Drives Service & Support > PowerFlex 70 > Fault Finder

Fault Number : 25

Fault Display : OverSpeed Limit

Fault Name : OverSpeed Limit

Fault Type : 1 - Auto-Reset Run

Fault Description : Functions such as Slip Compensation or Bus Regulation have attempted to add an output frequency greater than that programmed in parameter 83 [Overspeed Limit].

Corrective Action : This is calculated by maximum speed + Overspeed limit which must be less than or equal to Maximum frequency. A very quick accel time may make the load overshoot and hit this fault. A sudden change in load may also cause this fault to occur.

An Autotune that was improperly finished may cause this. Wrong motor nameplate data being entered may also cause this fault to occur. Open the value of parameter 83 [Overspeed Limit]. Factory default is 10 hertz. By moving this parameter wider than 10 hertz, it will allow the drive to compensate for speed changes.

Overspeed Limit is a user programmable value that allows operation at maximum speed, but also provides an “overspeed band” that will allow a speed regulator such as encoder feedback or slip compensation to increase the output frequency above maximum speed in order to maintain maximum motor speed.

The figure below illustrates a typical Custom V/Hz profile. Minimum Speed is entered in Hertz and determines the lower speed reference limit during normal operation. Maximum Speed is entered in Hertz and determines the upper speed reference limit. The two “Speed” parameters only limit the speed reference and not the output frequency.

The actual output frequency at maximum speed reference is the sum of the speed reference plus “speed adder” components from functions such as slip compensation.\

The Overspeed Limit is entered in Hertz and added to Maximum Speed and the sum of the two (Speed Limit) limit the output frequency. This sum (Speed Limit) must is compared to Maximum Frequency and an alarm is initiated which prevents operation if the Speed Limit exceeds Maximum Frequency.