1004 - E115 - Medium Voltage Circuit Breakers - 09 .
NRC Medium Voltage CircuitBreaker TrainingCHAPTER 9INTRODUCTION TO ALLISCHALMERS MA CIRCUITBREAKERS
Learning Objectives The basic function of the MA circuit breaker.How the MA breakers are classed or grouped.How the breaker frame size method further identifies the breaker.The component attributes of the MA breaker: Chassis Mounting ArrangementPrimary CircuitCircuit, Support Assemblies and Arc ChutesElectrical Devices including wiringMechanical and Safety InterlocksOperator Assembly and JackbarPuffer AssemblyBasic understanding of maintenance scheduling.Basic understanding of subcomponent replacement.Basic understanding of design upgrades for the MA breakers.Proper lubrication type for MA breakers.Basic understanding of routine maintenance using the PreventativeMaintenance Manual for the MA Circuit Breaker.
WHAT IS AN ALLIS-CHALMERSCIRCUIT BREAKER Allis Chalmers was theoriginal name of themanufacturer of theMA style breaker theybecame Siemens Allisin 1978 and are nowSiemens. In the1960’s they developedthe MA, FB and FCseries of circuitbreakers.
WHAT IS AN ALLIS-CHALMERSCIRCUIT BREAKER The MA breaker was the first series in thedesign that eventually became FC. The MAb k isbreakeri classedld byb VoltageV ltclass,lAmpereAsize and Interrupting capacity. The 5KV MAmodels include the MA-75, MA-150, MA-250and the MA-350 with continuous currents of1200A and 2000A.
PRIMARY CONTACT ASSEMBLYFOR THE MA BREAKER Stationary Arcing ContactsDesigned to withstand theenergy of the arc when thebreaker opens under load.loadTypically made of a SilverTungsten alloy or similarmaterial. Arcing contactsalways “MAKE” first and“BREAK” last.
COMMON ELECTRICAL DEVICESFOR THE MA BREAKER Auxiliary Switch- There is one switchwith 8 contacts (4 N/C and 4 N/O onthe switch) with an actuator linkageconnected to the jackbar. TheAuxiliary switch provides remoteindication of breaker status and apermissive path to the Shunt TripCoil, allowing the breaker to OPENelectrically. The switch consists ofboth “A” and “B” contacts. “A”contacts are OPEN when breaker isOPEN and CLOSED when thebreaker is CLOSED. “B” contacts dothe opposite of “A” contacts.
COMMON ELECTRICAL DEVICESFOR THE MA BREAKER Close Coil and Trip Coil- Theclose coil closes the breakerelectrically, and the trip coilopens the breakerelectrically The close andelectrically.trip coils are usually thesame physically andelectrically.
COMMON ELECTRICAL DEVICESFOR THE MA BREAKERReset RelayThe Reset Relayconsists of 2 sets ofcontacts,, 1 N/C/ and 1N/O. The Reset Relaytakes the place of theLatch Check switch andprovides a permissivepath for the closesignal.
COMMON ELECTRICAL DEVICESFOR THE MA BREAKER 88 SwitchesThere are three 88switches on the MAbreaker, with1 N/Cand 1 N/O contacton each switch.
COMMON ELECTRICAL DEVICESFOR THE MA BREAKER The 88-1NC is in the motor circuit and is used to start themotor when the springs are DISCHARGED and stop the motorwhen the springs are fully CHARGED. The 88- 1NO and provides a permissive path for the closecircuit when the springs are fully CHARGED.CHARGED The 88-2NC is in the close control lockout circuit. The 88-2NO energizes an indicator light when the springs arefully CHARGED. The 88-3NC is in series with 88-1NO, holding the close controlcircuit open. The 88-3NO introduces a resistor into the motor circuit toslow it down when the springs are CHARGED.
COMMON ELECTRICAL DEVICESFOR THE MA BREAKER Resistorslows the motordown after thesprings are fullyCHARGED. It ismounted on theleft rear of thechassis.
COMMON ELECTRICAL DEVICESFOR THE MA BREAKER Charging MotorCharges theClosing Spring viaa series of gearsand cams.
