In power plants and substations (booster stations), the power supply systems that supply power to control, signal, protection, automation devices and some actuators are collectively referred to as control power supplies. If they are DC power supplies, they are called DC power systems; if they are AC power supplies , it is called an AC power system. In the DC system, DC circuit breakers are often used, so how should we choose the DC system in the DC system?
The DC circuit breaker should have instantaneous current quick-break and inverse-time overcurrent protection. When the cooperative relationship of selective protection is not satisfied, short-delay current quick-break protection can be added.
The selection of DC circuit breakers should meet the following requirements:
1. The rated voltage should be greater than or equal to the maximum working voltage of the loop.
2. The rated current should be greater than the maximum working current of the loop.
3. The interrupting capacity should meet the requirements of the maximum expected short-circuit current of the DC power system at the installation site.
4. The rated current of the emergency tie breaker of the DC power system should not be greater than 50% of the rated current of the battery outlet fuse.
5. When short-circuit short-time delay protection is used, the rated short-circuit breaking current and short-time withstand current of the DC circuit breaker should be greater than the maximum short-circuit current at the installation site (flowing through the circuit breaker).
6. The protective operating current and operating time of circuit breakers at all levels should meet the requirements of the selective cooperation between the upper and lower levels, and should have sufficient sensitivity coefficients. The selective coordination of upper and lower circuit breakers shall meet the following requirements.
7. The rated current of the power circuit breaker of the DC distribution cabinet should be selected according to the sum of the calculated currents of all the power circuits on the DC distribution cabinet.
8. Protection setting of DC circuit breaker.
The selection principle of DC circuit breaker should be considered according to the above eight points.