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31 January, 2023

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How to choose between MV and LV drives

14 November, 2022

Medium-voltage drives are thought to be more costly and complex than low-voltage drives, and better suited to higher power applications. But, as Alberto Ricci, ABB’s system drives sales manager, explains, modern MV drives are less daunting, more versatile, and can be more cost-effective than LV equivalents.

For very low or high-power applications, the choice between using an LV or MV drive is often fairly straightforward, and can be determined largely by power requirements. For anything below 400kW, LV can often be the easiest and most cost-effective option. However, above this level, the best option is less clear-cut. Many manufacturers offer both LV and MV drives in the same power ranges, so the best option for an application will depend on more than just the required power rating.

For instance, cabling is an important consideration, because it can comprise a significant portion of the installation costs. MV drives operate at higher voltages, with much lower currents for the same output power. As a result, they use cables with much smaller diameters and less copper. For applications with particularly long cable runs, this can lead to substantial savings on installation costs, while losses on MV cabling can also be lower, leading to higher efficiencies over the lifetime of the drive.

Infrastructure

Available infrastructure is another consideration when retrofitting to an existing MV application. LV drives may need extra equipment, such as separate transformers and sine filters, which add to the cost and complexity of the installation. MV drives will need a transformer as well, but systems exist with built-in transformers. This makes the drive integration very easy, with “three cables in, three cables out” for ease of installation. If the new drive is replacing an existing MV application, you may be able to keep the existing motor and much of the cabling.

Many MV drives use a design known as an NPC (neutral point clamped) inverter topology. It’s one of the least complex and most robust drive constructions. It uses MV power semiconductor switches which are ideal for MV applications. The resulting drives have low parts counts, offering higher reliability and lower Opex costs than other MV drives topologies.
Finally, MV drives are seen by some as being more difficult to operate and maintain, but some MV drives operate with the same keypad, menu structure, architecture and functions as equivalent LV drives. Put simply, if you can operate an LV drive, you can operate an MV drive.




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