ELECTRICAL MAINTENANCE AND

TROUBLE SHOOTING OF MACHINES AND

EQUIPMENT

PREVENTIVE MAINTENANCE:

It is the orderly and routine checking, cleaning, drying, tightening of bolts, re-greasing, testing, monitoring, etc. of electrical equipment, machines and devices, to ascertain their normal operations. Every date and activity done must be properly recorded.

PREDICTIVE MAINTENANCE:

It is the use of computer simulation on the operation of certain electrical equipment or machine and to predetermined the operating time before any of its component or part fails to perform its function. (Avery good computer program is needed here).

3 Circuits Comprising Electrical Machines and Equipment

1. Electric circuit – electron flow2. Magnetic circuit – magnetic lines3. Dielectric circuit – insulation system

Of these 3 circuits, the most critical is the dielectric, it has the lowest melting point temperature being only hundreds of degrees centigrade compared to the thousands of degrees centigrade for the other two.

CLASSES OF INSULATION:

For ordinary building wiring based on 30°C or 80°F ambient.60°C – RUW, T, TW, UF etc.75°C – FEPW, RH, RHW, RUH, THW, THWN, XHHW, ZW85°C – V, MI.90°C – TA, TBS, SA, AUB, SIS, FEP, FEFB, RHH, THHN, XHHUH

CLASSES OF INSULATION FOR MACHINES/EQUIPMENT:

Class “O” - 90°C thermal limit

Class “A” - 105°C thermal limitClass “E” - 120°C thermal limitClass “B” - 130°C thermal limitClass “F” - 155°C thermal limitClass “H” - 180°C thermal limitClass “220°C” - 220°C thermal limitClass “C” – Above 220°C thermal limit

Knowing the surface temperature of any insulation using highly accurate thermometers like the infrared thermal scanner, you will know if overheating either due to high current or accumulation of dirt is the primary cause.

To get the value of the hottest spot use,T H.S = surface temperature + ambient temp. + 15°C

ExampleThe surface temp. is 40°CThe ambient temp. is 40°CTherefore T H.S = 40 + 40 15 = 95°CA class “O” thermal limit insulation may fail

MEASURING INSULATION RESISTANCE:The instrument used to measure insulation resistance for low voltage system is the “megger”, and for the high voltage it is the “hi-pot”.SPOT TEST- This is the one minute reading of the insulation tester.

Another test that can be done on an insulation tester is the determination of the insulation’s Polarization Index (P.I.)

Megger Reading 10 min.Polarization Index (P.I.) = ----------------------------------

Megger Reading 1 min.

If P.I. is 1.4 or lower – insulation is unsafe to use.If P.I. is 1.5 – insulation can be use with cautionIf P.I. is 1.6 and up – insulation is very safe to use

What “megger” voltage rating is to be used? (megger voltage ranges from 100 to7500volts)

12 – 24 volt system - 100 V megger110 – 120 volt system - 250 V megger230 – 480 volt system - 500 V megger660 – 1000 volt system - 1000 V

megger1200 – 2400 volt system - 2500 V

megger3300 – 4800 volt system - 5000 V

megger5000 – 7200 volt system - 7500 V

megger

MINIMUM ACCEPTABLE INSULATION RESISTANCES USING SPOT TEST:

Conductors and Bus bars – kV rating + 1Rotating machine – kV rating + 1For dry type transformers – 2 MΩ / kV rating

To be able to get the correct insulation resistance, the ambient temperature must be considered. For correction factors (k) to be used, the following values are given:

k = 4@ 60°Ck = 2@ 50°Ck = 1@ 40°Ck = 0.5@ 30°Ck = for other temp., use ratio and proportion

(k @ 0°C is 0.06)

All resistance if insulation must be correct and recorded at 40°C, the internationally accepted ambient temperature. If megger is not available to measure insulation resistance of machines/ equipment or even devices, and alternate method called the voltmeter can be used.

(25% to 50% of the rated AC or DC voltage rating of machine)

R1 = R2 (V1-V2) / V2where:

R1 = insulation resistanceR2 = voltmeter resistance (voltmeter

sensitivity times full deflection)V1 = voltmeter reading with switch closedV2 = voltmeter reading with switch open

Using high Potential tester (hi-pot) to evaluate insulation resistance of high voltage machines or system.

Kinds of Hi- pot Tester:1. AC Hi- Pot2. DC Hi- Pot

When using Hi- Pot tester, the voltage to be injected must be the non destructive value, that is, it should not destroy the di-electric strength of the insulation.

