On-line stator ground-fault location method for synchronous generators based on 100% stator low-frequency injection protection

• The ground fault can be located in on-line operating conditions.
• The fault resistance value is obtained by the low-frequency injection protection.
• The effect of the capacitance to ground of the system is very determinant.
• This location algorithm provides acceptable results in a laboratory scale machine.

Locating stator-winding ground faults accurately is a very difficult task, especially in high-impedance grounded generators. Through the conventional measurements of power plants, obtaining the precise location of these defects in on-line operating conditions is not possible, because the fault resistance is unknown. This paper presents a general algorithm for locating stator-winding ground faults in on-line operating conditions, based on the measurements provided by the 100% ground-fault low-frequency injection protection, and other available measurements. Some simplifications are applied to the general algorithm, and a simplified method is also presented for generators with especially low capacitance-to-ground, whose implementation in modern protective relays is more simple. The location through the general algorithm, and the simplified algorithms, has been validated by simulation and experimental tests, for several fault resistance values at different points of the stator winding. These algorithms assure an acceptable accuracy for a wide range of fault resistance values and locations, without the need of any additional equipment.