Air Circuit Breakers - Industrial Products

Tech-ArticleINNOVATIVEDESIGNAIR CIRCUITBREAKER(Fully designed & developed by Indian engineers)Suresh DuggalHAVELLS INDIA LTD.P U R P O S EThe Air circuit breaker located at the key point of low voltagedistribution system is the most vital link, since apart from its basicfunction of making, carrying and breaking the normal service currents and providingO/L protection to the equipment or the system, it should be capable of protectingitself and the system from the high short circuit currents without affecting the otherhealthy circuits.R E Q U I R E M E N T SThe Breaker should be fast opening typestored energy mechanism the opening timeincluding arcing time to be within 30m sec,the system is subjected to electro dynamicstresses to shortest possible time.The Breaker should have all the accessoriese.g. Shunt Trip, Closing Coil, Magnetic holdtrigger, micro processor trip device fitted inthe front under the Control Box to facilitatemaintenance replacement withoutwithdrawing the breaker or taking shutdowns.Manually operated (MDO) ACB can beupgraded to electrically operated (EDO) atsite.The Breaker mechanism & Contactarrangement should be sturdy enough towithstand 12500 mechanical operationswithout requiring any maintenance orreplacement of parts. The design furtherhelp in achieving a very high electrical lifeequivalent to mechanical life of ACB withleast maintenance of Arcing contact.The operating mechanism should becommon for the complete range ofBreakers so as to keep low inventory andspares level.The Breaker should have minimum 2 Nos.Tungsten Silver Sintered metal arcingcontacts per pole, capable of withstandingrepeated higher short circuit faults withoutmuch deterioration of contacts.During short circuit faults, the openingoperations should utilize the electro140 PURCHASE December 2012

Tech Articlesintered metal tips of 50% silver and 50%tungsten on copper conductors. The maincontact tips thus provide a high degree ofconductivity and desired hardness, resultingin low temperature rise at the same timeretaining a high mechanical and electricalendurance capability.Flexible ConnectorsIt has been observed that the flexibleconnectors made out of copper braidedwires plated with tin or silver often loosetheir flexibility or get welded together whenexcessive heating is caused by short circuitcurrents. Also the rubbing of braided wirescauses deterioration in flexibility andconductivity. In TITANIA-ACB, a bunch ofcopper strips (foils) having 99.96 % purity,with their ends fuse welded is used asflexible connectors. Since the melting pointof pure copper is very high , the chances offlexible connectors loosing there flexibilityor getting welded are totally eliminated,while maintaining desired rigidity to achievefull advantage of compensation principle.Arc ChuteThe arcing time and consequently breakingcapacity of a breaker also depends on thedesign of the arc chutes. It is the design ofarc chute which determines as to howquickly and effectively the arc can bequenched and the energy released in theform of hot ionized gases can be dissipatedand removed without influencing otherparts of the breaker.The design of de-ion grids in arc chute ofTITANIA-ACB has been so arranged thatthese engulf the triangular shape arc hornfrom two sides and thus arc is scattered in amuch larger area.Isolating BarriersFurther the arc chute and the insulatedbarrier around the contact mechanismpractically seals the arcing area and thus thehot ionized gases escape only in upwarddirection at a great speed. The othermechanism of the breaker thus remains unaffectedfrom these ionized gases andbreaker is complete by free from shockhazards.Auxiliary Isolating ContactsIn TITANIA-ACB design, the auxiliaryisolating contacts are located on top of thebreaker providing full accessibility evenwhen breaker is in housed condition. Theterminal block on the front side, facilitatingeasy inspection and termination of wires.This unique design of auxiliary isolatingcontacts of TITANIA-ACB not onlyguarantees the fault less control supply tothe breaker but completely eliminatesservicing and maintenance problems.Microprocessor based over current trip devices.The trip device is located right in front of theACB providing precise current and timesetting facility. It requires no extra powerand has a built in operation check function.One piece rigidly mounted polyester resinmoulded current transformers adds to itsreliable tripping operation. Due to its mostaccurate and reliable operation, the highestdegree of system protection co-ordinationcan be achieved.Microprocessor based OCR providesfacilities for over load, short circuit,instantaneous trip and earth faultprotection.ACCESSORIES OF THE BREAKERELECTRICAL ACCESSORIES:Charging Motor:It is provided in anelectrical operatedACB to charge theclosing springsautomatically.These areavailable in 110Vand 220V AC/DC.The VA burden of this motor is 150 VA onlyand the charging time is 3 to 4 seconds.Shunt Trip Coil / Closing CoilThese coils are used for electrical trippingand closing of ACB. These coils are144 PURCHASE December 2012

