By Steve Wetzel, Technical Sales Manager for Automation Products, Southwire Company
Editor’s Note: This article is adapted from the white paper, “Medium Voltage Drive Cables,” from Southwire Co. Download the full paper at https://bit.ly/tj0423wpso for comprehensive information about the difference between low voltage and medium voltage drives and cables, grounding considerations, and how that impacts motor performance. Also, learn about 4 key characteristics needed for a low voltage drive system’s inverter to motor cable, and how that compares to medium voltage drives.
There’s been much discussion about which cable to use between a variable-frequency drive (VFD) inverter and the motor. Most conversation has focused on low voltage drives — drives rated under 2,000V. But what about medium voltage drives? They need cable too. Let’s look at those.
Most medium voltage drives use the same basic technology as low voltage drives: the insulated gate bipolar transistor (IGBT), a voltage-sourced device. Most, if not all, of today’s low voltage drives rely on IGBT technology. It’s a fast device with rise times in the tens or hundreds of nanoseconds.
The IGBTs are located in the drives inverter section and allow the drives to create an output of Pulse Width Modulated (PWM) waveforms. These waveforms look like a series of square waves of different wavelengths. They trick the motor into thinking it’s seeing a waveform of a different fundamental frequency than the 60 Hz traditionally used. IGBT-based drives offer many benefits like increased efficiency, better control, lower cost and reduced drive size.