No U.S. Standards Yet for Drives and EMI
According to ABB Inc., currently, no U.S. codes or standards exist that specifically and completely cover electromagnetic compatibility of adjustable frequency drives (AFDs).
Part 15 of the Federal Communications Commission rules and regulations covers unlicensed equipment that emits radio frequency energy. It would apply to any adjustable frequency drive as an “incidental radiator.” The operation of any equipment covered by Part 15 is subject to the general conditions of operation listed under paragraph 15.5. Essentially, the requirements are that the equipment must not interfere with any licensed broadcast,
navigation or safety services and must accept any interference caused by other equipment. Under Part 15.13, the manufacturer of an incidental radiator “shall employ good engineering practices to minimize the risk of harmful interference.”
Microprocessor controlled AFDs also are covered by FCC Part 15 as digital
devices that are exempted and subject only to the general conditions of operation in 15.5. However, the FCC strongly recommends that “the manufacturer of an exempted device endeavors to have the device meet the specific technical standards.”
A drive's microprocessor is not likely to be a significant source of EMI. The most significant potential source of EMI and RFI in a drive is the power-switching circuitry. This potential is largely unrelated to the design of the microprocessor or other type of control circuitry. EMI is generated in a drive by switching the output terminals back and forth between the positive and negative sides of the DC bus to synthesize an AC output waveform. Each time the output transistor switches operate, the terminal voltage jumps (in a 480V drive) from 650V of one polarity to 650V of the opposite polarity. This nearly instantaneous voltage change has the potential to generate a significant amount of radio frequency energy.
According to ABB, evaluating the drive as a microprocessor controlled “digital device” does not correctly target the most significant source of EMI.
Because the applicable requirements are not very specific or restrictive, almost any drive could be said to meet the requirements of Part 15 without actually providing a significant level of electromagnetic filtration.
A drive could be required to meet the conducted and radiated emission limits listed in Part 15 for a Class A or Class B digital device, but Part 15 does not contain or specify a testing procedure that is designed for use with drives. Without specifying a suitable testing procedure, any declaration that a drive meets the specified limits might be suspect. The conducted emission limits listed in Part 15 were revised in 2002 to “harmonize our domestic requirements” with the international standards developed by the International Electrotechnical Commission and
The International Special Committee on Radio Interference (CISPR).
CISPR 22 covers digital devices, while CISPR 11 covers industrial scientific and medical equipment. The U.S. Food and Drug Administration encourages manufacturers of electromedical equipment to use CISPR 11.
In the European Economic Community, the EU Council Directives set standards for various products. Many of these standards are derived from standards written by the International Electrotechnical Commission (IEC). The EMC Product Standard for Power Drive Systems, EN 61800-3 (or IEC 61800-3) is used as the main standard for adjustable speed drives. This standard contains test procedures that are specifically suitable for drives and the standard is comprehensive. It covers both the drive's electromagnetic emissions and its immunity from received emissions.
For a copy of ABB's “Technical Guide No. 2, EU Council Directives and Adjustable Speed Electrical Power Drive System” or “Technical Guide No. 3, EMC Compliant Installation and Configuration for a Power Drive System,” contact Peter Walter at (262) 780-3876 or firstname.lastname@example.org.