Vector Inbox March 2014

March 14th, 2014, Published in Articles: Vector

This month, our readers address the issue of temperature rise in minisubs; question the new VC9012 standard for luminaires; express general dissatisfaction with the new IEC164-6 plug and socket configuration, and comment on the state of the skilled labour force, among others.

Our winning letter

Temperature rise in minisub transformers

Dear Editor

I would like to raise an issue regarding allowed temperature rise in miniature substations (“minisubs” for short). We all know minisubs with an MV switching compartment, a transformer, LV compartment, and sometimes streetlight and/or metering compartments, all combined in one steel box.

Clause 5.1.2.1 of SANS 10142-1 states that, unless otherwise permitted by an applicable standard in table 4.2, electrical equipment shall be so designed, positioned and protected that accessible parts under normal operating conditions do not reach a temperature (safe touch temperature) exceeding 70°C in the case of metallic parts and 90°C in the case for non-metallic parts. This requirement makes sense as it prevents the public from getting hurt or burnt by any accessible part forming part of an electrical installation.

Table 4.2 in the standard lists

SANS 780 for transformers (and therefore creates an exclusion). Regarding rise in temperature, SANS 780 refers to

SANS 60076 (following IEC 60076), which allows a 60 – 65°C rise in transformer (oil) temperature at an environmental temperature of 40°C, which means the total temperature allowed is 100 – 105°C. This may make sense for transformers as they are either positioned on top of a pole, inside a transformer room or enclosed in a fence prohibiting the general public from touching live (and also hot) parts. Transformers are generally not accessible and the general limit of 70°C for steel parts as stated here may therefore be considered a non-requirement.

However, in the case of minisubs which include a transformer, part of which is accessible (the cooling fins), they are positioned anywhere on sidewalks, on office and shopping centre sites etc. and are generally accessible to the public. According to some local manufacturers, their minisub transformers are designed in full compliance to SANS 780, and they are designed not to exceed 100°C at an outside temperature of 40°C. Most of the minisubs do not have much ventilation and bake in the sun with no forced ventilation. Only natural ventilation passes over the cooling fins and almost none exists inside.

This results in the following: the cooling fin temperature, which is accessible to the public, can exceed the 70°C limit by far and injure those who touch them.

The equipment inside has to endure temperatures exceeding 100°C – this includes CTs, circuit breakers, meters, fuses and wiring.

The first point is a safety issue. If we want to keep our public safe with the current designs, we will have to put fences around every minisub or take other measures to keep the public at bay. The municipalities won’t like this as it will necessitate wider sidewalks in many cases. Developers don’t like this because they see extra costs and extra area taken up on their properties. But, given the above facts, we have no choice, in my humble opinion.

The second point can create all sorts of issues, especially issues of reliability. Over the past few years, we have seen a drastic rise in minisub transformers packing up, transformer fins blowing up, circuit breakers in minisubs exploding (not always the “cheapie” types sourced from a certain country), electronic circuit breakers failing and thermal circuit breakers tripping on lower-than-rated current. The cause of these is most probably the heat generated from both the transformer inside and the sun outside, creating temperatures for which the equipment is not been. Also consider that the outside temperature may exceed 40°C in many areas in South Africa.

The minisub manufacturers will not address this situation themselves without being required to do so by either specification, standard or law, as they compete mainly on price, perceived quality and after-sales service. Designing to the limit means less material, reduced cost and improved market position. As it stands, they say they comply with the standards and can even produce certificates in this regard.

Consultants wanting to keep competitive in the market also no longer have a 100% margin in their designs (if they ever had this in the past), as that would make their designs and network cost too expensive for the client.

To have the standards changed will take ages, especially where they are based on international standards, as is currently the case.

In my humble opinion, the situation should be addressed. Consultants (and municipal and mine engineers) could start by specifying a maximum of 70°C for any accessible part – but all consultants must do this. One or two would not make an impression and may even be disadvantaged as their end-product would become more expensive. Alternatively, they could design in such a way that minisubs are used at only about 60% of their rated load – with the same disadvantage.

My question is, shouldn’t we take this issue further on several fronts? Especially as it concerns safety and reliability?

Harm Boer

vector-inbox-march2014


New compulsory specification for luminaires

The purpose of the proposed VC9012 (Vector, February 2014) is well intentioned and I am sure it will be an improvement on VC8055, however it appears to continue with the notion that one can somehow easily discern which luminaires are “portable” , “adjusted regularly” and “installed by the ordinary man”.

Even if that could be done, what happens to the rest of the luminaires on the market which are installed by skilled persons in fixed installations, and to which

VC 9012 does not apply? As a contractor I can refer to SANS 10142-1 which provides a list of “applicable standards”. In particular, it deals, in table 4.2, with luminaires and lists a safety standard only for ELV systems, swimming pools and lighting track. What about every other type of luminaire which is not covered by either SANS 10142-1 or the new VC9012? Is there another standard?

If not, it means that, as a registered person, I can install any type of luminaire without proof of compliance because a luminaire is defined as an appliance and is therefore not part of the fixed installation, and not covered by my Certificate of Compliance. Somehow, there seems to be a gap here!

Bernie Carr


 

IEC164-6 plugs, sockets: why re-invent the wheel?

