In civil building design, low-voltage circuit breakers play a crucial role in protecting electrical systems from various faults such as overload, short circuits, overcurrent, voltage loss, under-voltage, grounding, leakage, and motor protection during infrequent starting. When selecting a circuit breaker, it is essential to follow not only the general principles of low-voltage electrical equipment but also consider several key factors:
1) The rated voltage of the circuit breaker must be equal to or higher than the line’s rated voltage.
2) The circuit breaker’s rated current and the overcurrent release’s rated current should be greater than or equal to the calculated line current.
3) The circuit breaker’s rated short-circuit breaking capacity must exceed the maximum short-circuit current in the circuit.
4) For selective power distribution, the circuit breaker must have sufficient short-delay short-circuit capability and proper delay settings to ensure coordinated tripping with downstream devices.
5) The undervoltage release’s rated voltage should match the line’s rated voltage.
6) When used for motor protection, the circuit breaker must be selected to avoid tripping during motor startup. This requires considering the motor’s starting current and ensuring the circuit breaker does not operate within the start-up period. Refer to “Industrial and Civil Power Distribution Design Manual†for detailed calculations.
7) Selective coordination between circuit breakers and other protective devices, such as fuses, must be taken into account.
When coordinating two levels of circuit breakers, the upper-level breaker’s instantaneous trip setting must be greater than the maximum expected short-circuit current at the lower-level outlet. If the loop resistance causes similar short-circuit currents at both levels, the upper breaker can use a short-time delay setting for better coordination.
If the short-circuit current reaches or exceeds the instantaneous trip setting, a current-limiting circuit breaker will trip within milliseconds. Therefore, the lower-level device should not rely on a circuit breaker for selective protection in such cases.
Circuit breakers with short-time delay functions may have reduced short-circuit breaking capacity when set to maximum delay. This must be considered in selective protection schemes to ensure compliance with system requirements.
Additionally, 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 circuit breakers in conjunction with fuses, the coordination between the upper and lower stages must be carefully evaluated. The circuit breaker’s second-stage characteristic curve should be compared with the fuse’s characteristic curve to ensure selectivity during short-circuit events.
For distribution lines, a circuit breaker with a long-time delay overcurrent release is typically recommended. In case 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 offer several key advantages:
1. Compact and space-saving design
2. Manufactured in accordance with the latest national standard GB 14048.2-2001
3. Meets isolation requirements for safe operation
4. High thermal stability for reliable performance
5. High breaking capacity with zero arc interruption, suitable for diverse power distribution needs
6. Excellent electromagnetic compatibility
7. Can be installed either vertically or horizontally depending on the application
1.2 Application Scope
The CW1 series intelligent universal circuit breakers are ideal for AC 50Hz power distribution networks operating up to 690V and 5000A. They are primarily used to distribute electrical energy and protect lines and motor equipment from overload, under-voltage, short circuits, and ground faults. These circuit breakers feature an intelligent controller that provides precise selective protection and multiple functions, making them especially suitable for power systems where improving reliability and avoiding unnecessary outages is critical.
The rated working voltage of the circuit breaker is available in 400V and 690V, with an insulation voltage rating of 1000V. The rated working current ranges 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. They provide protection against overload, under-voltage, short circuits, and ground faults and are suitable for motors that are started infrequently.
1.3 Overall Structure
The CW1 series intelligent universal circuit breakers come in fixed or drawer types. A fixed-type circuit breaker can be mounted in a dedicated drawer base to function as a drawer-type unit. The main body consists of a contact system, arc extinguishing system, operating mechanism, current transformer, intelligent controller, auxiliary switch, secondary terminal block, and undervoltage release. The drawer base includes side plates, guide rails, base frame, and brackets, providing a stable and secure installation platform.
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