8.24
SEL-400 Series Relays
Instruction Manual
Date Code 20171006
Monitoring
Station DC Battery System Monitor
trol Voltage Supply” (Section 6.5) as an alternating component (ripple) of 5 per-
cent peak or less. (This definition is valid if the minimum instantaneous voltage
is not less than 80 percent of the rated voltage.) The relay measures ac ripple as a
peak-to-peak waveform, consequently, DC1RP and DC2RP should be set at or
greater than 10 percent (2 • 5% peak) of the equalizing voltage.
shows
the ac ripple threshold settings for this example.
DC Ground
If a battery system is centered around chassis ground, then the magnitude of the
voltage measured from the positive terminal to ground and from the negative ter-
minal of the battery to ground should be approximately one-half of the nominal
battery system voltage. The ratio of the positive-to-ground battery voltage to the
negative-to-ground battery voltage is 1 to 1, or 1.00.
is the balanced
(no grounding) ratio for a 125-Vdc battery system.
Equation 8.5
If either terminal is partially or completely shorted to chassis ground, then the
terminal voltage will be less than the nominal terminal-to-ground voltage. This
causes the ratio of positive voltage to negative voltage to differ from 1.00.
is an example of the unbalanced (grounding) ratio for a partial short
circuit to ground on the negative side of a 125-Vdc battery system.
Equation 8.6
The relay uses this voltage ratio to calculate a ground detection factor.
shows a graphical representation of the ground detection factor set-
ting and battery system performance.
Table 8.10
Example DC Battery Monitor Settings—AC Ripple Voltages
Setting
Description
Indication
Value (Vac)
DC1RP
AC ripple threshold, Mon. 1
Charger malfunction
14
DC2RP
AC ripple threshold, Mon. 2
Charger malfunction
6
k
Vdc1
pos
Vdc1
neg
---------------------
62.50 V
62.50 V
-------------------
1.00
=
=
=
k
Vdc1
pos
Vdc1
neg
---------------------
62.50 V
59.10 V
-------------------
1.06
=
=
=
Summary of Contents for SEL-421-4
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