The safe values to be used are:1. for AC = 1.5 x V rating of machine2. for DC = 1.7 x 1.5 x V rating of machine

The correct connection of the tester into the machine is as shown.

When using AC Hi- Pot, bring the non-destructive test voltage right away into the machine as shown above, for one minute. If no breakdown (indicate by lamp or steady test current) occurs, the insulation is considered safe for use. AC Hi-pot is used therefore just to answer the question, can we use this machine or not. A preliminary test using megger 500V is needed. 1MΩ/KV is the minimum acceptable test result before Hi-Pot testing is allowed.

The DC Hi-pot is better because the polarization index of the insulation can be established. When using the test, one third of the non destructive test voltage will be injected and maintained for ten (10) minutes. After which the test current recorded, the remaining 2/3 of the non destructive test voltage will be injected in ten (10) uniform steps at one minute interval. In every interval test voltage and current are as well recorded. When the 100% of the NDTV has been injected, the test current is to be taken and recorded after one minute and also after ten (10) minutes. P.I. being one (1) minute reading divided by ten (10) minutes reading. For the interpretation of P.I., it is the same as earlier presented.

I 1 minuteP.I. = ---------------------- (for Hi-pot)

I 10 minutes

Other insulation resistance test that are being used well-financial companies are:

1. insulation power factor test2. slot- discharge test3. surge- comparison test4. corona probe test5. inter- laminar insulation test

These are highly specialized and are covered separately.

INSULATING LIQUIDSUsed for oil immersed transformer for cooling

and insulation and also used for breakers and switches as insulation, coolant and as arc quencher.

Three kinds of insulating oil are available.• Mineral Oil• Insert Synthetic insulating oil, popularly known

as askarel. Askarel are sold with such trade names as, Pyranol, Chlorextol, Inertene, WEMCO-C etc.

• High temperature insulating liquids like silicon.

Mineral oil is expensive being a by-product of the fossil-hydrocarbon being mined by petroleum companies, plus the fact that it is flammable, hence the production of “askarel”

ADVANTAGES OF INERT SYNTHETIC INSULATING OIL

1. Non – inflammable2. Chemically stable3. Non – sludging (can not corrode, sludge

means oxidized oil).

DISADVANTAGES OF INERT SYNTHETIC OIL

1. It is toxic to humans and other living things (causes different illnesses to respiratory system)

2. It affects the reproductive system of humans, animals and also fishes. Offspring's of persons and animals are often mutants (mutants are living things with deformities).

TESTING AND SAMPLING OF INSULATING LIQUIDS

Bottles or glass container for oil samples taken from Transformer or Oil Circuit Breakers tanks must PROPERLY CLEANED in this manner to avoid contamination with impurities.

1. First, it is cleaned with white gasoline.2. After drying, it is washed with soapsuds.3. It is rinsed with distilled water.4. It is baked in an oven for at least 8 hrs. at 105°C

to 110°C.

In getting oil samples, care and cautions must be observe at all cost. If oil is askarel and it is accidentally came in contact with the skin, castor oil is used to wash the oil from the skin.

Gap between electrodes = 0.1”

Diameter of electrodes = 1”

(ANSI Standard) Rate of voltage rise = 3 KVP

Minimum Acceptable DBV

For mineral oil = 22 KV For askarel = 25 KV

Five test on five samples to be used average DBV is to be used.

DBV AVE = DBV1+DBV2+DBV3+DBV4+DBV5 5

DBV-Di- Electric Breakdown VoltageIf the DBV is less than the acceptable minimum, oil

filtering is to be done.

TYPE OF FILTERING

• Filter Press• Centrifugal Purifier• de- gasifying method.

WHEN IS CLEANING OF ELECTRICAL APPARATUS NECESSARY?

3. Visual determination of accumulated dirt on the windings.

4. The operating temperature is 10°C to 15°C above its normal operating temperature.

5. Insulation – evaluation measurements indicate the presence of dirt or moisture as indicated by low value of P.I.

METHODS OF CLEANING

For large machines where a person can enter it, like propulsion motor of a ships, or big HP ball mill motors, all pockets of a person doing cleaning should be emptied. This can cause serious damage to the machines if they accidentally fall.

Loose dry dust is best accomplished with vacuum cleaner.

Encrusted dirt that blocks air passages should be removed carefully with hardwood or fiber scraper, don’t use metal scraper, it can damage the insulation.

