4.35
Date Code 20100129 Instruction Manual SEL-751A Relay
Protection and Logic Functions
Voltage-Based Protection
Voltage Input VS Connected Phase-to-Phase or Beyond Delta-Wye
Transformer
Sometimes synchronism-check voltage VS cannot be in phase with voltage
VA, VB, or VC (wye connected PTs); or VAB, VBC, or VCA (delta-
connected PTs). This happens in applications where voltage input VS is
connected
➤ Phase-to-phase when using a wye-connected relay
➤ Phase-to-neutral when using a delta-connected relay
➤ Beyond a delta-wye transformer
For such applications requiring VS to be at a constant phase angle difference
from any of the possible synchronizing voltages (VA, VB, or VC; VAB, VBC,
or VCA), an angle setting is made with the SYNCPH setting (see Table 4.19
and Setting SYNCPH on page 4.35).
Setting SYNCPH
Enable the two single-phase synchronism-check elements by setting E25 := Y.
Wye-Connected Voltages
NOTE: Settings SYNCPH := 0 and
SYNCPH := VA are effectively the
same (voltage VS is directly
synchronism checked with voltage VA;
VS does not lag VA). The relay will
display the setting entered (SYNCPH
:= VA or SYNCPH := 0).
The angle setting choices (0, 30, …, 300, or 330 degrees) for setting SYNCPH
are referenced to VA, and they indicate how many degrees VS constantly lags
VA. In this case, voltage input VA-N has to be connected and has to meet the
“healthy voltage” criteria (settings 25VHI and 25VLO—see Figure 4.21). For
situations where VS cannot be in phase with VA, VB, or VC, the angle setting
choices (0, 30, …, 300, or 330 degrees) are referenced to VA.
Table 4.19 Synchronism-Check Settings
Setting Prompt Setting Range
Setting Name :=
Factory Default
SYNCH CHECK Y, N E25 := N
VS WINDOW LOW 0.00–300.00 V 25VLO := 105.00
VS WINDOW HIGH 0.00–300.00 V 25VHI := 130.00
V RATIO COR FAC 0.50–2.00 25RCF := 1.00
MAX SLIP FREQ 0.05–0.50 Hz 25SF := 0.20
MAX ANGLE 1 0–80 deg 25ANG1 := 25
MAX ANGLE 2 0–80 deg 25ANG2 := 40
SYNCH PHASE VA, VB, VC, or 0, 30, 60, 90, 120,
150, 180, 210, 240, 270, 300, 330
deg lag VA
a
a
Range shown for DELTA_Y := WYE
SYNCPH := VA
SYNCH PHASE VAB, VBC, VCA, or 0, 30, 60, 90,
120, 150, 180, 210, 240, 270, 300,
330 deg lag VAB
b
b
Range shown for DELTA_Y := DELTA
SYNCPH := VAB
BRKR CLOSE TIME OFF, 1-1000 ms TCLOSD := 50
BLK SYNCH CHECK SV BSYNCH := 52A
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