A Novel Inverse Time Protection Scheme of Large Generator Based on Polynomial Optimal Fitting

摘要

Inverse time protection is a typical backup protection for large generator, and the suitable setting value is critical to ensure the security of both the generator and power system. The existing protection setting methods recommended by the standard or specification cannot meet the coordination relationship of the protection, and the determined operating time may exceed the generator's affordability. A polynomial optimal fitting based inverse time protection for large generator is proposed in this paper. Firstly, the operation characteristic of the protection is determined according to the heating process of the generator under abnormal conditions. The least square method is then used to fit the coefficients in the characteristic expression. Finally, the proposed method is tested by actual generator parameters, and the results demonstrate that the protection can achieve the optimal matching between the operation characteristic and the generator capacity curve. Besides, the protection can operate in a time extremely close to the maximum ability of the generator, which means to provide more effective support for the power system while ensuring the generator safety.