pulling tension is important and depends on the method of pulling.

Maximum allowable pulling tension:

The maximum allowable tension on cable conductors that should be used during

pulls must be based on experience as well as good engineering. Factors that have an impact

on the value include type of metal, temper, and factors of safety.

METAL TEMPER POUNDS PER

CIRCULAR MILL

Copper

Aluminum

Aluminum

Aluminum

Aluminum

Soft

Hard

Hard

Hard

Soft

0.008

0.008

0.006-0.008

0.003-0.004

0.002-0.004

Ref: AEIC CG5-(2nd Edition)-2005

Pulling tension calculation:

The basic equation to calculate the pulling tension is

T= W*L*f

Where T= tension in pounds

W= weight of one foot of cable in pounds


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L= length of pull in feet

f = co-efficient of friction for the duct material and outer layer of the cable.

Horizontal drilling is employed where excavation of roads for cable laying is not possible. In

this method the road is drilled horizontally and cables are laid through Hume pipes which are

inserted into the drilled holes.

CABLE INSTALLATION PLAN:

On completion of laying, termination and jointing of cables, a computerized

drawing is prepared, which contains the following details of the installation.

Type of cables, cross-section area, rated voltage, details of construction, cable number and

drum number;

a. Year and month of laying;

b. Actual length between joint-to-joint or ends;

c. Location of cables and joints in relation to certain fixed reference points, for e.g.-

Buildings, hydrant etc;

d. Name of the jointer who carried the jointing work;

e. Date of making joint and Result of original electrical measurements and testing on

cable installation;

All subsequent changes in the cable drawings are entered after the job. All drawings are

maintained in digital format.

CABLE MARKING AND LOCATION:


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Cables shall be marked with one tag indicating direction or exit from underground

facilities

This tag shall indicate the general direction of the cable(s) to the next facility where

the cable is located.

All tags will be labeled with the next point of connection (i.e. transformer 1 to

transformer

A redplastic warning tape shall be spread above the underground electrical cable

within the right-of-way at a depth of 0.6 m from the ground surface.

ANNEXURE-D:

TESTING OF CABLES:

The testing methods are

Direct voltage testing

Low voltage D.C testing

High voltage D.C testing

Power frequency testing

Low voltage testing:

This test is used to determine the insulation resistance of the cable. In this test Cable phases

not under test should have their conductors grounded. Ends, both at test location and remote,

should be protected from accidental contact by personnel, energized equipment and grounds.

Apply the prescribed test voltage for specified period of time. It may be advantageous to

conduct the test with morethan one voltage level and record readings of more than one time

period.


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High voltage testing:

This test is used to determine the leakage current in the cable. Apply the prescribed test

voltage for the specifiedperiod of time.Totalapparent leakage output current is recorded asa

functionof time at a prescribed voltage level.

Power frequency testing:

As the name implies, these test methods are based on using alternating current at the

operating frequency of the system as the test source. This test is used to determine the Partial

Discharge.Partial discharge measurement is an important method of assessing the quality of

the insulation of power cable systems, particularly for extruded insulation materials.

PD testing is an evolving technology for periodic diagnostic testing of XLPE-

insulated cables. Partial discharges occur at voids in insulation and at the interface layers

between cable and accessory insulation. These discharges emit broadband radiation in the

range of 50 kHz to 500 MHzs PD testing is a nondestructive testing method, generally

accepted as one of the most effective techniques for locating defects in XLPE cables.

ANNEXURE-E:

Insulation Resistance Test Values Electrical Apparatus and Systems

Nominal Rating

of Equipment in Volts Minimum Test Voltage, DC

Recommended Minimum

Insulation Resistance in

Megohms

250 500 25


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600 1,000 100

1,000 1,000 100

2,500 1,000 500

5,000 2,500 1,000

8,000 2,500 2,00015,000 2,500 5,000

25,000 5,000 20,000

34,500 and above 15,000 100,000

REF: INTERNATIONAL ELECTRICAL TESTING ASSOCIATION (NETA)

ANNEXURE-F: ELECTRICAL TOOL KIT FOR MAINTENANCE WORKS

S.No Tool name


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1

2

3

4

5

67

8

9

10

11

12

13

14

15

16

1718

19

20

21

22

23

24

25

26

27

28

D-24 Reversible Screwdriver, 3/set

D-74-L Screwdriver w/Checker

D-81 Reversible Stubby Screwdriver

D-331-150 Screwdriver

D-332-150 Phillips Screwdriver

N-9-150 Diagonal Cutting PliersN-838 Snips

P-15-150 Long Nose Pliers w/Cutter

P-56-175 Pliers w/Side Cutter

P-86-125 Tweezers

P-211Z-150 Slip Joint Pliers

P-245 Slip Joint Pliers

P-704 Crimping Tool, w/Stripper

P-95 Wire Stripper

W-210-200 Adjustable Wrench

W-210-300 Adjustable Wrench

W-521 Open End Wrench SetZ-341 Measure Tape

Hammer

Quick-point Knife (Large)

Sealing Tape

Vinyl Tape

Plastic mallet

Penlight (with Batteries)

Brush

Hex Wrench Set

Multi meter

B-56-B Tool Box


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List of Standards:

IEEE Standard 43-2000 is the .Recommended Practice for Testing Insulation

Resistance of Rotating Machinery.

IEEE Standard 389-1996 is the IEEE Recommended Practice for Testing Electronics

Transformers and Inductors.

IEEE Standard 1415-2006 IEEE Guide for Induction Machinery Maintenance Testing

and Failure Analysis.

NACE SP0169:2007 - Control of External Corrosion on Underground or

Submerged Metallic Piping Systems.

NACE TM 0497 - Measurement Techniques Related to Criteria for Cathodic

Protection on Underground or Submerged Metallic Piping Systems.

NEMA (National Electrical Manufacturing Association) TR1-1993(R2000)

Transformers.

IS: 2705 for current transformer compilation.

IS: 3156 for voltage transformer compilation.

AEIC (Association of Edison illuminating Companies) G7-90 testing practices of

underground cables.

IEEE P-400 Guide for Field Testing and Evaluation of Shielded Power Cables

elecrical equipment maintenance in pipelines

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