engleski

Special Instrument Transformers For Precise Measurement of Voltages and Currents

ABSTRACT In this paper, methods for precise measurements of high voltages and currents by application of special instrument transformers: a Rogowski coil (RC) developed in Croatia and the 20 kV combined current-voltage instrument transformer (CCVIT) in Macedonia, will be presented. To strengthen the cooperation between the Primary Electromagnetic Laboratory (PEL) in Zagreb and Metrological Laboratory for Electromagnetic Quantities (MLEQ) in Skopje a bilateral project has been launched by the two governments, through which the methods for precise measurements of high voltages and currents are developed. The MLEQ at the Faculty of Electrical Engineering and Information Technologies (FEIT) in Skopje performs the measurements of high currents and voltages by using the originally developed prototype of a combined instrument transformer (CCVIT). The CCVIT must comply with the rigorous metrological requirements of the IEC 60044-3 standard. The task to determine the metrological characteristics of the CCVIT for the purposes of its correct design and further metrological application is a very tedious job, because of its very complicated electromagnetic system. The leakage reactances, determined by FEM-3D are the main contribution factors of the measurement uncertainty budget of the CCVIT and its four main metrological parameters. The CCVIT metrological optimal design is done by application of the genetic algorithm. A prototype of the CCVIT has been realized in the Instrument transformer production company, EMO A. D.-Ohrid, R. Macedonia. High voltage testing has been done over the prototype according to the IEC 60044-3 standard. CCVIT metrological improvement has been achieved. PEL is operating as part of Department of Electrical Engineering Fundamentals and Measurements, Faculty of Electrical Engineering and Computing in Zagreb, Croatia (FER). It is a national measurement and calibration laboratory for electrical quantities since 2006, after acquiring accreditation in accordance with the ISO 17025 from German DKD service. PEL is primarily scientific and research laboratory where new measurement methods are developed, like the Rogowski coil. A Rogowski coil is well-known currentto- voltage transducer, and in order to use it for the high-accuracy measurement of AC current (at power supply frequency) all influencing quantities and their contribution are analyzed. The measured deviation of the mutual inductance of realized model is in very good agreement with the theoretical prediction, which gives possibility to the construction of sensor for laboratory application. This research results in precise instrument transformer, which is based on rigid Rogowski coils in astatic coupling and designed for AC current measurement in range of 0, 1 A to 20 A and frequencies up to 1 kHz.

Instrument transformers; Rogowski coil

nije evidentirano