Calculation and simulating experiment on effectiveness of anti-ferroresonance methods for 10kv transmission line
In medium voltage distribution networks with the non-grounding neutral, the electromagnetic potential transformers (PT) are generally used to monitor the phase to ground voltages. However, the PT may be induced the magnetic saturation by the transient electromagnetic disturbances caused by the single phase grounding, disconnection faults and so on. The magnetic saturation often motivates the ferroresonance in the distribution networks, and result in the PT fuse breaking and even PT exploding. In order to investigate the characteristics of ferroresonance and the effectiveness of anti-ferroresonance methods in distribution networks, a 10kV experimental system for simulating ferroresonance in laboratory was set up in this paper. Meanwhile, the calculating models of PT with the characteristic of non-linear magnetic excitation were developed based on PSCAD software. A number of the simulating experiments and calculations were carried out to represent the ferroresonance phenomena in the distribution networks. The research results indicate that the highest overvoltage in the case of high frequency resonance related to the zero sequence parameters can reach 3.5 p.u., and the overcurrent in the PT winding can be up to 80 p.u.. It is also discovered that, although the primary resonance eliminator shows the excellent performance in eliminating ferroresonance, the effectiveness of anti-ferroresonance is not always reliable especially when the grid distributed parameters or initiation modes change. A anti-ferroresonance strategy with the combined resonance eliminator and arc suppression coil is proposed to enhance the ability in suppressing the ferroresonance, which can perform the more advantageous on suppressing ferroresonance than with a single resonance eliminator or arc suppression coil. The contrastive researches provide guidelines for evaluating the anti-ferroresonance capability of the distribution networks and designing effective protection strategies.
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