Date Code 20011205
Breaker Monitor and Metering Functions
8-15
SEL-311A Instruction Manual
DC Under- and Overvoltage Elements
Refer to Figure 8.9. The station dc battery monitor compares the measured station battery
voltage (Vdc) to the undervoltage (low) and overvoltage (high) pickups DCLOP and DCHIP. The
setting range for pickup settings DCLOP and DCHIP is:
OFF, 20 to 300 Vdc, 1 Vdc increments
This range allows the SEL-311A Relay to monitor nominal battery voltages of 24, 48, 110, 125,
and 250 V. When testing the pickup settings DCLOP and DCHIP, do not operate the SEL-311A
Relay outside of the power supply limits listed in
Section1: Introduction and Specifications
.
Figure 8.9: DC Under- and Overvoltage Elements
Logic outputs DCLO and DCHI in Figure 8.9 operate as follows:
DCLO = 1 (logical 1), if V
dc
£
pickup setting DCLOP
= 0 (logical 0), if V
dc
>
pickup setting DCLOP
DCHI
= 1 (logical 1), if V
dc
³
pickup setting DCHIP
= 0 (logical 0), if V
dc
<
pickup setting DCHIP
Create Desired Logic for DC Under- and Overvoltage Alarming
Pickup settings DCLOP and DCHIP are set independently. Thus, they can be set:
DCLOP
<
DCHIP or
DCLOP
>
DCHIP
Figure 8.10 shows the resultant dc voltage elements that can be created with SEL
OGIC
control
equations for these two setting cases. In these two examples, the resultant dc voltage elements
are time-qualified by timer SV4T and then routed to output contact OUT106 for alarm purposes.
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