Differential Protection Based On The Harmonic Identification Computer Mother

It's well known that the saturation of current transformer (TA) can cause the misfunction of the busbar protection. This paper presents a new method which can reliably judges the saturation of TA and avoids this kind of misfunction. Firstly, in order to get the credible current wave of the saturate TA, a simulate program of TA is written, and a little TA which can easily saturates is also made. After analysing the characteristic of the saturate current wave, one method is put forward, it uses the harmonic portion of the current, including its magnitude and variety to restrain the protection. Base on further research, the harmonic restrain method is improved. Finally this method is realized in microprocessor based busbar protection, the result of a lot of experiments indicates that this protection can reliably avoid misfunction of the busbar protection, and when the fault is developed, the fault can be rapidly eliminated by the protection. This method avoids the conflict of reliability and security that exist in the conventional current percentage protection.