In civil building design, low-voltage circuit breakers play a critical role in protecting electrical circuits from various faults such as overloads, short circuits, overcurrent, voltage loss, under-voltage, grounding, and leakage. They also ensure the safe operation of motors during infrequent starts and support the automatic switching of dual power supplies. When selecting a circuit breaker, it's essential to consider several key factors beyond general environmental conditions:
1) The circuit breaker’s rated voltage should be equal to or higher than the line’s rated voltage.
2) Its rated current and the overcurrent release setting must be greater than or equal to the calculated load current of the circuit.
3) The short-circuit breaking capacity of the circuit breaker must exceed the maximum short-circuit current that could occur in the line.
4) For selective power distribution, the circuit breaker should have the capability to handle short delays and provide appropriate time-delay protection levels.
5) The undervoltage release must match the line’s rated voltage for proper operation.
6) When used for motor protection, the circuit breaker must be chosen with consideration for the motor’s starting current, ensuring it does not trip during the start-up period. Refer to the “Industrial and Civil Power Distribution Design Manual†for detailed calculations.
7) Selective coordination between circuit breakers and other protective devices, such as fuses, is crucial for reliable system performance.
When coordinating two levels of circuit breakers, the upper-level device’s instantaneous tripping value should be higher than the maximum expected short-circuit current at the lower level’s outlet. If the loop resistance varies, leading to similar short-circuit currents, the upper breaker may need a short-time delay feature for better selectivity.
If the short-circuit current exceeds the instantaneous release setting, a current-limiting circuit breaker will trip within milliseconds. In such cases, the lower-level protection should not rely on another circuit breaker for selective protection.
Circuit breakers with short-time delay functions experience reduced on-off capabilities when set to maximum delay. Therefore, their breaking capacity must still meet the requirements of the selective protection system.
The short-time delay characteristic curve of the upper-level circuit breaker should not intersect with the action time curve of the lower-level device. Similarly, the short-time delay curve should not overlap with the instantaneous trip curve.
When using a circuit breaker with a fuse, the coordination between the two stages must be considered. The second-by-second curve of the circuit breaker should be compared with the fuse’s curve to ensure selective protection during short-circuit events.
For distribution lines, a circuit breaker with long-time delay overcurrent release is recommended. In the event of a single-phase ground fault at the end of the line, the short-circuit current should be at least 1.5 times the instantaneous or short-time delay setting of the circuit breaker.
The CW1 series of intelligent universal circuit breakers are designed with advanced features, including compact size, high thermal stability, and excellent electromagnetic compatibility. They are manufactured according to the latest national standards (GB 14048.2-2001) and are capable of handling high short-circuit currents with zero arc interruption. These circuit breakers are ideal for modern power distribution systems requiring high reliability and minimal downtime.
The CW1 series is suitable for AC 50Hz power distribution networks with voltages up to 690V and currents up to 5000A. It provides protection against overload, undervoltage, short circuits, and ground faults, making it ideal for both line and motor protection. The rated working voltage is 400V or 690V, with an insulation voltage of 1000V and a working current range from 630A to 5000A.
Circuit breakers with a rated current of 1000A or less can also be used for motor protection in 400V, 50Hz AC networks, particularly for applications with infrequent motor starts.
The overall structure of the CW1 series includes fixed and drawer types. The fixed model is installed in a dedicated drawer base, while the body consists of components like contact systems, arc extinguishing units, operating mechanisms, current transformers, intelligent controllers, auxiliary switches, and secondary terminal blocks. The drawer base comprises side panels, guide rails, a frame, and brackets, offering flexibility and ease of installation.
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