Automatic transfer switch (ATS) is divided into two types: PC and CB. The world-leading products representing the PC level include ASCO from the United States; those representing the CB level include Muller from Germany and Schneider from France.

ATS generally consists of two parts: ① switch body; ② controller.

1.1 Switch electrical body

The switch body is divided into two categories:

The first category is the CB level. It is composed of two circuit breakers and mechanical interlocking, with short circuit protection function;

The second category is PC-level, one-piece structure. It is a special switch for dual power switching. It has the advantages of simple structure, small size, self-interlocking, fast switching speed (within 0.2s), safety and reliability, but it needs to be equipped with short-circuit protection appliances.

1.2 Controller

The controller also has two forms: one is composed of traditional electromagnetic relays; the other is digital electronic intelligent products. It has the advantages of good performance, adjustable parameters, high precision, high reliability and convenient use.

2. Analysis and comparison of product structure and selection of ATS

At present, there are roughly three kinds of switching appliances used for switching between two power sources in the domestic market: ①CB-level ATS; ②PC-level ATS;

The following is a comparison and analysis of CB-level and PC-level ATS from three aspects of product structure, performance and standards. It is not difficult to find that PC-level ATS is an ideal two-way power switching electrical product.

2.1. The mechanical design concepts of the two are different

The CB class is composed of circuit breakers, and the circuit breaker is responsible for breaking the arc, and its machinery is required to trip quickly. Therefore, the mechanism of the circuit breaker has the problem of sliding and re-buckling; but PC-level products do not have this problem. The reliability of PC-level products is much higher than that of CB-level products.

2.2 The circuit breaker does not carry the short-circuit withstand current, and the contact pressure is small

When a short circuit occurs in the power supply circuit, when the contacts are bounced, the current limiting effect occurs, thereby breaking the short circuit current; while the PC-level ATS should withstand an overload current of 20Ie and above. The contact pressure is not easy to be bounced off, so the contact is not easy to be welded. This feature is particularly important for fire-fighting power supply systems.

2.3 There is a power supply superposition problem in the conversion process of the two-way power supply

PC-level ATS takes this factor into full consideration. The clearance of PC grade ATS is 180% and 150% of creepage distance (standard requirement). On this basis, American ASCO ATS is the first in the industry to have the function of phase angle synchronous detection and switching. Therefore, PC-level ATS is more secure.

2.4 The selection angle of the contact material is different

Circuit breakers are often paired with silver tungsten and silver tungsten carbide materials, which are conducive to breaking the arc. However, this type of contact material is easy to oxidize, and the spare contact is exposed for a long time, and it is easy to form oxides that hinder conduction and are difficult to remove. When the spare contact is put into use, the temperature rise of the contact may cause the switch to burn or even explode. ; And the PC-level ATS fully considers the consequences of contact material oxidation.