Ans: CIRCUIT BREAKERS:
In the case of outdoor type installation, the circuit breakers have fixed location and the
station layout is such that adequate section clearances are always available from the live parts.
In case of indoor type of installation, the circuit breakers of the draw-out type are used so as to
facilitate removal of the breaker to a safe place for maintenance purposes.
(b) Maintenance of circuit breakers:
Of many items which need inspection and maintenance, the circuit -breaker is
perhaps the most important. Because of the duty on circuit- breakers, their relative
complexity and the fact that they contain moving parts and elements subject to deterioration,
circuit-breakers usually need more frequent and more prolonged maintenance. In general, for
maintenance of CB the instructions of the manufacturer should be followed. A few salient
points on maintenance of CB are given below:
Under normal operating conditions during regular inspections following checks
should be made.
The contacts should be checked for proper alignment and their surfaces should bear with
firm , uniform pressure.
• The oil level should be checked and maintained.
• The oil condition should be tested and if dielectric strength is lower than
specified, oil should be filtered While taking oil samples normal precautions should
be followed.
• All insulating parts should be thoroughly cleaned to remove all traces of carbon
which may remain after the oil has been drained from the tank.
• Check the tripping of the breaker through devices which will have to function on
fault or overload.
• Check indicating devices such as mechanical on and off indication, as an incorrect
indication may at some times lead to a fatal accident.
• Check auxiliary switches for cleanliness and contact making.
• Check all bolts and nuts for tightness.
• Check links of operating mechanism for smooth movement. A small quantity of
appropriate lubricant should be applied at joints.
If a CB operates under fault conditions to interrupt a fault, then maintenance after
such occurrence should be carried out giving special attention to the following items.
Current carrying parts: All contacts including isolator contacts should be examined,
dressed or replaced if necessary.
• Insulation should be cleaned of carbon deposits. Examination be made of cracks,
tracking or other damages.
• Arc control devices should be checked and dismantled, if any carbon or metallic
deposits are found these should be removed.
• All joints and seals should be examined for tightness.
• Oil should be checked in case of oil circuit breaker.
• The general inspection of mechanical damage or distortion of the structure and
mechanism should be made . The switchgear should be closed and tripped by each of the
methods provided.
In addition to the periodical maintenance carried out as above, every circuit
breaker will be completely overhauled after five year interval.