Table 477: Time constant and the respective phase current values
Time constant (tau) in use Phase current
Time constant start Any current whose value is over 2.5 x I
r
Time constant normal Any current whose value is over 0.12 x I
r
and
all currents are below 2.5 x I
r
Time constant stop All the currents whose values are below 0.12 x
I
r
The
Weighting factor p
setting determines the ratio of the thermal increase of the
two curves θ
A
and θ
B
.
The thermal level at the power-up of the protection relay is defined by the
Initial
thermal Val
setting.
The temperature calculation is initiated from the value defined in the
Initial thermal
Val
setting. This is done if the protection relay is powered up or the function is
turned off and back on or reset through the Clear menu.
The calculated temperature of the protected object relative to the operate level, the
TEMP_RL output, is available through the monitored data view. The activation of the
BLOCK input does not affect the calculated temperature.
The calculated temperature of the protected object relative to the operate level,
the TEMP_RL output, is available through the monitored data view or through the
output signal TEMP_RL. The activation of the BLOCK input does not affect the
calculated temperature.
The thermal level at the beginning of the start-up condition of a motor and at
the end of the start-up condition is available in the monitored data view at the
THERMLEV_ST and THERMLEV_END outputs respectively. The activation of the BLOCK
input does not have any effect on these outputs.
Alarm and tripping logic
The module generates alarm, restart inhibit and tripping signals.
When the thermal level exceeds the set value of the
Alarm thermal value
setting,
the ALARM output is activated. Sometimes a condition arises when it becomes
necessary to inhibit the restarting of a motor, for example in case of some extreme
starting condition like long starting time. If the thermal content exceeds the set
value of the
Restart thermal val
setting, the BLK_RESTART output is activated. The
time for the next possible motor start-up is available through the monitored data
view from the T_ENARESTART output. The T_ENARESTART output estimates the
time for the BLK_RESTART deactivation considering as if the motor is stopped.
When the emergency start signal START_EMERG is set high, the thermal level is set
to a value below the thermal restart inhibit level. This allows at least one motor
start-up, even though the thermal level has exceeded the restart inhibit level.
When the thermal content reaches 100 percent, the OPERATE output is activated.
The OPERATE output is deactivated when the value of the measured current falls
below 12 percent of
Current reference
or the thermal content drops below 100
percent.
The activation of the BLOCK input blocks the ALARM, BLK_RESTART and OPERATE
outputs.
Protection functions
1MRS759142 F
414 REX640
Technical Manual
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