In order to accurately calculate the motor thermal condition, different time constants are
used in the above equations. These time constants are employed based on different motor
running conditions, for example starting, normal or stop, and are set through the
Time
constant start
,
Time constant normal
and
Time constant stop
settings. Only one time
constant is valid at a time.
Table 309:
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 disabled and
then enabled 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 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.
Section 4
1MAC059074-MB A
Protection functions
302
615 series ANSI
Technical Manual
Summary of Contents for Relion 615 series
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