Variable frequency drives (VFD) may experience a fault that is known as “Overload”. This is triggered to protect the motor from overheating and burning up the internal windings. Generally, a VFD will display “oL”, ‘lt2’ or “overload” depending on the manufacturer to indicate this condition.
Overload levels are determined by the motor nameplate and the duty requirements of the application. Normal Duty (ND) applications are those that require a varying amount of torque depending on the loads RPM. ND drives are most found on pump and fan applications. Heavy Duty (HD) are constant torque applications that require the same amount of torque at any point of operation.
Configuring a VFD to Normal duty allows 120% of the motors Full Load Amps (FLA) for 60 seconds while heavy duty allows 150% of the Motors FLA for the same time. Knowing the required duty of the motor application is essential to properly sizing a VFD.
Below are common issues and solutions associated with an overload fault:
Motors have a run life, and the components wear over time.
- This often creates increased internal friction making it harder for the load to move. To overcome this friction, the motor must pull more current to maintain the applications needed speed/torque. This is the root of the overload fault.
- Regularly have critical motors serviced to ensure functioning components.
- Condition based monitoring is key to staying ahead of underlining issues. As technology evolves more solutions are available that offer 24/7 monitoring which includes temperature and vibration readings.
Undersized motors must compensate by using more power than they were designed to operate at to meet the load conditions.
- Ensure the installed motor is the correct size and type for the application.
- If that is not the case, it should be replace when possible.
- In some applications, there are specific motors for the niche applications, such as crushing as it requires a high torque level as it being loaded and unloaded.
Trust, but verify!
- Drive parameters must match the motor nameplate.
- As motors are installed or replaced it is critical to verity the data in the VFD is accurate.
- This is often an innocent oversight, and a few minutes of inspection can mitigate the issue.
These are great way to troubleshoot and understand why your VFD experienced an overload fault. The team at EECO is here to serve you with VFD support and you can connect with us here to learn more.