Issues with the
IEEE P1775 BPL EMC Standard
The draft standard, P1775,
Standard for Powerline Communication Equipment - Electromagnetic Compatibility
(EMC) Requirements - Testing and Measurement Methods, is being completed by the
IEEE. The next step is for the IEEE to
form a balloting pool to determine whether this draft should be come an IEEE
consensus standard.
Although there are a number
of good portions of the draft, notably in the area of EMC immunity test methods
and acceptance criteria, there are a number of unresolved issues in the content
of most of the draft that should preclude it from being made into a standard at
this time. The value in IEEE standards is that they represent the consensus of
a broad range of stakeholders. In this case, the BPL industry stake is well
represented, but in its present form, this draft does not sufficiently include
the needs of some other stakeholders who will also be impacted by the final
standard’s content.
The Value and Importance of Voting in IEEE Balloting
Pools
The IEEE Working Group (WG)
that developed the draft document was heavily dominated by BPL, utility and EMC
testing companies doing business with both industries, with only the ARRL
serving to represent the radiocommunications interests throughout the entire
process. In many cases, ARRL’s positions
were voted down by the heavily dominated group, with a statement that indicates
that the concerns that were being raised should be addressed during the IEEE
ballot.
The IEEE balloting process is
an important part of the strength of IEEE consensus standards. All stakeholders
have an opportunity to participate. The ballot process is as much a part of the
standards-writing process as is the WG that developed the text, because votes
and comments made during the ballot are used not only to approve or disapprove
the standard, but to ensure that stakeholders who were not able to participate
in the extensive travel often needed for WGs to meet and develop standards can
also have input and control of what should be included in the approved
standard. Under the IEEE’s rules, all
negative votes and comments made during the ballot must be considered by the WG
and a reasonable effort made to resolve them, just like would be done at WG
meetings.
Voting on IEEE standards is a
responsibility that should be taken seriously. Those who sign up to ballot must
submit ballots. The votes cast and
comments offered should be made in the spirit of trying to develop a good
standard, not to stop a standard from being created. Each stakeholder should cast a vote that
indicates whether they believe that their interests are properly represented in
the draft document’s content, but if a vote is negative, specific reasons
should be given as to the reasons for a negative vote. The balloter should also
explain what changes to the draft would cause the balloter to change his or her
vote and support the revised standard. A simple negative ballot without reasons
cannot be resolved, so it would have no real influence on the standard’s
content.
The long term value of having
the IEEE develop standards that can have the support of a wide range of
stakeholders is important, so as a stakeholder, although you can and should use
the balloting process to influence the standard’s development, that should be
done as productively as possible, to truly be a helpful part of the IEEE’s
process.
The IEEE Project Authorization Request
When a Working Group wants to
develop a standard, they find an IEEE Society to sponsor the standard. That Society then submits a Project
Authorization Request (PAR) to the IEEE, which then approves the standard. The PAR for P1775
outlines the purpose scope and sponsorship of the standard.
The P1775 PAR contains a
number of important provisions. It establishes
that the standard is to reference existing national and international
standards, a statement that is immediately followed by a statement that it will
not set emissions limits, as these are the subject of national regulations. It also requires that the standard contain
test methods and EMC criteria
(standards for judging whether compatibility goals have been achieved).
Regulations, standard and the PAR
One of the major deficiencies
in this P1775 draft is that for the emission testing portion of the document,
the test method it defines in the text is a virtual parroting of the test
methods referenced in the FCC rules.
This is not what the IEEE PAR directs the WG to do. In fact, the PAR
says that the standard will draw on existing standards, with the very next sentence explaining what would not be
covered by the standard because that aspect of EMC is covered by regulations. For the PAR to make that distinction and for
the draft to immediately turn to one nation’s regulations for the major part of
its emissions test method is inappropriate, and on that first major point, the
document does not meet the requirement set forth in the PAR.
