27Tn/59N - 100% Stator Ground Fault Protecton "Vx Meas H3" - Woodward High PROTEC MRU4 Manual

Protective Elements
27TN/59N - 100% Stator Ground Fault Protecton »VX meas H3«*
*=only available in Generator Protection Relays
With this setting the relay can detect stator ground faults at high impedance grounded generators near the
machines stator neutral.
In order to detect 100% Stator Ground faults, a 27TN element has to be or-connected with a 59N element within the
programmable logic.
With the 27TN element the 3 rd harmonic of the connected voltage is monitored at the generator neutral side. It is
able to detect ground faults, which occur between the stator neutral and up to approx. 20% of the winding towards
the stator terminals. In combination with the 59N element, that detects ground faults from the stator terminals down
to approximately 10% of the stator winding towards the neutral, a 100% stator ground fault protection can be
realized.
The following figure shows the combination of a 27TN with measuring criterion » VX meas H3« (third harmonic) and
a 59N element.
Both elements have to be or connected via Programmable logic.
In addition to that it is recommended to provide the 27TN element with a voltage release via a AND-Logic with an
59 element in order to prevent faulty tripping e.g. during generator standstill (see logic diagram next page).
392 MRU4 DOK-HB-MRU4-2E