Mechanical Jam - GE 339 Instruction Manual

CHAPTER 6: SETPOINTS

Mechanical Jam

339 MOTOR PROTECTION SYSTEM – INSTRUCTION MANUAL
A motor load can become constrained (mechanical jam) during starting or running. The
starting current magnitude alone cannot provide a definitive indication of a mechanical
jam, so the starting load jams are detected by monitoring acceleration time and speed.
However, the running current magnitude can indicate load jams. Therefore, the Mechanical
Jam element is specially designed to operate for running load jams. After a motor has
started and reached the running state, a trip or alarm occurs should the magnitude of any
phase current exceed the setting MECH JAM PKP for a period of time specified by the
setting MECH JAM DELAY. The thermal protection element will also operate during
mechanical jams but after a delay when the thermal capacity reaches 100%. Not only
does the Mechanical Jam protect the motor by taking it off-line quicker than the thermal
protection, it may also prevent or limit damage to the driven equipment in the event of a
locked rotor during running.
The Mechanical Jam is armed as long as the motor status is not STARTING. When two-
speed functionality is deployed, the 339 will block Mechanical Jam Protection during the
acceleration time from Low Speed to High Speed until the motor current has dropped
below overload pickup level. At that point of time when the motor reached the high speed
running stage, the Mechanical Jam will be enabled with the High Speed FLA.
The MECH JAM PKP level should be set higher than motor loading during normal operation,
but lower than the motor stall level. Normally the delay is set to the minimum time delay or
set so that no nuisance trips occur due to momentary load fluctuations.
Mechanical Jam operation is a serious event, and therefore results in a lockout that cannot
be reset unless an Emergency Restart or a Lockout Reset is issued.
PATH:
SETPOINTS > S3 PROTECTION > MECHANICAL JAM
MECH JAM FUNC
Range: Disabled, Latched Alarm, Alarm, Trip
Default: Disabled
The selection of the Latched Alarm, Alarm, or Trip setting enables the Mechanical Jam
function. If the operating condition is satisfied when Trip is selected as the function, the
"LOCKOUT" LED will be turned on, and the logic operand ANY TRIP OP will be asserted,
which in turn will activate the "TRIP" LED and operate the "Trip" output relay. If Alarm is
selected, the "ALARM" LED will flash upon Mechanical Jam operation, and will
automatically reset when the activating condition clears. If Latched Alarm is selected,
the "ALARM" LED will flash upon Mechanical Jam operation, and will stay "ON" after the
condition clears, until a reset command is initiated. The TRIP output relay will not operate
if the Latched Alarm or Alarm function is selected. Any assignable output relays can be
selected to operate when the setting MECH JAM FUNC is selected as Latched Alarm,
Alarm, or Trip.
MECH JAM PKP
Range: 1.01 to 4.50xFLA in steps of 0.01xFLA
Default: 4.00xFLA
This setting defines the excessive current condition that identifies a mechanical jam. As
the element is not armed during motor starting, this threshold can be set below the
starting current.
MECH JAM DELAY
Range: 0.00 to 30.00 s in steps of 0.01 s
Default: 0.00 s
This setting specifies the pickup delay for the Mechanical Jam.
S3 PROTECTION
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