The
Blocking mode setting has three blocking methods. In the "Freeze timers"
mode, the operation timer is frozen to the prevailing value. In the "Block all" mode,
the whole function is blocked and the timers are reset. In the "Block OPERATE
output" mode, the function operates normally but the
OPERATE
output is not
activated.
4.1.8.5
Application
The motor protection during stall is primarily needed to protect the motor from
excessive temperature rise, as the motor draws large currents during the stall
phase. This condition causes a temperature rise in the stator windings. Due to
reduced speed, the temperature also rises in the rotor. The rotor temperature rise is
more critical when the motor stops.
The physical and dielectric insulations of the system deteriorate with age and the
deterioration is accelerated by the temperature increase. Insulation life is related to
the time interval during which the insulation is maintained at a given temperature.
An induction motor stalls when the load torque value exceeds the breakdown
torque value, causing the speed to decrease to zero or to some stable operating
point well below the rated speed. This occurs, for example, when the applied shaft
load is suddenly increased and is greater than the producing motor torque due to
the bearing failures. This condition develops a motor current almost equal to the
value of the locked-rotor current.
JAMPTOC is designed to protect the motor in stall or mechanical jam situations
during the running state. To provide a good and reliable protection for motors in
a stall situation, the temperature effects on the motor have to be kept within the
allowed limits.
4.1.8.6
Signals
Table 342: JAMPTOC Input signals
Name
Type
Default
Description
I_A
SIGNAL
0
Phase A current
I_B
SIGNAL
0
Phase B current
I_C
SIGNAL
0
Phase C current
BLOCK
BOOLEAN
0=False
Block signal for acti-
vating the blocking
mode
Table 343: JAMPTOC Output signals
Name
Type
Description
OPERATE
BOOLEAN
Operate
1MRS757644 H
Protection functions
620 series
Technical Manual
353