Insulation coated with oily film should be cleaned by wiping or rubbing with cheesecloth or lint less rag

Apparatus covered w/ heavy oily scum should be cleaned w/ chlorinated solvent like methyl chloroform.

CLEANING SUBMERGE OR FLOODED ELECTRICAL APPARATUS

Fresh warm water not hotter than 80°C (176°F) is used to wash flooded electrical apparatus until (water pressure at no more than 25 psi) shows no sign of salt and other impurities, after which, it is blown with compressed air (not more than 30 psi).

DRYING ELECTRICAL INSULATION

• By external heat like oven, on top of boilers, electric heater or radiant lamps, steam heaters and also hot air furnaces, provided the temperature do not exceed the thermal limit of the insulation (for machines the lowest value is 90°C).

• Baking with internal heat, If the insulation resistance using megger is 50,000Ω or higher, current fed at low voltage until current is about 50 to 80 % of its rated current (voltage controlled by variac). This is done at a minimum of 6 hrs. or until such time that P.I. is acceptable.

CARE OF ELECTRICAL APPARATUS DURING PERIODS OF INACTIVITY

Make sure that the apparatus temperature is several degrees higher than the surroundings, this is to prevent oxidation. This can be done by application of space heaters or heating lamps. For large rotating machines it must be rotated by small motor to prevent the motor from sagging.

BATTERY

To be sure of performance, when recommending dry cell (primary battery) specify only those with expiry dates marked on the battery itself.

LEAD ACID BATTERY

Should never be left in a discharged condition for a very long time (more than a month) because the plates will be hardened (Lead Sulfate)

To determined the state of charged of the lead acid battery, a voltmeter is never used. It is the hydrometer that is to be used.

HYDROMETER

CONDITION OF LEAD ACID BATTERY

As indicated by specific gravity of electrolyte:

Sp. Gravity (80°F) % charge

1.285 100%

1.245 75%

1.225 66%

1.205 50%

1.165 25%

1.125 discharge

Correction factors if temperature is not 80°F(30°C)

130°F - +0.020 120°F - +0.016 110°F - +0.012 100°F - +0.008 90°F - +0.004 80°F - 0.000 70°F - -0.004 60°F - -0.008 50°F - -0.012

When the level of lead acid battery electrolyte is lowered due to its evaporation. It must be top-up with distilled water. Ordinary water has lots of impurities that can damage the active materials.

When mixing Sulfuric Acid and water to form electrolyte for lead acid battery it is the acid that is poured to the water and not the water into the acid. This will cause violent splashing and may cause serious burns. If burns occurs due to splashing it must be neutralized with baking soda or diluted ammonia solution. If it splashes on the eye, it should be wash with large quantity of water and medical treatment must be administered.

I. BATTERY CHARGING

The current to charge the battery must not be higher than the ampere-hour (AH) rating of the battery. Example, If the battery has a rating of 100AH, the current must not exceed 100amps.

• TRICKLE CHARGING

Because of some impurities of the active materials of the battery, a certain degree of local discharging occurs. To neutralize this, a small amount of charging current is needed, this is called trickle charging.

I. SAFEST PRECAUTION WHEN CHARGING

Do not smoke and sufficient ventilation be provided.

IV. BATTERY MAINTENANCE

6. Corroded poles should be brushed using steel brush while washing with water.

7. To avoid oxidation on the poles, it must be treated with petroleum jelly.

AC GENERATOR

BRUSHLESS GENERATOR

ALTERNATOR MOTORIZATION

In the parallel operation of the alternators, if one of them draws power from the bus rather that supplying power to it, this is called motorization. The synchronous generator will run as a synchronous motor. The possible causes of motorization are ; Low speed and low voltage, although no mechanical damage will be done to that motoring unit. Since the direction of rotation is the same yet the harm is on the fact that the remaining unit will be overloaded and eventually trip causing total power failure.

SYNCHRONIZING PROBLEM

If two alternators are to be operated in parallel, synchronizing is a very critical condition- when only synchroscope is installed, a possibility of deliberate wrong reconnection for the purpose of sabotage or to destroy the credibility of operations Engineer and is very common occurrence. To make sure of proper synchronization, synchronizing lamps are installed to confirm synchroscope indications.

A.

* Relation between synchronizing lamp and synchroscope, when lamps are dark the pointer of the synchroscope must be at zero, otherwise, the scope is defective or its connection altered.

SINGLE GENERATOR OPERATION PROCEDURE

Make sure that the generator breaker is open. Bolt or close disconnect links to the connection

bar. Switch the voltage regulator to “automatic”. Start prime mover and bring it to speed. Adjust the frequency to its rating using the

governor switch. Adjust the voltage regulator to obtain rated

voltage. Close alternator breaker.

