Responding to the needs of industry
10 December 2012
I am writing this at the end of September in the middle of the IEC General Meeting in Oslo. So far I have been at two meetings and both have brought out ideas that I thought I might share about how those of us involved in the standards writing process try to meet the needs of industry.
Care and Repair of Motors
Everyone should now be familiar with the existence of IEC 60079-19, the standard which controls the repair procedures applicable to Ex Equipment. Its origins were in a BEAMA/AEMT code of practice for repair which originated in the UK several years ago. This came about as a result of the coal industry divesting itself of in-house repair facilities, and the desire to have some guidance available to be followed by all the independent workshops that would now be turning round motor rewinds in double-quick time.
The code fully addressed all the issues related to Ex d equipment and bolted on a few thoughts related to the other protection concepts. Unfortunately, even though now an international standard, there has been little development in the other concepts.
A particular issue affects the re-winding of Ex e Motors. Because tE time, used to set protective relays, is such a critical part of the data for use of the motor, and because there was concern that rewinding a motor might seriously affect the value of tE time, the writers of the current edition decided to play safe and say that if an Ex e motor is rewound, the certified value for tE should be reduced by 25%.
This has meant that many Ex e motors may not be usable in their current applications after rewinding, and at least one major user of such machines has indicated that it may have to avoid specifying such motors in future, simply because it cannot afford to have motors on its sites that cannot be quickly repaired and rewound.
There is also the problem of the introduction of “in gas testing”, relating to potential incendive discharges from high voltage winding systems, with the edition of the standard first published in 2007. Unless the repair workshop is able to reproduce the exact winding, as originally fitted by the manufacturer, compliance is not assured. It would not be common for the repairer to be able to do this, as it would mean sourcing coils from the manufacturer and having a compatible impregnation system, both unlikely.
The present situation has resulted in many commercial problems, of repair facilities not being able to repair “e” and even “nA” motors where the incendivity test requirement needs to be applied. This is therefore a major problem.
A task force of TC31Working Group 27 has been addressing these issues and is preparing guidelines which it hopes to bring forward in a future edition of IEC 60079-19, to overcome the problems with the tE time by ensuring the use of best practices for the rewinding. It also hopes to formalise a way for a repair workshop to get acceptance of its own coil manufacturing and impregnation systems by testing representative samples in accordance with IEC 60079-7.
The timescale is not yet certain, but there are many manufacturers, users and repair workshops who will be relieved once the problem is solved.
A matter of definition
How many readers of HazardEx bother to read the definitions usually found in clause 3 of a standard? I suspect the answer is: not many! But it is worth considering the value that this section of a standard brings to the document, and the hierarchy of the definition tree that we work to in the IEC 60079 series of standards.
It is very important that every reader and user of a standard has a full and complete understanding of every term used in the document, otherwise misunderstandings can arise. It is also important that the same term means exactly the same in every standard where it is used.
For this reason, IEC committee TC31 took the decision some time ago that all definitions that are common to more than one standard for the types of protection should appear just once, in IEC 60079-0. Additionally, a compendium of all the definitions used in all the TC31 standards can be found in the International Electrotechnical Vocabulary (IEV), available as an on-line database from IEC. Take a look at http://www.electropedia.org/ and you will find every definition given in each of nine languages. Definitions related to Ex equipment and installations are given in chapter 426.
One of the problems of different standards being issued at different times is that definitions can start to vary between individual standards, and between the standards and the IEV, particularly as changing technology brings a requirement for new definitions. Working Group 22 has spent two very full days on aligning and refining the definitions, ready for the next update of the IEV. With this hidden but vital work, we are assuring that the standards are both easier to read and apply.