Special Topic on Design, Setting, and Commissioning of Automatic Transfer Switch/Fast Switching Devices (ATS)

Standby power auto-transfer logic: The standby power auto-transfer function for two types of electrical components, namely sectional (or bridge) circuit breakers and incoming lines (or double/wheel transformer), includes four different modes of automatic standby power transfer. Methods 1 and 2: Correspond to the two operating modes where 1# and 2# feeders (or transformers) serve as mutual hot standby. Methods 3 and 4: correspond to the two operating modes in which Bus II and Bus I serve as mutual standby units through sectional (or bridge) circuit breakers. Automatic switching on of sectional (bridge) switches (Modes 3 and 4) (Modes 1 and 2 omitted): When the two busbars operate separately, the device selects the automatic switching-on scheme for sectional (bridge) switches. Charging conditions: 1) Both Bus I and Bus II have three-phase voltage ； 2) 1DL and 2DL are in the closed position, while 3DL is in the open position. Charging is completed after the standby auto-transfer charging time. Method 3--Ⅰ Mother voltage loss: Discharge conditions: 1) 3DL is in the closed position with a short delay ； 2) Both Phase I and Phase II are under no voltage (all three-line voltages are below Uwyqd); delay for 15S ； 3) When this device has no trip output, manually operate 1DL or 2DL (KKJ1 or KKJ2 becomes 0). (This condition can be disabled by the user by setting the “Manual operation does not lock out automatic backup switching” control word to 1.) ； 4) External blocking signals leading to ‘Blocking Mode 3 Automatic Reset’ and ‘Overall Automatic Reset Blocking’ ； 5) TWJ abnormalities in 1DL, 2DL, 3DL ； When using the sectional operation circuit of this device, the control circuit is disconnected and the spring is not charged (abnormal closing pressure) ； 6) 1DL, 1DLF switches fail to trip ； 7) It is not allowed to enable automatic sectional switching upon loss of voltage in bus I when using control words or soft pressure plates for setting ； Operation process: Once charging is complete, Mother I has no voltage (the voltages of all three wires are below the voltage threshold for start-up), and there is no current in I1. Mother II then has voltage and starts up; after a delay of Tt3, the two pairs of switching contacts in power supply 1 operate to open 1DL as well as the switches that need to be disconnected from Mother I. After confirming the 1DL trip and 1DLF trip (when JLT1 is activated), and with no voltage on bus I (all three line voltages being below the voltage threshold for closing without voltage), or when condition 3 for synchronization is met (when Check Synchronization 3 is activated), 3DL is closed after a delay via Th34. Mode 4--II Mother Voltage Loss: Discharge conditions: 1) 3DL is in the closed position with a short delay ； 2) Both Phase I and Phase II are under no voltage (all three-line voltages are below Uwyqd); delay for 15S ； 3) When this device has no trip output, manually operate 1DL or 2DL (KKJ1 or KKJ2 becomes 0). (This condition can be disabled by the user by setting the “Manual operation does not lock out automatic backup switching” control word to 1.) ； 4) External blocking signals leading to ‘Blocking Mode 4 Automatic Reset’ and ‘Overall Automatic Reset Blocking’ ； 5) TWJ abnormalities in 1DL, 2DL, 3DL ； When using the sectional operation circuit of this device, the control circuit is disconnected and the spring is not charged (abnormal closing pressure) ； 6) 2DL, 2DLF switches fail to trip ； 7) It is not allowed to enable automatic sectionalizing upon loss of voltage in bus II when the control word or soft pressure switch is set ； Operation process: Once charging is complete, there is no voltage at bus II and no current flows in I2; voltage appears at bus I and startup occurs. After a delay of Tt4, the trip contacts of the two pairs of power supplies 2 operate to open the switches that need to be disconnected from buses 2DL and II. After confirming 2DL trip and 2DLF trip (when JLT2 is activated), and when bus II is de-energized or the synchronization conditions 3 are met (when Check Synchronization 3 is activated), close 3DL after a delay via Th34.

As for the quick switching devices, taking the single bus segmented operation mode as an example below, a brief explanation of various quick switching methods is provided; the situation is similar in the single bus operation mode. a) Parallel switching. Parallel switching can only be triggered in a manual start mode. As shown in the figure above, take the switch from 1DL in parallel to 3DL as an example. After manual startup, if the parallel operation conditions are met (i.e., the frequency difference, phase difference, and voltage difference across the switch are all below the predetermined values for parallel switching), the device first closes the 3DL switch; at this point, the two power sources, Inlet 1 and Inlet 2, are connected in parallel for a short period of time. After a preset delay (the parallel switching trip delay), the device then opens the 1DL switch. If, during this delay period, the newly closed 3DL is tripped (for example, due to a protection action that trips the 3DL), then the switching process ends, and the device will no longer trip the 1DL in order to prevent an expansion of the power outage area. If 1DL refuses to trip, the device will then trip the 3DL switch to prevent the two power sources from remaining connected in parallel for an extended period. If the parallel switching conditions are not met after manual startup, the device will immediately lock up and enter a waiting state until it can be reset. The parallel switching method is suitable for switching between two power supplies of a system operating at the same frequency under normal conditions; it can be used for manual switching during line maintenance or for manual restoration after a fault occurs. b) Series switching. As shown in the figure above, take switching from 1DL to 3DL as an example. After the device is started, the 1DL switch is first opened; once it is confirmed that 1DL is open, a command is issued to close the busbar connection switch 3DL based on the closing conditions. If 1DL refuses to trip, the switching process ends, and the device will no longer close 3DL. Series switching is mainly used for automatic switching in emergency situations. There are several closing methods (also known as implementation ways) for series switching: rapid switching, synchronous capture switching, residual voltage switching, and long delay switching. When the fast switching condition is not met, it automatically switches to the evaluation of switching conditions such as synchronous capture, residual voltage, and long delay. c) Switch simultaneously. As shown in the figure above, take switching from 1DL to 3DL as an example. After the device is started, a command to switch off 1DL is issued first; then, after a predetermined simultaneous switching-on delay, a command to switch on 3DL is sent based on the switching-on conditions. If the 1DL switch ultimately refuses to trip, the device will then trip the 3DL switch in order to prevent the two power supplies from remaining connected in parallel for an extended period. Compared to series switching, simultaneous switching does not require waiting to confirm that 1DL has been disconnected before checking the conditions for closing 3DL; instead, a delay is sufficient before assessing those closing conditions, with the aim of minimizing the time during which the bus is de-energized. Simultaneous switching can be accomplished in several ways (also known as implementation methods): rapid switching, synchronous capture switching, residual voltage switching, and long-delay switching. When the fast switching condition is not met, it automatically switches to the evaluation of switching conditions such as synchronous capture, residual voltage, and long delay.