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ATS Training Outline

Learn about transfer switch mechanisms, application issues, codes and standards, causes of interruptions, impact of ATS failures, and design considerations for reliable power transfer. Discover why transfer switches are crucial for various industries.

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ATS Training Outline

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  1. ATS Training Outline • What is a Transfer Switch? • Application • What Makes A Transfer Switch Reliable? • Segmented Contacts, Arc Gaps • Transfer Switch Mechanism Analysis • Control Panel Evolution • Application Issues • Motor Load transfer (Inphase, DTTS, etc.) • Switching The Neutral in Ground Fault Systems • What Are The Codes & Standards • UL 1008, CSA, IEC 60947-6, NFPA 700, 701, 702

  2. ATS Training Outline • Automatic Transfer Switches & Derivatives • Automatic Transfer Switch • Closed Transition Switch • Automatic Transfer/ Bypass Switch • Static Transfer Switch & Hybrid Static Transfer • Communication Products • Remote Annunciators • PC Based Software Systems

  3. Why Are Transfer Switches Needed? • To assure continuity of vital electrical power for essential loads: • Prevent accidents, theft, panic, loss of revenue • Comply with codes & standards • Comply with government regulations • Whenever two or more sources of power are utilized for essential electrical loads.

  4. Causes of InterruptionsUp & Downstream • Heavy utility demands • Lightning • Fires • Earthquakes • Ice storms • Auto accidents • Short circuits • Ground faults • Human errors

  5. Impact of ATS Failures • Panic & Confusion • Loss of lights (10 second rule) • Elevators, escalators, electric doors • Traffic control • Communications • Loss of Life • Hospital equipment • Life support, Operating Rooms & ER • Radar equipment

  6. Impact of ATS Failures • Loss of revenue • Cash registers • Assembly lines • Toll gates • Refrigeration • Loss of property • Fire alarms, fire pumps • Intrusion alarms • Loss of information • Computers • Data Centers

  7. Where Are Transfer Switches Used? • Hospitals & other health care facilities • Telecommunications & other utilities • Banks & computer facilities • Industrial buildings & WWTPs • Office buildings • Airports • Government & military installations • Police & security systems • Bridge & tunnels 16

  8. Automatic Transfer SwitchDesign Considerations

  9. UTILITY LOAD GENERATOR Transfer Switch Definitions • A device which transferselectrical loads between twodissimilarsources of power by using either manual or automatic controls.

  10. UTILITY LOAD GENERATOR Transfer Switch Legal Definitions • IEEE, NEMA ICS. 10-199 (replaced 2-447) and EGSA: “An Automatic Transfer Switch is self-acting equipment for transferring one or more load conductor connections from one power source to another. • UL-1008: “1.4 A transfer switch as covered by these requirements is a device that automaticallytransfers a common load from a normal supply to an alternate supply in the event of failure of the normal supply,and automatically returns the load • to the normal supply when the normal supply is restored.”

  11. UTILITY LOAD GENERATOR Transfer Switch Legal Definitions • IEC 60947.6.1: A device for transferring of one or more load circuits from one supply to another. A self acting equipment containing the transfer switching device(s) &othernecessary devices for monitoring supply circuits and fortransferring one or more load circuits from onesupply to another.

  12. Seven Major Functions of Automatic Transfer Switches • Carry Current Continuously • Detect Power Failures • Initiate Alternate Source • Transfer Load • Sense Restoration of Normal • Re-Transfer Load to Normal • Withstand and Close- In On Fault Currents

  13. Transfer Switch & Overcurrent Protective Device Locations Transfer Switches should be located as closeto the load as possible to protect against internalbuilding failures in addition to utility outages. Overcurrent Protective Devices (Fuses or Circuit Breakers) should be located as close to the source as possible to provide protection of serviceconductors. NEC requires CB no more than 20 ft. from source. This also helps assure proper system coordination. X CB CB X X X X CB CB UTILITY LOAD GENERATOR

  14. Basic Transfer Switch Types • Automatic transfer switches operateautomatically upon source failure or voltage reduction. • Non-automatic transfer switches must be manuallyinitiated and can be either electricallyor mechanically operated. • For manual or auto-start engine - generators • Switches with selector/ toggle switches that disable automatic transfer or retransfer must me labeled non- automatic per UL 1008 standard

  15. Transfer Switch Types Non - Automatic Transfer Switches • Electrically Operated • No or Basic Sensing • Full Sensing • Electrically Operated Automatic Transfer Switches • Most Transfer Switches Are Normal Seeking • Selective Normal • Non - Selective Normal

  16. Power Switching Solutions Selective Normal ATS • Definition:A transfer switch whose control circuitry is configured for “Normal Seeking Operation”. In other words, it always wants to be connected to a preferred source. The user can choose which service is the normal/preferred source. • Typical Configurations • Utility to Generator • Standard/Conventional type ATS • Utility to Utility • Generator to Generator

  17. Power Switching Solutions Selective Normal ATS • Generator to Generator - • Description of Operation: The transfer switch is configured to transfer a critical load between two (2) engine generator sources, where one of the generators is the preferred source. • Utility to Utility - • Description of Operation:The transfer switch is configured to transfer a critical load between two (2) utility sources, where one of the utilities is the preferred source. Most applications require the same time delays on both sources and three phase U.V. sensing on both sources as a minimum.

  18. Power Switching Solutions Non - Selective Normal ATS • Definition: A transfer switch whose control circuitry is configured such that it has no preference as to which source it is connected to. In other words, it is a power seeking device. • Typical Configurations • Utility to Generator • Utility to Utility • Generator to Generator

  19. Power Switching Solutions Non - Selective Normal ATS • Description of Operation: • The transfer switch is configured to transfer a critical load to an emergency source upon normal source failure. • The transfer switch does not retransfer upon restoration of the normal source. • The transfer switch only re-transfers to the normal source if the emergency source fails, or toggle switch is activated.

