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Baseefa Ltd

Raising the temperature in Canada

12 April 2015

SGS Baseefa General Manager Ron Sinclair MBE is chairman of the IEC Cenelec TC31 committee. Here he outlines some of the results from the series of TC31 meetings held in the CSA Conference Centre in Toronto in March 2015.

Toronto - Shutterstock
Toronto - Shutterstock

In 12 days over a cold fortnight in March, 20 separate and overlapping groups met for between one and four days each; a total of 30 meeting days with typically between ten and 30 people at each meeting.

WG22 is responsible primarily for the maintenance of IEC 60079-0, and we spent three days discussing the comments received on the first draft for the next edition of the standard, due for publication in 2017.  Most of the modifications are comparatively simple and just acknowledge necessary changes in technology since the last edition was published in 2011. 

However, following work done elsewhere resulting in the publication of the new documents related to electrostatics (IEC TS 60079-32-1 and IEC 60079-32-2), it was agreed to reinstate a charge transfer test that was removed in 2011.  With the work behind the development of IEC 60079-32-2, it is hoped that the inconsistencies seen with the previous version of the test will now be brought under control.

WG 27, responsible for looking at horizontal issues (across all standards) relating to motors, continues to work on a project to be able to specify the “equivalence” of electronic variable speed drives, to avoid the current problem of having to perform temperature tests with the actual motor and convertor coupled together. 

This is not a problem for 5 kW drives, but becomes a major logistical (as well as technical) problem when you get above 500 kW.  It is not only the pulse repetition frequency that can affect motor temperature, but there are also a number of other factors including the ratio of the supply voltage to the motor operating voltage and the presence or not of a harmonic filter system.

We also discussed issues relating to temperature protection of motors causing nuisance tripping of motors (possibly with expensive issues for the plant and process) where we agreed that some form of voting logic could be appropriate if the motor had a sufficient number of temperature detectors.  Historically, the detectors are as likely to become defective as the motor is likely to overheat, and it can be very expensive to invoke a plant shut down for a single defective temperature detector.

Much of the IEC 60079-15 standard for Ex n equipment has now been dispersed in other concept standards to provide level of protection Gc (for example Ex nL has become Ex ic, most of Ex nC has become either Ex dc or Ex mc).This fact, coupled with the forthcoming publication of the next edition of 60079-7 providing Ex ec as a replacement for Ex nA equipment, meant the MT for 60079-15 had to begin  the process of pruning the standard to leave only those things that have not been transferred elsewhere. 

Basically, this means Restricted Breathing (Ex nR), Sealed Equipment and Non-Incendive Components.  This latter concept is a hybrid between Enclosed Break (now Ex dc) and Energy Limitation (now Ex ic), but it does not totally fit within either concept, as it relies on a quenching effect of the contacts as well as a limitation in the available energy.

MT 60079-11, responsible for Intrinsic Safety, continues to spend time on a total reorganisation of the standard to improve its readability and ease of application.  This has proved more difficult than originally envisioned, partly as a result of the realisation that the integration of the previous Ex nL requirements as Ex ic is adding a different approach that is not totally compatible with the way that Ex ia and Ex ib equipment is assessed.  However the final result should be a standard with a more logical layout and easier cross-references between related requirements.

MT 60079-33, looking after the comparatively new standard for Ex s “Special Protection”, reviewed the Operational Document published by IECEx two days before the MT meeting.  IECEx OD 233 lays out the methodology for IECEx Certification Bodies to use the new standard.  Although following the principles outlined in the standard, the MT were concerned that some of the detail in the OD may be difficult to operate in practice. 

However, it was agreed that the OD formed the basis for moving forward, and that any formal comment would wait until after some operational experience had been gained.  With the publication of the OD, Certification Bodies now understand what they have to do to apply to the IECEx Secretariat to put the standard in their accepted scope.

Inevitably, I have only been able to cover a few aspects resulting from the total of about 500 man meeting days here. I will provide further information in my next column.


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