Residual current monitoring to the final circuit

In modern electrical installations, extensive monitoring by different sensors is required. This is the only way to guarantee both safety and high availability.

Wherever an uninterrupted power supply has to be ensured, whether in industrial plants, data centres or building technology, but at the same time the use of an unearthed power supply (IT system) is not possible for various reasons, monitoring using residual current technology has become established. This technology makes it possible to detect fault currents* in electrical installations long before critical system states or even a shutdown by residual current devices occurs.

Fault currents do not usually occur spontaneously, for example due to component burning out. Fault currents usually arise over a longer period of time. Various environmental factors are primarily responsible for it. Heat, cold, moisture, mechanical stress and ageing can lead to insulation deterioration in cables and components and thus cause fault currents. The fault currents often do not suddenly increase, but become higher and higher over a longer period of time.

Residual current monitoring makes it possible to detect fault currents in electrical installations long before critical system states or even a shutdown by residual current devices occurs.

Size and complexity require precise monitoring

Modern electrical installations are becoming larger and more complex. Monitoring in the main distribution board using residual current technology is therefore no longer sufficient to ensure high availability. The installations to be monitored are far too large and the currents occurring are far too high to be able to detect gradual changes in parts of the installation (e.g. due to individual faulty loads). System operators who only use residual current measurement technology in the main distribution board and believe that their installation is sufficiently protected against possible failures are therefore lulled into a false sense of safety.*

Example calculation: In an electrical installation with a total of 1000 loads with an average output of 150 watts, around 650 A flow through the main distribution board at a voltage of 230 V. This high current flow makes it difficult to detect fault currents. The source of the fault can usually not be identified.

The larger and more complex electrical installations are, the more precise the monitoring should be. This is the only way to clearly detect fault currents in large installations, identify and locate the sources of faults better (or faster or more easily) and thus prevent unplanned downtimes.

To ensure high availability of data centres, complex industrial plants and building installations, monitoring in the main distribution board using residual current technology is in many cases no longer sufficient.

Residual current monitoring at all levels of the power supply

Conventional devices are usually not suitable for monitoring in sub-distribution boards and final circuits. Their measuring ranges are too large to detect smaller fault currents. Bender has therefore developed special sensors and evaluators that are suitable for monitoring electrical installations from the main distribution board to individual final circuits*.

The consistent use of residual current sensors from the main distribution board to the final circuit allows faults to be detected in good time. The further the equipment is installed towards the final circuits, the more accurately actual fault currents can be distinguished from leakage currents and the better faults can be located.

The Bender portfolio of residual current monitoring devices is designed for installation-wide use and offers flexible solutions for every location. On the one hand, there are powerful products with a high current-carrying capacity for use in the main distribution board and, on the other, compact and cost-effective sensors for monitoring final circuits. The various devices and sensors are equipped with communication interfaces. They can be connected to form a system that is monitored from a central location.

The further residual current sensors are installed towards the final circuits, the more accurately actual fault currents can be distinguished from leakage currents and the better faults can be located.

Special technology for residual current monitoring of final circuits

The modular CTUB100 series and RCMB300 series were developed for use in final circuits. The portfolio is complemented by the multi-channel RCMS150 residual current monitor and the RCMB330 split-core sensors for AC/DC-sensitive residual current monitoring.

All devices have extensive frequency filter options for the wide frequency range up to 100 kHz and thus support the analysis of leakage and fault currents in the installation, allowing better conclusions to be drawn about sources of faults.

In addition, all the devices described here for final circuit applications are equipped with a Modbus RTU interface so that they can be easily integrated into a larger overall system (such as a PLC).

Residual current monitoring devices RCMS150

Multi-channel for many outgoing circuits

If a larger number of outgoing final circuits are to be equipped with residual current monitoring systems, a six-channel solution can be used with the RCMS150. Like the devices in the RCMB13x series,they combine a measuring current transformer and evaluation electronics in one housing. The technical features are also essentially identical to this device series, meaning that the performance of the RCMS150 is also specially designed for final circuits up to 32 A.

Residual current monitoring device RCMS150

Flexible and suitable for direct use in individual loads

The high-performance devices of the CTUB100 series and RCMB300 series are ideal for industrial use of residual current technology in final circuits. Thanks to their modular design with different transformer sizes, these sensors can be used in a wide variety of final circuit applications with low to high load currents. They can also be used to monitor applications with special requirements in terms of measuring accuracy or insensitivity to external interference, as the measuring current transformers are optionally available with a full magnetic shield. In applications with very high and pulsed load currents, this shield ensures that the detection of residual currents is not affected by the rapid load changes.

Residual current monitoring devices RCMB300-series

Split-core for retrofit applications

Retrofitting residual current monitoring in existing installations poses particular challenges. On the one hand, there is often very little space available for sensors and evaluators, and on the other hand, installing the sensors is anything but easy. In order to disconnect the cables, the installation must be switched off.

The split-core devices of the RCMB330 series provide a smart single-channel solution that can be easily installed in existing systems: Open the current transformer, place it around the conductors, close it again and wire the interface - done. The installation does not have to be switched off. The RCMB330 combines evaluator and measuring current transformer in a compact housing so that this series can also be used for monitoring final circuits.

Residual current monitoring device RCMB330

Conclusion

With a wide range of solutions for final circuits, Bender offers the option of individually monitoring the loads in an electrical installation in contrast to classic residual current monitoring. This is because loads in particular are often sources of leakage and fault currents. Only through targeted monitoring can insulation faults be found and eliminated quickly.