IEC 61869-2 standard claims, CT test can be done in lower frequency than the rated, and avoid secondary windings the risk of failing to allow the terminal voltage.

The frequency of CT iron core’s excitation knee point voltage is proportional to the applied voltage’s frequency. For example, for a knee point 5000V, power frequency 50Hz CT, if we let the test voltage frequency down to 5Hz, the knee point becomes 500V. If the test frequency is down to 1Hz, the knee point becomes 100V. For relatively high knee point CT such as 5000V/1A knee point, the instrument output power is greater than 5000VA, then the volume of this instrument will be very large, very heavy weight. So by reducing the frequency, we can significantly reduce the output voltage and power of the instrument to 100V/1A. The excitation characteristics test of CT knee point up to 5000V can be completed, which only need 100VA.

The CT/PT Analyzer CTP-200P developed by HAOMAI is the revolutionary testing system for various CTs and PTs according to IEC and IEEE/ANSI standard. The Analyzer can automatically complete the test within seconds by one click of the patented multifunctional rotary mouse. It allows to test the knee-point voltage up to 40kV CTs and PTs on-site in power grids or in manufacturers' production facilities or test labs.