What support products does it take to maximize the impact of using VFDs and VSDs? - Part 1
entire cable assembly is encased in a polyvinyl chloride (PVC) jacket for environmental protection. Belden Basic cables are suited for use in class 1 division 2 hazardous locations as defined in the National Electrical Code (NEC). Class 1 refers to facilities for handling flammable gases, vapors, and liquids. Division 2 specifies that these flammable materials are not ordinarily present in concentrations high enough to be ignitable. Some cable series, like LAPP's ÖLFLEX VFD 1XL, are available with and without signal wires. Applications that benefit from having signal wires can turn to LAPP’s 701710 cable. It includes three power conductors, a ground conductor, and a pair of signal wires. The power conductors are 16 AWG (26x30 stranding) with XLPE (plus) insulation. The signal pair are individually foil shielded. The entire assembly is shielded with barrier tape, triple-layer foil tape (100% coverage), and tinned copper braid (85% coverage). The outer jacket is a specially formulated thermoplastic elastomer (TPE) resistant to disinfecting solutions and is typically used in the food, beverage, chemical, and related industries. In addition to reliably and efficiently handling power and signals, VFD cables need to be able to handle high
Figure 2: Uncontrolled high voltage spikes can pierce the insulation and result in cable failure. (Image source: LAPP)
voltage spikes and electromagnetic interference (EMI) noise levels resulting from the drive's high- frequency operation. While VFD cables are designed to contain and manage high voltage spikes and EMI, they have their limits (Figure 2). That’s when load reactors reduce high voltage spikes and EMI. For a more detailed discussion of VFD cable selection, see “Specifying and Using VFD Cables to Improve Reliability and Safety and Reduce Carbon Emissions.” Load reactors Load reactors, also called output reactors, are connected close to the drive's output to reduce the
impact of high voltage spikes and EMI, and they protect wire insulation in both the cable and motor. VSDs/VFDs produce a high- frequency (usually between 16 and 20 kHz) output. The high-frequency switching results in voltage rise times of a few microseconds, causing high voltage spikes that can exceed the motor’s peak voltage rating, resulting in insulation breakdown. Depending on the type of motor used, load reactors are often recommended if the VFD cable length exceeds 30 m (100 ft.). There are exceptions; for example, if the motor meets the NEMA MG-1 Part 31 standard, it may be possible to have a 90 m cable (300 ft) without using a load reactor.
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