How to choose the parameters of the circuit breaker?
Release time:
2020-12-07
The general selection principle is to select the type and number of poles of the circuit breaker according to the application; select the rated current of the circuit breaker according to the maximum working current; select the type of release, the type and specification of accessories according to the needs. Low voltage equipment is usually powered by a transformer. In such low-voltage networks, the uninterrupted short-circuit current (I k ) calculated from the rated voltage and the AC resistance (impedance) of the short-circuit also has a superimposed DC component that decays slowly to zero. The peak value of Ik is an important value for the short-circuit definition in the standard.
Depending on the specific application, designers may refer to different standards when specifying circuit breakers or related equipment for grid protection: The IEC/EN 60898-1 standard applies to circuit breakers for overcurrent protection in households and similar Installations - such as shops, offices, schools and small commercial buildings. These circuit breakers are designed to be operated by untrained personnel without maintenance. The IEC/EN 60947-2 standard applies to circuit breakers used primarily in industrial applications accessible only to instructors. The isolating switch has been tested according to IEC/EN 60947-3 standard. Switchgear components or switchboards have been tested according to IEC/EN 61439.
Due to differences in the scope of the standards, in some cases different definitions are used for the same electrical process. Therefore, the engineer must ensure that he fully understands which specific definition (eg short circuit capacity) applies to the design he is working on. The IEC/EN 60947-3 standard is used when a switch-disconnector, switch-disconnector or fuse combination unit is included in the design. Disconnectors are capable of switching currents on and off under specified conditions. In the open position, the isolating switch provides the isolation function.
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