Motor Protection Devices Save You Time and Money

GD Rectifiers partners with Enerdoor to provide a state-of-the-art motor protection series designed for VFDs, servo drives and long cable applications, carrying CE and UL approvals

Enerdoor’s motor protection series protects motors from harmful overvoltage and dV/dt spikes generated by the drive’s output and is important for applications with variable frequency drives, servo drives and long cable applications.  It is increasingly common for engineers to experience dV/dt spikes which are caused by the rising edge of the pulse-width-modulation signal at the output of the VFD. These harmful dV/dt spikes can damage the insulation, motor windings and bearings, and lead to decreased motor life.

The challenge for OEMs, system integrators and distributors is to ensure installed motors are efficiently protected from overvoltage. GD Rectifiers partners with Enerdoor to offer various motor protection solutions which are ideal for all applications and various motor cable lengths. Due to the “reflective wave” phenomena, the greater the distance between the VFD and the motor, the greater the effect of the dv/dt spike. By adding additional protection between the VFD and motor, engineers can expect increased motor life, less downtime, and better EMC compliance for conducted and radiated emissions, which improves machine efficiency whilst providing a cost-effective solution.

These motor protection output filters work with various carrier frequencies, output frequencies and applications, and include differential mode inductance (load reactors), common mode inductance (chokes), sine wave filters, snubbers, and dV/dt filters. Enerdoor’s motor protection series carries CE and UL approvals, offering a current range from 3 to 1100A with unique features including: high linearity vs frequency and current, very low operating temperatures and compact dimensions.

Benefits of Motor Protection:

  • Increase motor life
  • Protect motor windings, insulation and bearings
  • Protect against voltage spikes on the motor
  • Solve problems associated with dV/dt spikes on the output of VFDs
  • Unique solution for high-speed motor applications
  • Works with various carrier frequencies, output frequencies and applications
  • Output frequencies up to 3 kHz using high-performance material that run at ambient temperatures
  • Pass European emission Standards; carries CE and UL approvals
  • Prevent EMC non-compliance due to radiated emissions from motor cables
  • Reduce motor temperature and provides very low power loss
  • High linearity vs frequency and current

Applications for Motor Protection:

  • Motors controlled by drives
  • Long cable applications > 25m
  • Pumps and conveyors
  • Automated machinery
  • Closed loop spindle motors
  • Water treatment plants
  • Packaging equipment
  • CNC machines

Custom Solutions

Sine Wave Filters: This filter line reduces the effect of the pulse-width-modulation by converting the drives output to a true sine waveform eliminating dV/dt. Sine wave filters are especially beneficial for long cable applications as they eliminate the need for shielded cable between the drive and the VFD, eliminating the need for a VFD rated motor. Additionally, a sine wave does not emit high frequency emissions and can solve EMC non-compliance issues due to radiated emissions.

Enerdoor’s FIN915SFH high frequency sine wave filter is used with fundamental frequencies up to 25 kHz and output frequencies up to 10 kHz.

Standard waveform measured when the motor is controlled by a VFD drive

Standard waveform measured when the motor is controlled by a VFD drive, with an Enerdoor FIN915SFH sine wave filter installed

Snubber:  The Enerdoor FIN47SNB snubber is a unique solution for reducing common mode and differential mode noise. The snubber is used in parallel to the system and is an ideal solution for improving the reliability of winding insulation and bearings.  It has very low power loss and only one model is required for unlimited HP motors.

The diagrams demonstrate how the Enerdoor FIN47SNB slows the rate of voltage increase and decreases the peak voltage seen at motor terminals.

Typical measurement of dV/dt on motor controlled by VFD with cable length of 100m (300ft), without Enerdoor snubber installed

Typical measurement of dV/dt on motor controlled by VFD with cable length of 100m (300ft), with Enerdoor snubber FIN47SNB installed

Benefits of using Enerdoor’s Motor Protection

Enerdoor provides decades of motor protection experience with a track record of solving power quality issues for companies around the world. Offering an advanced support system of global EMC and motor protection engineers and affiliated organisations, helping expedite the process of protecting systems and equipment.

GD Rectifiers offers competitive pricing, expert technical support and fast delivery on all Enerdoor products. As Enerdoor’s exclusive UK distributor, GD Rectifiers works closely with customers on their product specification, budget and delivery requirements and are able to organise call-off and scheduled orders to ensure stock is always on the shelves at their factory in Burgess Hill, West Sussex.

For further information on Enerdoor’s Motor Protection Filters or to discuss your requirements, please call GD Rectifiers today on: 01444 243 452 or email:

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