In the roof fire protection system of civil buildings, the smoke exhaust fan is located at the end of the system, and its importance cannot be ignored. According to Article 6 of the Code for Design of Low-Voltage Distribution (GB50054-2011).3.6, for the overload power failure may cause serious consequences, the overload protection should not cut off the line, but act on the signal. Therefore, for this important fan equipment, the protection circuit breaker of its line adopts a single magnetic tripping setting, that is, it does not trip when overloaded, and only short-circuit protection is set. This protection is clear and unambiguous, providing designers with precise guidance when it comes to implementation.
However, when a ground fault occurs at the end of the fan, whether the line overcurrent protection appliance can cut off the fault circuit within the specified time is a problem that designers are easy to confuse. In fact, this involves tuning the way the higher-level circuit breaker is set. In order to solve this doubt, we will analyze the current status of the line in the event of a ground fault and the operating characteristics of the protective appliance, so as to clarify the tuning method of the circuit breaker at the upper level.
Calculation and analysis of single-phase ground short-circuit current:
Calculation of single-phase ground short-circuit current after increasing the cross-section
Summary:
The internal structure of the high-voltage switchgear, the five-proof function and the comprehensive relay protection are explained clearly at one time
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