VFD Undervoltage in Roll Forming Machines – Causes, Drive Shutdowns, Inspection & Repair Guide

VFD Undervoltage

Roll Forming Machine Electrical & PLC Failure Guide

VFD undervoltage is an electrical protection fault in roll forming machines where the Variable Frequency Drive (VFD) detects that the incoming supply voltage or internal DC bus voltage has dropped below the minimum safe operating level.

Variable Frequency Drives are responsible for controlling the speed and torque of electric motors in many roll forming machine systems.

These drives convert incoming AC power into DC power inside the drive and then convert it back into controlled AC output for the motor.

The internal DC bus must maintain a stable voltage in order for the VFD to generate the correct motor output.

If the DC bus voltage falls below a safe threshold, the drive may not be able to control the motor properly.

To protect the drive electronics and motor, the VFD will trigger an undervoltage fault and shut down the motor.

VFD undervoltage faults commonly affect roll forming machines producing:

metal roofing panels
metal wall cladding panels
standing seam roofing systems
structural deck profiles
C and Z purlins
light gauge steel framing components

Typical production symptoms associated with VFD undervoltage include:

VFD displaying undervoltage fault alarms
motor stopping unexpectedly
machine failing to start or accelerate
drive resetting during operation
production interruptions
difficulty restarting the drive after faults

In many cases, undervoltage faults occur due to unstable electrical supply conditions or excessive load conditions.

Maintaining stable electrical power and proper machine loading helps prevent this issue.

Causes of Wear or Failure

VFD undervoltage typically occurs when the electrical supply voltage drops below the drive’s minimum operating requirement.

Several factors may contribute to this condition.

Low Incoming Supply Voltage

Electrical supply problems may reduce voltage.

Power Grid Instability

Fluctuations in the power network may affect machine operation.

Loose Electrical Connections

Poor connections may cause voltage drops.

Overloaded Electrical Circuits

Heavy loads may reduce available voltage.

Transformer or Power Supply Problems

Faulty power equipment may cause voltage loss.

Large Motor Starting Loads

Simultaneous motor startups may temporarily drop voltage.

Why It Happened and What Caused It

From an electrical engineering perspective, VFDs rely on a stable electrical input supply in order to generate controlled motor output.

When AC power enters the drive, it is rectified into DC and stored in the DC bus capacitors.

This stored energy provides the electrical supply used by the drive to power the motor.

If the incoming AC voltage drops too low, the DC bus voltage will also fall.

When the DC bus voltage drops below the minimum safe level, the VFD may not be able to generate sufficient voltage for the motor.

If the drive continued operating under these conditions, the motor could stall or the drive electronics could be damaged.

To prevent these risks, the drive automatically triggers an undervoltage protection fault and stops the motor.

Maintaining proper electrical supply conditions helps ensure stable drive operation.

How to Inspect the Problem

Inspection Procedure

Diagnosing VFD undervoltage faults requires inspecting the electrical power supply and drive configuration.

Step 1 – Check VFD Fault Code

Confirm that the drive indicates an undervoltage condition.

Step 2 – Measure Incoming Voltage

Use a meter to verify supply voltage levels.

Step 3 – Inspect Electrical Connections

Check terminals and wiring for loose connections.

Step 4 – Inspect Electrical Distribution System

Verify transformer and power supply performance.

Step 5 – Monitor Machine Load

Ensure the machine is not drawing excessive electrical current.

Step-by-Step Technician Guide – How to Fix

Correcting VFD undervoltage faults usually requires restoring stable electrical power conditions.

Method 1 – Restore Proper Power Supply

Ensure incoming voltage meets drive requirements.

Method 2 – Tighten Electrical Connections

Secure all power wiring connections.

Method 3 – Reduce Electrical Load

Avoid simultaneous startup of multiple motors.

Method 4 – Inspect Power Distribution Equipment

Repair faulty transformers or power supplies.

Method 5 – Reset the VFD

Restart the drive after correcting the voltage problem.

Preventative Maintenance Tips

Preventing VFD undervoltage faults requires maintaining stable electrical supply conditions.

Monitor Electrical Supply Voltage

Regular monitoring helps detect power problems early.

Maintain Electrical Connections

Tight connections prevent voltage loss.

Avoid Electrical Overloading

Ensure circuits are not overloaded.

Inspect Power Distribution Equipment

Routine checks help identify potential issues.

Maintain Stable Power Infrastructure

Reliable electrical supply supports consistent machine operation.

FAQ Section

What is a VFD undervoltage fault in roll forming machines?

It occurs when the drive detects that the supply voltage is too low for safe operation.

What causes undervoltage conditions?

Low supply voltage, loose connections, or overloaded electrical circuits may cause undervoltage.

Can undervoltage stop machine production?

Yes. The VFD will shut down the motor to protect the system.

How can undervoltage be detected?

The VFD will display an undervoltage alarm or fault code.

Can power grid problems cause undervoltage?

Yes. Electrical supply fluctuations may trigger the fault.

How can VFD undervoltage be prevented?

Maintaining stable electrical supply and proper electrical connections helps prevent this issue.