Question:
"UL conformity": Is the I²xt monitoring function also required for motors equipped with temperature sensors?
Answer:
Yes, the I²xt monitoring function is also required for motors equipped with temperature sensors.
Monitoring the motor temperature exclusively by means of temperature sensors (KTY, PT1000, PTC,...) in the motor windings does not fully meet the requirements of UL 508.
Monitoring the motor utilisation exclusively by means of the I²xt monitoring function does, however, meet the requirements of UL 508, provided that parameter setting is adapted to the motor.
If no I²xt monitoring function can/shall be used in the drive controller, UL-compliant motor protection requires additional switch-off devices to reliably detect extreme operating conditions as well. UL-approved motor protection switches, motor protection relays or switch disconnectors can, for instance, be applied.
Lenze controllers contain the functionality for monitoring the motor utilisation (I²xt). This functionality can be used as overload protection of the motor (see above).
Advantage: No additional hardware components are required (no additional costs).
The above applies to the following Lenze series:
- i700 servo inverter
- 9400HL servo inverter
- Inverter i510
- Inverter i550
- Inverter Drives 8400 SL / HL / TL
- Inverter Drives 8400 protec / motec
Note:
The I²xt monitoring function is based on an mathematical simulation of the motor utilisation by means of the measured motor currents (math. fct.: ∫i²dt) taking the motor speed into account. Even extreme operating situations, e.g. with extremely high short-time overcurrents can reliably be detected by means of the I²xt monitoring function.
In such cases, temperature monitoring by means of temperature sensors would only trip with delay, because the sporadic temperature rise in the windings only reaches the temperature sensor with a time lag (thermal time constants).
We always recommend to use the I²xt monitoring function, irrespective of the UL requirements.
In particular for motors that are only equipped with one temperature sensor and for motors featuring extremely high overcurrent loads ( I_peak / I_rated = 2...10 ), an optimum motor protection can only be achieved by using the I²xt monitoring function.
