Schweitzer Engineering Laboratories SEL-351-5, Instruction Manual

Page: 124 / 706

3.44
SEL-351-5, -6, -7 Relay Instruction Manual
Date Code 20070117
Overcurrent, Voltage, Synchronism Check, Frequency, and Power Elements
Synchronism Check Elements
Voltages V
P
and V
S
Are “Static” or Setting TCLOSD = 0.00
To implement a simple fixed-angle synchronism check scheme, set
TCLOSD = 0 and 25SF = 0.500. With these settings, the synchronism check is
performed as described in the top of
Figure 3.27 .
If there is the possibility of a high slip frequency, exercise caution if
synchronism check elements 25A1 or 25A2 are used to close a circuit breaker.
A high slip frequency and a slow breaker close could result in closing the
breaker outside the synchronism check window. Qualify the breaker close
command with a time delay, such as:
SV1 =
25A1
CL = CC * SV1T
Set SV1PU with enough pickup delay to ensure that the slip frequency is low
enough for the circuit breaker to close within the synchronism check window.
Voltages V
P
and V
S
are “Slipping”
and
Setting TCLOSD
≠
0.00
Refer to bottom of Figure 3.27 . If V
P
and V
S
are “slipping” with respect to
one another and breaker close time setting TCLOSD
≠
0.00, the Angle
Difference (compensated by breaker close time TCLOSD) changes through
time. Synchronism check element 25A1 or 25A2 asserts to logical 1 for any
one of the following three scenarios.
1. The top of Figure 3.28 shows the Angle Difference
decreasing —V
S
* is approaching V
P
. When V
S
* is in phase
with V
P
(Angle Difference = 0 degrees), synchronism check
elements 25A1 and 25A2 assert to logical 1.
2. The bottom of Figure 3.28 shows the Angle Difference
increasing —V
S
* is moving away from V
P
. V
S
* was in phase
with V
P
(Angle Difference = 0 degrees), but has now moved
past V
P
. If the Angle Difference is increasing , but the Angle
Difference is still less than maximum angle settings 25ANG1
or 25ANG2, then corresponding synchronism check elements
25A1 or 25A2 assert to logical 1.
In this scenario of the Angle Difference increasing, but still
being less than maximum angle settings 25ANG1 or 25ANG2,
the operation of corresponding synchronism check elements
25A1 and 25A2 becomes
less restrictive . Synchronism check
breaker closing does not have to wait for voltage V
S
* to slip
around again in phase with V
P
(Angle Difference = 0 degrees).
There might not be enough time to wait for this to happen.
Thus, the “Angle Difference = 0 degrees” restriction is eased
for this scenario.
3. Refer to Reclose Supervision Logic on page 6.5 .
Refer to the bottom of Figure 6.2 . If timer 79CLSD is set
greater than zero (e.g., 79CLSD = 60.00 cycles) and it times
out without SEL
OGIC
control equation setting 79CLS (Reclose
Supervision) asserting to logical 1, the relay goes to the
Lockout State (see top of
Figure 6.3 ).
Refer to the top of Figure 6.2 . If timer 79CLSD is set to zero
(79CLSD = 0.00), SEL
OGIC
control equation setting 79CLS
(Reclose Supervision) is checked only once to see if it is