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PT transient over-current analysis based on instantaneous symmetrical component method for ungrounded-neutral power system
Author(s): 
Pages: 157-164
Year: Issue:  11
Journal: Electric Power Automation Equipment

Keyword:  power transformersungrounded-neutral power systeminstantaneous symmetrical component methodtransient over-current;
Abstract: Based on the nonlinear PT(Potential Transformer) model including losses,the instantaneous symmetrical component method is applied to deduce the expressions of PT transient over-current during single phase grounding fault and after its removal for the ungrounded-neutral power system. It is found that the PT transient over-current consists of the positive-sequence exciting current in normal operating condition and the decaying zero-sequence over-current. The PT transient over-currents during single phase grounding fault and after its removal are analyzed with MATLAB / Simulink for different arc suppression coil compensation modes. The simulative results show that,when single phase grounding fault occurs,the PT transient overcurrent is mainly related to its nonlinear excitation characteristics;when the fault is removed,larger exciting over-current is generated in PT,which contains the steady-state component and the decaying transient component,greatly influenced by the zero-sequence network. Therefore,it is proposed to restrain the PT damage by changing the zero-sequence parameters of system.
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