Sel SEL-421 - Synchronism-Check Voltage Reference; Normalized Synchronism

R.2.57
Date Code 20111215 Reference Manual SEL-421 Relay
Auto-Reclosing and Synchronism Check
Synchronism Check
Figure 2.25 Synchronism-Check Voltage Reference
For a given secondary base voltage, phase-to-phase voltages are a factor of
1.73 (3) times the magnitude of the phase-to-neutral voltages. In reverse,
phase-to-neutral voltages are a factor of 0.58 (1/3) times the magnitude of
the phase-to-phase voltages. Therefore, you must compensate the Bus 1
voltage V
BC
magnitude with setting KS1M to reference it to the synchronism-
check voltage reference V
P
magnitude.
KS1M := 0.58 Synchronism Source 1 Ratio Factor (0.10–3)
You do not need special magnitude compensation for the Bus 2 voltage V
C
to
reference Synchronism Source 2 to the synchronism-check voltage reference
V
P
magnitude; these are both phase-to-neutral voltages with the same nominal
rating (for example, 67 V secondary).
KS2M := 1.00 Synchronism Source 1 Ratio Factor (0.10–3)
As another example of synchronism-source magnitude adjustment flexibility,
suppose Bus 1 voltage V
BC
is 201 V secondary (phase-to-phase), and the
synchronism-check voltage reference V
P
is 67 V secondary (phase-to-
neutral). Then, the magnitude compensation setting would be as in
Equation 2.2.
Equation 2.2
Normalized Synchronism-Check Voltage Sources V
S1
and V
S2
The Figure 2.25 example continues in Figure 2.26, which graphically
illustrates how the introduced settings adjust the Bus 1 and Bus 2
synchronism-check input voltages in angle and magnitude to reference to the
synchronism-check voltage reference V
P
. The resultant Bus 1 and Bus 2
voltages are the normalized synchronism-check voltage sources V
S1
and V
S2
,
respectively.
V
BC
Voltage V
BC
Connected to
Voltage Input VAZ
Voltage V
C
Connected to
Voltage Input VBZ
SYNCS1 := VAZ
KS1M := 0.58
KS1A := 90
90˚
V
C
240˚
V
A
V
A
V
P
SYNCS2 := VBZ
KS2M := 1.00
KS2A := 240
Bus 2
Bus 1
Line
BK2
BK1
Synchronism-Check
Voltage Reference
Voltage V
A
connected to
Voltage Input VAY (other 2
three-phase line voltages not
shown). Voltage Input VAY
designated as synchronism-check
voltage reference by setting SYNCP := VAY.
1
3
1
. . . . . .
KS1M
67 V
201 V
---------------
0.33:= =