Wide Range Measurement Theory And Practical Method For Current Transformers

In some place of electric system, the load change wide range and the existing current transformers can't meet the measure request. On the base of consulting a great amount of materials, a deep research on wide range current transformer by active compensation was done in this paper. The author has finished the following several jobs in core of the centre:1) The active compensation method based on Bang-Bang control was put forward to realize the wide range current transformer. The method converts the complex statement space to I/O description by the two-stage current transformer. With the compensation method, the accuracy of 0.2 grade current transformer can be improved to less than the 0.1 grade standard at 100% rating when the primary side current is changed from 2% to 120% of the rating.2) An efficient model based on physical similarity was made to simulate the current transformers' nonlinear magnetizing characteristics and to compensate error from outside. A similar magnetizing current extracting method based on Bang-Bang control was advanced to maximally extract the similar magnetizing current. This method can effectively compensate the current error caused by magnetizing current at power frequency.3) Because most current transformers have the turn compensation, the characteristic of which was analyzed and the anti-turn compensation model was adopted to offset the action for current transformer with turn compensation.4) A comprehensive active electronic compensation is given which keeps the characteristics of the similar magnetizing current compensation and adds the function of anti-turn compensation. The constitution of the compensation is simplified, and the working area is enlarged by anti-turn compensation method. The coordination control between the angle error and the ratio error was realized through analyzing the common characteristics between the similar magnetizing current compensation and the anti-turn compensation. With the compensator, the accuracy of an 2 grade current transformers can be improved to less than the 0.2 grade standard at 100% rating when the primary side current is changed from 2% to 120% of the rating.