A Novel Loss of Excitation Protection Principle for Synchronous Condenser Based on Leading Rate

There is a fundamental difference between loss of excitation protection of synchronous condenser and generator. The low excitation limit of synchronous condenser is very low, which is close to leading reactive power when full loss of excitation occurs. Loss of excitation protection may maloperate when synchronous condenser operating under low excitation limit. Moreover, the power angle cannot be applied to constitute protection criterion. The stepped characteristic curve is adopted by the existing loss of excitation protection of synchronous condenser which resulting in protection dead zone. Under high system voltage condition, the existing protection may refuse to operate when partial loss of excitation occurs. A novel loss of excitation protection principle for synchronous condenser based on leading rate is proposed in this paper. The stator side plane and the rotor side plane are constructed respectively by using stator internal potential and excitation voltage. The characteristic curve based on hyperbolic function is proposed to avoid the dead zone. The leading rate detector is proposed to distinguish partial loss of excitation and normal regulation under high system voltage condition. In addition, blocking criterion is introduced in this paper to prevent the maloperation of leading rate detector when sudden increase of system voltage occurs. The novel loss of excitation protection reliably operates when partial loss of excitation occurs under high system voltage condition. The reliability and sensitivity of loss of excitation protection is substantially improved. The PSCAD simulation results verify the inadequacy of existing protection and the superior performance of novel protection principle .