Injecting-VFVV-Source Based Protection Scheme For Stator Single Earth-fault Of Generator

ABSTRACT:Injecting voltage scheme for stator ground protection of the generator has some good characteristics, such as no influence from operating conditions, high sensitivity, no dead zone, and so on. It can not only measure the stator ground fault resistance in the range of 100%, but also reflect the decline of stator winding insulation, and play a role of monitoring the aging of the insulation. So it has a wide range of application prospects.But for the current injecting 20Hz voltage protection principle, there exists the operating dead zone during the generator starting and stopping, and the amplitude of output square-wave voltage of the protection device is not adjustable. This paper proposed an improved protection scheme, using injecting variable frequency and amplitude voltage(VFVV). Thus, the interference from the operating frequency of generator is eliminated, and the sensitivity of protection devices applicated in different operating situations is also improved.By analyzing and researching the setting value of grounding resistance, this paper proposed a kind of self-adaptive setting scheme, which achieved self adaptive stator grounding protection according to the allowable value of ground current for injecting electric source.This paper proposed the scheme of application of injecting 20Hz source-based stator ground fault protection for generators in the expanded unit connection, which solved the problem that the current injection of stator ground protection does not have selectivity. The scope of application for the injecting scheme is expanded, too.The variable frequency and amplitude power source is used to achieve the injection generator rotor ground fault protection scheme based on stator ground fault protection device. The new scheme eliminates the impact of the excitation voltage fluctuation to grounding resistance calculation, and increases the sensitivity of injection generator rotor ground fault protection.The hardware platform for injection variable frequency and amplitude generator stator ground fault protection device was completed. The performance of protection device was tested on this platform. And the stator ground fault protection experiments were also accomplished. The experimental results prove that the designed protection devices are sensitive and reliable.