Sel SEL-787 - Table 4.2 Configurations and Ratings (Phase Cts, Power Transformer)

4.3
Date Code 20150130 Instruction Manual SEL-787 Relay
Protection and Logic Functions
Group Settings (SET Command)
Configuration
Settings
The winding CT connection settings are used to appropriately configure
protection (differential, overcurrent, etc.) and power metering functions.
The CT ratio settings configure the relay to accurately scale measured values
and report the primary quantities. Calculate the phase and neutral CT ratios by
dividing the primary rating by the secondary rating.
EXAMPLE 4.1 Phase CT Ratio Setting Calculations
Consider an application where the Winding 1 CT rating is 600:5 A.
Set CTR1 := 600/5 := 120.
Use the highest expected transformer rating, such as the FOA (Forced Oil and
Air cooled) rating or a higher emergency rating, when setting the maximum
transformer capacity (MVA).
The ICOM setting defines whether the input currents need any correction,
either to accommodate phase shifts in the transformer or CTs or to remove
zero-sequence components from the secondary currents. If this setting is Y,
the relay permits the user, in the next group of settings, to define the amount of
shift needed to properly align the secondary currents for the differential
calculation.
The amount of compensation to each set of winding currents is defined by
settings W1CTC and W2CTC for Winding 1 and 2 respectively. These
settings properly account for phase shifts in transformer winding connections
and also in CT connections. For example, this correction is needed if both wye
and delta power transformer windings are present, but all of the CTs are
connected in wye. The effect of the compensation is to create phase shift and
removal of zero-sequence current components.
Set VWDG1 and VWDG2 equal to the nominal line-to-line transformer
terminal voltages of Winding 1 and Winding 2 respectively. If the transformer
differential zone includes a load tap-changer, assume that it is in the neutral
position. The setting units are kilovolts.
Table 4.2 Configurations and Ratings (Phase CTs, Power Transformer)
Setting Prompt Setting Range
Setting Name :=
Factory Default
WDG1 CT CONN DELTA, WYE W1CT := WYE
WDG2 CT CONN DELTA, WYE W2CT := WYE
WDG1 PHASE CTR 1–10000 {5 A IW1NOM}
1–50000 {1 A IW1NOM}
CTR1 := 100
WDG2 PHASE CTR 1–10000 {5 A IW2NOM}
1–50000 {1 A IW2NOM}
CTR2 := 1000
MAX XFMR CAP OFF, 0.2–5000.0 MVA MVA := 50.0
DEFINE CT COMP Y, N ICOM := N
WDG1 CT COMP 0, 1, … 12 W1CTC := 12
WDG2 CT COMP 0, 1, … 12 W2CTC := 12
WDG1 L-L VOLTS 0.20–1000.00 kV VWDG1 := 138.00
WDG2 L-L VOLTS 0.20–1000.00 kV VWDG2 := 13.80