Schweitzer Engineering Laboratories SEL-311C - Synchronism Check Elements Voltage Inputs; Synchronism Check Elements Operation

3.48
SEL-311C Relay Instruction Manual Date Code 20060320
Distance, Out-of-Step, Overcurrent, Voltage, Synchronism Check, and Frequency Elements
Synchronism Check Elements
Synchronism Check
Elements Voltage
Inputs
The two synchronism check elements use voltage inputs V
P
and V
S
for both
elements:
V
P
Phase input voltage (V
A
, V
B
, V
C
, V
AB
, V
BC
, or V
CA
), designated by
setting SYNCP (e.g., if SYNCP = VB, then V
P
= V
B
)
V
S
Synchronism check voltage, from SEL-311C rear-panel voltage input VS
For example, if V
P
is designated as phase input voltage V
B
(setting
SYNCP = VB), then rear-panel voltage input VS is connected to B-phase on
the other side of the circuit breaker. The voltage across terminals VB–N is
synchronism checked with the voltage across terminals VS–NS (see Figure 1.2
and Figure 2.13 and Figure 2.14).
System Frequencies Determined From Voltages V
A
and V
S
To determine slip frequency, you need to determine the system frequencies on
both sides of the circuit breaker. Voltage V
S
determines the frequency on one
side. Voltage V
A
determines the frequency on the other side.
Synchronism Check
Elements Operation
Refer to Figure 3.30 and Figure 3.31.
Voltage Window
Refer to Figure 3.30.
Single-phase voltage inputs V
P
and V
S
are compared to a voltage window, to
verify that the voltages are “healthy” and lie within settable voltage limits
25VLO and 25VHI. If both voltages are within the voltage window, the
following Relay Word bits assert:
59VP
indicates that voltage V
P
is within voltage window setting limits 25VLO
and 25VHI
59VS
indicates that voltage V
S
is within voltage window setting limits 25VLO
and 25VHI
As discussed previously, voltage V
A
determines the frequency on the voltage
V
P
side of the circuit breaker. Voltage V
A
is also compared against voltage
limits 25VLO and 25VHI to assure “healthy voltage” for frequency
determination, with corresponding Relay Word bit output 59VA. If V
P
is a
phase-to-phase voltage, V
A
is multiplied internally by √3 for the 25VLO and
25VHI checks.
Other Uses for Voltage Window Elements
If voltage limits 25VLO and 25VHI are applicable to other control schemes,
Relay Word bits 59VP, 59VS, and 59VA can be used in other logic at the same
time they are used in the synchronism check logic.
If synchronism check is not being used, Relay Word bits 59VP, 59VS, and
59VA can still be used in other logic, with voltage limit settings 25VLO and
25VHI set as desired. Enable the synchronism check logic (setting E25 = Y)