Figure 280: Low voltage test arrangement. The three-phase low voltage source can
be the station service transformer.
The
Tapped winding
control setting parameter has to be set to “Not in use” to make
sure that the monitored current values are not scaled by the automatic adaptation
to the tap changer position. When only the angle values are required, the setting
of
Tapped winding
is not needed since angle values are not affected by the tap
changer position adaptation.
When injecting the currents in the high voltage winding, the angle values
I_ANGL_A1_B1, I_ANGL_B1_C1, I_ANGL_C1_A1, I_ANGL_A2_B2, I_ANGL_B2_C2
and I_ANGL_C2_A2 have to show +120 deg. Otherwise the phase order can be
wrong or the polarity of a current transformer differs from the polarities of the
other current transformers on the same side.
If the angle values I_ANGL_A1_B1, I_ANGL_B1_C1 and I_ANGL_C1_A1 show -120
deg, the phase order is wrong on the high voltage side. If the angle values
I_ANGL_A2_B2, I_ANGL_B2_C2 and I_ANGL_C2_A2 show -120 deg, the phase order
is wrong on the low voltage side. If the angle values I_ANGL_A1_B1, I_ANGL_B1_C1
and I_ANGL_C1_A1 do not show the same value of +120, the polarity of one current
transformer can be wrong. For instance, if the polarity of the current transformer
measuring IL2 is wrong, I_ANGL_A1_B1 shows -60 deg, I_ANGL_B1_C1 shows -60
deg and I_ANGL_C1_A1 shows +120 deg.
When the phase order and the angle values are correct, the angle values
I_ANGL_A1_A2, I_ANGL_B1_B2 and I_ANGL_C1_C2 usually show ±180 deg. There
can be several reasons if the angle values are not ±180 deg. If the values are 0
deg, the value given for
CT connection type
is probably wrong. If the angle values
are something else, the value for
Clock number
can be wrong. Another reason is
that the combination of
Winding 1 type
and
Winding 2 type
does not match
Clock
number
. This means that the resulting connection group is not supported.
Example
If
Winding 1 type
is set to "Y",
Winding 2 type
is set to "y" and
Clock number
is set to "Clk num 1", the resulting connection group "Yy1" is not a supported
combination. Similarly if
Winding 1 type
is set to "Y",
Winding 2 type
is set to
"d" and
Clock number
is set to "Clk num 0", the resulting connection group
"Yd0" is not a supported combination. All the non-supported combinations
of
Winding 1 type
,
Winding 2 type
and
Clock number
settings result in the
default connection group compensation that is "Yy0".
Protection functions
1MRS757644 H
544 620 series
Technical Manual
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