Transients in a 20 kV Network Due to Single-Phase Short-Circuit Faults in 220 kV Cable Lines
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Vol. 54, No. 3, September, 2020
TRANSIENTS IN A 20 kV NETWORK DUE TO SINGLE-PHASE SHORT-CIRCUIT FAULTS IN 220 kV CABLE LINES A. V. Maiorov1 and A. A. Chelaznov2
Translated from Élektricheskie Stantsii, No. 3, March 2020, pp. 22 – 26.
The transient processes in a 20 kV network due to single-phase short circuit fault in the 220 kV lines of a 220/20 kV supply substation are considered. Combinations of parameters at which overvoltages are the highest are determined. The overvoltages limited by surge arresters installed on 20 kV busbars are estimated. Keywords: single-phase short circuit in 220 kV network; neutral grounding of 20 kV network; overvoltage in 20 kV network.
The long lengths of 220 kV deep input CLs that can reach 10 to 15 km in cities are responsible for intensive transients caused by 220 kV short-circuit faults. Let us consider a single-phase short-circuit fault (SPF) at the feed end of the 220 kV CL (point 1, Fig. 1a). Generally, the transient behavior and overvoltage amplitudes are determined by the parameters of the circuit elements and the voltage phase when the SC occurs. The occurrence of SPF at the maximum voltage leads to overvoltage across the faulty phase of the 220 kV CL because of wave reflections from the fault and from the substation busbars. The transients were analyzed using EMTR software [3]. The parameters of the circuit elements are collected in Table 1, and the equivalent circuit is shown in Fig. 2. The equivalent circuit includes all elements of the substation. The cable lines are modeled by elements with distributed parameters. The transformer model accounts for the nonlinearity of the magnetizing branch. The SPF is modeled as the maximum voltage of the phase A in the busbars of the power supply system. In the general case, the period of high-frequency voltage oscillations across the 220 kV busbars caused by a single phase-to-earth (SPE) fault in the 220 kV CL (Fig. 3) depends on the full cycle of reflections of an electromagnetic wave moving along the CL and equals the quadruple time it takes the wave to traverse the line. If the supply system is high power, the frequency of oscillations of the voltage upon SPF is mainly determined by
Scheduled and emergency switchings occurring at highvoltage substations (SS) lead to transients causing overvoltage that can damage the insulation of the equipment. For large delivery substations supplying power to low-voltage busbars via high-power transformers, overvoltage on the high-voltage side can be dangerous to the equipment connected to the low-voltage busbars. Figure 1a shows the circuit diagram of a 220 kV substation that energizes a 20 kV city cable network. The voltage to the high-voltage busbars of the SS is supplied by a 220 kV cable line (CL) from a remote system. The 20 kV busbars are powered by 220/20 kV double-wye transformers of 100 MV · A capacity with resistance-earthed neutral. A resistor Rn = 12 Ù is connected to the neutral of the 20 kV network [1, 2]. SS 220/20
220 kV
C
CL1
20 kV
P
CL2
1
Xc
2 T 220/20 Rn
a 220 k
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