Schweitzer Engineering Laboratories SEL-700G Series, Инструкция по эксплуатации

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4.27
Date Code 20170814 Instruction Manual SEL-700G Relay
Protection and Logic Functions
Group Settings (SET Command)
There are two criteria for setting TH5P:
TH5P

minimum (0.05 • INOMn/TAPn)
where:
n = X, Y
INOMn = nominal current of the corresponding CT
Example of Setting the SEL-700G Relay (Unit Differential).
The
example represents a typical unit differential application and demonstrates the
use of CT compensation settings and tap calculations.
Figure 2.20 illustrates the application. The transformer is a 138 kV to 13.8 kV.
The transformer has a maximum rating of 30 MVA. Both windings have wye-
connected current transformers, with ratios of 200/5 A at 138 kV, and 2000/
5 A at 13.8 kV. We have connected the transformer per IEEE standards, with
the low voltage delta lagging the high-voltage wye by 30 degrees.
Step 1. Enable the differential settings as follows:
E87 := TRANS
Step 2. Select settings for the current transformer connection and ratio
for each winding. All CTs connect in wye. The ratios are equal
to primary current divided by secondary current. The settings
are as follows:
Step 3. Set the transformer maximum rating. We use this rating for all
windings in the later tap calculation:
MVA := 30
Step 4. Decide whether to use internal CT compensation and determine
compensation settings.
Because there are both wye and delta transformer windings but
only wye CTs, we must adjust for the phase angle shift. In the
“traditional” differential relay connection the wye transformer
windings would have their CTs connected in delta to produce a
shift in the same direction as that produced in the transformer.
In this case a “DAC” or “30-degree lagging” connection would
have been used. This would not only shift the currents, but it
would remove the zero-sequence current component by
physically subtracting the appropriate phase currents via the
delta connection. We achieve the same effect within the relay
by using the selected compensation. The settings are:
The relay will multiply the wye CT currents from the wye
transformer windings by the matrix [CTC(11)] to give the same
results as the physical DAC CT connection.
Step 5. Enter winding line-to-line voltages. The relay needs these
voltages for the tap calculation. Voltages are in units of kV. For this
example we enter the following values:
138 kV 13.8 kV
CTCONX = WYE (hidden) CTCONY = WYE
CTRX = 400 CTRY = 400
ICOM := Y (choose to define the CT compensation)
CTCX := 0
CTCY = 11
VWDGX = 13.80 VWDGY = 138.00
NOTE:
Setting CTCX is not available
for changing. It is hidden and set
automatically by the relay.