I.12
SEL-751 Relay Instruction Manual Date Code 20170927
Synchrophasors
Synchrophasor Relay Word Bits
The Relay Word bit TSOK provides the indication that the time
synchronization is OK. The SEL-751 determines the suitability of the IRIG-B
signal for normal accuracy by applying several tests:
➤ Seconds, minutes, and day fields are in range
➤ Time from two consecutive messages differs by one second,
except for leap second or daylight-saving time transitions
➤ When IRIGC = C37.118, the signal contains the correct
parity bit
The SEL-751 determines the suitability of the IRIG-B signal for high-
accuracy timekeeping by applying two additional tests:
NOTE: The jitter measurement for
the IRIG signal could take up to 15
seconds to determine. During this
time TSOK is not asserted.
➤ The jitter between positive transitions (rising edges) of the
clock signal is less than 500 ns
➤ The time error information contained in the IRIG-B control
field indicates time error is less than 10
–6
seconds (1 µs)
When IRIGC = NONE, the relay asserts TSOK when only the first test is met.
When IRIGC = C37.118 and an appropriate IRIG-B signal is connected,
Relay Word bit TSOK only asserts when these two tests are met. The time
error information in the IRIG-B control field is mapped to the TQUAL bits in
the relay. Table I.9 provides the information for the TQUAL bits and how they
translate to time quality. The values 0 (Locked) and 4 (1 microsecond)
indicate that the relay is receiving high-accuracy IRIG.
When the IRIG signal is lost, IRIGOK deasserts. However, TSOK remains
asserted for a holdover period as long as 15 seconds. If the IRIG signal is not
restored within 15 seconds, TSOK also deasserts.
Table I.9 TQUAL Bits Translation to Time Quality
TQUAL8 TQUAL4 TQUAL2 TQUAL1 Value Time Quality
00000 Locked
000111 nanosecond
0010210 nanoseconds
00113100 nanoseconds
010041 microsecond
0101510 microseconds
01106100 microseconds
011171 millisecond
1000810 milliseconds
10019100 milliseconds
1010101 second
10111110 seconds
110012100 seconds
1101131 000 seconds
11101410 000 seconds
111115 Fault
To Next Page
Loading...
