Published by MeggerJuly 2010

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ELECTRICALTESTER

Getting the birdWhy streamers give problems in overhead lines. See page 8.

Why ‘new’ is not easy‘Innovation is essential’. Every chief executive will have used those words to staff, and we all know it to be true. Yet in reality, some companies find it difficult to innovate; their product ranges consequently age and the company may eventually go out of business. The concept called ‘ Voice of the Customer’ is a simple to say, but difficult to implement phrase that ensures product innovation reflects the needs of customers. One reason it is difficult is because research sometimes contradicts internally ‘known facts’ that are actually myths. Find out more on page 4.

Who else wants the truth?If you depend on a datasheet to check specifications before you buy, you are not alone. It’s standard practise to depend on manufacturer’s data before committing to purchase. Yet all is not as it seems. While no responsible manufacturer would deliberately be dishonest, sometimes you will need to dig deep to get the real information you need, and ensure you are not persuaded either by data that is misleading or that is downright incorrect. A controversial article on this subject on page 5

21st century tigerCould India be the global power of the 21st century? With its democratic heritage; massive, highly skilled population and powerhouse economy, there are indications that as with China, the sub-continent could overtake western economies. Megger’s investments in India have certainly paid off for the company. Indian engineers are helping Megger to power the next generation of innovations, and the company’s technical support office in Mumbai is benefiting Indian power utilities with their modern-isation programs. Read more on page 2.

In the world of power generation and transmission, the Smart Grid is one of today’s hottest topics. In fact, at the high-profile IEEE T&D Show this year, Smart Grid was the main theme – there was even a Smart Grid day at the show. This is an extract from the IEEE promotional material for the event:

“The term ‘Smart Grid’ is becoming well recognised all over the world. Development of ‘smart’ technology to promote and coordinate more efficient electricity usage has become a key element in the plan to lower energy costs for consumers, achieve energy independence and reduce greenhouse gas emissions.

Smart Grid and green power: The perfect partners?

Although Smart Grid technology presents opportunities for utilities and consumers to benefit from the efficient management of energy, significant challenges need to be addressed to integrate and deploy these innovative technologies.”

It is addressing those ‘significant challenges’ that is going to keep us all busy for years to come. For example, everyone wants to link the Smart Grid to green power. The two have to go hand in hand. How can you make use of green energy with all of its inherent problems, not the least of which is its intermittent availability, without having a smart transmission network that can cope with these problems?

So let’s push ahead with the Smart Grid! Unfortunately, the issues are not quite that clear cut. Let’s look at wind energy, for example,

bearing in mind that in the USA, the goal is to derive 20% of electricity from wind power by 2030. This is going to create a lot of problems, as can readily be appreciated by examining the present-day situation in Texas.

There’s already a lot of wind power in Texas, with most of the wind farms – or should that be wind ranches? – way out in the west of the state. The principal load centres, like Dallas/Fort Worth, Austin, San Antonio and Houston, are in the middle of the state. And it’s no real surprise, given the heritage of the transmission network, that a recent article in the IEEE publication Power and Energy states that, even today, the available wind generating capacity exceeds the transmission capacity to the load centres.

Surely this is a great opportunity to add more transmission capacity, and at the same time take advantage of the new Smart Grid technologies? That certainly sounds like a good proposition, until you start thinking about minor practicalities like cost.

Building new transmission capacity is expensive – very expensive – and Smart Grid technologies will only add to the cost. In fact, it’s not unreasonable to postulate that, for about the same cost as adding the new transmission capacity that will be needed to meet the renewable energy goals that have been set in the USA, the country could instead double its nuclear generating capacity.

There are currently 66 nuclear power plants in the USA, some of which have more than one reactor. The newer plants have almost twice the capacity of the older plants. Many of the older plants will be reaching the end of their life span in the next 10 to 15 years, so wouldn’t it make sense to upgrade those sites with more powerful plants, or possibly with several of the newer, less expensive “mini-nukes”?

