1. Factors influencing the characteristics of level difference matching
In the Xiushan system, due to the different technical requirements of the power supply bureaus in the selection of the battery capacity of each substation, the power supply mode of the DC screen and the measurement and control protection screen, the connection mode and the protection importance, the distribution positions are correspondingly different, resulting in the selection of wires and conductors. The cross-sectional area and length are different, and the difference of these factors will cause the loop resistance value to change, and the change of the resistance value will also cause the short-circuit current value to change, causing the short-circuit current of each station to be different. Therefore, the design of the level difference coordination scheme of the circuit breaker of the DC system of the substation, due to the large changes of the above-mentioned factors, has not been solved very well.
2. Existing hidden dangers
In order to meet the selective requirements of level difference coordination, the upper-level circuit breaker does not malfunction, or even if the upper-level malfunctions, it will not cause the accident to spread. Nowadays, the circuit breaker and measurement and control protection on the feeder screen (or the power distribution screen) in many DC systems The circuit breaker on the screen adopts a one-to-one power supply mode. The problem caused by this method is that there are two wires between each pair of circuit breakers. A few meters, as many as hundreds of meters, this many and long wires are bundled together, and after years of operation and use, complex and chaotic problems will occur, such as: loose connection between the wires and the circuit breaker; the insulation of the wires has dropped; accidental damage, Bite; the intertwined wires hide the hazards such as multi-circuit short circuit or arc discharge fire, which will cause a major hidden danger of total loss of power to the measurement and control protection screen.
3. The importance of level difference matching characteristics
Whether the upper and lower levels of soosan breakerbreakers can achieve the level difference coordination depends on the value of the short-circuit current flowing in the loop and the action time difference of the upper and lower circuit breakers. The basic implementation is to improve the current-limiting performance and breaking speed of the 2A~6A circuit breakers of the measurement and control protection screen, and the second is to increase the short-circuit instantaneous release threshold of the DC circuit breaker on the power distribution screen and the feeder screen. To delay the action. Only when the short-circuit current value in the circuit is lower than the instantaneous value of the upper-level circuit breaker, or the lower-level circuit breaker breaks before the upper-level breaker even though the instantaneous value of the upper-level circuit breaker is reached, can the level difference coordination between the circuit breakers be realized. Therefore, in order to achieve the level difference coordination, one way is to achieve the difference in the action time of the upper and lower circuit breakers, and the other way is to reduce the circuit short-circuit current value. The current-limiting DC circuit breaker with a small fixed value has a significant effect on reducing the circuit short-circuit value. Therefore, the current-limiting performance of the last-stage small interrupter is the key element for the selective coordination of the entire DC system.
Post time: Aug-19-2021
