Plum blossom contact-double stabilized permanent magnet mechanism vacuum circuit breaker opening and closing selection and determination

At present, the domestic and foreign production of permanent magnet mechanism (bistable) moving core stroke (i.e., moving core and yoke between the air gap) are relatively small (usually not more than 25mm), much smaller than the conventional electromagnetic, spring, hydraulic and pneumatic actuator stroke. Therefore, at present it can only be used in the contact stroke smaller medium voltage vacuum circuit breaker. So what is the selection and determination of the double-stabilized permanent magnet mechanism vacuum circuit breaker opening and closing? The following is to give you an introduction to it!

1. Permanent magnet mechanism splitting and closing state holding force selection

Permanent magnet mechanism has simple structure, high reliability of action, no need for closing and closing position mechanical maintenance and offline device, it is generated by the magnet suction force to keep the circuit breaker in the opening and closing position.

Vacuum circuit breakers require a certain contact pressure, therefore, the suction force of the permanent magnet mechanism must not only be able to overcome the reaction force of the contact springs and other reaction forces, but also must have enough effective holding force of the closing position to prevent automatic false breaking under the action of possible external factors (mechanical vibration, electric power, etc.). The size of the holding force not only determines the circuit breaker closing holding performance, but also determines the important parameters such as breaking work and breaking speed.

According to the test of the effective holding force: when the breaking current of 20kA and below, it is appropriate to choose 500-700N; breaking current of 31.5kA and above, it is appropriate to choose 700-1000N.

Because the double-coil permanent magnet mechanism does not need to be equipped with a full-stroke breaking spring, the actuator mechanism only needs a not too large holding force to keep the circuit breaker reliably in the breaking state. Considering the permanent magnet mechanism must have a sufficiently large closing work to ensure that the circuit breaker has sufficient closing capacity. Therefore, the breaking holding force of the permanent magnet mechanism cannot be too small. According to the test, the effective holding force of the permanent magnet mechanism should be selected from 2000 to 3000N.

Permanent magnet mechanism of the magnet circuit is usually according to the suction requirements of the side (closing side) design, and the other side must take measures to reduce its suction, in the dynamic core and yoke suction surface between the magnetic separator and reduce the effective suction surface area; installed on the side of the split short-circuit spring to offset some of the split holding force, in order to meet the characteristics of the circuit breaker at the same time, the requirements of the closing and splitting.

2. Determination of breaking and closing time of vacuum circuit breaker

Equipped with permanent magnet mechanism vacuum circuit breaker breaking time usually can reach 30ms (magnetization time 25ms plus contact overtravel movement time 5ms) or so, from 12 ~ 40.5kV power distribution network requirements, no need for circuit breaker with such a short breaking time, usually with 50ms breaking time is enough.

When the circuit breaker tripping time is short, it is difficult to take measures to extend the tripping time on the circuit breaker or actuator, usually only in the outlet of the tripping operation circuit to install additional time-delay relay, so that the circuit breaker tripping time is extended to 50ms or so, the closing time of the circuit breaker is usually 40-45ms (excitation time 30-35ms plus the contact open distance movement time 15-20ms). 12 ~ 40.5kV MV circuit breaker is not necessary to have such a short tripping time from the 12 ~ 40.5kV distribution network requirements, usually with a 50ms tripping time is sufficient. 40.5kV medium-voltage circuit breaker with such a short closing time is also rare. A shorter closing time has no negative effect on the circuit breaker or the power system, and there is no need to take measures to lengthen it.

The lowering of the supply voltage has a significant effect on the opening and closing times of the circuit breaker, because a lower supply voltage results in a longer excitation time.