PARALLEL OPERATION PROCEDURE

1) Secure the incoming alternator breaker is OPEN.

2) Close the disconnecting switch of the incoming to the connection bar.

3) Switch the voltage regulator to automatic. 4) Start the prime mover and bring it to speed. 5) Adjust the frequency of the incoming machine

to one-tenth (1/10) higher using the governor. 6) Adjust the voltage regulator of the incoming

machine so that its voltage is slightly higher than the bus.

1. Switch the synchroscope to the in-coming machine, adjust the frequency until the synchroscope revolves slowly in the “FAST” direction.

2. Close the in-coming breaker when the synchroscope pointer is 2 to 1 degrees before 12 o’clock position. (This is to provide time to breaker moving contact to travel).

3. Turn the synchroscope switch to “OFF” position.4. Turn the governor switch of the in-coming to

“RAISE” and to one running to “LOWER” until the KW load is proportionally shared.

5. If the KVAR of the two machine is not equal, lower the voltage regulator setting of the one higher and raise the one with lower value until both have same power factor.

REMOVING THE ALTERNATOR FROM THE BUS

Lower the governor switch of the machine to be removed and simultaneously raising the one to stay until the KVA load of outgoing is zero, after which the breaker of the outgoing is turned “OFF”

Maintenance of a generator, particularly stand by generators

Dripping liquids on the generator must be prevented at all cost.

Using the combination of compressed air (about 20 PSI) on one end of the generator, and a vacuum cleaner of the opposite end, removal of build-up dust must be conducted at least every six months

Every after five (5) years, the alternator must be detached from its prime mover, disassembled, steam washed, re-varnished with at least class “F” insulating varnish and its both end bearings replaced with new one

MINIMUM INSTUMENTATION AND CONTROL OF

AC GENERATOR IN PARALLEL

PHASE SEQUENCE INDICATOR ( PSI)

VOLTAGE FAILURE OF AC GENERATOR

3 Open in the field circuit

5 Open in the field rheostat

7 Failure of the exciter generator

9 Absence of residual magnetism on the poles of exciter for the self excited type system.

AC MOTOR

Before operating any electric motor, the following information must be checked:

5. Service – AC or DC6. Kind for AC, squirrel-cage, wound rotor,

induction motor or synchronous motor.7. Operating voltage and frequency8. Type of enclosure- ODP, TEFC, weather proof,

explosion proof, etc.9. Class of insulation10. Service factor11. Number of terminal leads12. NEMA code letter classification

Maintenance for motors

3. Once in a year, it must be disassembled, cleaned using steam washer with the proper solvents to remove encrusted dirt, bake to dry and replace both end bearings. Re-varnishing /baking is also done prior to its assembly.

2. Test the winding using the following: spot testing, determine P.I., conduct surge comparison testing, and finally at no load test, measure no load current, power drawn, and speed.

CLASSIFICATIONS OF MOTORS ACCORDING TO NUMBER OF LEADS

A.

A. STANDARD CONNECTION FOR MULTI SPEED

INDUCTION MOTORS

A.

A.

CHECKING MOTOR PERFORMANCE ( USING HOOK ON VOLT AMMETER )

A.

RECOMMENDED REGREASING SCHEDULE

HORSEPOWER

TYPE OF SERVICE TYPICAL EXAMPLE ½-7.510-40 50-200

EASY OPERATING 1 HR/DAY 10YRS. 7 YRS. 5 YRS.STANDARD MACHINE TOOLS, FANS 7 YRS. 5YRS. 3 YRS.

PUMPS, TEXTILE MACHINERYSEVERE CONTINOUS OPERATION, 4 YRS. 2 YRS. 1 YRS. SEVERE VIBRATION, POWER

PLANTS, COAL MININGVERY SEVERE DIRTY, VIBRATING,SHAFT END 9 MOS. 4 MOS.

