Introduction:
Air circuit breaker is a mechanical switching device capable of making, carrying
& breaking current under normal & under specified abnormal conditions
such as short circuit.
Circuit breaker switching capabilities:
|
|
Make |
Carry |
Break |
|
No |  |
|
|
|
Overload |
|
|
|
|
Short Circuit |
|
|
|
Types of ACB:
ACB can be operated manually or electrically.
According to type of mechanism, ACB can be manually operated or Electrically
operated. In manually operated ACB operator has to close the breaker manually
by operating the mechanism of ACB through operating handle. Whereas in case of
electrically operated ACB, breaker has charging motor and closing coil, breaker
mechanism is charged through motor & breaker is closed by giving an
electrical command to the closing coil.
Also with respect to the way of termination of ACB can
be fixed type or Draw out type ACB. In fixed type of ACB Termination is done
directly on breaker terminals whereas in case of draw out ACB, breaker is
having additional housing (Cradle), termination is done on cradle terminals.
Hence with respect to the way of operation as well as
Terminations ACB are of four types viz.
I.
Manually operated fixed type (MF)
II.
Manually
operated draw out type(MDO)
III.
Electrically
operated fixed type(EF)
IV. Electrically operated draw out type(EDO)
Troubleshooting of L&T make C-Power ACB:
1. Breaker not Closing:
|
Probable
Cause |
Possible
Solution |
|
Undervoltage
release not connected to supply. |
Give
rated voltage to undervoltage release |
|
Undervoltage
release, Shunt release, magneto thermal release connecting link not adjusted
properly. |
Adjust
the connecting linkage of release correctly. |
|
Magneto
thermal release removed from ACB, but trip bar of release kept free. |
Lock
the trip bar at given position |
|
Latch
of the mechanism spring not in proper position or misplaced |
Fix
the spring correctly |
|
Under
voltage release coil burnt out or open circuited. |
Replace
the under-voltage release |
|
Bimetal
element of magneto thermal release bent permanently. |
Replace
the magneto thermal release. |
|
After
overload or short circuit fault, breaker not reset (only for manually
reset type breaker) |
Reset
the button by pressing off/reset button. |
|
Sticking
of tripping mechanism due to excess dust. |
Clean
the tripping mechanism with CRC 2-26 & grease them |
2. Breaker is not tripping wit under-voltage or Shunt release:
|
Probable
Cause |
Possible
Solution |
|
Shunt
release does not get supply |
Check
control wiring of shunt release & ensure that shunt release gets supply |
|
Supply
of under-voltage release does not get cut off |
Check
control wiring |
|
Link
point of under-voltage & shunt release misplaced. |
Ensure
that pins are in position |
|
Due
to dust release becomes sticky |
Remove
the dust from the release and clean it with CRC 2-26 |
3. Breaker is not charging with motor.
|
Probable
cause |
Possible
Solution |
|
Motor
is not getting supply |
Check
the limit switch of motor. Replace it if it is damaged. |
|
Loose
connection in secondly isolating contact |
Fix
the secondary isolating contact properly |
|
Motor
is burnt out |
Replace
the motor |
4. Breaker is not tripping with manual trip push button
|
Probable
Cause |
Possible
Solution |
|
Trip
push button connecting link is short |
Adjust
the push button link correctly |
|
Latch
of the mechanism jammed because of dust |
Clean
the latch of mechanism with CRC 2-26 |
5. Breaker is not racking in the cradle freely
|
Possible
Solution |
|
|
Threads
of mechanical indicating assembly worn out. |
Replace
the mechanical indicating assembly. |
|
Shutter
assembly is not properly set in the cradle. |
Fix
the shutter assembly properly in the cradle. |
|
Secondary
isolating contacts not matching properly. |
Match
the fixed and moving secondary isolation contacts properly. |
|
Dovel
pin broken |
Replace
the Dovel pin |
|
Telescopic
rail becomes jammed. |
Clean
the telescopic rail with CRC 2-26. Remove dust, grease
& re-lubricate it. |
6. Erosion of Arching Contact
|
Probable
Cause |
Possible
Solution |
|
Rough
design plates of arc chutes |
Clean
the deion plates and side insulating strips of arc chutes with CRC 2-26 |
|
Breaker
is operated without arc chute in position |
Always
operate ACB with arc chute in position & keep the arc chute clean. |
7. Overheating
|
Probable
Cause |
Possible
Solution |
|
Poor
termination (High milli-Volts drop across termination on ACB. |
Clean
the terminals with CRC 2-26 and do proper re-termination. Ensure that milli
volt drop within specified limits |
|
Dusty
atmosphere |
Do
periodic cleaning of ACB |
|
Use
of undersized cable or busbar |
Use
cable or busbar of adequate rating. |
|
High
ambient temperature., |
Reduce
load current or select & install correct rating of ACB. |
8. Breaker is not closing
remotely
|
Probable
Cause |
Possible
Solution |
|
Breaker
is not in service position.
|
Take
the breaker in service position |
|
Closing
coil not getting supply
|
Check
control circuit and ensure coil gets supply. |
|
Closing
coil burnt out or open circuited.
|
Replace
the closing coil |
9. ACB is not tripping in case
of overload or short circuit fault.
|
Probable
Cause |
Possible
Solution |
|
Connection between C.T. and
protection release is loose or open circuited. |
Tighten the terminals in
case of open circuited |
|
Overloading setting of
protection release is more than actual load current |
Make the overload setting as
ACB as pr actual load current |
|
Protection release linkage
not adjusted properly |
Connect the linkage of
protection release to trip bar properly & ensure its tripping operation. |
10. Main Contacts one of
the pole of ACB not closing
|
Probable
Cause |
Possible
Solution |
|
Excessive dust accumulated
in the pole assembly. |
Clean the pole assembly
mechanism with CRC 2-26. Remove grease and dust
with brush & apply fresh grease. |
|
Nylon rollers of the pole
assembly are not rotating smoothly. |
Clean the nylon rollers with
CRC 2-26 and re-lubricate them. |
|
Pole connector setting
disturbed |
Consult the manufacturer of
ACB |
|
Nylon rollers of the pole
assembly are broken |
Consult the manufacturer of
ACB |
11. Pitting of the main
contacts.
|
Probable
Cause |
Possible
Solution |
|
Arching contact gap is not
adjusted properly |
Adjust the gap of arching
contacts, it should be 0.9 mm approximately. |
|
Thickness of arcing
contact is reduced below the specified limit(>0.5 mm) |
Replace the fixed and moving
arcing contacts. |
Good
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