Siemens siprotec 7SD5 User Manual page 57

the current transformers have different nominal currents at the ends of the protected
object, set the highest nominal current value for all ends.
This setting will not only have an impact on the indication of the operational measured
values in per cent, but must also be exactly the same for each end of the protected
object, since it is the basis for the current comparison at the ends.
Topological Data The statements under this margin heading apply to cases where the differential pro-
for Transformers tection has been configured as the main protection function and where a power trans-
(optional) former is situated within the protected zone (i.e. to models with transformer option, or
if address 143 TRANSFORMER has been set to YES, see Section 2.1.1.3). If no trans-
former is part of the protected zone, this paragraph can be passed over.
The topological data make it possible to relate all measured quantities to the nominal
data of the power transformer.
With address 1103 FullScaleVolt. you inform the device of the primary nominal
voltage (phase-to-phase) of the transformer to be protected. This setting is also
needed for computing the current reference value of the differential protection. There-
fore, it is important to set the correct nominal voltage for each end of the pro-
tected object even if no measured voltages are applied to the relay.
In general, select the nominal voltage of the transformer winding facing the device.
However, if the protected transformer is equipped with a voltage tap changer at one
winding, then do not use the nominal voltage of that winding but the voltage that cor-
responds to the mean value of the currents at the ends of the control range of the tap
changer. In this way the fault currents caused by voltage regulation are minimized.
Calculation example:
Transformer
This results for the regulated winding (110 kV) in:
maximum voltage
minimum voltage
Setting voltage (address 1103)
The OPERATION POWER (address 1106) is the direct primary nominal apparent power
for transformers and other machines. For transformers with more than two windings,
state the winding with the highest nominal apparent power. The same operation
power value must be set for each end of the protected object since it is the basis
for the current comparison at the ends.
The power must always be entered as a primary value, even if the device is generally
configured in secondary values. The device calculates the nominal current of the pro-
tected winding from this power.
The VECTOR GROUP I (address 1162) is the vector group of the power transformer,
always from the device's perspective. The device which is used for the reference end
of the transformer, normally the one at the high voltage side, must keep the numerical
7SD5 Manual
C53000-G1176-C169-1
YNd5
35 MVA
110 kV / 25 kV
Y–winding with tap changer ±10 %
U = 121 kV
max
U = 99 kV
min
2.1 General
57