In the civil building design, the low-voltage circuit breaker is mainly used for line overload, short circuit, over current, voltage loss, under voltage, grounding, leakage, automatic switching of dual power supply and protection and operation of the motor during infrequent starting. In principle, in addition to the basic principles of observing the environmental characteristics of low-voltage electrical equipment, the following conditions should be considered:
1) The rated voltage of the circuit breaker should not be less than the rated voltage of the line;
2) The rated current of the circuit breaker and the rated current of the overcurrent release are not less than the calculated current of the line;
3) The rated short-circuit breaking capacity of the circuit breaker is not less than the maximum short-circuit current in the line;
4) Selective power distribution circuit breakers should consider the short-delay short-circuit on-off capability and the delay protection level;
5) The rated voltage of the undervoltage release of the circuit breaker is equal to the rated voltage of the line;
6) When used for motor protection, select the circuit breaker to consider the starting current of the motor and make it not operate within the starting time; for design calculation, see “Industrial and Civil Power Distribution Design Manualâ€;
7) Circuit breaker selection should also consider the selective cooperation of circuit breakers and circuit breakers, circuit breakers and fuses.
(1) The matching between the circuit breaker and the circuit breaker should consider the instantaneous tripping action value of the upper circuit breaker, which should be greater than the maximum expected short-circuit current at the outlet end of the lower-level circuit breaker. If the resistance of the loop component is different due to the short-circuit at the two-stage circuit breaker Small, so that the short-circuit current value does not differ much, the upper circuit breaker can choose the trip unit with short delay.
(2) When the short-circuit current is greater than or equal to the instantaneous release setting value, the current-limiting circuit breaker will trip within a few milliseconds, so the lower-level protection device should not use the circuit breaker to achieve selective protection requirements.
(3) Circuit breakers with short delays, when their time limit is set at the maximum delay, their on-off capability is reduced. Therefore, in the selective protection loop, the short-break on-off capability of the circuit breaker should be considered to meet the requirements. .
(4) It should also be considered that the short-circuit delay returnable characteristic of the upper-level circuit breaker should not intersect with the action characteristic time curve of the lower-level circuit breaker, and the short-delay characteristic curve should not intersect with the instantaneous characteristic curve.
(5) When the circuit breaker is used with the fuse, the cooperation of the upper and lower stages should be considered. The second-second characteristic curve of the circuit breaker should be compared with the second characteristic curve of the fuse so as to have protection selectivity in case of short-circuit current. .
(6) When the circuit breaker is used as the protection of the distribution line, the circuit breaker with long delay action overcurrent release should be used. When the single-phase grounding short circuit occurs at the end of the line, the short-circuit current is not less than the instantaneous or short delay of the circuit breaker. The overcurrent trip is set at 1.5 times the current. [1]
The CW1 series of intelligent universal circuit breakers have the following main features:
1, small size, compact structure
2. Production and production in strict accordance with the new national standard GBI4048.2-2001
3, meet the isolation requirements
4, has a high thermal stability
5, high breaking, zero arcing, to meet the various needs of the power distribution system
6, with high electromagnetic compatibility
7, the circuit breaker can be up or down the line
1.2 Scope of application
The CW1 series of intelligent universal circuit breakers are suitable for AC 50HZ. The power distribution network with voltage up to 690V and current to 5000A is mainly used to distribute electrical energy and protect the line and motor equipment from overload, undervoltage, short circuit and ground fault. The circuit breaker adopts an intelligent controller with precise selective protection and multi-function, which is especially suitable for distribution networks that need to improve power supply reliability and avoid unnecessary power outages. The rated working voltage of the circuit breaker is 400V, 690V, the rated insulation voltage is 1000V, and the rated working current is 630A to 5000A.
Circuit breakers with rated working current of 1000A or less can also be used as overload, undervoltage, short circuit and ground fault protection of the motor in AC 50HZ and 400V networks, which can be used for infrequent starting of the motor.
1.3 overall structure
The CW1 series of intelligent universal circuit breakers are fixed and drawer type. The body of the fixed circuit breaker is installed in a dedicated drawer seat to become a drawer type. The body is composed of a contact system, an arc extinguishing system, an operation cymbal, a current transformer, an intelligent controller and an auxiliary switch, a secondary circuit terminal, an undervoltage release, and the like; the drawer seat is composed of left and right side plates with guide rails, The base frame and the bracket are composed.
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