4 MOS. HOT AND HIGH AMBIENT

TROUBLE SHOOTING CHART FOR MOTORS

TROUBLE POSSIBLECAUSE

A.SYNCHRONOUS MOTORS

Fail to start 1. blown fuse/ tripped breaker

2. open in one phase3. over load4. low voltage

Runs hot 1. overload2. clogged

ventilating ducts3. shorted stator

coils4. open stator coils5. high voltage6. grounded stator7. field current set

low8. field current too

high9. un-even air gap

10. rotor rubbing on

stator

Runs fast 1. high frequency

Runs slow 1. low frequency

Pulls out of 1. over loadsynchronization 2. open in field coils

3. no exciter voltage

4. open in the field5. rheostat set too high

Will not synchronize 1. field current set too low 2. open in field

circuit3. no exciter

voltage4. open rheostat

Vibrates severely 1. out of synchronism

2. open armature coil

3. open phase4. misaligned

A. 3Ø SQUIRREL-CAGE INDUCTION MOTOR

Fails to start 1. tripped breaker / blown fuse 2. open in one phase

3. shorted stator coils 4. low voltage

5. high voltage6. low frequency7. open stator coils8. one phase open9. grounded stator10. uneven air gaps

11. rotor rubbing on stator

Runs slow 1. over load2. low voltage3. low frequency4. broken rotor bars5. shorted stator

coils6. open stator coils7. one phase open

A. WOUND-ROTOR INDUCTION MOTOR

Fails to start 1. breaker tripped / blown fuse 2. open one phase

3. overload4. open in rheostat5. inadequate brush

tension 6. brushes do not

touch collector ring

7. open in rotor circuit

Runs hot 1. overload

2. clogged ventilating ducts

3. low voltage 4. high voltage

5. uneven air gap6. shorted stator coils7. open stator coils8. one phase open9. low frequency10. grounded stator11. rotor rubbing or stator

Runs slow 1. overload

2. low voltage3. low frequency4. too much resistance in

rheostat5. shorted stator

coils6. open stator coils7. one phase open8. open in rotor

circuit

A. SINGLE-PHASE INDUCTION MOTOR

Fails to start 1. tripped breaker/blown

fuse2. defective starting mechanism3. open in auxiliary winding

4. open in main winding

5. shorted capacitor6. open capacitor7. over load

Runs hot 1. over load2. starting

mechanism does not open3. low voltage4. high voltage5. clogged

ventilating ducts6. shorted stator

coils7. worn bearings8. low frequency

9. rotor rubbing on stator

Runs slow 1. over load2. low voltage3. low frequency4. broken rotor bars5. shorted stator

coils

MOTOR CONTROLLER / STARTER

Function of the protective – to protect the controller and motor against shunt fault.

Function of the controller / starter1. to provide stop / start control for the motor2. to reduce in rush current (except DOL or

ATL starters)3. to protect the motor against series fault

For PLC, the auxiliary contacts like that of the timer contacts are replaced with a programmed contacts that closes or opens when needed.

Among the components of the conventional motor controllers are, start/stop buttons, seal in contacts, contactors, NO/NC auxiliary, OL relays, timers, indicating lamps and depending on the type, we can have also, resistors, reactors or even auto-transformers.

TYPES OF MAGNETIC STARTERS AVAILABLE COMMERCIALLY IN THE

PHILIPPINE MARKET

1. Direct on line of across the line starter – all leads2. Part winding starter – 9 and 12 leads3. Primary resistors starter – all leads4. Primary reactor starter – all leads5. Auto transformer starter – all leas6. Wye- Delta starter – 6 and 12 leads

SCHEMATIC DIAGRAMS OF THE DIFFERENT TYPES OF STARTER

B.

A.

A.

A.

A.

TROUBLE SHOOTING CHART FOR MAGNETIC STARTERS

TROUBLE POSSIBLE CAUSE

Contact buzz (loud buzzing noise) 1. broken shading coil

2. misaligned magnetic

faces3. dirt on magnetic faces

4. low voltage

Contact charter 1. poor contact in the operating coil

2. fluttering of a relay in the control

circuit

Excessive burning of contacts 1. excessive current2. weak spring pressure

3. oxidized contacts4. poorly bolted connections

5. defective arcing horn

Welding of contacts 1. excessive and rapid jogging2. low spring

pressure3. excessive current4. low voltage on operating coils

5. bouncing of contacts

Failure of contactor 1. low voltageor relay to pick up 2. open coil

3. excessive magnet binding4. mechanical binding5. open circuit in series with operating coil

Failure of contactor or 1. welded contactsrelay to drop out 2. improper adjustment

3. accumulation of gum and other foreign

matter4. misalignment5. voltage maintained at coil because of failure of contacts in series with operating coil

TRANSFORMER

Transformer to be highlighted in this seminar is the substation type transformer, both outdoor and the indoor type.

Outdoor Type Substation Transformer Breathes

How is its breathing done?

