Siemens siprotec 7SA6, Manual

Page: 198 / 876

Functions
6-8
7SA6 Manual
C53000-G1176-C156-2
When connected to the e-n winding of a set of voltage transformers, the voltage
transformation ratio of the voltage transformers is usually:
In this case the factor
Uph / Udelta
(address
0211
, matching ratio for the sec-
ondary nominal voltages of phase voltage transformers and open-delta voltage)
must be set to 3/
√
3 =
√
3
≈
1.73. For other transformation ratios, e.g. when the dis-
placement voltage is generated by means of interposing transformers, this factor
must be adjusted accordingly. This factor is of importance for the monitoring of the
measured values and the scaling of the measurement and disturbance recording
signals.
•
In case the busbar voltage is connected to the U4 input for synchronism check, refer
also to Appendix A, e.g. Figures A-46 or A-47. In this case address
210
is set to:
U4 transformer
=
Usync transf.
If the transformation ratio differs from that of the line voltage transformers this can
be adapted with the setting in address
215 U-line / Usync
. In address
212
Usync connect.
, the type of voltage used for synchronism check is configured.
According to this setting, the device automatically selects the appropriate phase to
phase or phase to ground voltage. If the two voltages used for synchronism check
— i.e. line voltage and busbar voltage — are not separated by a unit that causes a
relative phase shift of the measured voltages (e.g. star-delta power transformer)
then the parameter in address
214
ϕ
Usync-Uline
is not required. If however a
transformer with a vector group unequal to zero separates the two voltage sources,
this setting must be used to compensate the phase shift according to the vector
group of the transformer. This setting can only be modified with DIGSI
®
4 under
“Additional Settings”.. The phase angle setting is defined as follows: place Usync
at zero degrees as reference voltage, draw in Uline with the correct phase relation-
ship relative to Usync; the setting corresponds to the angle of
Usync
measured in
counter-clockwise direction.
Example (refer also to Figure 6-9):
Busbar 400kV primary
110 V secondary
Feeder 220 kV primary
100 V secondary
Transformer 400 kV / 220 kV
Vector group Dy(n) 5
The vector group of the transformer defines the phase shift of the voltage from the
high voltage to the low voltage side (Vector group 5 corresponds to a phase shift of
5 x 30
°
in the clockwise direction of the low voltage side relative to the high voltage
side). In this example, the feeder voltage is connected to the low voltage side of the
transformer. If Usync (busbar or high voltage side) is placed at zero degrees, then
Uline is at 5 x 30
°
in the clockwise direction, i.e. at –150
°
. According to the definition
for the setting, the angle from
Usync
to
U-line
in the counter-clockwise direction
must be taken, i.e.
+ 210
°
.
Address
214A
:
ϕ
Usync-Uline
= 360° - 150° = 210°
Since the busbar voltage transformer provides 110 V secondary with nominal pri-
mary voltage and the line voltage transformer 100 V under the same conditions, this
difference must also be considered:
U
Nprim
3
------------------
U
Nsec
3
----------------
U
Nsec
3
----------------
⁄ ⁄