Immunity of Residual Current Devices to the Impulse Leakage Current in Circuits with Variable Speed Drives

Abstract

This paper concerns reliability of supply in variable speed drive circuits with residual current devices. During normal operation of these circuits high value of leakage current causes unwanted tripping of residual current devices. Immunity of residual current devices to the impulse leakage current should be evaluated. The system for testing of residual current devices and results of the test are presented.

Refinement of the mathematical model of frequency converter cable branch with a single­phase short circuit

“…The inability to determine the impedance of the phaseto-ground short circuit at the FC output if the protective device is connected in the common part of the network complicates the construction of protection devices [7]. Erroneous operation of regular ground fault protection devices can also be caused by the semiconductor converter as a part of the mine section electrical network [8].…”

“…Defined resistances that correspond to the current state of the semiconductor devices are the inputs of the AVI model 5. The latter implements the matrix equation (8) and distinguishes the vector U of the inverter output phase voltages from the calculated vector U R . Block 6 solves the matrix differential equation (18) of the cable line state, taking into account the capacitances C g of the cable insulation.…”

“…The AVI model (Fig. 4, block 5), according to (8), performs the following operations (Fig. 5, item 7).…”

“…The Ud block specifies the voltage U d value of the FC direct current circuit. The matrix multiplication unit Matrix Multiply, according to (8), calculates the voltage vector U R on the resistive elements of the AVI equivalent circuit. The Selector block distinguishes the phase output voltages of the AVI.…”

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

“…It leads to the problem of RCDs compatibility with such types of current. This problem is discussed in many papers [2][3][4][5][6][7][8][9][10]. Voltage and current harmonics are mainly produced by power electronics converters [2].…”