At the peak load, the current flowing on the windings dissipate large value of heat, aggravated by the radiant heat from the sun. The result is high temperature within the tank, which causes the expansion of oil (rise in elevation). This in turn will push the air above the oil surface, making the air to escape thru the provided breather (exhale) and during base load, normally during the wee hours of the early morning, the oil is cooled hence it will contract (lower oil level). The negative pressure created due to the lowering of the oil causes the atmospheric air to rush-in, thru the breather (inhale).

What is the damaging effect of the transformer breathing and how is it correct?

The “inhaling” of atmospheric air into the transformer tank will surely subject the insulating oil to “slugging” due to the presence of moisture in the air. Slugged is oxidize on corroded oil and causes the DBV of the oil to lower. To eliminate sludging brought about by the transformer breathing, a filter is attached to the breather.

To minimize the volume of the air to be breath by the transformer, hence minimizing sludging, an extension tank called “conservator” tank is installed.

INDOOR TYPE SUB-STATION TRANSFORMER (sealed type)

If leak is suspected due to negative pressure, bur no oozing of oil is visible, the leak is most likely above the oil level. If this is so, de-energized the transformer and apply soap suds after purging with nitrogen gas, bubbles will indicate leak indicative. To repair this, electric welding sporting is allowed directly on the crack even with the oil on the tank. ( This is so because insulating oil is non flammable). But if the leak crack is above the oil surface (99%) Nitrogen gas), with the transformer de-energized, drill the crack and pen it with hardwood and covered with “duvan” cement.

The underneath of the transformer cover must be checked every 10 years with the core sufficiently exposed.

The base oil immersed transformers must be inspected every 25 years with the oil drained. This is to check the mechanical strength of the bottom.

The oil of transformer must be treated for DBV, color and viscosity once a year.

Dry type transformer must be “dusted” regularly and properly ventilated (natural or by fan)

Never use step down autotransformer as power supply for continuous operation (more than 3 hrs). An accidental opening on the common winding will surely burn the load.

Never open the secondary of current transformer when its primary is energized. It will destroy the insulation due to high-induced voltage in the secondary windings and its magnetic circuit made biased. Before removing the “burden” of a loaded CT (primary energized). Make sure to short its secondary terminal first.

INDOOR TYPE POWER TRANSFORMER

INDOOR TYPE

Maintenance for power transformers

3. Once a year, test the insulation liquids for DBV, viscosity, color and have it undergo dissolve gas analysis.

4. Once a year, conduct insulation power factor test.

5. Once a year, conduct hot collar test in the bushings.

6. If IPF is no available, conduct DC hi-pot testing or determine the P.I. if its small dry by transformer.

7. For insulating liquids with low DBV, de- should be done

Circuit Breakers Circuit breakers can be classified according to the

following; * Service- AC or DC * Mounting- Outdoor or Indoor * Enclosure- Bakelite, metal,etc * Voltage- Low, medium, high and extra high * Medium of interruption- air, vacuum, SF6, oil etc * Contacts- bayonet, explosion chamber, de-ion etc. * Operation- gravity open, gravity close etc. * Control- manual, electrically, remote etc * Trip unit- thermal and magnetic * Charging mechanism- spring, motor etc

Maintenance of a Circuit breakera) MCCB b) VCB c) GCB d) OCB

In the past, to check the contact pressure and surface area of contact, the cover of the breaker is remove and spring balance is hooked up to the moving contact and its reading recorded for the value just enough to cause that contact to start being lifted up.

For the surface area of contact, a union skin and a very thin carbon paper is placed in between the open contacts and then closed later. Opening the contacts and getting the union skin with carbon imprinted on it. The area of the imprint is then measured and if is 50% or higher as compared to the actual surface area of the two contacts, then the breaker is said to be okay as far as area of contact is concerned.

In our present time, the maintenance practice is now different and more scientific in its approach.

The breaker cover is no longer remove, but just like in the past, the breaker is taken out from its panel or switch board.

The beaker is phantom loaded with its current rating using the SOLGEN’S circuit breaker and relay tester (CBRT) and the surface temperature near its line and load side terminals are measured using thermographic or infrared scanners and considering the relationship between, surface temperature, ambient and hottest spot temperature, Ths= Tsurf + Tamb + 15.

For the surface area of contact and pressure between contacts to be considered normally operating, Ths which is the hottest spot temperature must not be more than 50 deg. Centigrade.

For the characteristic testing of the breaker, see drawing below

Connection of CBRT to MCCB

This is the control board of a CBRT

THANK YOU!!“END OF SEMINAR”

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