GE M60 Instruction Manual page 310

GROUPED ELEMENTS
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
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
element is not armed during start conditions, this threshold can be set below the starting current. Since the element is
5
armed during overload conditions, make this setting higher than the maximum overload current. The setting is entered in
multiplies of FLA (defined in the
MECH JAM PICKUP DELAY
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
tripping command.
5.7.3.6 Undercurrent
SETTINGS  GROUPED ELEMENTS  SETTING GROUP 1(6)  MOTOR  UNDERCURRENT
 UNDERCURRENT

5-182
MECH JAM PICKUP

DELAY: 0.10 s
MECH JAM RESET

DELAY: 0.00 s
MECH JAM BLOCK:

Off
MECH JAM TARGET:

Self-reset
MECH JAM EVENTS:

Disabled
— This setting defines excessive current condition that identifies a mechanical jam. As the
SYSTEM SETUP  MOTOR
— This setting specifies the pickup delay of the element. In the case of large motors that can feed
— This setting defines the reset delay of the element. Typical application includes time seal-in of the
Figure 5-94: Mechanical jam logic
UNDERCURRENT

FUNCTION: Disabled
Range: 0.10 to 600.00 s in steps of 0.01
Range: 0.00 to 600.00 s in steps of 0.01
Range: FlexLogic operand
Range: Self-reset, Latched, Disabled
Range: Disabled, Enabled
SYSTEM SETUP  MOTOR  MOTOR LINE SOURCE
menu).
Range: Disabled, Enabled
M60 MOTOR PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 5: SETTINGS