Siemens SIPROTEC 6MU805, Руководство пользователя, Страница: 27 / 162

Functions
2.1 General
SIPROTEC, 6MU805, Manual
C53000-G1140-C380-5, Release date 06.2018
23
Internal Normalization of the Measured Voltages
The capacitance values for the three voltage inputs are usually not identical. Then, voltages identical on the
primary side are mapped differently at the voltage inputs. The measured voltages are normalized by the device
so that the three phase-to-ground voltages can be correctly used in calculation (e.g. to calculate the phase-to-
phase voltages of the positive sequence system and of the negative sequence system etc.). By normalizing,
the same primary nominal voltages result to same secondary nominal voltage, even though the real voltages
at the input terminals are different.
When you set the address 0461
PhaseIndepRatio
as
Enabled
, the device offers 4 parameters to set the
channel rated secondary voltage at address 0571, 0573, 0575, and 0577.
The setting of secondary nominal voltage should be roughly equivalent to the primary nominal voltage. If ca-
pacitive voltage measurement is selected, a setting range of 34 V to 140 V is sufficient for this parameter.
Impact of the Capacitive Voltage Measurement
Capacitive voltage measurement can cause increased tolerances for all voltage-dependent protection func-
tions due to an unfavorable capacitance ratio to the rated voltage.
Nominal Values of Current Transformers (CTs) (Only For 3-phase System)
At addresses
0204 CT PRIMARY
and 0
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
0217 Ignd-CT PRIM
and
0218 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),
0217 Ignd-CT PRIM
and
0204 CT PRIMARY
must be set to the same
value.
Nominal Values of Current Transformers (CTs) (Only For 1-phase System)
Currently 4 channels current are supported. Each channel has its own configuration regarding to the primary
and secondary ampere ratings of the current transformers. Address 0
562, 0564, 0566, 0568
are for Channel
Rated Primary Current Values, and Address 0
563, 0565, 0567, 0569
are for Channel Rated Second Current
Values. These addresses are important to ensure that the rated secondary current of the current transformer
matches the rated current of the device, otherwise the device will calculate incorrectly.
Nominal Values of Voltage Transformers (VTs) (Only For 3-phase System)
At addresses
0202 Vnom PRIMARY
and
0203 Vnom SECONDARY
, information is entered regarding the
primary nominal voltage and secondary nominal voltage (phase-to-phase) of the connected voltage transform-
ers.
At addresses
0333 Vnom prim Vx
and 0
325 Vnom sec Vx
, you can enter the primary and secondary rated
voltage for the 4th voltage input Vx.
Matching Ratio
With the parameter
Vph/Vdelta
at address 0206A, you set the deviation between the calculated zero-sequence
voltage and the residual voltage measured directly via a measurement input. The different transmission ratio
of the voltage transformers is the cause for the deviation. The zero voltage is calculated as phase-to-ground
voltages. The residual voltage is measured on the open delta winding of the voltage transformer. For single-
phase voltage transformers, the residual voltage is measured in the generator or the transformer neutral point.