Harmonizing IEEE and IEC standards
What does it mean?
John Tengdin, Editor-in-Chief
May 2001
In the current discussions of IEEE and IEC standards, the favorite word is
“harmonize”. It’s meaning is, like beauty, in the eyes (or minds) of the
beholder. Some believe that IEEE standards should be scrapped in favor of
“comparable” IEC standards. Others believe that there are sometimes
excellent reasons for retaining IEEE standards, particularly where the IEEE
requirements are more stringent than IEC.
One case in point is C37.90.2 IEEE Standard for Withstand Capability of Relay
Systems to Radiated Electromagnetic Interference from Transceivers, often called
the “walkie talkie” standard. The first version of C37.90.2 was published in
1987 as a Trial Use Standard. The work on the standard within the PES Power
System Relaying Committee (PSRC) was in reaction to false
operations of relays and control systems when nearby hand held transceivers
(walkie-talkies) were transmitting. Numerous tests were run, and the result was
a requirement that relays withstand a field strength of 10 –20 volts/meter.
This corresponded to the radiated field strength from a 5 watt transceiver at a
distance of 1 meter. The document contained a strong caution that operation of
transceivers closer than 1 meter to any face of a relay was outside the scope of
the standard.
Subsequently, the IEC created standard IEC 255-22-3 (1989) covering
essentially the same application, but did contain differences from C37.90.2 in
the modulation method to be tested. It contained three severity levels of 1, 3,
and 10 volts/meter, with the user to specify the severity class to be met.
Work on updating the IEEE Trial Use Standard began in 1993, as field
experience had shown that the published caution regarding proximity was
unworkable. Relays that met C37.90.2 withstand requirements were nonetheless
false tripping when transceivers closer than 1 meter to the relays were keyed to
transmit. Additional tests were conducted to determine the field strength from 5
watt transceivers when in much closer proximity. As a result, the field strength
level in the revised standard was increased to 35 V/m. It represented the
consensus of both electric utilities and the manufacturers, and roughly
approximates the effect of a walkie-talkie operating at 15 cm (6 in) from the
relay. Additional changes were made in the test methods, but the most
significant change was the withstand requirement. IEEE C37.90.1-1995 was
published 19 September 1995 as a full (not trial use) standard.
With this significant change in withstand levels, the relay manufacturers had
to embark on completely new testing, and in many cases, new redesign programs.
At the same time, effort was made to persuade IEC to update their standard. The
IEEE representatives were unsuccessful, as the position of the IEC TC95 members
was that walkie-talkies should not be operated closer than 1 meter to a relay.
Nor were they unwilling to add a new 35 V/m severity class.
IEEE standards have a five year life, so in 1999 a working group in PSRC
began work to review the 1995 version for possible update or reaffirmation. The
conclusion was that the 1995 document should go to ballot requesting
reaffirmation. At the same time, a renewed effort was made to persuade IEC TC95
to add a 35 V/m severity class – again without success. The reaffirmation
ballot was successful in 2000. However, there were several negative ballots that
were resolved only with a promise to harmonize with IEC on the next update.
This is but one example of efforts to “harmonize” an IEEE standard with
IEC. In this case, the two standards covered almost exactly the same topic. In
other cases, the overlap is significantly less than 100 %, which makes any
harmonization effort much more difficult.
Harmonization between IEEE and IEC standards is a noble goal. The words sound
nice, but their precise meaning is – at the moment – elusive. Does it mean
that IEEE standards should never be more stringent than IEC? Hardly the case.
Does it mean that minor differences should be resolved? Certainly desirable, but
clearly a two way street is needed. Also, there must be recognition that –
sometimes – there may be differences of technical opinion that cannot be
resolved.
Finally,
we need a clear direction for “harmonization”. This guidance should lead the
volunteer engineers through the complex issues in standards development. The PES
leadership must provide that direction, or “harmonization” will not be
achieved.
Where do you want to go now?
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