Schweitzer Engineering Laboratories SEL-351A - Page 109

3.37
Date Code 20080213 Instruction Manual SEL-351A Relay
Overcurrent, Voltage, Synchronism Check, and Frequency Elements
Synchronism Check Elements (Not in SEL-351A-1)
Setting SYNCP
Wye-Connected Voltages
The angle setting choices (0, 30, …, 300, or 330 degrees) for setting SYNCP
are referenced to V
A
, and they indicate how many degrees V
S
constantly lags
V
A
. In any synchronism check application, voltage input VA-N always has to be
connected to determine system frequency on one side of the circuit breaker (to
determine the slip between V
S
and V
A
). V
A
always has to meet the “healthy
voltage” criteria (settings 25VHI and 25VLO—see Figure 3.27). Thus, for
situations where V
S
cannot be in phase with V
A
, V
B
, or V
C
, it is most
straightforward to have the angle setting choices (0, 30, …, 300, or 330
degrees) referenced to V
A
.
Delta-Connected Voltages
The angle setting choices (0, 30, …, 300, or 330 degrees) for setting SYNC
are referenced to V
AB
, and they indicate how many degrees V
S
constantly lags
V
AB
. In any synchronism check application, voltage input VA-VB always has to
be connected to determine system frequency on one side of the circuit breaker
(to determine the slip between V
S
and V
AB
). V
AB
always has to meet the
“healthy voltage” criteria (settings 25VHI and 25VLO—see Figure 3.27).
Thus, for situations where V
S
cannot be in phase with V
AB
, V
BC
, or V
CA
, it is
most straightforward to have the angle setting choices (0, 30, …, 300, or 330
degrees) referenced to V
AB
.
Figure 2.24 shows a relay wired with delta-connected phase PTs, and a
C-phase-to-ground connected VS-NS input. With ABC rotation, the correct
SYNCP setting for this example is 270 degrees, the amount that V
C
lags V
AB
.
See the Application Guide entitled Compensate for Constant Phase Angle
Difference in Synchronism Check with the SEL-351 Relay Family for more
information on setting SYNCP with an angle setting.
SYNCP synchronizing phase
or
the number of degrees that synchronism
check voltage V
S
constantly lags voltage V
A
(wye-connected voltages) or V
AB
(delta-con-
nected voltages)
VA, VB, or VC (wye-
connected voltages)
VAB, VBC, or VCA
(delta-connected volt-
ages)
0°–330°, in 30° steps
TCLOSD breaker close time for angle compensation 0.00–60.00 cycles
BSYNCH SEL
OGIC control equation
block synchronism check setting
Relay Word bits
referenced in Tab le 9 .6
Table 3.13 Synchronism Check Elements Settings and Settings Ranges
(Sheet 2 of 2)
Setting Definition Range
NOTE: On setting SYNCP = 0
Settings SYNCP = 0 and SYNCP = VA
are effectively the same (voltage V
S
is
directly synchronism checked with
voltage V
A
; V
S
does not lag V
A
). The
relay will display the setting entered
(SYNCP = VA or SYNCP = 0).
NOTE: On setting SYNCP = 0
Settings SYNCP = 0 and SYNCP = VAB
are effectively the same (voltage V
S
is
directly synchronism checked with
voltage V
AB
; V
S
does not lag V
AB
). The
relay will display the setting entered
(SYNCP = VAB or SYNCP = 0).
Courtesy of NationalSwitchgear.com