Presentation on theme: "Automatic Transfer Switch (ATS)"— Presentation transcript:
1 Automatic Transfer Switch (ATS) The Key to High Reliability Source Switching
2 Presentation Overview ATS – The Key to High Reliability Source SwitchingVarious technologies are used to switch critical loads from a primary to a backup power source. When nothing goes wrong in the facility (overloads, short circuits, etc.) most technologies perform adequately. When problems occur, certain ATS technologies will keep the power on…others will not. Knowing the differences and correctly applying ATS in your facility is key to providing high reliability source switching.This presentation will include:A definition of ATSAn overview of typical ATS applications, constructions, and typesA review of the IEC codes and testing procedures for ATSA comparison of the performance of each technology under IEC testing –under normal and abnormal circumstancesApplication guidelines for selectively coordinated, high reliability, fault-tolerant source switching.Overall recommendations for a Power Quality installations.
3 Section 1 – ATS Basics What is an ATS ? What are typical applications of ATS?Common constructions of ATSCommon types of ATS
4 What is an Automatic Transfer Switch (ATS) ? An ATS is a device designed to Automatically switch (transfer) between (2) sources of power to improve the reliability of the electrical supply to a connected load.Backup Source(typically a Generator Supply(Normally De-Energized)GPrimary Source(typically a Utility Supply or Utility Bus)(Normally Energized)
5 Typical Applications of ATS Utility and Engine GeneratorSingle unit standby applications are very commonUtility and UtilityDual utility applications are becoming more commonGenerator and GeneratorPrime power / standby application
6 Types of ATS construction KnifeBladeTypeTwin ContactorTypeTwin MCCBTypePower ContactorTypeStatic TransferTypeGE Power QualityGE componentsMarket Trend
7 Typical ATS Constructions Knife Blade Typically Non-Load breakingUsually Manually Operated (and slow)Sometimes motor operated (still slow)Low withstand ratings – no arc chutes or ventsLow endurance ratings = limited life
8 Typical ATS Constructions Twin Contactor IECSwitching device having 1 position of rest (IEC def’n)Returns to position of loss power (un-latched type) or add’l latching arrangement to hold position on loss of powerBuilt using 1 of up to 12 types of contactors under IEC Code, from basic contactor to high-capacity motor starters.Often very basic controllerMechanical/safety interlock often not available or optionalVariety of operators, from motor to electromagnetsNot a True double throw device - possible to close into both Sources
9 Typical ATS Constructions Twin MCCB (Molded Case Circuit Breaker) IEC2 Position device, typically operated from add-on motorsBuilt using 1 of up to 2 types of breaker under IEC Code, from basic instantaneous-trip type to short-time rated devices.Mechanical/safety interlock is an add-on, sometimes optionalMotor operators usually slow, often unreliable for high duty.Wide range of manf-assigned withstand ratings (low, med, or high)Not a True double throw device - possible to close into both Sources
10 Typical ATS Constructions Power Contactor Type (GE Zenith Std.) UL 1008IECStd. Double Throw mechanism - Inherent mechanical interlock against closing to both sourcesNo add-on interlocks requiredFewer moving partsHigh Withstand Current ratings to allow fault clearing coordinationIntegrated Arc quenching componentsSolenoid Operated (very fast)
11 Power Contactor ATS - Composition Arc quenching grids & enclosed arc chutesMovable contact assembly has 2 pieces, arcing contact and main current carrying contact.Arcing contacts make first, break last [See Video].Silver alloy contactsResists weldingEnhanced withstand ratings“Over center” switching principal to achieve a mechanically locked position in either Source 1 or 2High speed solenoid actuated drive assures contact transfer in msec(Click to see video)
12 Typical ATS Constructions Static EN12LTwo live sources required. Solid-state switching >> no moving partsExtremely FAST operation, transfer in less than ¼ cycle.SCR technologyTypically used on critical loads where 2 reliable and independent power supplies available, or switching 2 x UPS Outputs.Both sources must be in syncOften cost prohibitive for Standby applications
13 Standard Transfer Switch: Types Transition(No Center Position)Delayed Transition(With Center OFF Position)NOTE: “OFF” Position indicates Neither Source connectedClosed Transition(Make-Before-Break Operation)NOTE: “P” Position indicates both sources paralleled for 5 cycles
14 TWO PATHS FROM SOURCE TO LOAD Bypass Isolation ATSMECHANICALINTERLOCKSTWO PATHS FROM SOURCE TO LOADWITHDRAWABLE ATSFIXED MOUNT MTSEssentially (2) ATS in Parallel, (1) Automatic Switch (ATS) & (1) Manual Switch (MTS).ATS is withdrawable, similar to withdrawable CB’s(2) redundant paths from each source to load.ATS & MTS are mechanically and electrically interlockedTo prevents accidental closure of both sourcesBypassing power from Source to Load permits testing or maintenance of ATS without interruption to load.Available in Open, Delayed, and Closed TransitionIf power fails while bypassed, Genset is auto started to permit fast transfer using MTS.
