Design Principle and Wiring Diagram of Dual Power Automatic Transfer Switch ATSE

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Design Principle and Wiring Diagram of Dual Power Automatic Transfer Switch ATSE
07 14 , 2022

The selection of automatic transfer switching appliances (ATSE) should mainly meet the following requirements:

  1. When using PC-class automatic transfer switching appliances, should be able to withstand the expected short-circuit current of the circuit, and the rated current of ATSE should not be less than 125% of the circuit calculation current;
  2. When class CB ATSE is used to supply power to fire load, ATSE consisting of circuit breaker with short circuit protection only shall be used. Its protection selectivity should be matched with the upper and lower protection appliances;
  3.  The selected ATSE should have the function of maintenance and isolation; When ATSE body has no maintenance isolation function, isolation measures should be taken in design.
  4. The switching time of ATSE should be coordinated with the relay protection time of power supply and distribution system, and continuous cutting off should be avoided;
  5. When ATSE supplies power to large capacity motor load, the switching time should be properly adjusted to ensure safe and reliable switching during the switching process.
YEQ3-63EW1 2 input 2 output


The key points of understanding and implementation are as follows: ATSE is used for automatic conversion between two power supplies, and reliability of power supply for important loads is crucial. The product is divided into PC class (composed of load switches) and CB class (composed of circuit breakers), and its characteristic has the function of “self-input and self-reply”.

The conversion time of ATSE depends on its own structure. The conversion time of PC class is generally 100ms, and that of CB class is generally 1-3S. In the selection of PC class automatic transfer switch, its rated capacity should not be less than 125% of the loop calculation current, in order to ensure that the automatic transfer switch has a certain margin. Due to the PC class ATSE itself does not have overcurrent protection function, so its contacts must be able to withstand the expected short-circuit current of the circuit, to ensure that the contact is not welded before the ATSE superior short-circuit breaker cuts off the fault, and can be switched correctly.

When class CB ATSE are used to supply power to fire fighting loads, atses consisting of only circuit breakers with circuit breaker protection should be used to prevent power failure of fire fighting devices due to over-load tripping. Its selective protection should be matched with the upper and lower protection appliances to prevent a larger range of power failure caused by tripping.

wiring diagram of dual power automatic transfer switch ATSE

wiring diagram of ATSE

When ATSE is used for dual power conversion, for the sake of safety, it is required to have maintenance isolation function. Here, maintenance isolation refers to the maintenance isolation of the ATSE distribution loop. When designing the power supply and distribution system has the function of automatic reclosing, or although no automatic reclosing function but at the next higher level substation has the function, work the power suddenly loses power, ATSE should not be cast to the standby power supply side immediately, should have a dodge automatic reclosing time delay, to avoid just switch to the standby power supply side, and from the complex to the power to work, this kind of continuous switch is more dangerous.

Due to the high inductive reactance of large capacity motor load, the arc is very large when opening and closing. Especially when the standby power supply is connected to the working power supply, both power supplies are charged at the same time. If there is no delay in the transfer process, there is the danger of arc short circuit. If a delay of 50 ~ 100ms is added in the switching process to avoid the time when arc light is generated at the same time, reliable switching can be guaranteed.

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