Schweitzer Engineering Laboratories SEL-351-5, Instruction Manual

Page: 135 / 706

3.55
Date Code 20070117
Instruction Manual SEL-351-5, -6, -7 Relay
Overcurrent, Voltage, Synchronism Check, Frequency, and Power Elements
Voltage Sag, Swell, and Interruption Elements (Available in Firmware Version 7)
➤
|V1| is within three percent of the calculated Vbase value/
√
3
(delta connected)
➤
At least 12 seconds have elapsed
As soon as the above Vbase initialization conditions are satisfied, the SSI
Relay Word bits will be allowed to change state according to their settings and
the present voltage conditions, and the SSI Recorder will be enabled.
Vbase Tracking Range
The Vbase quantity will track the positive-sequence voltage over a large range
of system voltages. The tracking limits are explained below. In normal relay
use, these limits are not likely to be reached, because one of the Sag, Swell, or
Interruption Relay Word bits would most likely assert for a large voltage
deviation, thus blocking the Vbase thermal element from tracking to one of
the range limits.
The minimum value that Vbase can achieve is equivalent to a positive-
sequence (V1) value of 25 volts secondary. In primary units, the lowest value
depends on the global setting PTCONN:
When PTCONN = WYE: minimum Vbase =
When PTCONN = DELTA: minimum Vbase =
The maximum value that Vbase can achieve is equivalent to 300 volts
secondary divided by VSWELL, so the maximum Vbase in primary kV is
The upper limit for Vbase is not affected by the PTCONN global setting.
If the expected higher end of the “normal” system voltage range is close to
300 V, secondary, then the VSWELL setting may need to be reduced, or
turned “OFF,” in order to allow Vbase to track the actual system voltage and
not run into the maximum value limit. For example, if connecting to an
industrial service rated at 277 V
LN
/480 V
LL
, using the wye-connection (with
no PTs), and the normal operating range goes up to 285 V
LN
, then the
maximum VSWELL setting that will allow for proper Vbase tracking is
105 percent.
SSI Reset Command
After commissioning tests or other maintenance activities that have applied
test voltages to the SEL-351, the Vbase element may have locked onto a test
voltage. Use the
SSI R (reset) command once normal system voltages are
restored on the voltage terminals. Powering up the relay automatically
performs this reset.
See Resetting the SSI Recorder Logic on page 12.39 for more details.
25 V PTR •
1000
------------------------------kV
43.3V PTR •
1000
---------------------------------kV
300 V PTR 100 • •
VSWELL 1000 •
------------------------------------------------
30 V PTR •
VSWELL
------------------------------ =