Automatic Transfer Switch (ATS) The Key to High Reliability Source Switching

Presentation Overview ATS – The Key to High Reliability Source Switching   Various 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 ATS An overview of typical ATS applications, constructions, and types A review of the IEC codes and testing procedures for ATS A comparison of the performance of each technology under IEC testing – under normal and abnormal circumstances Application guidelines for selectively coordinated, high reliability, fault- tolerant source switching. Overall recommendations for a Power Quality installations.

Section 1 – ATS Basics What is an ATS ? What are typical applications of ATS? Common constructions of ATS Common types of ATS

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) G Primary Source (typically a Utility Supply or Utility Bus) (Normally Energized)

Typical Applications of ATS Utility and Engine Generator Single unit standby applications are very common Utility and Utility Dual utility applications are becoming more common Generator and Generator Prime power / standby application

Types of ATS construction Knife Blade Type Twin Contactor Type Twin MCCB Type Power Contactor Type Static Transfer Type GE Power Quality GE components Market Trend

Typical ATS Constructions Knife Blade Typically Non-Load breaking Usually Manually Operated (and slow) Sometimes motor operated (still slow) Low withstand ratings – no arc chutes or vents Low endurance ratings = limited life

Typical ATS Constructions Twin Contactor IEC 60947-4-1 Switching device having 1 position of rest (IEC def’n) Returns to position of rest @ loss power (un-latched type) or add’l latching arrangement to hold position on loss of power Built using 1 of up to 12 types of contactors under IEC 60947-4-1 Code, from basic contactor to high-capacity motor starters. Often very basic controller Mechanical/safety interlock often not available or optional Variety of operators, from motor to electromagnets Not a True double throw device - possible to close into both Sources

Typical ATS Constructions Twin MCCB (Molded Case Circuit Breaker) IEC 60947-2 2 Position device, typically operated from add-on motors Built using 1 of up to 2 types of breaker under IEC 60947-2 Code, from basic instantaneous-trip type to short-time rated devices. Mechanical/safety interlock is an add-on, sometimes optional Motor 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

Typical ATS Constructions Power Contactor Type (GE Zenith Std.) UL 1008 IEC 60947-6-1 Std. Double Throw mechanism - Inherent mechanical interlock against closing to both sources No add-on interlocks required Fewer moving parts High Withstand Current ratings to allow fault clearing coordination Integrated Arc quenching components Solenoid Operated (very fast)

Power Contactor ATS - Composition Arc quenching grids & enclosed arc chutes Movable contact assembly has 2 pieces, arcing contact and main current carrying contact. Arcing contacts make first, break last [See Video]. Silver alloy contacts Resists welding Enhanced withstand ratings “Over center” switching principal to achieve a mechanically locked position in either Source 1 or 2 High speed solenoid actuated drive assures contact transfer in 30-50 msec (Click to see video)

Typical ATS Constructions Static E N 1 2 L Two live sources required. Solid-state switching >> no moving parts Extremely FAST operation, transfer in less than ¼ cycle. SCR technology Typically used on critical loads where 2 reliable and independent power supplies available, or switching 2 x UPS Outputs. Both sources must be in sync Often cost prohibitive for Standby applications

Standard Transfer Switch: Types Transition (No Center Position) Delayed Transition (With Center OFF Position) NOTE: “OFF” Position indicates Neither Source connected Closed Transition (Make-Before-Break Operation) NOTE: “P” Position indicates both sources paralleled for 5 cycles

TWO PATHS FROM SOURCE TO LOAD Bypass Isolation ATS MECHANICAL INTERLOCKS TWO PATHS FROM SOURCE TO LOAD WITHDRAWABLE ATS FIXED MOUNT MTS Essentially (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 interlocked To prevents accidental closure of both sources Bypassing power from Source to Load permits testing or maintenance of ATS without interruption to load. Available in Open, Delayed, and Closed Transition If power fails while bypassed, Genset is auto started to permit fast transfer using MTS.

Section 2 - Codes & Standards for equipment applied as ATS What are the Internationally- recognized codes? What is the Performance difference of devices tested to these codes?

Internationally-recognized ATS Codes and Standards Devices arranged for Source Switching, but not IEC rated as ATS Devices arranged for Source Switching, IEC rated as ATS Contactors & Motor Starters Circuit Breakers Contactors & Motor Starters Circuit Breakers Power Contactors IEC 60947-4-1 UL 508 IEC 60947-2 UL 489 IEC 60947-6-1 UL 1008 Devices may be arranged to function as an ATS, but not be rated as ATS by a Recognized body

Transfer Switching Equipment 60947-6-1 IEC Performance Testing of ATS - Overview GE ATS Ratings Twin Contactors Twin CB’s CB: Breaker type PC/CC: Contactor types. Contactor 60947-4-1 Circuit Breaker 60947-2 IEC Code Transfer Switching Equipment 60947-6-1 Util. Cat. (IEC ‘AC-1’) (IEC ‘A’) (AC-31A, 31B) (AC-33A, 33B) 31A: High Operations @ Rated Current 33A: High Operations @ 2 x Rated Current 31B: Low Operations @ Rated Current 33B: Low Operations @ 2 x Rated Current Operational Performance High Operations @ Rated current Low Operations @ majority No Current Overload or Low current short circuit Performance Low Operations @ 6x Rated Current, High pf, for up to 630A Rating. (N/A >630A) Low Operations @ 1.5x Rated Current, High pf 31A: High Operations @ 1.5 Rated Current 33A: High Operations @ 6x Rated Current 31B: Low Operations @ 1.5 Rated Current 33B: Low Operations @ 6x Rated Current CC/PC Type: Break SC: No Make SC: Yes Make & Hold: Yes Withstand SC: Yes High/Short Circuit Performance CB Type: Break SC: Yes Make SC: Yes Make & Hold: No Withstand SC: No Break SC: Yes Make SC: Yes Make & Hold: No Withstand SC: No No Requirements

Short Circuit Testing of PC-Type ATS Contactors and Circuit Breakers have Fault current ratings, expressed in kAIC PC-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)

Performance of ATS Technologies - Summary Twin CB’s CB: Breaker type PC/CC: Contactor types. “Real life” performance of ATS in your facility Twin Contactors Building Event Low Operation switching of Rated Load    OK Not OK OK    High Duty Cycle/Switching 33A, 33B OK Not OK  31A, 31B   Switching Motors w/ 6-10X inrush @ start OK (up to 630A)   33A, 33B Not OK  >630A 31A, 31B     Short on load side of ATS Need upstream SCPD to trip Inst. Trip. Selectivity w/ downstream SCPD ??? Same as CB Designed to withstand & permit downstream SCPD to clear  Switching into a short circuit on load side of ATS.   Designed to close into and withstand to permit downstream SCPD to clear Big problem Same as above

Section 3 - Application Guidelines for PQ Installations

PQ Application Recommendations for ATS Specify ATS certified As an ATS to IEC 60947-6-1 or UL 1008 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 application Specify an ATS with adequate overload capability for switching inductive loads “31” or “33” IEC Utilization Catagories, based on application Specify 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.