Reliability Improvement Strategy for Transformer Zero-Sequence Differential Protection Based on Zero-Sequence Current Amplitude Difference Characteristics

doi:10.11930/j.issn.1004-9649.202409080

Abstract

Abstract:

The zero-sequence differential protection of transformer may cause the reliability to decrease or even malfunction due to the fault of current transformer (CT) when dealing with complex inrush current and fault. To solve this problem, a strategy to improve the reliability of transformer zero difference protection is proposed. The zero-sequence current and its amplitude characteristic are analyzed and studied to obtain the relevant auxiliary criterion and the simulation model is established to simulate the typical working conditions such as zone fault, outside fault and complex inrush current. The simulation results show that the auxiliary criterion can effectively improve the reliability of zero-sequence differential protection and avoid the malfunction caused by the deterioration of the transmission characteristics of current transformer.

Key words: zero-sequence differential protection, zero-sequence current, excitation inrush current

ZHENG Junchao, GE Yaming, KONG Xiangping, REN Xuchao, CHEN Shi, WANG Chenqing. Reliability Improvement Strategy for Transformer Zero-Sequence Differential Protection Based on Zero-Sequence Current Amplitude Difference Characteristics[J]. Electric Power, 2025, 58(8): 147-155.

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URL: https://www.electricpower.com.cn/EN/10.11930/j.issn.1004-9649.202409080

https://www.electricpower.com.cn/EN/Y2025/V58/I8/147

Figures/Tables 13

Fig.1 The single-phase grounding fault in the area is accompanied by CTN saturation condition

Fig.2 Outside single-phase grounding fault with differential second harmonic content under CTN saturation condition

Fig.3 Branch of the transformer

Fig.4 Zero sequence network in case of regional failure

Fig.5 Out-of-area faults are accompanied by severe CTN saturation

Fig.6 System model of a 220 kV substation

Fig.7 The unloaded energization of the transformer is accompanied by a single-phase grounding fault occurring at the position 1% close to the neutral point of the A-phase winding

Fig.8 The A phase short-circuit grounding fault with CTN saturation occurs near 2% of the neutral point in the A phase winding of the transformer

Fig.9 Outside AB phase short-circuit grounding fault with CTN saturation

Fig.10 The magnetizing inrush current condition accompanied by CTN saturation

Fig.11 Recovery inrush flow condition with CTN saturation

Fig.12 The external AB phase short circuit grounding fault condition is accompanied by CTN and phase CT saturation

Fig.13 The magnetizing inrush current condition is accompanied by CTN and phase CT saturation

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