ABB RELION REX640 Technical Manual page 736

Protection functions
If the neutral of a star-connected power transformer is earthed, any earth fault in
the network is perceived by the protection as differential current. The elimination of
the zero-sequence component can be selected to be on or off for that winding by
the
Commissioning
The settings for the connection group compensation (
shift Wnd 1-2 and, in case of a three-winding transformer, also CT connection
1-3 and Phase shift Wnd 1-3 settings) can be verified by monitoring the angle
values (I_ANGL_A1_B1, I_ANGL_B1_C1, I_ANGL_C1_A1, I_ANGL_A2_B2, I_ANGL_B2_C2,
I_ANGL_C2_A2, I_ANGL_A1_A2, I_ANGL_B1_B2 and I_ANGL_C1_C2 and in case
of three-winding transformer also I_ANGL_A3_B3, I_ANGL_B3_C3, I_ANGL_C3_A3,
I_ANGL_A1_A3, I_ANGL_B1_B3 and I_ANGL_C1_C3) when injecting the current into
the transformer. These angle values are calculated from the compensated currents.
When a station service transformer is available, it can be used to provide current
into the winding 1 side, for example, HV windings, while the winding 2 side, for
example, LV windings are short-circuited, as shown in
three-winding transformer, the tertiary winding side is short-circuited). This way
the current can flow both in high-voltage and low-voltage windings (and in winding
3 in case of three-winding transformer). The commissioning signals can also be
provided through other means. The currents need to be at least 0.015 pu to allow
the phase current and angle monitoring.
A1
B1
C1
Figure 420: Low-voltage test arrangement. The three-phase low-voltage source can
be the station service transformer, for example
The control setting
that the monitored current values are not scaled by the automatic adaptation to the
tap changer position. When only the angle values are taken, this is not needed since
the angle values are not affected by the tap changer position.
When injecting the currents into the HV 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,
and in case of three winding transformer, I_ANGL_A3_B3, I_ANGL_B3_C3 and
I_ANGL_C3_A3, should be +120.
Otherwise, the phase order may be wrong or the polarity of one 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°, the
phase order is wrong on winding 1, for example, the high-voltage side. If the angle
values I_ANGL_A2_B2, I_ANGL_B2_C2 and I_ANGL_C2_A2 show -120°, the phase
order is wrong on winding 2, for example, the low-voltage side. If the angle values
736
Zro A elimination setting. By default, the elimination is done for every winding.
3 phase
low voltage
source
Tapped winding should be set to value "Not in use" to ensure
CT connection 1-2 , Phase
Figure 420 (in case of a
YNyn0
1MRS759142 F
A2
B2
C2
REX640
Technical Manual