Predictive maintenance

Preventive maintenance through residual current monitoring in the earthed system (TN-S/TT system) and ...

© Bender

If an earthed power supply system (TN-S system) is installed, the solution is permanent residual current monitoring, such as the residual current monitoring devices from Bender. This involves permanently measuring the total or residual current at particularly important or neuralgic points in the network. If the residual or fault current that is critical for this part of the system becomes too high, the monitoring device sends an alarm. System technicians can then react immediately so that shutdowns and system downtimes or even fires caused by insulation faults are a thing of the past.

... through insulation monitoring in the unearthed system (IT system).

© Bender

Getting started with residual current monitoring is possible with little effort if measurement data is tapped at eight to twelve measuring points and thought is given to evaluating and forwarding the information. The space for this can usually be found in existing switch cabinets.

For control and auxiliary circuits in which, for example, commands are issued or measured, opened, locked, signaled, heated or cooled, the operational safety of the system is paramount. The production plant only runs when specific control voltages are applied. In IT systems, insulation monitoring devices provide information about the insulation status of the system. In TN-S systems, residual current monitoring devices measure and display the insulation level. Current values can be read off at any time and impermissible deterioration is reported in good time.

A look at the standard

There are numerous laws, regulations and standards that define the framework for safe system operation. A key aspect of this is the periodic testing of the electrical system. This can largely be carried out during operation (e.g. by visual inspection) - with the exception of the insulation resistance measurement (DIN VDE 0100-600:2008-06 Erection of low-voltage installations - Part 6 Tests: 61.3.3 Insulation resistance of the electrical installation) and the measurement of the earthing resistance; both can only be carried out when the system is switched off.

However, switching off the power supply is often associated with high downtime costs and costly restarting of the systems or is completely impossible, such as in the complex system parts of the beverage industry. However, standards such as DIN VDE 0105-100:2015-10 (Operation of electrical systems) and DGUV Regulation 3 (Electrical systems and equipment, formerly BGV A3) offer two alternatives for the safe operation of systems that must always be available - without having to be switched off:

• permanent monitoring of the insulation resistance in the IT system and
• permanent residual current measurement in the TN-S system.

Permanent monitoring of the insulation level of the electrical system (standard DIN VDE 0105-100:2015-10) allows the electrician to adjust the test intervals for recurring insulation measurement if this procedure is approved by the property insurer. DGUV Regulation 3 also allows the possibility of adjusting the intervals for tests to maintain the proper condition of the system through continuous monitoring.

In the IT system, it is therefore possible to permanently monitor the insulation resistance of the system using an insulation monitoring device. Another option is the residual current monitoring system in the TN-S system, which continuously measures and evaluates the residual currents of the entire system. Deterioration of the insulation resistance is detected and reported. In both cases, it is not necessary to switch off the system for insulation resistance measurement during periodic testing.

Communication variants

All-current sensitive transformers with residual current monitoring systems, such as the RCMS460 and RCMA423 series (from left) from Bender, are ideal for permanent residual current monitoring.

© Bender

With the monitoring systems mentioned above, messages can be communicated centrally in both unearthed and earthed networks - either via TCP/IP protocol to any network-compatible computer or via e-mail or cell phone; operating, warning or fault messages can be sent to almost any location. In this way, early information about the cause and location of faults enables the technology to carry out service calls in a cost-optimized manner and minimize consequential damage to expensive system components or machines.

The web-based software solution 'Powerscout' from Bender also provides further possibilities for predictive maintenance. It provides insight into the complete data of the system, as all measured values are automatically and continuously saved. The tool creates easy-to-understand visualizations, records data across all locations and simultaneously supports the analysis of device data. It thus documents the condition of the electrical system. With such a well-founded database, trends can be displayed in order to identify faults and correlations at an early stage and eliminate the causes. The software tool also creates and saves the residual current test logs. This automated report forms the basis for measuring without switching off in accordance with DGUV Regulation 3.

Authors:
Hans-Joachim Feigl was Sales Manager Germany at Bender in Grünberg and is now retired;
Marita Schwarz-Bierbach is responsible for press relations and customer communication at Bender in Grünberg.