What should be paid attention to when choosing a vacuum circuit breaker?

Selection principle of high voltage vacuum circuit breaker:

First select according to normal conditions, and then check according to short-circuit conditions. In addition, the rated breaking current of the vacuum circuit breaker must be greater than the maximum short-circuit current that may pass through the circuit breaker in the circuit to ensure reliable arc extinguishing of the circuit breaker. The specific content selected is:

1. Select according to normal working conditions.

1) The rated voltage of the high-voltage vacuum circuit breaker should be consistent with the grid voltage at the installation site.

2) The rated current of the high-voltage vacuum circuit breaker should be greater than or equal to the long-term maximum working current in the circuit.

3) The type of high-voltage vacuum circuit breaker should be selected according to the installation environmental conditions. If it is installed outdoors, outdoor circuit breakers should be selected; if installed indoors, indoor circuit breakers should be selected. 2. Check according to the short-circuit condition. Circuit breakers selected for normal operating conditions must also be verified for short-circuit conditions. That is, the normal operation can meet the requirements of safe and reliable operation. When a short-circuit fault occurs in the circuit, the circuit breaker can still work safely and reliably and cut off the short-circuit current. The verification according to the short-circuit condition is mainly to verify the thermal stability and dynamic stability of the circuit breaker. The so-called thermal stability means that when the maximum possible short-circuit current passes through the circuit breaker, the heating temperature of the circuit breaker does not exceed its short-term allowable temperature. That is, when the maximum possible short-circuit current passes through the circuit breaker, the circuit breaker will not burn out due to the thermal effect of the current. The so-called dynamic stability means that the maximum possible short-circuit current passes through the circuit breaker, and the circuit breaker will not be damaged or deformed by the strong electric force. For the methods of thermal stability check and dynamic stability check, please refer to relevant manuals and materials.

3. The rated breaking current of the vacuum circuit breaker must be greater than the maximum short-circuit current that may pass through the circuit breaker in the circuit to ensure reliable arc extinguishing of the circuit breaker.

Fourth, according to the transformer capacity to select the vacuum circuit breaker method:

1) Select the type of circuit breaker according to the cabinet type. For indoor fixed 10KV switch cabinets, most of them use ZN28 vacuum switch, equipped with a spring operating mechanism, which can be operated by AC, DC electric operation or manual operation; for indoor removable type 10KV Switch cabinet (such as KYN type), VS1 type vacuum switch can be selected, equipped with a spring integrated operating mechanism, which can be operated by AC, DC electric operation, or manually;

2) The rated current of the selected circuit breaker. Generally, there are four types of power distribution circuit breakers: 630A, 1000A, 1250A, and 1600A. You should calculate the load current flowing through the circuit breaker according to the load situation, and then select the rated current after leaving a margin; for a 2000KVA transformer, its Rated current I=2000/(1.732*10)=115.5A, a 630A circuit breaker can be selected initially, but it should also be verified;

3) Verify the breaking current of the selected circuit breaker. Calculate the short-circuit current value of the installation site of the circuit breaker, and compare it with the breaking current value of the circuit breaker that was initially selected. After leaving a margin, the breaking current value of the circuit breaker should be greater than the maximum short-circuit current value of the installation site, so as to ensure In the event of a short circuit, the circuit breaker can operate reliably and remove the fault without being damaged. Generally, the rated short-circuit breaking current value of 10KV vacuum circuit breaker is mostly 20KA, 25KA, 31.5KA, 40KA, corresponding to the above 630A, Four rated currents of 1000A, 1250A and 1600A; if the installation site of the 2000KVA transformer is relatively close to the outlet of the substation and the maximum short-circuit current is 26KA, then the rated short-circuit breaking current of the 630A switch is 20KA, which cannot meet the requirements of the point of use It is necessary to choose a circuit breaker with a rated current of 1250A and a rated short-circuit breaking current of 31.5KA.

4) Check other cases. Such as phase-to-phase distance, installation size, interlocking situation, whether there is blocking, whether it has an overcurrent coil, whether it has a voltage loss, etc.