Electromagnetic compatibility (EMC) is the
ability of electrical/electronic equipment to operate in its
installation environment while neither causing nor
experiencing electromagnetic interference (EMI). EMI is any
interference with normal equipment operation caused by
abnormal energy entering the equipment either by conduction
though wiring connections or by radiated wave reception.
Radiated EMI is also called radio frequency interference (RFI).
Conducted EMI is also called high-frequency line noise.
Codes and
Standards in the U.S.
In the U.S., there are no codes and standards that
specifically and completely cover electromagnetic
compatibility of adjustable frequency drives (AFDs).
FCC Rules and
Regulations
Part 15 of the Federal Communications Commission (FCC) rules
and regulations covers unlicensed equipment that emits radio
frequency energy. Part 15 would apply to any AFD 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. The
essential requirements of 15.5 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 are also
covered by FCC Part 15 as "digital devices." As
commercial or industrial equipment, AFDs are "exempted
devices" subject only to the general conditions of
operation in 15.5 described above. However, the FCC strongly
recommends "the manufacturer of an exempted device
endeavors to have the device meet the specific technical
standards [of Part 15]."
Part 15 lists limits for radio frequency
voltage conducted to the public utility power lines by digital
devices. The range of frequencies covered is 0.15 to 30 MHz.
Part 15 also lists limits for the field strength of radiated
emissions from digital devices. The range of frequencies
covered is 30 MHz and above. At frequencies lower than the
radio frequencies regulated by the FCC, voltages conducted to
the power lines would be considered to be harmonic distortion
voltages. IEEE Standard 519 covers harmonic distortion issues.
(FCC information and documents are available at www.fcc.gov
and/or links from www.fcc.gov
to the Government Printing Office web site.)
Evaluating a Drive
As an FCC Part 15 "Digital Device"
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
480 V drive) from 650 volts of one polarity to 650 volts of
the opposite polarity. This nearly instantaneous voltage
change has the potential to generate a significant amount of
radio frequency energy.
Evaluating the drive as a microprocessor
controlled "digital device" does not correctly
target the most significant source of EMI.
Requiring a Drive
to Meet the FCC Requirements
Since 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 (IEC), International Special
Committee on Radio Interference (CISPR)" [see FCC
02-157]. The CISPR 11 standard provides a suitable test
procedure for testing drives to verify conformance with these
limits.
The radiated emission limits
specified by CISPR 22 are lower than the limits listed in Part
15. Accordingly, in 2003, Part 15 was revised to include
15.109(g): "As an alternative to the radiated emission
limits shown in paragraphs (a) and (b) of this section,
digital devices may be shown to comply with (CISPR) Pub. 22
(1997)" [see FCC DA 03-3848].
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.
EU Council
Directives
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 quite comprehensive.
It covers both the drive’s electromagnetic emissions and its
immunity from received emissions.
IEC 61800-3 Defines Two Installation
Environments
First Environment
"The First Environment includes domestic premises. It
also includes establishments directly connected without
intermediate transformer to a low-voltage power supply network
which supplies buildings used for domestic purposes."
Second Environment
"Second Environment includes all establishments other
than those directly connected to a low-voltage power supply
network which supplies buildings used for domestic
purposes."
IEC 61800-3
Defines Sale or Distribution to Two Levels of Customer
Competence
Unrestricted Distribution
"Unrestricted distribution is a mode of sales
distribution in which the supply of equipment is not dependent
on the EMC competence of the customer or user for the
application of drives."
Restricted Distribution
"Restricted distribution is a mode of sales distribution
in which the manufacturer restricts the supply of equipment to
suppliers, customers or users who separately or jointly have
technical competence in the EMC requirements of the
application of drives." The installer must install the
drive in conformance with the instructions provided in the
installation manual.
Recommendations to
Specifiers
For drives with the most comprehensive electromagnetic
compatibility, specifiers should require drives to meet the
IEC 61800-3 EMC standards and emission limits for restricted
distribution, and installation in the first environment.
Manuals should be required to include instructions for
installing the drive equipment so that it meets the specified
emission limits as installed.
Drives that meet the above
requirements will typically meet the technical requirements of
FCC Part 15, including the emission limits for a Class A
digital device.
Photo
1. Meeting EMC Standards - ABB’s ACS550 AC Drive family
combines simplicity, convenience, fieldbus connectivity,
harmonic mitigation and programmability to a degree not seen
in drives before. A built-in EMI/RFI filter guarantees
trouble-free operation of surrounding equipment and
instrumentation. And the 208/240 and 380/480-volt class of
drives meets compliance to CE’s first environment standards
Additional
Information
Additional information is available in two ABB publications:
—Technical Guide No. 2, EU
Council Directives and Adjustable Speed Electrical Power Drive
System
—Technical Guide No.3, EMC
Compliant Installation and Configuration for a Power Drive
System
Mark Kenyon has been with ABB since
1997. While at ABB, he’s worked with low voltage AC
drive product marketing and has brought ABB’s ACS140,
ACS400, ACH400, ACS800 and ACS550 products to market.
Currently, he’s participating in a Global Reference
Group responsible for defining ABB’s next generation
Micro Drive. Mark graduated from Marquette University
(Milwaukee, Wisconsin) with a bachelor of science degree
in 1973 and has an MBA, with a marketing focus, from
University of Wisconsin – Parkside (Kenosha,
Wisconsin). He has over 23 years of AC drive product
marketing experience, having worked for Eaton
Cutler-Hammer’s Drives Division and MagneTek prior to
ABB. |