Consider the benefits of the nuclear power option. Nuclear plants deliver safe, reliable power, whether or not the sun is shining or the wind is blowing. They don’t infest hundreds of square miles of land with unattractive, noisy

Stan ThompsonProduct Manager

turbines or bury the land under solar panels. They also have near zero carbon emissions and they can take advantage of the existing transmission infrastructure.

That’s not to say that there’s no place for the Smart Grid. Upgrading the existing infrastructure to incorporate Smart Grid technologies will still be beneficial, but upgrading is a lot less costly than building a huge amount of extra transmission capacity from scratch.

Of course, the naysayers will protest that nuclear power is dangerous, citing no doubt, the incidents at Three Mile Island and Chernobyl. There is no way that the seriousness of these incidents should be minimised, but it is important to remember that they involved only two of the many hundreds of nuclear reactors in use around the world.

Two is still too many, of course, but it’s also important to bear in mind that the safety systems of those reactors were developed in the 1960s, almost half a century ago.

With today’s safety techniques and technologies, it is surely possible to build nuclear plants where the possibility of serious problems is vanishingly small.

So what’s it to be? Should we make enormous investments in so-called green power and building the huge Smart Grid transmission systems that will be needed to make green power even marginally workable? Or should we invest a similar amount of money in nuclear plant and more modest Smart Grid upgrades to the existing transmission network, to end up with a source of power that’s completely dependable and controllable?

The answer from a technical and engineering point of view is, I think, very clear. However, as always, the path we choose is more likely to be decided by politics than on the basis of engineering realities.

The end of the DRIP!

See page 6

The secret of CT testing

See page 2

ELECTRICALTESTER

Do you speak Goose?

See page 4

SAFETY AND CONVENIENCE IN INSULATION TESTING 3 2 ELECTRIFYING INDIA

The industry’s recognised information toolELECTRICAL

TESTERContentsSmart Grid and green power: ............... 1Stan Thompson, Product Manager

Electrifying India ................................... 2Arvind Shinde, Marketing Communications Manager (Megger India)

Proven Technology ................................ 2David Milner, Product Manager

Germany’s locomotive spirit ................. 3Georg Halfar, Marketing Communications Manager (Megger Germany)

Safety and inconvenience in insulationtesting .................................................... 3Dave Moore, Product Manager

Guided innovation ................................ 4Mark Hadley, Product Manager

Putting engineers back in control ........ 4Romain Douib, Product Marketing Manger

Specified to mislead! ............................. 5Paul Swinerd, Product Manager

The Biddle backstory ............................. 5Graeme Thomson, VP Americas’ Distribution & Telco

Oil Testing without slicks! ..................... 6Paul Swinerd, Product Manager

Earth leakage tests on Portable Appliance ............................................... 6

How safe are magnetic fields? ............. 7Dr Stan Zurek, Magnetics Technical Specialist

Q&A ........................................................ 8

Megger shows off its wares worldwide .............................................. 8

Get ahead with training ....................... 8

The flying flashover .............................. 8

Editor Nick Hilditch. T +44 (0)1304 502232E nick.hilditch@megger.com www.megger.com

Megger LimitedArchcliffe Road Dover Kent CT17 9ENT +44 (0)1304 502100E electricaltester@megger.com www.megger.com

‘Views expressed in Electrical Tester are not necessarily the views of Megger.’

The word ‘Megger’ is a registered trademark

Note from the Editor

Time for your say. We have introduced a ‘Questions and Answers’ section and would like your input. If you have any questions or stories that you think we could use, then please email electricaltester@megger.com

Arvind ShindeMarketing Communications Manager (India)

By any measure, India is a big country. It has a population of more than a billion, and a total land area of 3.3 million square kilometres. It’s also a country that’s facing some of the world’s biggest energy challenges. Demand for electrical power, in particular, consistently exceeds the available capacity. In 2008/9, for example, national demand outstripped supply capacity by an average of 9.5%, increasing to 13.8% during peak hours, according to figures from the Indian Power Ministry.

