Rated Voltage Enlargement for High-Speed PTC Current Limiter by Using a Series Transformer

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In this paper, using Positive Temperature Coefficient (PTC) elements, we propose a simple repetitive high-speed PTC Current Limiter (PTC-CL) whose rated voltage is increased by using a series transformer (ST) at levels far beyond their intrinsic voltage rating. The PTC-CL consists of PTC resistors connected in series and in parallel to each winding of the ST. The PTC-CL was numerically studied by using the electro-magnetic transient program (EMTP) and the electrical equivalent model for PTC. The winding resistance effects and whether all of PTCs will trip or not under the fault current condition were studied. The experimental results in case of two PTCs, where the PTC element is rated (60V/40A), show that the sufficient voltage is applied on the non-tripped PTC even after another PTC trippd at first, and all PTCs of PTC-CL tripped within 0.2 ms where the fault current was suppressed from 1200 A to 52 A at rated voltage 120 V. But, the saturation current started to flow after 2 ms and reached above 1500 A because of the small size of the used core. In order to reduce it, RC components were proposed and the measurement results indicate that the saturation current can be eliminated adopting a suitable parameter for RC components.
社団法人電気学会の論文
2005-12-01