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Inspection &
Preventive maintenance
of breakers
Developments - Industry
Why and what has to be maintained
on breakers ?
 Case
 Mechanism
 Arc chute
 Main contacts
 Control unit
 Connection systems
 Auxiliary Devices
 Communication system
DDI - Department - Name - Date
Developments - Industry
Maintenance of case
 Function of case :
 isolate the main contacts and protect from arcing effects
 support the mechanism, tripping device, auxiliary devices, terminals
 Must withstand the stresses during short circuit
 Damaged case is the consequence of :
 shocks,
 moisture,
 high short circuit,
 overheating ( loose connection)
 Preventive maintenance includes :
 visual inspection of dust, dirt, grease, moisture, cracks, soot,
 cleaning, ( dust, dirt, soot,) with dry cloth, brush or vacuum cleaner
 replacement in case of cracks
DDI - Department - Name - Date
Developments - Industry
Maintenance of the mechanism
 Breaker mechanism
 Spring energy on Masterpact
 Tumbler on Compact NS
 operate the contacts to establish and interrupt the circuit
 Chassis mechanism
 to rack in and out the breaker, test the breaker
 Jammed mechanism is the consequence of :
 dust :
 shocks : bending of mechanical part
 corrosive atmosphere : rust and corrosion of metallic part
 No operation for a long time
 Preventive maintenance includes :
 dust removal : vacuum cleaner recommended
 cleaning : dry cloth, brush, solvent prohibited
 greasing : only Schneider recommended greases, in small quantity
 operation of breaker / chassis : to give the spring charged energy
and the mechanism their original characteristics
DDI - Department - Name - Date
Developments - Industry
Maintenance of the arc chute (Power breaker only)
 Function of arc chute :
 splitters : extinguish the arc and absorb the energy under normal
condition and electric fault
 filter : blow the pressured gas out , cool down the gas
 Arc chute deteriorates
 under In : the insulation material of the arc chamber can perforate
 under Icc : the metal part is vaporised
 Arc chute in bad condition may result in a non interruption of the arc,
decrease of the isolating function and ultimately destruction in case of
high short circuit current.
 Filters : avoid compound (made of dust + grease) covering the filter
 Preventive maintenance includes :
 periodic inspection after a fault : splitters should not present holes
and be too thin, plastic part should not have holes ( decrease of
insulation level)
 replacement
 cleaning of filter
DDI - Department - Name - Date
Developments - Industry
Maintenance of main contacts
(Power breaker only)
 Function of main contacts :
 To make or break the circuit under normal ( In) or fault conditions
(overload and Short-circuit )
 Contacts get worn during each mechanical and electrical open / close
operation and after short circuit ( maxi 2 cycles at Icu)
 Worn contacts will result in :
 over heating of the breaker ( increase of contact resistance)
 decrease of life expectancy
 Preventive maintenance includes :
 periodic visual check, control of the mechanical contact wear
indicator and electronic wear indicator on Micrologic P & H
 measurement of individual pole resistance
 replacement
DDI - Department - Name - Date
Developments - Industry
Maintenance of electronic control unit
 Function of control unit :
 permanently analyse the phase current compare it to the protection
set and in case of fault trips the breaker
 Control unit is sensitive to :
 environment : ambient temperature, humidity, corrosive
 operating conditions : vibration, electro-magnetic field,
 A malfunctioning of the trip unit will result in :
 a non interruption of the fault current
 damage of equipment and breaker
 Preventive maintenance includes :
 periodic push to trip test or trip test
 control of the complete tripping channel
 curve adjustment
 saving of log event, settings ( Micrologic P & H)
DDI - Department - Name - Date
Developments - Industry
Maintenance of thermal-magnetic trip unit
 Function of thermal-magnetic trip unit :
 Connected permanently in series with the phase currents
 based on the bending of a bimetal for overload and the movement
of a magnet in a strong magnetic field
 Thermal -magnetic trip unit is sensitive to :
 ambient temperature, corrosive atmosphere
 A malfunctioning of the trip unit will result in :
 a non interruption of the fault current
 damage of equipment and breaker
 Preventive maintenance includes :
 primary injection test to trip the breaker
DDI - Department - Name - Date
Developments - Industry
Maintenance of connection systems
 Function of connection systems :
 Link together various types of devices by mean of electrical
distribution systems (bus bars, cables, auxiliary wires, ).
 Bad connection ( too tight or too loose) will result in :
 Thermal effect leading to destruction of devices
 short circuit or fire
 Preventive maintenance includes :
 For fixed connectors : No need of control if done with Schneider
recommendation . otherwise : check temperature rise, if loose,
dismantle and tighten with new screws, bolts & washers
 For sliding connectors : (mainly chassis)
– periodic cleaning and greasing with Schneider recommended
– if corrosive atmosphere ( SO2 / H2S) : clean with special
solution ( Thiourée) and re grease
 Wires : check tightening and the insulation material
DDI - Department - Name - Date
Developments - Industry
Maintenance of auxiliary devices
 Function of auxiliary devices :
 Shunt trip release, under voltage release, OF contacts, SD/SDE
alarm contacts , electrical motor MCH
 Malfunctioning of the auxiliary device will result in a wrong operation of
the breaker
 the consequences can be :
 no safety operation ( emergency)
 wrong operation in the circuit
 Preventive maintenance includes :
 functional test of auxiliary device at nominal voltage
 replacement
DDI - Department - Name - Date
Developments - Industry
Maintenance of communication systems
 Function of communication systems :
 allow the dialogue with control unit ( read, write)
 allow the remote control of breaker ( open close)
 Bad communication will result in :
 loss of information (status, monitoring, maintenance, production)
 loss of control of breaker
 Preventive maintenance includes :
 testing of reading network parameters
 testing of reading setting and changing setting
 testing of remote control
DDI - Department - Name - Date