GE Power Management 750/760 Feeder Management Relay 10-
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10 S3 LOGIC INPUTS 10.1 OVERVIEW
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10 S3 LOGIC INPUTS 10.1 OVERVIEW 10.1.1 INTRODUCTION
The 750/760 relay has 20 logic inputs which can be used to operate a variety of logic functions for circuit
breaker control, external trips, blocking of protection elements, etc. The relay has ‘contact inputs’ and ‘virtual
inputs’ that are combined in a form of programmable logic to facilitate the implementation of various schemes.
The relay has 14 rear terminal contact inputs. These contacts can be either wet or dry (see Section 3.2.13:
LOGIC INPUTS on page 3–14 for typical wiring of the logic input contacts). External contacts are either open
or closed and are debounced for one power frequency cycle to prevent false operation from induced voltage.
Because of debouncing,
momentary contacts must have a minimum dwell time greater than one power
frequency cycle
.
The relay also has 20 virtual inputs which are analogous to software switches. They allow all the functionality
of logic inputs to be invoked via serial communications or from the front panel. This has several advantages
over only having contact inputs:
• The number of logic inputs can be increased without introducing additional hardware.
• Logic functions that must be invoked from a remote location can all be done over a single RS485 commu-
nications channel.
• The same logic function can be invoked both locally via contact input, front panel keypad, and/or remotely
via communications.
• Panel switches can be replaced entirely by virtual switches to save cost and wiring.
Virtual inputs are simply memory locations in the relay which can be assigned a value via communications or
from the front panel display menu
\ ACTUAL VALUES \ A1 STATUS \ VIRTUAL INPUTS
. If the value stored in memory is
0
then the virtual input is Off, otherwise the virtual input is On. The state of virtual inputs is written as if it were
a setpoint; these values are non-volatile and are found in the Memory Map at locations 0090 to 00A4 hex.
Momentary virtual inputs are simulated by first writing a ‘1’ to the corresponding register followed by writing a
‘0’. Due to communications delay there will be a dwell time of 50 to 200 ms. Maintained virtual inputs are simu-
lated by writing a ‘1’ to the corresponding register.
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