15 Section 2 - Codes & Standards for equipment applied as ATS What are the Internationally-recognized codes?What is the Performance differenceof devices tested to these codes?
16 Internationally-recognized ATS Codes and Standards Devices arranged for Source Switching, but not IEC rated as ATSDevices arranged for Source Switching, IEC rated as ATSContactors & Motor StartersCircuitBreakersContactors & Motor StartersCircuitBreakersPower ContactorsIECUL 508IECUL 489IECUL 1008Devices may be arranged to function as an ATS, but not be rated as ATS by a Recognized body
17 Transfer Switching Equipment 60947-6-1 IEC Performance Testing of ATS - OverviewGE ATS RatingsTwin ContactorsTwin CB’sCB: Breaker typePC/CC: Contactor types.ContactorCircuit BreakerIEC CodeTransfer Switching EquipmentUtil. Cat.(IEC ‘AC-1’)(IEC ‘A’)(AC-31A, 31B)(AC-33A, 33B)31A: High Operations @ Rated Current 33A: High 2 x Rated Current31B: Low Rated Current33B: Low 2 x Rated CurrentOperational PerformanceHighRated currentLow majority No CurrentOverload or Low current short circuit PerformanceLow6x Rated Current, High pf, for up to 630A Rating. (N/A >630A)Low1.5x Rated Current, High pf31A: High Operations @ 1.5 Rated Current 33A: High 6x Rated Current31B: Low 1.5 Rated Current33B: Low 6x Rated CurrentCC/PC Type:Break SC: NoMake SC: YesMake & Hold: YesWithstand SC: YesHigh/Short Circuit PerformanceCB Type:Break SC: YesMake SC: YesMake & Hold: NoWithstand SC: NoBreak SC: YesMake SC: YesMake & Hold: NoWithstand SC: NoNo Requirements
18 Short Circuit Testing of PC-Type ATS Contactors and Circuit Breakers have Fault current ratings, expressed in kAICPC-type ATS are tested to:Withstand fault currents (remain closed), for a set period of time, permitting downstream devices to trip and isolate the fault.Close into faults, to permit the Backup supply fault current necessary to clear the fault.For this reason, PC-type ATS have Withstand and Close Ratings (WCR) vs. Traditional kAIC Fault rating (as in a CB).FaultTesting (click to see video)
19 Performance of ATS Technologies - Summary Twin CB’sCB: Breaker typePC/CC: Contactor types.“Real life” performance of ATS in your facilityTwin ContactorsBuilding EventLow Operation switching of Rated LoadOKNot OKOKHigh Duty Cycle/Switching33A, 33BOKNot OK31A, 31BSwitching Motors w/ 6-10X startOK (up to 630A)33A, 33BNot OK>630A31A, 31BShort on load side of ATSNeed upstream SCPD to tripInst. Trip.Selectivity w/ downstream SCPD ???Same as CBDesigned to withstand & permit downstream SCPDto clearSwitching into a short circuit on load side of ATS.Designed to close into and withstand to permit downstream SCPD to clearBig problemSame as above
20 Section 3 - Application Guidelines for PQ Installations
21 PQ Application Recommendations for ATS Specify ATS certified As an ATS to IEC or UL Un-certified ATS have not been tested for the purposes of source switching.Specify an ATS with adequate duty cycle rating“A” or “B” IEC Utilization Catagories, based on applicationSpecify an ATS with adequate overload capability for switching inductive loads“31” or “33” IEC Utilization Catagories, based on applicationSpecify PC Type of ATS for critical load application …Specify PC-type where fault withstand, vs, tripping under faults, is required for proper system Selective Coordination for faults below ATS.
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