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18
Field Testing and Commissioning
Measured Values of the Restricted Ground Fault
Protection
The current Io* and Io** are referred to the rated relay
current and correspond to the values Io' and Io" which
are relevant for the actual protection function.
Io* is the current that flows through the star-point
current transformer. Io** is the sum of the phase
currents. When the rated primary currents of all these
CTs are equal, the Io* and Io** are almost equal.
If the display shows undefined values, such as "****",
the test arrangement must be checked as well as the
assignment of the additional measured current inputs
IA and IB (addresses 7806 and 7807).
The display of the measured current of the star-point
in Address 4181, referred to the relay current, should
be approximately the star-point current.
The display of the sum of the phase currents, referred
to rated relay current, should be approximately three
times the phase current.
The phase angle between Io* and Io** must be 0
o
is 180
, the star-point CT has wrong polarity. Recheck
and correct the related parameters:
•
Address 1108, when Winding 1 is assigned to the
restricted ground-fault protection, i.e.,
Address 7806 on SIDE 1 for current input IA or
Address 7807 on SIDE 1 for current input IB.
•
Address 1128, when winding 2 is assigned to the
restricted earth fault protection, i.e., Address 7806
on SIDE 2 for current input IA or Address 7807 of
SIDE 2 for current input IB.
•
Address 1148, when winding 3 is assigned to the
restricted earth fault protection, i.e., Address 7806
on SIDE 3/V. OBJ for current input IA or
Address 7807 on SIDE 3/V. OBJ for current
input IB.
•
Address 1405, when a virtual object is assigned to
the restricted earth fault protection, i.e.,
Address 7806 on SIDE 3/V. OBJ for current input
IA or Address 7807 on SIDE 3/V. OBJ for current
input IB.
204
Before the tests are terminated, the differential and
stabilizing currents are checked. When assessing the
currents, note that the differential and stabilizing
values are referred to the rated current of the
protected object. If considerable differential currents
occur, recheck the concerned parameters:
•
Address 1107, when Winding 1 is assigned to the
restricted ground-fault protection, i.e.,
Address 7806 on SIDE 1 for current input IA or
Address 7807 on SIDE 1 for current input IB.
•
Address 1127, when winding 2 is assigned to the
restricted ground-fault protection, i.e.,
Address 7806 on SIDE 2 for current input IA or
Address 7807 on SIDE 2 for current input IB.
•
Address 1147, when winding 3 is assigned to the
restricted ground-fault protection, i.e.,
Address 7806 on SIDE 3/V. OBJ for current input
IA or Address 7807 on SIDE 3/V. OBJ for current
input IB.
•
Address 1404, when virtual object is assigned to
the restricted ground-fault protection, i.e.,
o
. If it
Address 7806 on SIDE 3/V. OBJ for current input
IA or Address 7807 on SIDE 3/V. OBJ for current
input IB.
The display of the differential current in Address 4181,
referred to the rated current of the protected object,
should correspond approximately to the star-point
current.
The display of the stabilizing (restraint) current,
referred to the rated current of the protected object,
should correspond approximately to twice the
star-point current.
The zero sequence current tests are now complete.
Disconnect the protected object and ground. Remove
the test arrangement.
7UT51 v3
PRIM-2330C
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