Study on Performance of Novel Optical Voltage Transformer Based on Current Measurement

Compared with traditional current sensors, the inherent advantages of fiber optic current transformers (FOCT) in terms of passive, immunity to electromagnetic interference, free hysteresis, free saturation, etc., make them quite attractive in high electromagnetic field environments. As a result, a fiber optic voltage measurement scheme (FOCT-OVT) based on FOCT together with a capacitive voltage divider (CVD) is proposed, in which a novel multiturn coil sensing structure and closed-loop square-wave modulation and demodulation scheme based FOCT technology is used to measure the small capacitance current ( $I$ ) flowing through the CVD to achieve the purpose of measuring high voltage ( $U$ ). A 110-kV FOCT-OVT prototype was developed, whose basic performances such as accuracy, frequency response, and impulse response were analyzed according to GB/T20840.7-2007 specifications. According to the test results, $I$ increases linearly with $U$ and is about 100 mA under the rated voltage of 63.5 kV, which can be effectively measured by FOCT. The prototype with an 8000-turn coil is proven to have an accuracy of 0.2% metering class and 3P protection class, whose steady-state and transient performances meet the limit requirements specified in GB/T20840.7-2007.

I. Introduction

ELECTROMAGNETIC voltage transformers [1], [2] and capacitive voltage divider (CVD) voltage transformers [3], [4], [5] are widely used in electric grid monitoring to provide voltage signals for metering and protection equipment. However, with the development of power system in the direction of ultrahigh voltage and large capacity, the traditional voltage measurement scheme gradually exposes defects such as huge volume, complex structure, difficult insulation, and susceptible to magnetic saturation.