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VFD Technology Reduces Harmonics At Partial Load

May 1, 2004
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NEW BERLIN, Wis. - "If you claimed that the sole purpose of a variable speed motor drive was to increase energy efficiency, it would be no exaggeration, of course," said Mike Olson, HVAC sales manager - Western Region, ABB Automation Technologies, Drives. "That's what they're designed for."

But with the company's new ACH550 drive for HVAC applications, ABB is applying its patent-pending Swinging Choke technology "to reduce harmonics at partial load, making an essentially efficiency-driven solution that much more efficient - at zero added cost to the user," said Olson.

According to ABB, motors powering mechanical equipment consume a large amount of energy. For example, they account for a full 60 percent of the total electrical energy consumed in the U.S. And when motors run at a fixed speed, much of the energy they use is simply wasted. Variable speed drives are designed to precisely control motor speed to reflect actual demand, eliminating waste caused by fixed-speed operation and generating end-user savings of up to 70 percent, says the company.

Even so, current harmonics cause energy loss in devices operating with variable speed drives. Harmonics are electrical disturbances generated by non-linear devices (just about anything with a microprocessor) connected to the supply system. They squander energy by causing excessive transformer heat loss. In addition, they require expensive compensation in the form of oversized cabling and can cause sensitive equipment to malfunction.

Reducing Harmonics At Partial Load

Conventional chokes bring down harmonics levels at full load to meet existing standards, but do nothing to reduce them at partial load, says ABB. Since devices operating with a variable speed drive operate at partial load most of the time, reducing harmonics at partial load can lead to savings in transformer heat losses. Through the use of ABB's Swinging Choke design, the ACH550 drive reduces harmonics at both full load and partial load for a total reduction of up to 30 percent compared to traditional choke designs.

"The Swinging Choke is important because it provides increased inductance at reduced current, something that quite literally has never been done before," remarked Olson. "When users realize what a 30 percent additional reduction in harmonics at partial load means in terms of energy saved, lowered first costs, and increased system reliability, they won't be prepared to live without it. So we foresee quite an impact on the industry."

The patent-pending Swinging Choke design reduces harmonics at full load and partial load for a total reduction of up to 30 percent compared to traditional choke designs.

Design Driven By Customers' Requirements

The ACH550 is a unique product in other respects as well. It was the first joint development effort between ABB in Finland and the U.S. And it's based on a customer needs assessment process that asked drive users worldwide what they wanted in a motor drive.

Because of that, the ACH550 drive has been developed to make "motor control easier than ever before," stated Olson.

As a result, the drive includes a simple keypad, modeled after a cell phone. Standard Start-Up Assistant software is designed to guide users through setup procedures and Maintenance Assistant software signals when it's time for routine maintenance. In addition, Diagnostic Assistant software provides users with suggestions for correcting faults.

Olson concluded, "The ACH550 offers precedent-setting harmonics mitigation," and it also is easier to install, start, and use - "benefits that our customers asked us for."

ABB Inc., Automation Technologies, Drives, of New Berlin, Wis., is a major drives supplier to the U.S. HVAC market. For more information, visit www.abb-drives.com.

Publication date: 05/03/2004

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