The situation is exacerbated by the strong growth in the demand for electrical power, which will undoubtedly continue unabated for the foreseeable future. As an example of the many factors driving this growth in demand, it is sobering to note that in August 2009, The Times of London reported that 400 million Indians were without access to mains electricity.

This situation has led the Government of India (GOI) to set up its ambitious “Power for All” program, one of the aims of which is to increase the country’s generating capacity by almost 80,000 MW between 2007 and 2012. While it is by no means certain that this target will be met, even if only half of the planned increase in capacity is achieved, there will be enormous benefits for all of those involved.

In a country with a burgeoning economy like that of India, it might be thought that domestic and international investors alike would be keen to play a role in filling the energy gap. Unfortunately, however, things are not that easy. Supply tariffs for some classes of consumer – for example, those in the agricultural sector – are heavily subsidised.

In effect, this means that the state utilities are obliged to sell power at a loss and they are, therefore, financially weak. As a result, there is little incentive for investors to put money into the building of new power plants that will derive their income from selling power to these utilities.

India also faces challenges in the field of transmission and distribution. The country is unfortunate in that, for historical reasons, its T&D infrastructure is relatively inefficient. Efforts are being made to improve this situation, but this is no easy task as attempts to satisfy fast growing consumer demand has, in many cases, led to the overloading of key elements like transformers.

A final challenge for India is finding ways to address its energy shortage while minimising damage to the environment. The country has some of the world’s largest reserves of coal, so the construction of thermal power stations is a tempting option. However, it has been predicted that, unless measures are taken to control present day trends, India will become the world’s third largest emitter of carbon dioxide by 2015, with over 60% of its emissions coming from coal burned in power stations.

So what is being done to address India’s power sector challenges? The GOI has programs in place to deal with the country’s high T&D losses; these are starting to have beneficial effects and to attract private investment.

On the power generation front, there is a high level of interest in using renewable resources

Electrifying India

to supplement the output of conventional power plants. Solar power is a particularly attractive option not only because the tropical location of much of India means that it has the capacity to generate up to 35 MW of solar power per square kilometre, but also because solar installations can be sited in the remote areas where delivering power by means of a conventional transmission system would be difficult and costly.

To capitalise on the potential benefits of solar power, late in 2009 India put in place its National Solar Mission, which sets an initial target of 20 GW of solar power capacity by 2020, and calls for a government investment of $19 billion over the 30-year life of the mission.

The GOI is also taking an increasing interest in nuclear power. The expansion of existing nuclear power stations and the construction of new nuclear plants are both on the agenda, and the plan is for the country to derive 25% of its electricity from nuclear sources by 2050.

Interestingly, India is outside the Nuclear Non-Proliferation Treaty, which means that it is to a large extent excluded from the international trade in nuclear materials. For this reason and also because the country lacks indigenous uranium, efforts are being concentrated on developing a nuclear fuel cycle based on thorium, of which India has large reserves.

There are also ongoing developments in the structure of the power industry. For the past ten years, there has been a move to split the state utilities (State Electricity Boards) into individual companies. For example, the former Maharashtra State Electricity Board has been split into the Maharashtra State Power Generation Company Limited, the Maharashtra State Electricity Transmission Company Limited and the Maharashtra State Electricity Distribution Company Limited.

These three companies now operate independently; they have their own managing directors and they are expected to produce profits. The managing directors have the power to take decisions in the interest of their specific companies, thereby ensuring that they operate smoothly and profitably. Similar changes have already taken place in all of the major states, including Gujurat, Karnatake, Andhra Pradesh, Madhya Pradesh, Orissa and Rajastan. Also in place are incentives for the new private power producers to sell part of the power they generate to nearby industrial users, and the rest to the state power utility.

To complement improvements in T&D efficiency and increases in generating capacity, India is also making strenuous efforts to ensure that energy is used efficiently.

In the commercial sector, consumers are being encouraged to adopt variable speed drives for motor control and to downsize motors wherever practicable. In the domestic sector, the emphasis is on switching to high-efficiency refrigerators and using compact fluorescent lamps in place of their incandescent counter-parts.