EMC Issues
In the process of developing
the standard and in the voting and discussions that took place as the IEEE
sponsoring committees approved this standard for ballot, a number of EMC issues
were raised. Many were addressed by the WG, but a number of critical issues were
raised, but not accepted by the WG.
As just a few examples of the
problems, the standard allows the BPL equipment under test to be configured at less than its
maximum operating data rates and operating levels (Clause 6 in an earlier
draft), essentially giving free reign to set the equipment to an operating
level that passes, even though it is capable of operating at a much higher
level, then reporting the results.
Naturally, a device set to a level that passes will pass. This is
inappropriate because neither the standard nor any operating practice by BPL
operators requires that every single component of a system be measured for
compliance when installed. The result is that BPL systems can exceed the emissions
limits if configured at an operating level greater than what may have been used
for compliance testing of the system.
The draft must be changed to require testing at the maximum operating
level that it would be possible for an end user to use in operating the system.
The draft also specifies how
conducted emissions are to be measured on the signal ports, but it
inappropriately and inexplicably allows the BPL
signal to be turned off to make this measurement. The majority of the emissions from a BPL
system come from the BPL signal, so if compatibility is to be assured, the
device must be tested in an operational state for all tests (as required in
There are other EMC issues,
but the above examples show why the EMC community needs to participate in the
ballot process to help ensure that the EMC discipline is fully represented in
what is as much an EMC standard as it is a standard for the power and BPL
industries.
EMC Criteria
In three separate places in
the PAR, that the standard will address test methods and EMC criteria for emissions and immunity EMC aspects of
BPL. Although it is doubtful whether
parroting FCC rules for test methods meets the PAR, the required immunity and
emissions test methods are included in the draft. The immunity test methods are
actually quite good, derived from recognized worldwide standards as required by
the PAR, not from a single country’s regulations. (Those regulations are not yet fully resolved
after a successful
The emissions section of the
document, containing no emissions limits, has no standard on which to compare
any of the test methods to judge whether compatibility has been met. It contains no information about the
protection needed to prevent harmful interference, so there is no way to judge
compatibility on that basis, either. The draft does contain a normative
reference section on how to respond to interference complaints, with some
criteria to use to determine whether a reported case of “BPL interference”
could be caused by some other source, but a single, informative reference with that single “criterion” is not
sufficient to meet the requirement of the PAR that the standard must contain
EMC criteria.
As the annex was being
developed, words that explained that to avoid causing harmful interference BPL
must avoid locally used spectrum were introduced by the author of the annex,
but removed by the WG. ARRL also asked
that the annex contain a statement that indicated that a notch depth of 35 dB
has been demonstrated to minimize the likelihood of harmful interference to
licensed users, but the WG voted not to include it, indicating that not all BPL
equipment could meet that level. Good
standards are not intended to support and justify the lowest common denominator
in any industry. The most useful standards offer information that allows an
industry to continue to improve and grow. Leaving out any guidance as to what
is required to avoid causing harmful interference does not meet that goal and
virtually excludes emissions EMC criteria from the draft.
Measurement Methods
In addition to parroting the
FCC emissions test methods, the draft also avoids important components
in the test methods. In the FCC rules, limits are specified at 30
meters distance, with a test method that measures at a closer distance and then
uses a 40 dB/decade of distance extrapolation to get to the 30 meters
regulatory reference distance. Even the
Standards typically drive
regulations, not the other way around, and many good standards, such as those
prepared under the ANSI asc C63 committee
have been incorporated in regulations by reference. This was not done by
writing standards that mirror existing rules; it was done by writing standard
that resolved issues through a broad consensus of stakeholders, solving regulatory
issues. The P1775 WG had an opportunity to do this, but chose to almost
completely avoid the issues of distance extrapolation, except in a annex that
describes how to make measurements of extrapolation along the ground and
determine the rate at which BPL signals actually fall off with distance, to be
used only in cases where national regulation does not provide any extrapolation
factor. (An ARRL observation that extrapolation is governed by the laws of
physics, which don’t change from country to country, was not considered to be
applicable.) The draft also does not
consider how fields vary with height, as another example of EMC-related issues
that are not addressed.
