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8.23
Date Code 20171006
Instruction Manual
SEL-400 Series Relays
Monitoring
Station DC Battery System Monitor
Set the low end of the allowable dc battery system voltage according to the rec-
ommendations of C37.90–1989 (R1994) IEEE Standard for Relays and Relay
Systems Associated with Electric Power. Section 6.4 in this standard is titled
Allowable Variation from Rated Voltage for Voltage Operated Auxiliary Relays.
This section calls for an 80 percent low-end voltage and 28, 56, 140, or 280 Vdc
high-end voltages for the popular nominal station battery voltages.
lists
expected battery voltages under various conditions using commonly accepted
per-cell voltages.
Use the expected battery voltages of
to determine the relay station dc
battery monitor threshold settings.
shows these threshold settings for a
nominal 125-Vdc battery system (the Vdc1 input) and a nominal 48-Vdc battery
system (the Vdc2 input).
AC Ripple
Another method for determining whether the substation battery charger has failed
is to monitor the amount of ac ripple on the station dc battery system. The IEEE
C37.90-1989 standard also identifies an “Allowable AC Component in DC Con-
Table 8.8
Example DC Battery Voltage Conditions
Condition
Calculation
Battery Voltage (Vdc)
Trip/Close
80% • 125 Vdc
100.0
Open-Circuit
60 (cells) • 2.06 (volts/cell)
123.6
Float Low
60 (cells) • 2.15 (volts/cell)
129.0
Float High
60 (cells) • 2.23 (volts/cell)
133.8
Equalize Mode
60 (cells) • 2.33 (volts/cell)
139.8
Trip/Close
80% • 48 Vdc
38.4
Open-Circuit
24 (cells) • 2.06 (volts/cell)
49.4
Float Low
24 (cells) • 2.15 (volts/cell)
51.6
Float High
24 (cells) • 2.23 (volts/cell)
53.5
Equalize Mode
24 (cells) • 2.33 (volts/cell)
55.9
Trip/Close
80% • 24 Vdc
19.2
Open-Circuit
12 (cells) • 2.06 (volts/cell)
24.7
Float Low
12 (cells) • 2.15 (volts/cell)
25.8
Float High
12 (cells) • 2.23 (volts/cell)
26.8
Equalize Mode
12 (cells) • 2.33 (volts/cell)
28.0
Table 8.9
Example DC Battery Monitor Settings—125 Vdc for Vdc1 and 48 Vdc
for Vdc2
Setting
Description
Indication
Value (Vdc)
DC1LFP
Low-fail threshold, Mon. 1
Poor battery performance
100
DC1LWP
Low-warning threshold, Mon. 1
Charger malfunction
127
DC1HWP
High-warning threshold, Mon. 1
Equalization
137
DC1HFP
High-fail threshold, Mon. 1
Charger malfunction
142
DC2LFP
Low-fail threshold, Mon. 2
Poor battery performance
38
DC2LWP
Low-warning threshold, Mon. 2
Charger malfunction
50
DC2HWP
High-warning threshold, Mon. 2
Equalization
55
DC2HFP
High-fail threshold, Mon. 2
Charger malfunction
57
Summary of Contents for SEL-421-4
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