Tech ArticleSpring charge Indication SwitchA micro switch is provided to get a remotesignal indicating the status of CircuitBreaker closing spring.Close open cycle counterIt indicates the number of mechanicaloperations of the circuit breaker and thesame is visible on the front of ACB Cover.OVER CURRENT RELEASE:IPR range of over current releases (OCR)provided in Titania breakers are highlyreliable,multi- functional, dedicatedprotection unit using advanced microcontrollerwith full benefits ofmicroprocessor technology offeringOverload, Short Circuit, Instantaneous andearth fault protection besides enhancedfeature of field testing for all models.These releases are true RMS sensing overcurrent trip devices, requiring no externalsupply for their basic functioning.Salient features include:Error free and user friendly settings ofcurrent and time delayTrue RMS sensing with immunity tosystem disturbancesMore Reliable and repetitive accuracy,using high end 16 bit micro-controllerSelf powered by built in CurrentTransformerThree phase protection and Earth faultprotection in same unitLED Indication for all the tripping faultsFunction 'OFF', setting availableSpecifications:Settings of Overload Current (LTD) LTDCurrent (I 1): 40% to 100% of ICT withfunction blocking option. LTD Time: 1 sec to35sec,Settings of Short Circuit Current (STD)STD Current (I2) : 300% to 900% of I1withfunction blocking option. STD Time: 5Omsto 700ms,Setting of Instantaneous Current (INST)INST Current (I 3) : 400% to 1600% of I 1 withfunction blocking option.Ground fault Selling (GFT) GFT Current(Ig):10% to 70% of I 1 with function blockingoption. GFT Time: 100ms to 5000ms,Besides these protection functions IPR-3 providesthe following additional functions also:RS Communication : Through RS485 PortPre Trip Alarm FunctionCurrent Setting (Ip) : 60 to 100% of LTDcurrent setting Time Setting (Tp) (Definite):10 to 200 secMeasurement function: 3 phase current, 3phase voltage, Tripping time, KvA. KWH,Power factor, Max demand (KVA & KWH),Breaker terminal temperatureUnder Voltage/ Over Voltage Indication:Under voltage setting from 40 to 85% ofrated voltage with a time delay of 50 to 400msec. Over voltage setting from 110 to150% with a time delay of 50 to 400 msec,Fault History : To record and display thelast 100 faults (50 faults in IPR2)Self Monitoring: To monitor the conditionof controller and In case of any fault same isindicated by “CPU FIT” LED.Temperature Sensing: To monitor thetemperature of Micro-controller and give anindication if the temperature exceeds theset value.Breaker Fault: When any mechanical faultprevents the tripping of the fault zonebreaker. The release of that breaker givesthe tripping command to the upper zonebreaker (if externally connected).Potential Free Contacts: Potential freecontacts for LTD. STD/INST, PTA. GFT TEMP,under and over voltage.LED Indications: LED Indications forfaults.Function Blocking : This feature isavailable for LTD. STD. INST and GFTOperation Counter: It records the numberof operations of ACB by counting thenumber of trip operations through OCR andstores them in 2 different categories: a)Current less than 300%, b) Current morethan 300%.Function Check: Field testing of LTD. STD& INST function can be performed with helpof Field Testing Kit.Specifications for IPR-E :LTD Current (I1) :55% to 100% of ICTrating.LTD Time: 5 Sec.fixed at 6 I n inversetime characteristics.INST Current: Fixed at 6 I n.148 PURCHASE December 2012