Automatic transfer switch (ats)


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Automatic transfer switch (ats)

  2. 2. Transfer Switch A transfer switch is an electrical switch that switches a load between two sources.
  3. 3. Manual transfer switch Automatic Transfer Switch
  4. 4. Manual transfer switch - an operator affects the transfer by throwing a switch.
  5. 5.  Automatic Transfer Switch - An ATS is a device designed to Automatically switch (transfer) between (2 or 3) sources of power to improve the reliability of the electrical supply to a connected load. - It automatically switches when it senses one of the sources has lost or gained power. Current range up to 4000 Amperes.
  6. 6. Automatic Transfer Switch
  7. 7. Operation of an Automatic Transfer Switch Not only does ATS transfer the load to the backup generator but also it commands the backup generator to start, based on the voltage monitored on the primary supply.
  8. 8. Example: ATS installed in homes In a home equipped with a backup generator and an ATS, when an electric utility outage occurs, the ATS will tell the backup generator to start. Once the ATS sees that the generator is ready to provide electric power, the ATS breaks the home's connection to the electric utility and connects the generator to the home's main electrical panel.
  9. 9. Example: ATS installed in homes
  10. 10. Example: ATS installed in homes The generator supplies power to the home's electric load, but is not connected to the electric utility lines. It is necessary to isolate the generator from the distribution system to protect the generator from overload in powering loads beyond the house and for safety, as utility workers expect the lines to be dead.
  11. 11. Example: ATS installed in homes When utility power returns for a minimum time, the ATS will automatically transfer the house back to utility power and command the generator to turn off, after another specified amount of "cool down" time with no load on the generator.
  12. 12. Typical Applications of ATS
  13. 13.  Utility and Engine Generator - Single unit standby applications are very common For facilities with a standby power system and a single utility feed. The transfer switch senses when utility power has been lost, sends a start signal to the standby generator and transfers the load.
  14. 14. Utility and Engine Generator
  15. 15.  Utility and Utility - Dual utility applications are becoming more common For use in facilities with redundant utility feeds but no standby generator. If one utility feed fails, the transfer switch automatically connects the load to the second utility feed.
  16. 16. Utility and Utility
  17. 17.  Generator and Generator - Prime power / standby application For facilities with a prime power system using multiple on-site generators. If the primary generator fails, the transfer switch sends a start signal to the second generator and then transfers the load.
  18. 18. Generator and Generator
  19. 19.  Three-source system For facilities with a standby power system and two utility feeds. The utility transfer switch controls the feeds from the two utilities based on a pre-established priority. If both utility feeds fail, the generator transfer switch sends a start signal to the standby generator and transfers the load.
  21. 21. Three-source system : Another three source system uses a standby generator in place of the second utility (dual standby). If the utility fails, the first transfer switch sends a start signal to the primary standby generator and transfers the load. If the primary standby generator fails, the transfer switch sends a start signal to the second generator set and transfers the load.
  23. 23. Types of ATS Transition Open transition TS Closed transition TS Soft loading TS Static TS
  24. 24. Open transition TS An open transition transfer switch is also called a break before make transfer switch. A break before make transfer switch breaks contact with one source of power before it makes contact with another.
  25. 25. It prevents backfeeding from an emergency generator back into the utility line Backfeeding occurs when electric power is being induced into the power grid. Power flows in an opposite direction. It can cause utility lineman to be electrocuted as they work in power lines. Reverse- power relay opens if backfeeding occurs in the power lines.
  26. 26. Applications: Emergency, coderequired and optional standby systems; resistive loads; small motor loads
  27. 27. Open transition TS: o Knife Blade Switch     Typically Non-Load breaking Usually Manually Operated Sometimes motor operated - Is a method of arc suppression Low withstand ratings – no that extinguishes arc chutes or vents arcs by  Low endurance ratings channeling them limited life into chambers - arc flash happens when electric current flows through an air gap between conductors. above the contacts.
  28. 28. Closed transition TS A closed transition transfer switch is also called a make before break transfer switch. A make before break transfer switch makes contact with another source before it breaks contact with the interrupted source.
  29. 29. There are some loads, however, that are affected by even the slightest loss of power. There are also operational conditions where it may be desirable to transfer loads with zero interruption of power when conditions permit.
  30. 30. For these applications, closed transition transfer switches can be provided. With closed transition transfer, the on-site engine generator set is momentarily connected in parallel with the utility source.
  31. 31. This requires getting approval from the local utility company. The switch will operate in a makebefore-break mode provided both sources are acceptable and synchronized.
  32. 32. Typical parameters determining synchronization are: •voltage difference less than 5% •frequency difference less than 0.2 Hz - Frequency counter is used to measure frequency •maximum phase angle between the sources of 5 electrical degrees - Is the difference between the phase of a sinusoidally varying quantity and the phase of a second quantity which varies sinusoidally at the same quantity.
  33. 33. Analog Voltage & frequency meter Digital Generator Frequency & Voltage meter
  34. 34. Closed Transition (Make-BeforeBreak Operation) NOTE: “P” Position indicates both sources paralleled for 5 cycles Applications: Critical power requirements, including hospitals and data centers
  35. 35. Delayed Transition (center off) - The delayed transition (center off) switch is especially suited to applications in which large inductive loads result in large inrush currents. The delayed transition allows magnetic fields to completely collapse before reconnection. - A time delay between the opening of the closed contacts and the closing of the open contacts allows large motor loads to demagnetize before transfer. This prevents the severe “bump” caused by switching a rotating motor (which momentarily acts as a generator) from one source to another source that is not in synchronism.
  36. 36. Types of ATS Construction & Design
  37. 37. Knife Blade Type Twin Contactor Type Twin MCCB Type Power Contactor Type Static Transfer Type
  38. 38. Knife Blade
  39. 39. Closed transition TS o Twin Contactor - contactor type is simpler design that is electrically operated and mechanically held. It operates faster than circuit breaker transfer switches, which reduces transfer time.        Switching device having 1 position of rest 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, 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
  40. 40. Twin Contactor
  41. 41. Closed transition TS o Twin MCCB (Molded Case Circuit Breaker) - circuit breaker type has two interlocked circuit breakers, so only one breaker can be closed any anytime.       2 Position device, typically operated from add-on motors Built using 1 of up to 2 types of breaker under, 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
  42. 42. Twin MCCB (Molded Case Circuit Breaker)
  43. 43. o Power Contactor Type  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)
  44. 44. Power Contactor Type
  45. 45. o 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 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
  46. 46. Power Contactor ATS - Composition
  47. 47. Static/ Solid-State Transfer Type The static/solid-state ATS lacks the traditional mechanical transfer switch. Because this unit relies on SCR or transistor technology, sub-cycle transfers are possible. Although there is technically a "break" in load current, the speed of these units prevents adverse effects to sensitive equipment.
  48. 48. Static Transfer Type       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 E N 2 1 L
  49. 49. Static Transfer Type
  50. 50. Bypass Isolation Transfer Allows maintenance to the main ATS without disconnecting the load. By having two transfer switches connected in parallel, the bypass transfer switch adds redundancy to the system. Applications: Critical power and maintenance requirements, including healthcare and data center
  51. 51. Bypass Isolation ATS • 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. TWO PATHS FROM SOURCE TO LOAD WITHDRAWABLE ATS MECHANICAL INTERLOCKS FIXED MOUNT MTS
  52. 52. Thank You!