GE M60, Instruction Manual

Page: 427 / 676

CHAPTER 5: SETTINGS GROUPED ELEMENTS
M60 MOTOR PROTECTION SYSTEM – INSTRUCTION MANUAL 5-219
5
A motor load can become constrained (mechanical jam) during startup or when running. The starting current magnitude
alone cannot provide a definitive indication of a mechanical jam. The running current magnitude can. The Mechanical Jam
element is specifically designed to operate for running load jams. Startup load jams are detected by monitoring
acceleration time and speed. The thermal element also operates during mechanical jams but after a delay when the
thermal capacity reaches 100%. Not only is this ineffective due to the delay, but it also implies the maximum waiting time
for cooling before a restart, which can be restrictive.
This element is armed as long as the motor status is not “Starting.” This includes “Running,” “Overload,” and “Offline.” As
soon as any phase current exceeds the user-selectable threshold, the element picks up and operates after the
programmed time delay. The element uses currents configured under
SYSTEM SETUP  MOTOR  MOTOR LINE SOURCE
and motor status asserted by the thermal model element. Both the signal source and thermal protection must be
configured properly in order for the mechanical jam protection to operate.
MECH JAM OVERCURRENT PICKUP
— This setting defines excessive current condition that identifies a mechanical jam. As the
element is not armed during start conditions, this threshold can be set below the starting current. Since the element is
armed during overload conditions, make this setting higher than the maximum overload current. The setting is entered in
multiplies of FLA (defined in the
SYSTEM SETUP

MOTOR
menu).
MECH JAM PICKUP DELAY
— This setting specifies the pickup delay of the element. In the case of large motors that can feed
close-in feeder faults, this setting can coordinate with feeder protection to avoid false tripping due to excessive fault
currents fed by the motor.
MECH JAM RESET DELAY
— This setting defines the reset delay of the element. Typical application includes time seal-in of the
tripping command.
Figure 5-118: Mechanical jam logic

MECH JAM PICKUP
DELAY: 0.10 s
Range: 0.10 to 600.00 s in steps of 0.01

MECH JAM RESET
DELAY: 0.00 s
Range: 0.00 to 600.00 s in steps of 0.01

MECH JAM BLOCK:
Off
Range: FlexLogic operand

MECH JAM TARGET:
Self-reset
Range: Self-reset, Latched, Disabled

MECH JAM EVENTS:
Disabled
Range: Disabled, Enabled