4.105
Date Code 20100129
Instruction Manual
SEL-751A Relay
Protection and Logic Functions
Breaker Monitor
Breaker Monitor
The breaker monitor in the SEL-751A helps in scheduling circuit breaker
maintenance. Refer to
for a detailed description
and
for settings.
Digital Input Debounce
To comply with different control voltages, the SEL-751A offers dc debounce
as well as ac debounce modes. Therefore, if the control voltage is dc, select
the dc mode of operation, and if the control voltage is ac, select the ac mode of
operation. In general, debounce refers to a qualifying time delay before
processing the change of state of a digital input. Normally, this delay applies
to both the processing of the debounced input when used in device logic, as
well as to the time stamping in the SER. Following is a description of the two
modes.
DC Mode Processing
(DC Control Voltage)
shows the logic for the dc debounce mode of operation. To select
the dc mode of debounce, set IN101D to any number between 0 and 65000
ms. In the figure, Input IN101 becomes IN101R (internal variable), after
analog-to-digital conversion. On assertion, IN101R starts Debounce Timer,
producing Relay Word bit IN101 after the debounce time delay. The debounce
timer is a pickup/dropout combination timer, with debounce setting IN101D
applying to both pickup (pu) and dropout (do) timers, i.e., you cannot set any
timer individually. For example, a setting of IN101D = 20 ms delays
processing of the input signal by 20 ms (pu) and maintains the output of the
timer (do) for 20 ms. Relay Word bit IN101 is the output of the debounce
timer. If you do not want to debounce a particular input, still use Relay Word
bit IN101 in logic programming, but set the debounce time delay to 0
(IN101D = 0).
Figure 4.59
DC Mode Processing
AC Mode Processing
(AC Control Voltage)
shows IN101R from Input IN101 applied to a pickup/dropout
timer. Different from the dc mode, there are no time settings for the debounce
timer in the ac mode: the pickup time delay is fixed at 2 ms, and the dropout
time is fixed at 16 ms. Relay Word bit IN101 is the output of the debounce
timer. To select the ac mode of debounce, set IN101D = AC.
Figure 4.60
AC Mode Processing
pu
do
IN101
Relay
Word
Bit
Input IN101
IN101R
Analog/Digital
Converter
Debounce Timer
2 ms
16 ms
IN101
Relay
Word
Bit
IN101R
Debounce Timer
Summary of Contents for 751A
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