Product Introduction Product Group: Inverter Product Line: EFR options (AC Chokes, DV/DT reactors, Sine-wave filters) Part 3

We are pleased to announce the release of new inverter options from the Inverter family.

5. EFR-DU – dv/dt Reactors (Output Reactors)  

5.1 Output Phenomena in PWM-Fed Motors

At the inverter output, fast PWM switching causes:

• High voltage rise rates (dv/dt)
• Voltage reflections at the motor terminals
• Peak overvoltages, especially on longer motor cables

These effects stress motor insulation and may significantly reduce motor lifetime.

5.2 Application Range of EFR-DU EFR-DU dv/dt reactors are intended for inverter-fed motor systems with motor cable lengths up to approximately 100 m.

The maximum permissible cable length depends on:

• Cable capacitance
• Shielded vs. unshielded cable
• PWM switching frequency
• Installation layout

EFR-DU reactors provide an economical and compact solution for mitigating output-side electrical stress in standard applications.

5.3 dv/dt Reduction Effect

dv/dt reactors reduce the voltage rise steepness and limit reflected overvoltages at the motor terminals.

By using dv/dt reactor reduction by a factor of several times (typically below 700V/μs) compared to the raw PWM output can typically be achieved, significantly lowering insulation stress.

5.4 Positioning: EFR-DU vs. EFR-SI

EFR-DU represents a technical compromise between protection level and cost, whereas EFR-SI is the solution for demanding applications..

5.5 Sample Nameplate

5.6 Technical data table

5.7 EFR-DU Material List