Motor Overload Protection (i2t)
Overview
This feature will evaluate the “overheating” status of the motor. If the motor is overheated more than the allowed limit, this feature will limit the RMS value of phase currents to protect the motor from being overheated beyond the permitted limits.
Note: This feature doesn’t directly measure the motor temperature. It is only a limiting feature which doesn’t allow the motor to overheat.
It is able to detect fast transients and can therefore react much faster than the attached temperature sensors.
Requirements
To use this feature, the following parameters must be set properly according to the motor data sheet:
| Object ID | Name | Description |
|---|---|---|
| 0x6075 | Motor rated current | Motor rated current (rms value) |
| 0x6073 | Motor maximum current | Motor maximum current (rms value) |
| 0x200A | i2t | Parameters to activate the i2t feature |
Description of Subitems for 0x200A:
| Object ID | Name | Description |
|---|---|---|
| 0x200A:1 | Enable | Set to 1 to enable the protection |
| 0x200A:2 | Peak Time | Maximum time period [ms] in which the motor is allowed to have its maximum current |
| 0x200A:3 | Percent max | The percent of the maximum transient energy allowable in the motor |
| 0x200A:4 | Protection active | When this flag is set, the output current is limited to equal or less the nominal current |
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!