Undercurrent - GE MI-869 Instruction Manual

PROTECTION

Undercurrent

4–142
The 869 relay provides one Undercurrent element per protection group. The element
responds to a per-phase current. When the motor is in the running state, an alarms occurs
if the magnitude of any phase current falls below the undercurrent alarm pickup level for
the time specified by the undercurrent alarm delay. Furthermore, a trip occurs if the
magnitude of any phase current falls below the undercurrent trip pickup level for the time
specified by the undercurrent trip delay. The alarm and trip pickup levels must be set lower
than the lowest motor loading during normal operations.
The Undercurrent element is active only when the motor is running and is blocked upon
the initiation of a motor start for a period of time defined by the setting Start Block Delay.
This block may be used to allow pumps to build up head before the undercurrent element
trips or alarms.
A second independent Undercurrent protection element is provided for Speed 2. If 2 speed
functionality is enabled, the 869 relay relies on the motor speed indication; so the main
Undercurrent protection element is only active when the motor is running at speed 1 (low
speed), and the Speed2 Undercurrent protection element is only active when the motor is
running at high speed (speed 2).
Path:
Setpoints > Protection > Group 1 > Motor > Undercurrent 1
TRIP FUNCTION
Range: Disabled, Trip, Configurable
Default: Disabled
This setting enables the Undercurrent Trip functionality.
START BLOCK DELAY
Range: 0.00 to 600.00 s in steps of 0.01 s
Default: 0.50 s
The Undercurrent element is active only when the motor is running and it is blocked
upon the initiation of a motor start for a period of time defined by the START BLOCK
DELAY setting (e.g., this block can be used to allow pumps to build up head before the
undercurrent element trips or alarms).
TRIP PICKUP
Range: 0.10 to 0.95 x FLA in steps of 0.01 x FLA
Default: 0.70 x FLA
This setting specifies a pickup threshold for the trip function.
TRIP PICKUP DELAY
Range: 0.00 to 180.00 s in steps of 0.01 s
Default: 1.00 s
This setting specifies a time delay for the trip function.
TRIP DROPOUT DELAY
Range: 0.00 to 180.00 s in steps of 0.01 s
Default: 1.00 s
This setting specifies a specifies a time delay to reset the trip command. This delay
should be set long enough to allow the breaker or contactor to disconnect the motor.
TRIP OUTPUT RELAY X
Range: Do Not Operate, Operate
Default: Do Not Operate
Any assignable output relay can be selected to operate upon Undercurrent trip function
operation.
869 MOTOR PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 4: SETPOINTS