It has only been possible to mention briefly a few of the many issues that impinge on the generation, distribution and use of electrical energy in India today. Hopefully, however, enough has been said to show that the challenges in this sector, combined with the innate inventiveness for which the country is rightly renowned, are driving the development of innovative solutions that will have benefits far beyond the country’s borders.

Based on the proven technology used in the MCT1600 range of instruments, Megger has launched the MCT1600B. These instruments perform a CT saturation test and calculate the rated knee point at the touch of a button. Tests can be performed at 50 Hz or 60 Hz, and the knee point calculations can be carried in line with IEEE C57.13.1, IEC 60044-1 or IEC 60044-6.

The MCT1605 and MCT1600B also offer the option of automatically demagnetising the CT under test. Demagnetisation prior to saturation testing helps to ensure that accurate results are obtained, and this procedure is recommended in ANSI C57.13.1. As a further aid to fast, convenient and comprehensive testing of CTs, the test sets incorporate a 500/1000 V insulation resistance test system, which ensures that the CT secondary winding and wiring are properly insulated as required by ANSI C57.13.1. The test set automatically switches the connections to perform all of the required insulation tests, including H-L, H-G, and L-G.

For maximum user convenience, the MCT1605 and MCT1600B catalogue and store all test results for later retrieval. Configurable test plans can be associated with individual CTs and stored along with the results, which greatly simplifies ongoing monitoring and profiling.

A particularly versatile option is to transfer the data to Megger’s PowerDB Lite software package, which has powerful facilities for generating reports in industry-standard formats. PowerDB Lite can also be used to control the instruments without the need for operator intervention, thereby allowing them to be used as fully automated computer- controlled CT test systems.

Today’s ever-increasing commercial pressures mean that power engineers now have less time available than ever before for carrying out routine yet essential tasks such as testing CTs. Fortunately, as we’ve seen, the latest CT test sets deliver big time savings complemented by greatly enhanced convenience, thereby providing at least a partial solution to this enduring problem.

Proven Technology

David MilnerProduct Manager

SAFETY AND CONVENIENCE IN INSULATION TESTING 3

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TESTER

Engineering excellence and long-term stability have always been the hallmarks of the “locomotive” companies that drive growth in the Germany economy. Names such as Siemens, founded in 1847 and Mercedes Benz, founded in 1879 as Benz & Co Rheinische Gasmotoren-Fabrik, come readily to mind. And in the field of test equipment, Megger, which is also now a major player in the German market, has an equally long and distinguished pedigree having been founded 1895 as the world’s first supplier of portable high-voltage insulation test sets.

In the immediate post-recession period, the strong engineering heritage and commitment to quality of the key players in German industry are starting to make their effects felt. As a result, the Germany economy is starting to gather momentum much faster than expected, and it now seems possible that the country’s deficit ratio will be brought into compliance with the terms of the Maastricht Treaty sooner rather than later.

In international terms, Germany is increasingly being seen as the new engine for growth that will pull the European sales and business performance out of the sidings. Traditionally, after an economic crisis, the resurgence of sales has first been seen among companies in the US. This time, however, US industry has failed in its role as the motor that drives the world economy, despite high levels of gov-ernment assistance.

Raising steam with exportsAccording to most economists, the primary driving force in the second half of 2009 was the export industry, with orders seeing five successive increases. The backbone of the German economy – the country’s export machine – is coming back up to speed, and the Federal Office of Statistics reported export growth of 2.3%.

The economy barometer is also predicting strong growth for the rest of 2010, and a whole range of economic data supports this prediction. The last time the German economic outlook was so positive was in early 2008, after which the GDP fell for an unprecedented four quarters in a row. A single statistic is all that’s needed to show just how deep the recession was: in the third quarter of 2009, despite the upturn, GDP was still 5% below that of the previous year. Nevertheless, the signals for growth are now very definitely set to green.

