Monitoring Method of Injection-type Generator Stator-to-earth Insulation State in Neutral Point Combined Grounding Mode

Aiming at the incompatibility of the existing protection method for the measurement of the ground insulation state under the combined grounding method of the generator stator neutral point (resistance parallel reactor on the secondary side of the grounding transformer), an injection-type monitoring method of insulation state of generator stator to ground in neutral point combined grounding mode is proposed in this paper. By connecting the variable frequency power injecting AC variable frequency signal supplied to the secondary side of the arc suppression coil reactor at the neutral point of the generator, it can search the resonance frequency of stator inductance and capacitance, and calculate the insulation state caused by the insulation damage of stator winding. So it can achieve the purpose that generator stator's insulation state can be real-time monitored. Through modeling and analysis in PSCAD/EMTDC, this method can be adapted to the measurement of the ground insulation state under the combined grounding mode of the generator stator neutral point and obtain the size of the excessive resistance.