ABB RELION REX640 Technical Manual page 400

Protection functions
The timer calculates the start duration value START_DUR, which indicates the
percentage ratio of the start situation and the set operating time. The value is
available in the monitored data view.
Blocking logic
There are three operation modes in the blocking function. The operation modes
are controlled by the BLOCK input and the global setting Configuration > System >
Blocking mode which selects the blocking mode. The BLOCK input can be controlled
by a binary input, a horizontal communication input or an internal signal of
the protection relay's program. The influence of the BLOCK signal activation is
preselected with the global setting
The
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.
4.1.7.6 Application
The motor protection during stall is primarily needed to protect the motor from
excessive temperature rise, as the motor draws high 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.
4.1.7.7 Signals
JAMPTOC Input signals
Table 453: JAMPTOC Input signals
Name
I3P
BLOCK
400
Blocking mode setting has three blocking methods. In the "Freeze timers"
Type
SIGNAL
BOOLEAN
Blocking mode .
Default
-
0=False
1MRS759142 F
Description
Three-phase currents
Block signal for acti-
vating the blocking
mode
REX640
Technical Manual