Generator Stator Earth Fault Relay (64G) - 27TN.

Generator Stator Earth Fault Relay   (64G) - 27TN.

-For high impedance grounded generators, a voltage relay across the secondary winding of the generator neutral grounding transformer is used to detect the ground fault on the generator stator winding.

-The neutral over voltage function (59N) responds to the fundamental frequency voltage at the generator neutral that appears when a ground fault occurs.

-Normally, it will protect up to 90≈ 95 % of the stator windings.

-The neutral under voltage functions responds to 3^rd harmonic voltage measured at the generator neutral. When used in conjunction with the neutral over voltage function, it provides 100% ground fault protection of the stator winding.

-In healthy state, the machine 3^rd harmonic voltage is distributed over the windings such that the maximum occur at the star point neutral and at the line terminal. For a ground fault close to the neutral, all the 3^rd harmonic voltage is transferred to the line terminals. Consequently, the relay function will see a 3^rd harmonic under voltage at the neutral end and will operate the protection element.