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Electrical Preventive Maintenance of Air Circuit Breakers

Electrical Preventive Maintenance of Air Circuit Breakers

Recommended minimum practice for preventive maintenance

Insulation

Remove and clean interphase barriers. Clean all insulating materials with vacuum and/or clean lint free rags. If it i

necessary to use cleaning solvents, use only solvents recommended by the manufacturer.

Inspect for (early) signs of corona, tracking , arcing , or thermal or physical damage.

Ensure that insulation is left clean and dry.

Contacts

Ensure that all contacts are clean , smooth, and in proper alignment . Ensure that spring pressures are maintaine

according to manufacturer’s specifications. On silver contacts, discoloration is not usually harmful unless caused by

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Insulation barriers (left: Interface barrier; right: Earth barrier)

insulating deposits. Clean silver contacts with alcohol or silver cleaner using non-abrasive cloths.

Contact resistance tests using micro-ohmmeter (photo credit: ecmweb.com)

Manually close breaker to check for proper wipe, contact pressure, contact alignment, and to ensure that all contacts

make at approximately the same time.

If possible, a contact resistance test should be performed to determine the quality of the contacts. Micro-

ohmmeters, which are used to perform contact resistance tests, apply a DC current through the entire closed circuit

breaker current path, including the contacts, pivot point, and stab connections of the circuit breaker. The test set rea

out displays the contact resistance directly in micro-ohms.

Older breakers equipped with carbon contactors generally require very little maintenance. Examine for proper

pressure, deterioration, or excessive dressing which may interfere with their proper operation.

Draw-out contacts on the circuit breaker and the stationary contacts in the cubicle should be cleaned and inspected

for overheating, alignment, and broken or weak springs. Coat contact surfaces with contact lubricant to ease mating


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(see manufacturer’s recommendations).

Arc Interrupters

Clean all ceramic materials of loose dirt and examine for signs of moisture, make sure the assemblies are clean and

dry. Examine for cracked or broken pieces. Dirt and arcing deposits may be removed by light sanding — do not use

emery cloth or wire brushes which may leave conductive residue behind. Repair or replace as necessary.

Examine arc chutes for dirt and/or dust accumulations and clean as necessary. Dielectric testing of arc shields ma

be recommended by the manufacturer. Check air puffer for proper operation.

Operating Mechanism

Inspect for loose, broken, worn, or missing parts (consult manufacturer’s schematics for required parts). Examine

for excessive wear of moving parts. Observe that operating mechanisms function properly without binding, hanging,

without delayed action.

Ensure any lubrication is done according to the manufacturer’s specifications.

Figure 1 – Cutaway view of the molded case circuit breaker

Ensure mechanisms are clean, properly lubricated, and all bolts and screws are properly secured. Repair or replace

as necessary.


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Auxiliary Devices

Inspect operating devices for proper operation and general condition. Ensure all indicating devices are fully functiona

and properly set.

Auxiliary devices (aux. switch, alarm switch, shunt trip and unrevoltage trip device)

Protective relays and circuit breaker trip devices should be inspected and tested according to manufacturers’

specifications and applicable industry standards such as those issued by the Institute of Electrical and Electronic

Engineers (IEEE) and the National Fire Protection Association (NFPA).

References:

Standard for and electrical preventive maintenance (EPM) program – The Hartford Steam Boiler Inspection

and Insurance Company

Fuji Electric FA Components & Systems Catalogue

About Author //

Edvard Csanyi

Edvard - Electrical engineer, programmer and founder of EEP. Highly specialized for

design of LV high power busbar trunking (


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2.

Sen

Nov 03, 2014

Hello Sir

My ACB now one terminal have been burn and it occur tree time , so how can i solve it ?

(reply)

3.

sachin s

Aug 13, 2014

Hello Sir..What is function of the micrologic control.?

(reply)

4.

karim pourmosa

Jul 11, 2014

nice

(reply)

5.

akhtar

Mar 30, 2014

DEAR SIR

HOW THE ACB GOT FEED INSIDE THE FRAME

(reply)

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6.

michael k kudahor

Mar 25, 2014

Better still what to consider in other to improve the power factor of a plant .

(reply)

vijay

Nov 03, 2014

Most of the plants were fitted with synchronous condenser or generator to cop up with

power factor issue. Also, condensers are fitted at various places where inductive loads are located.

While installing a new inductive machinery it is advisable to take its pf into consideration.

(reply)

7.

michael k kudahor

Mar 25, 2014

it educative to know you share such a deep insight, i would love to know what are the best and

affordable ways of improving power factor of a plant?

(reply)

8.

DEEPAK AGRAWAL

Feb 07, 2014

Hello Sir,

Can we control kvar ratings of a power factor capacitor by varying voltage supplied to it, by varying the

triggering of thyristors and thus control power factor in a more significant manner?

(reply)

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