One of the most common problems that can impact variable frequency drives (VFDs, also referred to as AC drives) is overcurrent faults. These can occur if the demands of the load are too high and the motor begins to draw excessive currents from the AC drive. When the current becomes too strong for the motor to handle, it causes an overcurrent fault.

In this article, we take a look at how to solve an overcurrent fault in an AC motor drive and provide some general troubleshooting tips to ensure that if something goes wrong your applications are back up and running smoothly.

 

Troubleshooting overcurrent faults

There are plenty of reasons why an overcurrent fault may occur in different types of AC drives, such as:

• An excessive load that is too heavy
• The drive capacity is too small for the motor
• Loose connection on the output motor wiring
• An external device present on the drive output is not operating effectively
• Motor is shorted or grounded 
• Motor insulation has deteriorated
• Encoder feedback issue
• Incorrect parameter setting.

It’s important to note that finding the exact cause of the overcurrent fault can be challenging,  and it’s always a good idea to look at motor and load dynamics to isolate the problem.

 

Also, be aware that dangerous voltages are a safety concern when working with VFDs due to the large capacitors present in their circuits, so only those with the correct qualifications should perform work within the electrical panels on AC drive equipment. Be sure to follow the correct safety precautions and lockout procedures as per your specific equipment.

With this in mind, here are some simple ways to troubleshoot overcurrent faults within VFDs.

A VFD overcurrent can occur during the startup process of the application. If this happens, follow these steps:

• Perform a visual inspection of the machine to check if it’s stuck or bound in a way that’s preventing the motor from turning. 
• Ensure there is no shortage in the motor
• Check whether or not the power module is damaged or shorted
• Match the drive parameters with the starting torque of the motor.

If an overcurrent occurs when the application is running you should try increasing the drive acceleration time if this is set too low or increasing the deceleration time if it’s set too low.

 

General troubleshooting tips

When it comes to troubleshooting VFDs, it’s important to look for the source of the problem as opposed to the symptoms. This means looking at the VFD application rather than the component itself.

 

Safety is a priority

Safety should always be your first concern. There are plenty of dangers involved when working with VFDs and any other type of industrial equipment. Be sure that the steps involved in the troubleshooting process are safe for you, safe for those around you, and safe for the equipment itself.

 

Use manuals

When troubleshooting modern equipment, it’s important to pay attention to the manual. Manuals are required to ensure the correct set up and operation of the equipment, and also provide vital information needed to effectively troubleshoot any issues that may arise.

 

Perform a visual inspection

The first thing you should do when troubleshooting any system is to look for visual indicators of why any given problem might be occurring. Look for things like running or dripping water, excessive temperatures, dirt or debris, high humidity levels or any corrosive agents in the immediate vicinity of the equipment. Environmental conditions are a common cause of AC drive faults, so be sure to check this before proceeding further.

 

Check wiring connections are tight

Loose connections in the wiring of the drive can lead to operational failure. When the drive is constantly operating, increases in temperature and cooling can lead to connections loosening over time which can contribute to overcurrent trips and other issues such as input rectifier failure and burn terminals.

 

Check input and output voltages and currents

Check that the line voltages coming into the drive are balanced, if this isn’t the case it can cause significant problems. These voltages should be balanced within 5%, although current levels can differ from phase to phase, it’s important to check that no lines are dead.

Additionally, check the voltage and current levels of the drive output. Voltage from the inverter section should be in balance as large variations can lead to motor problems and outages.

 

Discover the range of AC motor drives from Preferred Spares

Preferred Spares is a supplier of electrical equipment and spare parts from leading industrial automation companies in the UAE and beyond. Whether you’re looking for a brand new VFD for your industrial equipment or a spare part for repairs, Preferred Spares supplies robust products from the world’s top AC drive manufacturers. 

 

For all your spare parts needs or for advice on implementing and troubleshooting AC drives, visit the Preferred Spares website or contact us today.