Comparison of Residual Current Devices Tripping Characteristics for Selected Residual Current Waveforms

S. Czapp


According to the international standards circuits for electrical devices in the area of high risk of electrocution should be protected by high sensitivity residual current devices. In order to achieve effectiveness of protection against electric shock, residual current devices should be capable of detecting a waveform of residual current under the given conditions. Laboratory tests performed by the author indicate that tripping current of residual current devices is strictly dependent on the residual current waveform. In some cases the tripping current for a distorted residual current may be much higher than for a sinusoidal waveform. For residual current with high-order harmonics, as in circuits with variable speed drives, some residual current devices do not trip at all. In the paper a comparison of tripping current of residual current devices for various residual current waveforms is presented. The impact of the waveform of residual current on the effectiveness of protec-tion against electric shock with the use of residual current devices is discussed. Ill. 4, bibl. 11, tabl. 2 (in English; abstracts in English, Russian and Lithuanian).

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