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Electric shock hazard in circuits with variable-speed drives

Czapp S., Guzinski J.

Bulletin of the Polish Academy of Sciences. Technical Sciences

2018

Vol. 66, nr 3

361--372

The conventional approach to electrical safety under fault condition in typical power systems considers earth fault currents of sinusoidal waveform and frequency of 50‒60 Hz. However, in circuits with variable-speed drives, there is earth fault current flow with harmonics, and these harmonics influence the threshold of ventricular fibrillation. The paper presents earth fault current waveforms in circuits with variable-speed drives without inverter output (motor) filter and with one of the two types of inverter output filters being used. The details of both filters are presented, and the effect of harmonics of earth fault current on ventricular fibrillation is evaluated. Furthermore, the effect of harmonics, which occurs in circuit of variable-speed drive, on the tripping current of residual current devices is presented. Residual current devices may be utilized to ensure protection against direct and indirect contact, but limitations in their proper operation, due to harmonics, may exist. Operational characteristics of a proposed residual current device dedicated to circuits with earth fault current containing harmonics, as in the variable-speed circuits, are presented.

Improving sensitivity of residual current transformers to high frequency earth fault currents

Czapp S., Dobrzyński K., Klucznik J., Lubosny Z., Kowalak R.

Archives of Electrical Engineering

2017

Vol. 66, nr 3

485--494

For protection against electric shock in low voltage systems residual current devices are commonly used. However, their proper operation can be interfered when high frequency earth fault current occurs. Serious hazard of electrocution exists then. In order to detect such a current, it is necessary to modify parameters of residual current devices, especially the operating point of their current transformer. The authors proposed the modification in the structure of residual current devices. This modification improves sensitivity of residual current devices when high frequency earth fault current occurs. The test of the modified residual current device proved that the authors’ proposition is appropriate.

Automatycznie strojona cewka Petersena firmy EGE z regulatorem A. Eberle

Lorek K.

Wiadomości Elektrotechniczne

2008

R. 76, nr 9

30-34

Omówiono wykorzystanie cewki Petersena do zapewnienia bezprzerwowego dostarczania energii elektrycznej podczas krótkotrwałych zwarć przemijających oraz podczas nieprzemijających jednofazowych zwarć doziemnych.

The paper discusses using of Petersen coil to ensure no brake power supply during short term transient short circuits and non-transient one phase earth faults.