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