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11.2
SEL-400 Series Relays
Instruction Manual
Date Code 20171006
Time and Date Management
PTP Timekeeping
NOTE:
The SEL-2407 Satellite-
Synchronized Clock meets both the
relay accuracy and IEEE C37.118
requirements for a high-accuracy time
source.
The IRIG-B inputs can be used for high-accuracy timekeeping purposes with as
high as 1 ms accuracy with an appropriate time source. See
for relay
timekeeping mode details.
NOTE:
If the time-code signal
connected to the BNC connector
degrades in quality, the relay will not
switchover to the IRIG-B pins of Serial
Port 1. The relay will only switch to
Serial Port 1 if the signal on the BNC
connector completely fails or the
accuracy is better on Serial Port 1 than
on the BNC input (e.g., the cable is
unplugged).
Only one IRIG-B time source can be used by the relay, and the signal connected
to the IRIG-B BNC connector takes priority over the Serial Port 1 IRIG-B pins. If
a signal is detected on the IRIG-B BNC input, the IRIG-B pins of Serial Port 1 will be
ignored, unless the Serial Port 1 IRIG-B has better quality than the BNC input.
The relay determines the suitability of the IRIG-B signal connected to the BNC
connector for high-accuracy timekeeping by applying two tests:
➤
Measuring whether the jitter between positive-transitions (rising
edges) of the clock signal is less than 500 ns.
➤
Decoding the time-error information contained in the IR IG-B
control field and determining that analog quantity TQUAL is less
than 10
–6
seconds (1
s).
If a valid source is detected on the BNC or serial port IRIG inputs, then BNC_TIM or
SER_TIM will be set, respectively. Similarly, if a high-quality source is detected on the
BNC or serial port IRIG inputs, then BNC_OK or SER_OK will be set, respectively.
PTP Timekeeping
In addition to IRIG-B, Precision Time Protocol (PTP), as specified in IEEE 1588-2008,
can be used for high-accuracy timekeeping. The relay can only be synchronized by
a grandmaster on the PTP timescale, not an arbitrary (ARB) timescale. With the
ARB timescale, the epoch is set by an administrative procedure and can change at
any time during normal operation. The PTP timescale uses the PTP epoch of Jan-
uary 1 1970 00:00:00 TAI (International Atomic Time), which corresponds to
December 31 1969 23:59:51.999918 UTC (Coordinated Universal Time). Its unit
of time is the SI second and accounts for leap seconds. As of June 2016, TAI is
36 seconds ahead of UTC.
The offset between TAI and UTC time is included in the PTP announce message,
along with a flag that indicates whether or not the offset is valid. The relay will
use the offset sent by the Grand Master (GM) clock to determine UTC time
Table 11.1
Relay Timekeeping Modes
Item
Internal Clock
IRIG
HIRIG (or High-Accuracy IRIG) PTP
HPTP
Best accuracy
(condition)
Depends on last
method of set-
ting, or synchro-
nization
a
500 µs (when time-
source jitter is less
than 3 ms)
1 µs (when time-source jitter is
less than 500 ns, and time-error is
less than 1 µs)
b
Determined by PTP
master (Master clock
sync and announce
interval <= 4s)
1 µs (Master clock
sync and announce
interval <= 4 s, and
TQUAL <1 µs)
IRIG-B connec-
tion required
None
BNC connector (pre-
ferred), or Serial Port 1
BNC connector (preferred), or
Serial Port 1
PTP time source
connected
PTP time source
connected
Relay Word bits
TIRIG = 0
TSOK = 0
BNC_TIM = 0
SER _TIM = 0
BNC_OK = 0
SER_OK = 0
TIRIG = 1
TSOK = 0
BNC_TIM = 1 or
SER_TIM = 1
BNC_OK = 0
SER_OK = 0
TIRIG = 1
TSOK = 1
BNC_TIM = 1 or
SER_TIM = 1
BNC_OK = 1 or
SER_OK = 1
TPTP = 1
TSOK = 0
TPTP = 1
TSOK = 1
a
The internal clock in the relay can be synchronized via SNTP, DNP3, SEL-2030 Communications Processor, or M
IRRORED
B
ITS
communications.
b
The time source must include the IEEE C37.118 IRIG-B control bit assignments and the Global setting IRIGC must be set to C37.118 to provide
the time-error estimate for the clock. In products that support line-current differential protection, the jitter requirement for HIRIG is 50 ns.
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