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Chen D.,North China Electrical Power University | Huang J.,North China Electrical Power University | Zhang L.,Xiamen Power Supply Bureau
Dianli Zidonghua Shebei/Electric Power Automation Equipment | Year: 2010

As the excitation inrush is seriously distorted while the fault current is nearly sinusoid, a method is proposed to identify the excitation inrush current of transformer. Full-wave Fourier algorithm and half-wave Fourier algorithm are used to respectively calculate the imaginary part of fundamental differential current, and the normalized correlation coefficient between them is then deduced by correlation analysis, which is compared with a setting to identify the inrush current. Dynamic tests are carried out for four transformer operating conditions: energizing without load, inter-phase short-circuit, phase-ground short-circuit and energizing with fault. Experimental data are analyzed, which verifies the correctness and effectiveness of the proposed approach. Source


Chen D.-Z.,North China Electrical Power University | Zhang L.,Xiamen Power Supply Bureau
Dianli Xitong Baohu yu Kongzhi/Power System Protection and Control | Year: 2010

A new algorithm based on half-wave fourier and two points product method is presented for solving the mal-operation in transformer differential protection due to magnetizing inrush current. The method is based on the principle that the waveform of the inrush distorts seriously and even forms into vertex sharp wave, while the fault current keeps nearly sinusoid. Based on the half-wave fourier, this method samples currents with differential filter continuously, gets groups of square sum of two neighboring PI/2 currents using trigonometric theorem, then distinguishes inrush current by the ratios of neighboring groups of square sum. Theoretical analysis and dynamic simulation results show that the method is correct and effective under various fault conditions. Source


Zeng J.,Xiamen Power Supply Bureau
Dianli Zidonghua Shebei/Electric Power Automation Equipment | Year: 2012

The unbalanced voltage protection is designed based on the voltage drift of neutral point during capacitor faults to effectively isolate the asymmetric faults of capacitor, but it may refuse to act when the single-phase wire-breaking fault happens in the ungrounded star-connecting capacitor bank, which is pointed out by the theoretical analysis in principle. As there is negative-sequence current in such case, the negative-sequence current protection is proposed to prevent the improper behaviour of unbalanced voltage protection, which is verified by theoretical analysis. Source


Zheng N.-Z.,Xiamen Power Supply Bureau | Zeng J.-S.,Xiamen Power Supply Bureau
Dianli Xitong Baohu yu Kongzhi/Power System Protection and Control | Year: 2010

The functions and hardware level of microprocessor-based relay equipments are highly uprated with the level of automatic system in substations. But the relay systems are working on asymmtric mode in many cases, for example, the secondary system plates are often changed with the operating mode of primary system. It will cause incipient fault when system is running and also bring much work to operators. Some misunderstandings will be discussed in this paper when microcomputer relay systems are running in different voltage levels. Source

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