du/dt Reactors for Variable-Frequency Drives
du/dt reactors are installed in drive systems where steep voltage edges occur at the output of a variable-frequency drive. Their purpose is to reduce the rate of rise of line-to-line voltage and limit the most harmful switching transients reaching the motor terminals.
A correctly selected du/dt reactor reduces reflected-wave overvoltage, parasitic currents and voltage stress on the motor insulation. It is particularly useful with medium-length motor cables, older motors or motors with reduced insulation withstand.
A du/dt reactor is an intermediate solution between a standard motor reactor and a sine-wave filter. It does not convert the PWM output into a fully sinusoidal waveform, but it significantly reduces the most severe voltage transients.
Benefits
Reduced stress on motor winding insulation, lower peak voltage at the motor terminals, lower electromagnetic noise and improved service life of the drive system.
Selection criteria
The reactor is selected according to system voltage, motor current and power, switching frequency, cable length and type, load characteristics and the drive manufacturer's recommendations.
Installation
The unit is installed on the output side of the drive, between the frequency converter and the motor. The available ventilation and permissible temperature rise must be considered when mounting the reactor in an enclosure.