Functions
2.1 General
SIPROTEC, 7SK80, Manual
E50417-G1140-C344-A4, Release date 08.2010
43
Nominal Values of Current Transformers (CTs)
At addresses 204 CT PRIMARY and 205 CT SECONDARY information is entered regarding the primary and
secondary ampere ratings of the current transformers. It is important to ensure that the rated secondary current
of the current transformer matches the rated current of the device, otherwise the device will calculate incorrect
primary data. At addresses 217 Ignd-CT PRIM and 218 Ignd-CT SEC, information is entered regarding the
primary and secondary ampere rating of the current transformers. In case of a normal connection (starpoint
current connected to I
N
transformer), 217 Ignd-CT PRIM and 204 CT PRIMARY must be set to the same
value.
If the device features a sensitive ground current input, parameter 218 Ignd-CT SEC is set to 1 A.
For US device models (order item 10= C) parameters 205 and 218 are set by default to 5 A.
If address 251 CT Connect. has been set so that ground currents are measured by two inputs (setting options
A,G2,C,G; G->B or A,G2,C,G; G2->B), you have to enter the primary rated current at address 238
Ignd2-CT PRIM. and at address 239 Ignd2-CT SEC. the secondary rated current of the second ground
current transformer connected to I
N2
.
For proper calculation of phase current I
B
, the primary rated current of the ground current transformer, which is
used for the calculation of I
B
(address 217 or address 238), must be lower than the primary rated current of
the phase current transformer (address 204).
Nominal Values of Voltage Transformers (VTs)
At addresses 202 Vnom PRIMARY and 203 Vnom SECONDARY, information is entered regarding the primary
nominal voltage and secondary nominal voltage (phase-to-phase) of the connected voltage transformers.
Transformation Ratio of Voltage Transformers (VTs)
Address 206 Vph / Vdelta informs the device of the adjustment factor between the phase voltage and the
displacement voltage. This information is relevant for the processing of ground faults (in grounded systems and
ungrounded systems), for the operational measured value V
N
and measured-variable monitoring.
If the voltage transformer set provides open delta windings and if these windings are connected to the device,
this must be specified accordingly in address 213 (see above margin heading "Voltage Connection"). Since the
voltage transformer ratio is normally as follows:
the factor V
ph
/V
N
(secondary voltage, address 206 Vph / Vdelta) must be set to 3/ √3 = √3 = 1.73 which
must be used if the V
N
voltage is connected. For other transformation ratios, i.e. the formation of the displace-
ment voltage via an interconnected transformer set, the factor must be corrected accordingly.
Please take into consideration that also the calculated secondary V
0
-voltage is divided by the value set in
address 206. Thus, even if the V
0
-voltage is not connected, address 206 has an impact on the secondary op-
erational measured value V
N
.
If Vab, Vbc, VGnd is selected as voltage connection type, parameter Vph / Vdelta is used to calculate
the phase-to-ground voltages and is therefore important for the protection function. With voltage connection
type Van, Vbn, Vcn, this parameter is used only to calculated the operational measured value of the „sec-
ondary voltage V
N
“.
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