  20. Control Panel Transfer Switch Alternate Source TD 2 Time Delay Transfer to Alternate Voltage & Frequency Sensing Transfer Operator Transfer Controls Time Delay Re-transfer to Normal Load TD 3 Time Delay to Start Engine- Gen. Voltage Sensing TD 1 T.D. E-G Cooldown TD 4 Normal Source Basic Transfer Switch Components

  21. Transfer SwitchesPhysical Elements TRANSFER PANEL CONTROL PANEL Power Switching Mechanism • TS Panel/ Contactor • Solenoid Operator • Motor Mechanism(s) • Main & Arcing Contacts • Control and Auxiliary Contacts • Power Connections • Mechanical Lugs • Bus Stab/ Bar Control Panel/ Controller • Voltage and Frequency Sensing • 4 Time Delays • Input/Output Controls • Annunciation Devices Over 90% of ATSs are supplied in enclosures by manufacturer, also mounted in switchboards & motor control centers.

  22. 600 - 800 Amps 225 - 400 Amps Typical Transfer Switch Amp Sizes600 Volts 1000 - 1200 Amps 1600 - 2000 Amps* 30 - 200 Amps *Available up to 4000 amps

  23. Normal Loads Emergency Contact Transfer Configurations • Break Before Make - Open Transition • One set of contactsopen before the other set close • Load is disconnected from power during all transfers 20-100 m/secs off -time

  24. Normal TS N Loads TS E Emergency Contact Transfer Configurations • Make Before Break - Closed Transition • Contacts overlap with hot-hot & acceptable sources • Load is not disconnected from power during transfers • Transfers Open Transition If Source Fails - Retransfers Closed Transition 100 m/secs overlap-time

  25. Transfer Switch Design Criteria Single Solenoid Operator • True double-throw design • Inherently interlocked • Simple and reliable • Speed of operation • Other Types of Industry Operators Available • Linear Motor(s) • Gear Motors Coil Core Weights

  26. ATS Control Circuit DesignTransfer Switch Controls • The single solenoidoperator of the power transfer device is powered via the SE & ER relays in the control panel. • The control panel logic initiates the transfer of the load by energizing the SE(normal) relay for emergency to normal transfers or the ER(emergency) relay for normal to emergency transfers. • The switch operator is alwayspowered from the source to which the load is being. • Prevents transfers to a bad source

  27. Transfer Switch Design Criteria Contact Designs • Electrical & Mechanical engineering designs • Specifically for ATS applications • Between Two Live Sources • Main contact material • Solid vs. segmented contacts • Arcing contact material • Contact pressure • Wiping action • Neutral switching • Easy to inspect and maintain

  28. Transfer Switch Design Criteria Arcing Isolation and Suppression • Speed of operation • Wide arc gaps • Arc chutes • Arcing tip or separate contacts • Neutral switching with overlapping contacts

  29. Transfer Switch Design Criteria Contact Design • Designed for transfer switch applications • Designed by ASCO • Main contact materials • Arcing contact material 18

  30. Transfer Switch Design Criteria Contact Design • Mechanical Pressure on Main Contacts • Solid vs. Segmented Contacts • Contact Wiping Action 18

  31. Easy Replacement Of Main Contacts

  32. Transfer Switch Design Criteria Arcing Isolation and Suppression • Speed of operation • Wide arc gaps • Arc chutes • Arcing tip or separate contacts • Neutral switching with overlapping contacts

  33. Transfer Switch Design Criteria

  34. Control Panel TD 2 Time Delay Transfer to Alternate Voltage & Frequency Sensing Transfer Controls Time Delay Re-transfer to Normal TD 3 Time Delay to Start Engine- Gen. Voltage Sensing TD 1 T.D. E-G Cooldown TD 4 ATS Control Circuit Design • Source Monitoring • Time Delays • Other Signals • Pilot Lights & Test Switch • Transfer Switch Controls

  35. ATS Control Circuit DesignSource Monitoring • The control panel monitors: • source voltage • RMS or average voltage (ignore spikes) • single phase or three phase • line to line • source frequency - 50/60, 100, 400 Hz • switch position • The control panel does not monitor • load current • Special control panels available • VDC - batteries • High Speed - less than 1 second • EG- EG applications

  36. ATS Control Circuit DesignTime Delays • MomentaryNormal Source Failure Override (Feat. 1) • How long must a normal source failure exist prior to starting the transfer sequence? • Normal to Emergency Transfer Time Delay (Feat. 2B) • How long must the emergency source be acceptable prior to transferring the load from normal to emergency? • Emergency to Normal Transfer Time Delay (Feat. 3A) • How long must the normal source be acceptable prior to re-transferring the load from emergency to normal? • Engine Cool Down Time Delay (Feat. 2E) • How long must the generator run unloaded after the load has been retransferred to the normal source?

  37. ATS Control Circuit DesignOther Signals • Engine Start Contacts (Feature 7/8) • Used by the controller to signal the generator to start • Switch Position Contacts (Feat. 14A/B) • Used for remote indication of switch position • Test Switch (Feat.5) • Used to simulate a normal source failure and start a test transfer sequence • Time Delay Bypass Switch (Feat.6B) • Used to bypass the emergency to normal time delay

  38. ASCO ATS Design Innovations • Modularized controls • Molded-panel TS units • Close differential sensing • Inphase transfer • Overlapping neutral transfer • ATS-Bypass/Isolation switches • High WCR designs • Microcomputer-controlled ATSs • Closed transition transfer switches • Network supervision • High shock ABTs • Class 1E nuclear-rated ATSs

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