Due to their non-linear power consumption, electrical loads such as PCs, electronic ballasts, copiers, etc. can generate a smooth fault current in modern electrical systems in the event of an error. This requires a complete rethink of protection and monitoring technology. The traditional fault current monitoring devices for alternating and pulsing direct fault currents (type A) used thus far have become unusable in these cases. For this reason, DIN VDE 0100-530 (IEC 60364-5-53) has, for some years, required AC/DC sensitive residual current monitoring.
The reason for this is in the detail: A conventional type A RCM (Residual Current Monitor) would not trigger in the event of a smooth direct error current, as there is no change in magnetisation over time in summation current transformers, and this is required for inductive energy transfer to the RCM trigger relay. Depending on the level, the direct fault current effects an initial magnetisation of the transformer core, thus increasing the RCM trigger threshold for other alternating fault currents which may still be present to the point of not triggering.
The aims of the development of the RCMS150 six-channel residual current monitoring system were varied and ambitious. For good reasons, it needed to be sensitive to all currents for space-sensitive final circuit applications (type B).
With the new RCMS150 residual currents of 0 to 2000 Hz and 0 to 300 mA can be measured and evaluated during operation. The information exchange between the individual type RCMS150 and RCMS460 evaluation devices and a gateway happens via an RS-485 interface. This means that a complete building or a complete supply section (with multiple measurement points and multiple devices) can be permanently monitored from a central point such as a control cabinet or a control room. The history memory and the data logger integrated into the gateway store up to 1000 messages with time stamp.
Further benefits of the RCMS150 are:
- adaptation of the internal diameter for residual current measurement in final circuits
- simple installation on and behind DIN rails in distribution cabinets
- cost-effective version without display, which can be configured via a gateway
- compatible with all RCMS460/490 units and gateways installed
It is important that a measurement set up in this way is refined enough to detect damage at an early stage. Monitoring the building feed is very rarely enough. The closer to the final circuit the RCMS technology is installed, the more accurately the fault location and fault currents can be recorded and it becomes clear that the six-channel RCMS150 was developed for exactly this measuring job.