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How to harmonise the use of RCDs with frequency converters

04 May 2017

Eaton’s whitepaper, “Enhance reliability with the right drives protection”, advises machine builders how to avoid nuisance tripping of Residual Current Devices (RCDs) when they are used with variable frequency drives.

The whitepaper explains how installing a suitable RCD guarantees the highest possible level of protection for both a machine and operator, and reveals how this can enable users to benefit from energy-efficient motor control.

“With demand for manufacturers to improve energy efficiency across their operations, modern machines are increasingly using frequency controlled drives,” said Chris Pack, Field Product Manager at Eaton UK. “However, these can cause problems with electrical protective devices, such as residual current devices (RCDs). Using the wrong type of RCDs in these applications can have devastating effects, as there will be unwanted tripping or even the complete loss of the protection function. This can lead to costly machine downtime and unsafe equipment.”

This is the fourth and final whitepaper in the series exploring residual current topics. It outlines how engineers can select the right RCD by reviewing all likely residual current scenarios and discusses suitable RCD solutions for different applications. The use of digital RCDs is also covered; which provide enhanced visibility of impending faults to improve machine performance and uptime. Finally, recommendations are given on why high leakage currents occur and how to best reduce them.

Variable frequency drives enable more energy-efficient processes. However, even during normal operation, these circuits can produce unavoidable high frequency leakage currents that will result in false tripping if the incorrect choice of RCD is made. Therefore, the paper explains the basic operation of frequency converters, how they generate additional leakage currents, and the types of RCDs that should be used.

As product life cycles have become increasingly compressed, pressure on engineers and organisations to continually drive efficiency and improve productivity has intensified. With this in mind, Eaton has developed the PowerXL Selection Aid. It is a simple online planning solution, designed to help engineers quickly select the drive required for the application; as well as the associated switchgear, protective elements, chokes and filters.  

“The PowerXL Selection Aid helps engineers to choose the right RCD. Based on the selected drive, the aid will recommend the correct type and size,” concluded Chris Pack. “Engineers only need to define the required protective goal and depending on that, a 30mA RCD will be used for additional protection or a 300mA RCD for fault protection.”

In addition to digital and analogue RCDs, Eaton has of products and solutions including MCB, MCCB, ACB, fuses and hydro-magnetic circuit breakers. As such, it is ideally positioned to help machine builders with all their circuit protection requirements from specification and selection, through to installation and maintenance.

The whitepaper is available free to download from www.eaton.eu/rcd-drives


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