3.22 Ground Differential Protection (Function Groups REF_1 to
REF_3)
The ground differential protection function (Br.: restricted earth fault protection)
can be applied to transformer windings with grounded neutral point where the
neutral-point-to-ground connection is fitted with a current transformer.
One ground differential protection function is available per transformer winding.
The P634 display shows the winding end associated with a particular ground
differential protection function. Connection for and operation of the ground
differential protection function will now be presented with end a as an example.
Equivalent considerations apply to end b and c.
Ground differential protection may be applied to transformer ends with a
grounded neutral-point, but in this case the neutral-point-to-ground connection
must be fitted with a CT.
Ground differential protection is based on comparing the vector sum I
N
of the
phase currents of the relevant transformer end to the neutral-point current I
Y
.
The P634 calculates the vector sum of the phase currents. For the connection,
see Section 3.12.1, (p. 3-63).
3.22.1 Enabling or Disabling Ground Differential Protection
Ground differential protection can be enabled or disabled from the local control
panel; see also Fig. 3-99, (p. 3-142). Moreover, enabling can be done separately
for each parameter subset.
3.22.2 Blocking ground differential protection
Blocking of the ground differential protection functions when the DIFF protection
was triggered may be enabled or disabled using setting parameters.
Furthermore, binary signal input functions (REF_1: Blocking EXT, for example)
are available to allow for a more flexible application of the functions. Since
operational readiness is no longer solely dependent on the device setting, the
readiness of ground differential protection is also indicated (by means of the
REF_1: Ready state, for example).
3 Operation P634
P634/EN M/R-42-A // P634‑311‑653 3-141
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