As the draft was being
developed, ARRL provided NEC-4 modeling that showed that the field strength
variation with distance is very much dependent on distance along the line,
height and frequency and other factors that make such a measurement in the
extreme radiating near field region of a power line surrounded by other
scatterers almost an impossibility. This information was not used to develop the
standard.
The draft also does not
completely measure the fields near radiators.
Again parroting the FCC regulations, the draft measures only two of
three axes in the magnetic field strength.
In the emissions test method taken from the FCC rules, the test antenna
is rotated horizontally, but never tipped forward to measure the Z axis of the
magnetic field. This is not in
concordance with the test method in the extrapolation-measurement portion of
the draft where all three axes are measured; leaving a document that is not
even self consistent in the way it treats measurements of the same fields for
different purposes. It should not escape any attention that the measurement of
the compliance of the system is the one that does not include measurements of
the entire field strength, resulting in a measurement that will be at least
somewhat below its true value.
Stakeholders
One may assume that only
Amateur Radio stakeholders are affected by this standard. In reality, that is
not the case. The BPL industry has made
progress in resolving interference to Amateur Radio. They have done so by implementing for Amateur
Radio things that this WG has chosen to not include, or even removed, from the
draft.
Other than
radiocommunications stakeholders, others are equally affected, although in
different ways. The BPL industry has
made progress resolving interference issues. It would benefit from taking its
successful models as part of an IEEE consensus standard. Information that advises BPL operators how to
identify and avoid locally used spectrum would strengthen the standard and
determining that this was done would be an excellent EMC criterion.
Electric utility companies
don’t benefit from the draft as written, either. If the draft were made a
standard, even in its present form, the BPL industry will at least get the
marketing benefit of being able to claim that a consensus had been reached on
the EMC aspects of BPL and that this consensus is documented in an IEEE
standard. The electric utilities generally won’t benefit from that aspect, but
will instead be given a standard with a very complicated and incomplete test
method and guidance on EMC that doesn’t actually explain how to operate a system
compatibly with local spectrum users.
What could be a good standard that provides guidance and assurance that
compatibility with licensed users can be achieved leaves many important points
for electric utility companies unaddressed. The utility industry is not better off with a final standard that does not fully address
its needs to deploy BPL systems without the major interference problems that
can be solved, but not by the guidance in this draft. The only way that they will
have access to that information is to allow the balloting process to require
that the WG develop and include it in its next draft.
EMC Community
This standard is sponsored by
the IEEE Power Engineering Society. The EMC Society and Communications Society
are co-sponsors. The WG intentionally chose
not to meet in any EMC venues, making it difficult for the EMC community to
have truly been an equal partner in the development of an EMC standard. The EMC community should pay special
attention to the EMC content of this draft, as the balloting process is the
most important direct influence that part of the sponsorship will have in the
development of the standard. Their expertise can only be brought to this table
through their balloting on the draft and ensuing that the EMC discipline is
fully included.
Unfinished work
Voting as part of standards
development is as important as participation in the WG. For a number of reasons, although there are
certainly some good and important parts of this draft, it represents unfinished
work on many fronts. At the first meeting of the WG, there were as many as 30
people in attendance. As time progressed, interest waned and the WG membership
gradually declined. It is not likely
that the present WG membership will continue to develop and refine the standard
if approved in its present draft form.
If the draft is approved, it will become a standard with its flaws and
good points. Both will be seen as representing
the best consensus of the IEEE engineering and EMC communities. If it is ever revised in the future, that
process will take years. In its present
form, this draft does not represent the best IEEE and EMC work and as such, the
balloting group can and should look closely at what needs to be done and allow
the ballot process to provide guidance to the WG as to what the greater
consensus of a wider range of stakeholders sees as necessary to the creation of
a good standard that can and will have the support of all at the standards
table.