News | company news | Aug 21,2024
How does an RCM work?
In circuit monitoring, all monitored circuit conductors (except the PE conductor) need to pass through the measuring current transformer. Under normal circumstances, the sum of the currents in these conductors is zero, so no voltage is induce in the measuring current transformer. However, if a fault current (IΔ) appears in the system, such as leakage current through PE or other paths, the unbalance of the current in the current transformer will induce a current, which will be detect by the residual current monitor (RCM). This measurement method is mainly suitable for RCM devices that detect pure AC current and pulsating DC fault current (called type A RCM according to IEC 60755 standard).
For RCM devices that are sensitive to both AC and DC currents, such as type B RCMA and RCMB, dedicate measuring current transformers and special measurement methods are require to be able to detect DC and AC currents of different frequencies.
Key points summary
Type A RCM (AC/pulsating DC fault current):
Working principle: Under normal circumstances, the sum of the currents in all conductors (excluding PE) passing through the measuring current transformer is zero, so no voltage is induce.
Fault detection: When a fault current occurs, the current is no longer balance, so a current is induce in the measuring current transformer, which is detect by the RCM.
Detection range: Type A RCM is mainly use to detect pure AC currents and pulsating DC fault currents.
Type B RCMA and RCMB (AC/DC sensitive):
Special requirements: Type B devices require specially designed measuring current transformers and specific measurement methods to detect DC and AC currents of different frequencies.
Application scenarios: This type of device is suitable for complex electrical systems containing power electronic equipment (such as inverters), where DC components or mixed frequency currents may occur.
In this way, Type B RCM devices provide a wider range of protection capabilities in power systems and can cope with more complex electrical fault situations.
How does an RCM work?
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