Definition of a New Graphic Pattern for Single Phase to Ground Fault in the Power Plant and Effects of the Neutral Grounding Impedance on It

The grounding system of the step-up transformers is one of the main issues in power plants especially in large industries such as petrochemicals and refineries. In addition to the effects of this system on the fault currents and voltages magnitude, the dynamic behavior of the generators is also affected at fault duration by the neutral grounding impedance. In this paper, at first analytical expressions of some parameters such as current, active power, and power angle of the generator are derived for a phase to ground fault. Then the validation of derived equations is examined by simulation of a real power plant located in a petrochemical complex. At last, these equations will be used to define a new graphic pattern of fault which is the locus of the active power vs short circuit current. The shape of this pattern is related to the type of the fault and grounding impedance. Hence it can be used to identify some faults in the power systems.