Study And Design Of Optical Current Transducer Based On The Rogowski Coils

In the electric engineering, Voltage and current are two most direct parameters. To insure the normal and safe operation of the power system, the current of the high-voltage power-lines needs be supervised and analyzed. Furthermore, there must be good electrical insulation between measure meter or relay and high-voltage instrument to guarantee the operator's safety. In consequence, current transducers are very important facilities and provide signal for measurement, protection, control and supervision of the power system.At present, electromagnetic current transducers are widely used in the power system. Their working principle is similar with conventional transformers. However, with the transmission capacity and the voltage level of the power line increasing, conventional electromagnetic current transducers are found to have many insurmountable questions. For example, more complicated insulation between the primary winding and the secondary causes the larger size, heavier weight and higher cost. Because of the nonlinear factors of the ferrous core, such as eddy current and hyteresis loss when the core is saturated with large malfunction current, ratio error and phase error are very large. The CTs can't work because the oil in the conventional transducers possibly blow up for the bad-working environment. The opening of the secondary circuit will yield high voltage that is potentially dangerous to the instrument and operators. So it is necessary to study the novel current transducers that are based on the new working principle.In recent years, considerable effort has been devoted to the optical current transducer (OCT) based on Faraday effect or optical communication technology, which is an attractive but difficult subject. For the difference of the sensor head, the OCT is divided into two kinds: full-optic CT and hybrid OCT.According to comparison and study, this paper proposes a novel electro-optic, hybrid current transducer, including its design principle and system components. In this kind of instrument, the Rogowski coils used as the sensor head, they have many advantages: they haven't direct touch with the detected power lines, so they have good electrical insulation between high-voltage power lines and secondary circuit. The frequency of the current signal that Rogowski coils can detect ranges from a couple of Hz to hundreds of MHz andthe hundreds of kA current can be measured by the Rogowski coils. In this novel electro-optic, hybrid current transducer, the current of high-voltage power lines is first detected by the Rogowski coils, followed by conversion of the detected current into optical pulse signal through data modulation and electronic-optic transform in the high-voltage area. Subsequently, the optical pulse signal is transmitted to the ground through an optical fiber cable. Finally, the measured current is recovered from the optical pulse signal by optic-electronic transform and ground-located signal processing. Optical fiber cable is only used to transmit the optical signal, so the shortcomings and technical difficulty in optical circuit layout of the sensor head in the full-optic CT are avoided. It is more practicable for the power system.The author mainly analyzes the working and theoretical characters of Rogowski coils used as the sensor head in the high-voltage and low frequency range. Through formula derivation and data analysis, the suitable parameters of the Rogowski coils are choosed. Practical electronic circuit is designed and possesses both analog and digital signal outputs. It is not only suitable for existing conventional meters, but also fitted to digital meters with appropriate improvements. By signal processing, the hybrid current transducer has functions of synthetic control, data memory, display and print. It can meet the requirements of the practical operation of power system. There have experiments and initial tests show that it can archive the specified functionsIn the end, The author sum up the study works about the novel, electric-optic, hybrid current transduc...