3.1.8.3.5.4 Operating principle
The difference between copper losses under rated conditions and overload conditions is calculated, and is
used to limit phase currents in case of motor overheating.
Once the motor phase currents are higher than their rated values, the overheat calculation starts by
integrating the difference between losses under rated and overload conditions.
When a current is injected that is above the nominal current, the tracking variable will rise. If the overcurrent is
less then the maximal value the peak time is extended accordingly.
Once the tracking variable reaches 100%, the calculated thermal energy storage is reached and the output
current in all phases will be limited to their rated values.
When the output current has fallen below the continuous limit, the difference between the actual current and
the continuous limit current will be negative and the i2t tracking variable will decrease.
When the i2t tracking variable falls to 50%, current limiting is turned off and the motor phase currents can
reach higher values again.
Attention
The tracking variable in subitem 0x200A:3 has a maximum value of 250%. Values that exceed this limit
are ignored. If the drive is used at values above 250%, the thermal energy in the motor is completely
untracked!
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