circuit breaker
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Who can explain the short-circuit protection and overload protection of circuit breakers? ? Is short-circuit protection a continuous high current over a certain period of time? Is it the thermistor used for overload protection, or something else that triggers the trip? ? Was it a current that exceeded the rated current by a certain amount but was still much lower than the current during a short circuit, and this condition persisted for some time before the protection device activated? Or some other reason? ? Who can explain the difference between short-circuit protection and overload protection? ? ? Also, can circuit breakers, residual current devices, and isolating switches all be used as knife switches? ? Can’t they all be opened and closed manually? ? What’s the difference?
I’m sorry, I forgot to mention one more thing: there’s also a load switch
Circuit breakers are capable of opening, closing, and carrying the normal current in the circuit, and they can also carry, close, and open specified abnormal currents within a given time frame, such as overload current and short-circuit current. When a fault occurs in the power system, the fault current can be several hundred times the rated current and last for several seconds; circuit breakers are capable of withstanding such currents and have the ability to interrupt them. Upon receiving a command to open, the circuit breaker disconnects the fault current within 10 MS; during the opening and closing operations, the contact shorting time is within 0.1 S
All of them can be used as switches, but their opening and closing must follow a specific sequence. For example, when powering a circuit on, the disconnect switch on the busbar side should be closed first, followed by the disconnect switch on the circuit side, and then the circuit breaker. When shutting down the circuit, the process is exactly reversed. Operate high-voltage isolators under load with caution. The isolating switch allows for the disconnection of voltage transformers, arresters, bus charging currents, the bypass current of switches, and the neutral grounding wires of unloaded transformers.
Generally, a short circuit causes an immediate trip. Classified by type, type B trips at 3 to 5 times the rated current, type C at 5 to 10 times, and type D at 10 to 50 times. The short-circuit current interrupts the fault current within 10 MS to 100 MS. If the load is too high, the time required increases; when the current is about 1.5 times the rated current, the switch will trip after a certain period of time, indicating that the load is excessive and the switch needs to be replaced.
A high-voltage load switch is a type of high-voltage electrical device that lies between a high-voltage isolator and a high-voltage circuit breaker. It is equipped with a simple extinguishing mechanism, which allows it to handle certain levels of load current and overload current; however, it is unable to interrupt short-circuit currents. Therefore, it must be connected in series with a high-voltage fuse, so that the fuse can be used to cut off short-circuit faults.