﻿ 基于双电流互感器的电缆故障差动保护方法

# 基于双电流互感器的电缆故障差动保护方法Cable Fault Differential Current Protection Method Based on Dual Current Transformer

Abstract: As the urban construction process accelerates, the proportion of cable distribution in distribution networks is increasing, and the incidence of cable failures is also increasing. Due to the various forms of single-phase grounding faults, fault protection is greatly affected by factors such as transi-tion resistance, neutral grounding mode and current transformer imbalance. Fault troubleshooting is difficult, and cable trench explosions and other accidents occur frequently, which seriously af-fects the reliability of power supply. Therefore, it is necessary to study and improve the grounding fault protection method for distribution network. In this paper, the zero-sequence current distri-bution characteristics of single-phase grounding faults are analyzed in distribution network with neutral point ungrounded, arc-suppression coil grounded and small-resistance grounded. On this basis, considering the influence of transition resistance and the current transformer error, a cable fault differential current protection method based on dual current transformer is proposed. By in-stalling two sets of current transformers with different ranges at the two ends of the cable, the cur-rent transformer error is reduced to some extent, and the sensitivity of the differential protection is improved. The simulation results show that compared with the traditional single transformer, the cable fault differential current protection based on dual current transformer has higher re-sistance to transition resistance and sensitivity.

1. 引言

2. 配电网单相接地故障特征

2.1. 零序电流分布特征

Figure 1. Schematic diagram of single-phase grounding fault of distribution network

${\stackrel{˙}{I}}_{0j}=j\omega {C}_{0j}{\stackrel{˙}{U}}_{\text{O}}$ (1)

${\stackrel{˙}{I}}_{0i}=-\left[j\omega \left({C}_{0\Sigma }-{C}_{0i}\right){\stackrel{˙}{U}}_{\text{O}}+{\stackrel{˙}{I}}_{\text{O}}\right]$ (2)

${\stackrel{˙}{I}}_{\text{O}}=0$ (3)

${\stackrel{˙}{I}}_{\text{O}}=\frac{{\stackrel{˙}{U}}_{\text{O}}}{j\omega {L}_{\text{p}}}$ (4)

${\stackrel{˙}{I}}_{\text{O}}=\frac{{\stackrel{˙}{U}}_{\text{O}}}{{R}_{\text{d}}}$ (5)

2.2. 接地故障过渡电阻影响

${\stackrel{˙}{U}}_{\text{O}}\text{=}-\frac{{\stackrel{˙}{E}}_{A}}{1+j3\omega {C}_{0\Sigma }{R}_{f}}$ (6)

${\stackrel{˙}{U}}_{\text{O}}=\frac{-{\stackrel{˙}{E}}_{A}}{1+j3\omega {C}_{0\Sigma }{R}_{f}-j\frac{{R}_{f}}{\omega {L}_{p}}}$ (7)

${\stackrel{˙}{U}}_{\text{O}}=\frac{-{\stackrel{˙}{E}}_{A}}{1+j3\omega {C}_{0\Sigma }{R}_{f}+\frac{{R}_{f}}{{R}_{d}}}$ (8)

3. 电缆故障零序差动保护方法

3.1. 电流互感器误差影响

${\stackrel{˙}{I}}_{2}=\left({\stackrel{˙}{I}}_{1}-{\stackrel{˙}{I}}_{\mu }\right)/{n}_{\text{TA}}$ (9)

Figure 2. Current transformer core magnetization curve

3.2. 基于双电流互感器的差动保护方法

Figure 3. Principle of differential current protection based on dual current transformers

${\stackrel{˙}{I}}_{\text{CD}}={\stackrel{˙}{I}}_{0M}+{\stackrel{˙}{I}}_{0N}$ (10)

${\stackrel{˙}{I}}_{\text{CD}}={\stackrel{˙}{I}}_{{C}_{0i}}$ (11)

${\stackrel{˙}{I}}_{\text{CD}}=-j\omega \left({C}_{0\Sigma }-{C}_{0i}\right){\stackrel{˙}{U}}_{\text{O}}$ (12)

${\stackrel{˙}{I}}_{\text{CD}}=-\left[j\omega \left({C}_{0\Sigma }-{C}_{0i}\right)+\frac{1}{j3\omega {L}_{\text{p}}}\right]{\stackrel{˙}{U}}_{\text{O}}$ (13)

${\stackrel{˙}{I}}_{\text{CD}}=-\left[j\omega \left({C}_{0\Sigma }-{C}_{0i}\right)+\frac{1}{3{R}_{\text{d}}}\right]{\stackrel{˙}{U}}_{\text{O}}$ (14)

${I}_{\text{ZD}}={K}_{\text{rel}}{I}_{\text{unb}}$ (15)

${I}_{\text{set}}=|j\omega \left({C}_{0\Sigma }-{C}_{0i}\right)\frac{{\stackrel{˙}{E}}_{A}}{1+j3\omega {C}_{0\Sigma }{R}_{f}}|$ (16)

${I}_{\text{set}}=|\left[j\omega \left({C}_{0\Sigma }-{C}_{0i}\right)+\frac{1}{j\omega {L}_{p}}\right]\frac{{\stackrel{˙}{E}}_{A}}{1+j3\omega {C}_{0\Sigma }{R}_{f}-j\frac{{R}_{f}}{\omega {L}_{p}}}|$ (17)

${I}_{\text{set}}=|\left[j\omega \left({C}_{0\Sigma }-{C}_{0i}\right)+\frac{1}{{R}_{d}}\right]\frac{{\stackrel{˙}{E}}_{A}}{1+j3\omega {C}_{0\Sigma }{R}_{f}+\frac{{R}_{f}}{{R}_{d}}}|$ (18)

Figure 4. Fault protection process based on dual current transformer

4. 仿真与分析

Table 1. Line parameters

Figure 5. Zero sequence differential current under internal and external faults

Table 2. The change of zero sequence differential current with transition resistance

5. 结论

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