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).
892 MCDGV4 DOK-HB-MCDGV4-2E
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