Dear Editor

After perusing the article on the new plugs in your magazine, (see Vector, February 2014), I must make some observations:

Firstly, unless I misunderstand, it appears to me that Crabtree had an individual who sat in on the government working group which actually promulgated the new standard?

Please correct me if I am wrong. If I am right, my question would be, why is a commercial enterprise sitting on a committee which should be untainted by any commercial self-interest?

I wonder what percentage of plugs sold in South Africa are in fact made in South Africa? I think close investigation would reveal that there are many players in the SA plug market who have tooled up overseas and this competition has driven plug prices down.

Surely, everyone who makes plugs locally or has tooled up in other countries such as China is now going to play catch-up?

Even more importantly, we have always had a “unique” plug and anyone who travels overseas will know that, in many countries, you can’t even buy an adapter which accommodates our three-pin plug.

I have been following the information on the new SA plug and socket system as per IEC164-6 and have the following concerns:

Noting that this system was designed in 2006 – eight years ago – as a “universal” system, I am not aware of any other countries which have adopted it. Is the IEC going to coerce the rest of the world to adopt the same new SA plug which will then be universal? If this is not the case, what are we doing, why are we doing it and who will benefit?

I believe that there is a very limited use of it in Brazil, but the major countries in Asia, Australia and the EU have not, to my knowledge, adopted it.

There is the advantage of being able to use the two-pin “Euro” plug top in it, but the disadvantage is that South Africans traveling abroad will not be able to use any of their appliances fitted with the three-pin plug top anywhere else, and there are, to my knowledge, no international multi-adaptors offering this three-pin option.

Noting that this will be almost exclusively used only in SA, the economies of scale will make it expensive for what it is, and comparing it as competitive in price to the current, much larger, and more cumbersome 16 A three-pin system simply negates any stated benefit of it being smaller, more compact, and, therefore, less expensive than the present system.

There are systems in place such as that used throughout much of Asia, including China and Australia (whose standards are exacting), which are proven, very safe, inexpensive, and manufactured in their millions every month, which we could have adopted. These would have required no R&D, and would save the end-user and the fiscus untold millions of rand annually. Some 50-million South Africans versus 1,5-billion Chinese and 23-million Australians makes no sense whatsoever in terms of economies of scale.

Who benefits from the new SA plug? Certainly not the end-user. Is it a matter of national pride that we have our own unique plug which won’t work anywhere else in the world? I think not. There is no benefit for the public at large or the electrical industry in reinventing the wheel. In the global village it makes sense to adopt standards for plugs which are used by billions (China) and, failing the Chinese-type plug, at least the standard adopted for the whole of Europe. It seems our view is to be as exclusive as possible and this will translate into high prices and lack of universalism, which is where we are coming from.

Once again, in my opinion, we see financial wastage on a grand scale here, caused by instituting standards which are neither necessary nor in the best public interest. We are re-inventing wheels which serve only the interests of a few at the expense of the masses.

Howard Page, Magnitech


 

New plugs are silly

Dear Editor

The relative amount of brass in [the new IEC164-6 plugs and sockets] is not a key concern (see Vector, February 2014). If your average home has, for instance a television; radio; computer; fridge; stove; three lamps; an iron and a few other appliances, the family will not be replacing plugs on a regular basis. The capital outlay on a plug is not high compared to all the other costs of living.

But, of course, people will want to put new plugs onto old appliances; people will even arrive in SA from other countries and will want to put plugs onto existing equipment. Every now and then, with Eskom and City Power’s power surges, people will need to replace damaged plugs where the equipment or appliances survive these surges but the plugs do not. Uninterruptible power supply units and surge and lighting protectors are expensive.

It would be so much better to adopt the British plug system which has a small fuse inside which can be replaced when damaged. This fuse protects much more expensive equipment than itself.

The UK system is better than the North America system, so why not emulate the best system around rather than moving towards something inferior?

Bronwen Jones


 

Online comments

Re: New IEC164-6 plugs, sockets

Firstly, why were the current suppliers of plugs and sockets in South Africa not consulted about this change? The new plug protrudes more than the standard South African plug which will cause it to be easily knocked out of its socket, thus becoming a fire hazard. Furthermore, how will this new plug cope with the higher amperage of portable appliances such as welding machines and what about the electricians who have to terminate the 3-core cables into such a small termination area? It seems that this plug top will only suit the fortunate few who are making this decision regardless of what the people want.
Royd

This new standard is not compulsory and the old plugs and sockets will continue. I do understand this new standard was drafted by the relevant SABS committee where the local manufactuers and suppliers of plugs and sockets are well represented.
Chris Yelland

The article is unclear as to whether the new plug will be rewirable or not. If not, it brings to mind a cartoon I saw about 30 years ago, when the repair vs. replacement argument became current in electronic devices. The illustration showed a worried-looking customer in conversation with a TV service technician, who was explaining, “I’m sorry sir, but your mains cord has failed. You will need to buy a new set!” Will things come to this?
Tony Fisher

As I understand it, the same flexibility which is currently enjoyed will continue, so it will be possible to purchase new units and rewire the existing plugs. These are already available in the country.
James Calmeyet

State of the skilled labour force

Thanks Mr Turner for a very comprehensive and, in my opinion, accurate summary of the current state of affairs. The part I was looking forward to – your expectations on what the future holds for South African industry if we continue along this path…?
Ernst Smith

Submit your letters to vector@ee.co.za or comment on www.ee.co.za.

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