I²T overload protection

To protect the motor and the drive controller from overload, separate I²T models are calculated for both components. These provide an estimate of the thermal load on the motor and the drive controller. The I²T models take into account the resistance losses, which are proportional to the square of the motor current. In addition, a thermal time constant is taken into account to model the heating and cooling behavior.

I²T utilization is compared against three thresholds:

• Warning threshold: Adjustable, default 80%
  If this threshold is exceeded, a warning is issued (Diagnostic History, warning bit in the status word); information for the control/user.
  Relevant parameters:
• 2002:29/2802:29 (Channel 1/2) Amplifier I2T warn level
• 2003:29/2803:29 (Channel 1/2) Motor I2T warn level
• Error threshold: Adjustable, default 105%
  If this threshold is exceeded, the axis is brought to a standstill using the error reaction configured in parameter 605E/685E (channel 1/2) Fault reaction option code. The error bit in the status word is set, and a message is logged in the diagnostic history. As the limit is fixed at 100%, the error threshold (default: 105%) is not reached during normal operation. In the default configuration, an I²T fault is therefore only triggered when the drive controller can no longer control an overload. This is particularly likely to occur in control loops with unstable parameter settings, wiring faults, etc.
  Relevant parameters:
• 2002:2A/2802:2A (Channel 1/2) Amplifier I2T error level
• 2003:2A/2803:2A (Channel 1/2) Motor I2T error level
• Limit: Fixed, 100%
  When the limit is reached, the motor current is limited to the rated value of the respective model (drive or motor).
  Note: You can prevent this reduction by setting the error threshold to a value < 100% (e.g., 98%). In this case, if the axis is overloaded, it will be shut down with an error message without any limit being applied first.