COMMON ELECTRICAL DEVICESFOR THE MA BREAKER Secondary DisconnectThe Secondary Disconnectconsists of a single assemblywith 16 spring-loadedgarrangedg in vertical afingersrow. The fingers slide onto aramped receptacle in thecubicle. The Secondary isthe electrical interface tooperate the breakerbetween the cubicle and thebreaker when the breaker isRACKED IN or RACKEDOUT.
MECHANICAL AND SAFETY INTERLOCKSFOR THE MA CIRCUIT BREAKER Breaker Cell Coding PlateMounted on the left rear underside of the chassis,this coding plate or rejection bracket, keeps breakersof dissimilar ratingsg from beingg RACKED IN to thewrong cubicle.
MECHANICAL AND SAFETY INTERLOCKSFOR THE MA CIRCUIT BREAKER Floor Tripping and Spring Release InterlockThe Spring Discharge Interlock also actuatesthe Tripping lever when the breaker is hits astop platelini theh cubicle.bi l A common linkageli kworks to safely DISCHARGE the Closingspring when the breaker is RACKED IN orRACKED OUT by a foot lever on the frontmiddle of the breaker chassis.
Operating Mechanism for the MABreaker The MA had a solenoid-operatedmechanism but the nuclear plantsthat have MA breakers were all builtafter these breakers were builtbuilt.There are several styles of storedenergy operated mechanism designsfor the MA breakers such as the SE4 and 515-1.
COMMON FAILURE MODES FORTHE MA BREAKER The Allis Chalmers or Siemens Type circuitbreakers are a low population breaker in theNuclear Industry we believe only 2 plants usestored energy ACB breakersbreakers. There are very fewspecific reports on these breaker types due tothe low population. The breakers would beprone to the same general failure modes thatare common to most breakers that havegenerated reportable issues.
COMMON FAILURE MODES FORTHE MA BREAKER Just behind the Stationary Arcing contact on each phase is a ceramic flashblock. Due to its proximity to the contact, the force of repeated operationsusually cracks the block. Damage has been noted due to Arc chutemisalignment and handling as well.The barriers are solid and with no alignment issues they hold up well. Overtime chips, cracks and burns may warrant replacement on an as neededbasis.basisThe horizontal insulator plate that incorporates the Puffer tubes over thetop of the Operator Assembly is very thin and doesn’t hold up well toadverse conditions. Warping, cracks and holes are common failures.The Puffer Tubes themselves are partially surgical tubing and can dry outand become brittle and prone to cracking.Alignment issues can lead to more significant damage to barriers, frameand Primary disconnects. Alignment issues also can damage the MOCswitch actuator or ground assembly.
Maintenance Manual for the MA Circuit Breaker. WHAT IS AN ALLIS-CHALMERS CIRCUIT BREAKER Allis Chalmers was the original name of the manufacturer of the MA style breaker they became Siemens Allisbecame Siemens Allis in 1978 and are now Siemens. In the 1960’s they developed
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circuit breaker is nothing more than a switch. It needs to be told when to close and when to open. Technology offers us many new and innovative ways to do just that Despite all these terrific ideas we stillto do just that. Despite all these terrific ideas we still have relays that are 30-40 years old that need to remain in service.
9.1 ALLIS CHALMERS Allis Chalmers was the original name of the manufacturer of the MA style breaker they became Siemens Allis in 1978 and are now Siemens. In the 1960's they developed the MA, FB and FC series of circuit breakers. These units were originally offered with solenoid operated closing mechanisms, but eventually the design was
using a Digital Multimeter, most all the switches on the Magne-Blast will read a high resistance ( 1 Ohm). COMMON FAILURE MODES FOR THE MAGNE-BLAST BREAKER The Primary Bushings and the Arc Chutes are problem areas. Due to there . Introduction
or Molybdenum Disulphide (Westinghouse #or Molybdenum Disulphide (Westinghouse # 53701QB). It is a graphite-based lubricant that is dark gray or black in color. It is somewhat fluid grease that adheres well to its components. For the current carrying parts, thick graphite grease, Westinghouse # 53701AN is required.
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