A Combined Electronic Current/Voltage Transformer Of High Voltage

With the popularization of embedded system and communication technology and the extension of IEC61850 protocol, the Intelligent Grid becomes the significant reform direction. As an important component of the Intelligent Grid, the digital substation has a number of advantages, such as digital output, networking and unification.As a key equipment of the digital substation process layer, electronic instrument transformer has the following advantages:digital output,easy insulation, large dynamic range, wide frequency response, high accuracy etc.It adapt the development trends of measurement and protection digitalization and automation. It is used for the measurement and monitoring of voltage/current, providing signal for the measurement and protection unit in bay level, guaranting a safe and reliable operation of the electric power system.This paper illustrates a combined electronic current/voltage transformer of high voltage based on air-core coil and coaxial capacitance sensor. Employing the simple but reliable insulation structure of conventional transformer and the unconventional sensing methods of electronic transformers at the same time, an innovative combined electronic instrument transformer is presented in this paper: Without high power laser apparatus, the reliability is improved; SF₆ coaxial capacitance enhance the anti-interference ability; Combined structure reduce the cost; Disappearance of Basin Insulator will enhance the dielectric strength greatly.The advantages and disadvantages of conventional and electronic transformer are summed up, the whole structure is designed, the measuring principle of air-core coil and coaxial capacitance are gived. Two kind combined transformer are completed, the rated voltage value are 220kV/ 3 ,110/ 3 kV, the rated current are 600A, 2500A. The experimental results of State Grid Electric Power Research Institute shows that the voltage transformer meet the requirement of the 0.2 level in IEC60044-8,the current transformer meet the requirement of the 0.2S level in IEC60044-7. The combined transformer of 110/ 3 kV has been running in the Di Shuijing substation of Hunan Power Grid.