AUTOMATIC TRANSFER SWITCHES自动转换开关

1、CommercialUtility PowerUPSUPS BatteriesAir conditioning, Lighting,Mechanical, Building Loads,etc.Network Computer LoadsTransfer SwitchgearGenerator ParallelingControl SwitchgearEmergencyGenerators Selective coordination was first required by the NEC in 1993 for elevator circuits. Amendments to the C

2、ode in 2005 and 2008 strengthened the requirements and expanded them to include emergency and legally required standby systems, as well as critical operations power systems. Selective coordination, as defined in the 2008 NEC, is the “localization of an overcurrent condition to restrict outages to th

3、e circuit or equipment affected, accomplished by the choice of overcurrent protective devices and their ratings or settings.” It is a complicated process of coordinating the ratings and settings of overcurrent protective devices, such as circuit breakers, fuses, and ground fault protection relays, t

4、o limit overcurrent interruption (and the resultant power outages) to the affected circuit or equipment (the smallest possible section of a circuit). In other words, the only overcurrent protective device that should open is the device immediately “upstream” from the circuit/equipment experiencing a

5、n overcurrent condition.Selective Coordination Requirements NEC(2008) 701.18 Coordination: requires “Legally required standby system(s) overcurrent devices shall be selectively coordinated with all supply side overcurrent protective devices.”GUtility4000AAPCB1600AAPCB1600AAPCB800AICCB400AMCCBAn over

6、current event (overload, short circuit, or ground fault) here should trip the 400A MCCBATSMCCBs (Molded Case Circuit Breaker) typically instantaneous or Current Limiting Devices.ICCBs (Insulated Case Circuit Breaker) are 30 cycle withstand or up to 4 Cycle Instantaneous.APCBs (Air Power Circuit Brea

7、ker) are typically 30 cycle withstand devices.GUtility4000AAPCB1600AAPCB1600AAPCB800AICCB400AMCCBFault on load side of ATS could see up to 30 cycles of fault current -depending on the Air Power Circuit Breaker settings that is feeding it- and could travel through the ATS and the ATS contacts.ATSIf t

8、he 400A MCCB does not trip/clearATSIn the absence of other means to satisfy selective coordination, the ATS must withstand a fault or even close on potential fault to be properly coordinated. Fuses 2005 NEC 1999 NEC 2002 NEC Local Adoption2005 NEC 8 StatesWVWIMTNDSDWAORNVIDUTAZNMTXCOWYNBM IKYTNMNIAM

9、OARLAMSILINOHALGAKSOKNHMENYPAVADENJMARIFLNCSCVTCALocal Adoption (10)MD2008 NEC 32 StatesM INote: Some local adoption states have earlier than 2005 adoptions in some jurisdictions Basically 2002 NEC but some islands back to 1993 NECCTAKRevised April 19, 2010State Adopted Unincorporated AreasState Ado

10、ptedS. Carolina Code Council adopted 2009 IRC with 2008 NEC 3/22/10 with implementation 1-1-11Expected July 10Expected January 2011 Expected July 2010“ Around 1989 UL introduced an optional 3 cycle test for any over- current protection device.Prior to this, manufactures could test with any over-curr

11、ent device.If a manufacturer didnt test to 3 cycles, they would be required provide a label that lists all breakers that the switch was “coordinated with”.This requirement did not take into consideration air power circuit breakers APCBs. Some of these breakers were 4-5 cycle devices (GE AKR and West

12、inghouse DS) January 9th, 2002 UL introduced an optional short time current rating test.A withstand and a close and withstand test is required to get a UL short time rating.36A.1 A switch marked with a short-time current rating in accordance with 41.20.1 shall be tested under the conditions describe

13、d in 36A.2 -36A.12 and shall withstand the short-time current for the period specified. At the conclusion of the test:28.1 Transfer switch equipment shall perform in an acceptable manner, as intended by the manufacturer, when subjected to an overload test consisting of the number of operations speci

14、fied in Table 28.1, controlling a test current as described in Table 28.2.Table 28.1 Overload TestSwitch rating, amperesNumber of cycles of operationRate of Operation* 0-300301- 400401- 600601- 800801- 16001601- 25002501 and above50505050502531 per minute1 per 2 minutes1 per 3 minutes1 per 4 minutes

