U.4.75
Date Code 20090715 User’s Guide SEL-421 Relay
Basic Relay Operations
Configuring High-Accuracy Timekeeping
➢ The IRIG-B clock does not use the IEEE C37.118
Control Bit assignments, or the IRIG-B signal is not of
sufficient accuracy.
➢ The termination resistor, required by some IRIG clocks,
is not installed.
➢ If the time-source clock is reporting that its time error is
greater than 1 µs.
➢ The IRIG-B clock source is connected via Serial Port 1
instead of the IRIG-B BNC connector.
➢ The IRIG-B clock source is connected to the unlabeled
BNC connector on older relay hardware (the previous
location of the IRIG-B BNC connector).
If neither TSOK nor TIRIG are asserted, the relay is not in an
IRIG time-source mode. Here is a list of possible reasons for
not entering IRIG mode:
➢ The IRIG-B clock signal is not of sufficient accuracy or
is improperly configured.
➢ The termination resistor, required by some IRIG clocks,
is not installed.
➢ The time source clock is not connected to an antenna.
➢ An IRIG-B clock source is connected both to serial port
1 and the unlabeled BNC connector on older relay
hardware (the previous location of the IRIG-B BNC
connector).
➢ A 1k PPS cable is still connected to the relay.
Step 5. Type TIME Q <Enter> to confirm that the relay is operating
in the high-accuracy IRIG (HIRIG) mode.
The relay displays information similar to Figure 4.67.
The Time Source will be HIRIG, indicating that the relay
internal clock is locked to the high-accuracy IRIG input signal.
=>TIME Q <Enter>
Relay 1 Date: 10/06/2004 Time: 15:44:30.840
Station A Serial Number: 0000000000
Time Source: HIRIG
Last Update Source: HIRIG
IRIG Time Mark Period: 1000.000000 ms
Internal Clock Period: 24.999995 ns
=>
Figure 4.67 Results of the TIME Q Command
TIME Q Descriptions
The TIME Q command provides details about relay timekeeping (see
Figure 4.67). The SEL-421 internal clock is initially calibrated at the SEL
factory. An external IRIG source is required to eliminate clock drift. For high-
accuracy timekeeping functions such as synchrophasor measurement, the
connected clock must support IEEE C37.118—Annex F, IRIG-B Control Bit
assignments. The Time Source field provides the present high-accuracy timing
input source; entries for this line are HIRIG and OTHER. The Last Update
Source reports the source from which the relay referenced the last time value
measurement. Entries for this line can be high-priority or low-priority sources.
Table 4.10 lists the possible Last Update Source values for the SEL-421.
NOTE: If the firmware in an already
installed SEL-421 is upgraded to
version R112 or later, and the
previous IRIG-B BNC cable is not
moved to the new location (see
Figure 4.63), the SEL-421 cannot
enter High-Accuracy mode.
NOTE: If the firmware in an already
installed SEL-421 is upgraded to
version R112 or later, and the
previous 1k PPS BNC cable is not
removed (see Figure 4.63), the
SEL-421 cannot use the IRIG time
inputs.
NOTE: When EPMU := Y, the relay
year is updated automatically from
the connected clock IEEE C37.118—
Annex F, IRIG-B Control Bit
information.
Courtesy of NationalSwitchgear.com
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