Chen Xianshun

Error analysis of capacitor voltage transformer in the operation environment

The capacitor voltage transformer (CVT) is a potential transformer (PT) composed of capacitive voltage divider and electromagnetic unit. In high voltage classes, the capacitor voltage transformer has the advantage of simpler structure and lower cost in comparison with electromagnetic potential transformer (PT), so potential transformers with voltage class of 220kV and above are CVT basically. Transformer acts as an important link of power trade measuring system, and its accuracy is directly related to the justness and fairness of power trade. CVT at transformer substation is usually installed outdoor and often runs in different natural environments, while periodic detection is adopted for CVT, but there is no relevant research on the impacts of CVT error characteristics from the natural environment during actual operation. In this paper, online monitoring system is used to compare a good-stability bus with line CVT, taking PT as standard, so as to research the CVT error characteristics in actual operation cases. As the result indicated, ratio error and angle error of the CVT present regular changes within 24h, two extreme inflection points of the ratio error respectively occur at 6:00 a.m. and 4:00 p.m., representing shifting towards negative values, similar phase errors, but no out-of-tolerance.

Simulation on influence of external electric field on error characteristics of CVT

Actual operation showed that the measurement error of capacitive voltage transformer (CVT) was influenced electric field. To study the error characteristic of CVT causing by external electric field, the paper established simulation model by using finite element simulation software (Ansoft Maxwell 14.0). The simulation results indicated that the measurement error increased gradually with the increase of the height (H) in a certain range. When the height(H) was beyond 4.5 meters, the measurement error was stable. When the distance(D) was less than 3.5 meters, the measurement error decreased. The error was linear with the voltage(U) of the object and the linearity was both related with distance (D) and height (H). The change in angle, diameter and length of high-voltage lead would also result in the change of capacitance of capacitive divider and bring errors.