15、1 per 5 minutes1 per 5 minutes1 per 5 minutes Device used forDevice rated in amperesPower test currentFactorMotor loads or total system a-c 6 times rated current 0.40- 0.50 Table 28.2 Method of determining test current for overload tests on transfer switches28.4 A cycle is defined as making and brea

16、king the required test current on both the normal and alternate contacts. During the test, the alternate source shall be displaced 120 electrical degrees from the normal source for a 3 phase supply or 180 electrical degrees for a single phase supply.28.6 The minimum on time in each contact position

17、is to be 1/6 second (ten electrical cycles based on a 60Hz source), unless automatic tripping of the over-current device occurs.30.1 A transfer switch shall perform as intended when subjected to an endurance test controlling a test current as described in Table 30.1 and at a rate and number of cycle

18、s described in Tables 30.2 and 30.3.Table 30.1Method of determining test current for endurance tests The test cycle is to be 1 second “on” and 59 seconds “off”. A controller may be operated at a rate of more than 1 cycle per minute if synthetic loads are used or if a sufficient number of banks of la

19、mps controlled by a each bank will cool for at least 59 seconds between successive applications of current.Table 30.2Endurance test cycles for emergency system switches including legally required stand-by systems. 29.1 Transfer switches when tested under the conditions described in 29.2 29.12 shall

20、not attain a temperature at any point high enough to constitute a risk of fire or to damage any materials employed in the device, and shall not show temperature rises at specific points greater than those indicated in Table 29.129.2 For the temperature test the transfer switch is to be operated unde

21、r intended use conditions and is to carry its test current continuously at the test potential specified in Table The test current shall be 100 percent of the rated current. No overlapping fault current of individual devices.This is coordinated properly.In a perfect world this is great.In t

22、his case, since it takes 8 cycles for the upstream breaker to clear the fault, a 3 cycle rated transfer switch is inadequate.ATS Feeder Breaker8 cycles to clearA 30 cycle UL rated Transfer Switch truly gives you complete coordination with any over-current protective device.Utility isLostLoad is fedb

23、y emergencypowerUtility isRestoredUnloadedenginecool down periodEngineshuts down system returnedto normaloperationNELOverlapping NeutralVsNELBreaksBeforeNELMakesNELNELELNNELLNE12NELLNEATS-1Life Safety &SupportBranchesATS-2CriticalBranchesATS-3EquipmentBranchesGEGEGEEmergencyDistributionSwitchgea

24、rGeneratorControl &SynchronizingSwitchgearUtilityDistributionSwitchgearLoadControlCircuitryUtilitySourceGELoss ofEngine #1ATS - 3 ShedsNon-Critical LoadsLNENORMALLOADEMERGENCYNORMISOLATEATSBPNBPEBPNBPEAUTOBypass/Isolation Switch One-Line Diagram(Normal operating mode)NORMALLOADEMERGENCYNORMISOLA

25、TEATSBPNBPEBPNBPEAUTONORMALLOADEMERGENCYNORMISOLATEATSBPNBPEBPNBPEAUTONORMALLOADEMERGENCYNORMISOLATEATSBPNBPEBPNBPEAUTONORMALLOADEMERGENCYNORMISOLATEATSBPNBPEBPNBPEAUTONORMALLOADEMERGENCYNORMISOLATEATSBPNBPEBPNBPEAUTOLOAD BYPASSED TO NORMALNORMALLOADEMERGENCYNORMISOLATEATSBPNBPEBPNBPEAUTOLOAD BYPASS

26、ED TO NORMALNORMALLOADEMERGENCYNORMISOLATEATSBPNBPEBPNBPEAUTOLOAD BYPASSED TO NORMALNORMALLOADEMERGENCYNORMISOLATEATSBPNBPEBPNBPEAUTOLOAD BYPASSED TO NORMALNORMALLOADEMERGENCYNORMISOLATEATSBPNBPEBPNBPEAUTOLOAD BYPASSED TO NORMALIf the transfer switch portion is bypassed & isolated to normal and the