How to protect the motor power distribution circuit?
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Code for Design of Power Distribution of General Electrical Equipment 2.3.1 AC motors shall be equipped with short-circuit protection and protection against ground faults. 1. Motor power distribution circuit, using a circuit breaker + thermal relay + contactor. Is the protection required by the standards met? I’m asking about Chint NM8N molded case circuit breakers: only the EMM electronic motor protection accessories with 4-stage protection provide ground fault protection functionality. We have been using the M type, and no mention of this was made during the design review. Could someone experienced please advise me on what to do? 2. Is it necessary to add a disconnect switch to the motor circuit? Some of our circuits (just any number of circuits) have an isolating switch, some cabinets have an isolating switch, while others do not have one. The review also didn’t mention it; when I asked Chint, they said that molded-case circuit breakers have an isolation function – is that because molded-case circuit breakers indeed possess such a function? It is also possible to not set isolation for the motor circuit. Could an expert please guide me on how to do this? Thank you so much
Copy and paste: The grounding fault protection measures for TN systems include the following methods: 1) When the overcurrent protection meets the requirements regarding sensitivity, use the short-circuit instantaneous or short-circuit short-time delay protection provided by the overcurrent protection. 2) When the overcurrent protection fails to meet the sensitivity requirements, zero-sequence current protection can be used. The ground fault current in TN systems is relatively high (greater than several dozen to hundreds of amperes), and zero-sequence current protection is sufficient for handling such situations. To this end, circuit breakers equipped with electronic trip units can be selected to have four protection functions, namely long-time delay Ir, short-time delay Isd, short-circuit instantaneous Ii, and ground fault protection Ig. Actually, this Ig is the zero-sequence current protection (remember this Ig; we will mention it later). 3) When overcurrent protection does not meet the sensitivity requirements, residual current protection can also be used (RCD operates to cut off the circuit, while RCM operates to issue an alarm). The use of residual current protection is primarily aimed at improving sensitivity in triggering, but its functions go beyond that; there are deeper purposes as well (see below). 4) The sensitivity of the protection actions for the above methods is increasing step by step (above 100 amperes → above several dozen amperes → above milliamps). Author: Teacher Di from Electrical Design https://www.bilibili.com/read/cv8594352/ Source: bilibili
There is an isolating switch at the top of the distribution switch, which facilitates future maintenance
Teacher S has been very active lately: lol