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 Europe under EN55022).

 

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 US court case to get the rules as written remanded back to the FCC.)  The immunity section of the P1775 draft also contains specified immunity levels that can be used and specified by BPL customers, and test methods to be used to measure them.  This addresses EMC acceptance criteria for immunity.  Missing from the immunity section is any indication of what real-world conditions may be encountered by BPL systems, as some licensed radio transmitters can create field strengths at power lines that are much higher than any of the immunity levels specified in the document. Information about these field strengths from Amateur stations was provided to P1775, but not included in the final version of the draft.

 

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 US courts agreed that the FCC had not adequately explained the justification for continuing to use that factor when other filings by authoritative stakeholders in the FCC rulemaking stated clearly that measurements had shown 40 dB/decade to be incorrect. 

 

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.