Functions
2.1 General
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
46
Voltage Connection
The device features four voltage measuring inputs, three of which are connected to the set of voltage trans-
formers. Various possibilities exist for the fourth voltage input U
4
:
• Connection of the U
4
input to the open delta winding Ue–n of the voltage transformer set:
Address 210 is then set to: U4 transformer = Udelta transf..
When connected to the e-n winding of a set of voltage transformers, the voltage transformation ratio of the
voltage transformers is usually:
The factor Uph/Udelta (secondary voltage, address 211 Uph / Udelta) must be set to 3/√3
= √3 ≈ 1.73.
For other transformation ratios, e.g. the formation of the displacement voltage via an interconnected trans-
former set, the factor must be corrected accordingly. This factor is important if the 3U
0
> protection stage is
used and for monitoring the measured values and the scaling of the measured values and fault recording
values.
• Connection of the U
4
input to perform the synchronism check:
Address 210 is then set to: U4 transformer = Usy2 transf..
If the voltage transformers for the protection functions U
sy1
are located on the outgoing feeder side, the U
4
transformer has to be connected to a busbar voltage U
sy2
. Synchronisation is also possible if the voltage
transformers for the protection functions U
sy1
are connected on busbar side, in which case the additional U4
transformer must be connected to a feeder voltage.
If the transformation ratio differs, this can be adapted with the setting in address 215 Usy1/Usy2 ratio.
In address 212 Usy2 connection, the type of voltage connected to measuring point U
sy2
for synchronism
check is set. The device then automatically selects the voltage at measuring point U
sy1
. If the two measuring
points used for synchronism check — e.g. feeder voltage transformer and busbar voltage transformer — are
not separated by devices that cause a relative phase shift, then the parameter in address 214 Ï• Usy2-
Usy1 is not required. This parameter can only be changed in DIGSI at Display Additional Settings. If, how-
ever, a power transformer is connected in between, its vector group must be adapted. The phase angle from
U
sy1
to U
sy2
is evaluated with positive sense.
Example
: (see also Figure 2-3)
Busbar 400 kV primary, 110 V secondary,
Feeder 220 kV primary, 100 V secondary,
Transformer 400 kV / 220 kV, vector group Dy(n) 5
The transformer vector group is defined from the high voltage side to the low voltage side. In this example,
the feeder transformers are those of the low voltage side of the transformer. Since the device „looks“ from
the direction of the feeder transformers, the angle is 5 · 30° (according to the vector group) negative, i.e. -
150°. A positive angle is obtained by adding 360°:
Address 214: ϕ Usy2-Usy1 = 360° - 150° = 210°.
The busbar transformers supply 110 V secondary for primary operation at nominal value while the feeder
transformers supply 100 V secondary. Therefore, this difference must be balanced:
Address 215: Usy1/Usy2 ratio = 100 V / 110 V = 0.91.
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