Abstract
One important problem in the operation of medium voltage networks is the detection of a single-line-to-ground fault in its incipient state, when the fault resistance values are very high. In a medium voltage (MV) distribution network with a neutral grounding resistor (NGR), one of the methods employed to discriminate a single line-to-ground fault is the use of an overcurrent relay with an operating characteristic adjusted according to the effective value of the current flowing through the limiting resistor. In case of a single line-to-ground fault with a high fault resistance value, the correct tripping settings of the protective relay require the precise computation of this current. In comparison to the assumptions made by the models from the literature—the three-phase voltage system of the medium voltage busbars is symmetrical and there are no active power losses in the network insulation—the model proposed in this paper considers the pre-fault zero-sequence voltage of the medium voltage busbars and the active power losses in the network insulation, which is necessary in certain fault conditions where the use of the former leads to unacceptable errors.
Highlights
500 Ω, the current through the limiting resistor can be calculated using the model presented in the literature, and the zero-sequence voltage of the medium voltage bus bars in normal conditions can be neglected
(b) Figures 14–17 show that the zero-sequence voltage of the medium voltage bus bars does not significantly influence the values of the zero-sequence current at the fault location; implicitly the ground fault current can be neglected in the calculation
The ground fault current can be calculated using the model presented in the literature
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. In the mathematical models presented in the literature for the calculation of the single line-to-ground fault current in the medium voltage electrical networks, the phase voltage system of the medium voltage bars in the transformer station is considered to be symmetrical. In insulating materials, including the insulation of medium voltage electrical networks, located in an electric field, active power losses occur For this reason, the electrical scheme equivalent to a real capacitor consists of an ideal capacitor connected in parallel with an ideal resistor (Figure 2a) [27]. From (1) it is found that as the total capacitive current of the medium voltage network network to ground
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