A record order for railAn outstanding example of success in the German engineering sector is the record order received in November 2009 by Deutsche Bahn to build passenger and freight rail networks in Qatar. The Emirate plans to invest €17 billion in this project. It includes a 300 km underground railway for the capital, Doha, and a 180 km route to Bahrain, on which trains will run at speeds up to 350 km/h. The project also includes a 325 km freight network.

And, there is no end in sight to this express train of success – positive news is continuing to emerge regularly. Production is increasing in the construction industry and in the companies that are associated with it, according to the German Federal Ministry of Economics. The chemical industry, which is traditionally seen as an economic bellwether because of the way other industries depend on its products, is also seeing signs of a slow recovery in Europe; industry representatives have reported a steady improvement in

Germany’s locomotive spirit

Georg HalfarMarketing Communications Manager (Germany)

production and sales over the last six months.

Turning up the heat on renewable energyEngineering excellence is also the key to success in the field of renewable energy. Siemens, for example, sees huge growth potential for wind energy over the next two decades. According to Andreas Nauen, head of Siemens Wind Power Business Unit, the world market will increase at a rate of around 30 billion Euros per year until 2030.

Until now, General Electric, Vestas in Denmark and Gamesa in Spain have been the leading suppliers in the wind generation sector. How-ever, five years ago, Siemens entered the wind energy market with the acquisition of the Danish company Bonus Energy. Between then and the financial year 2008/9 reports Nauen, the number of employees had increased seven-fold to almost 5,500 and further expansion is planned. Over a year, sales have climbed from €2.1 billion to €2.9 billion. These figures include Siemens solar energy business, but this accounts for only around 10% of the division’s turnover.

The order book at Siemens stands at a record €6 billion. In the spring of 2009, the company received an order for 500 wind turbines for the “London Array”, which will be located in the Thames Estuary. For land-based wind power installations, Siemens has won orders for six wind farms in North America, as well as for projects in Mexico and New Zealand.

The route is set for electric carsAnother important sector is electric cars. If German automobile manufacturers want to retain their position as world leaders, the only way is through the development of battery-powered cars. This is especially true now that the development of hydrogen-powered vehicles has come to a halt; both Volkswagen and BMW have decided that this supposed way out of the energy crisis is a dead end, and are phasing out hydrogen technology. This is good news for battery-powered cars, and for suppliers of test equipment for electrical systems.

The previous German government announced that it wants 1 million electric cars to be on the road by 2020, but this can only be achieved if there is a massive government investment programme. The former environment minister and current SPD leader, Sigmar Gabriel has achieved great media coverage for the first 100 battery-powered Minis, which have been made available in Munich and Berlin as a large-scale field experiment. Mercedes Benz has also trialled the technology through its Smart Car subsidiary.

So the good old battery, which has not changed in its essentials since it was invented in the 19th Century, has become a key technology for 21st Century automobiles. And, as we said at the outset, those companies that have shown stability and commitment to engineering excellence over a similar period, such as Siemens, Mercedes Benz and Megger, are still the principal drivers of progress and innovation.

Compact insulation testers are undoubtedly valuable tools for equipment maintenance, but all testers are by no means created equal.

Safety is, of course, the first consideration, and the best insulation testers now fully meet the requirements for CAT IV 600 V applications, as defined by IEC 61010. This means that they can be used in all normal electrical service, maintenance and utility applications. Rugged construction is also important, as is a compact design that will allow convenient single-handed operation.

Versatility is another key issue. A choice of test voltages is essential and many users will also need a choice of test methods. For them, the tester should offer PI (polarisation index) and DAR (dielectric absorption ratio) testing, as well as straight-forward spot-measurement of insulation resistance.

The type of display has a big influence on how convenient the instrument is to use. Digital displays make it easy to record test results precisely, but analoguedisplays are invaluable for showing trending, rate-of-change and assit in diagnosis on varying readings. So why not have both? It’s perfectly possible to add an arc to a digital display to simulate an analogue movement.

While sometimes its sufficient to record the measured insulation resistance on its own, there are many occasions where the test voltage also has to be noted. A display that shows insulation resistance and test voltage simultaneously not only provides direct indication of correct range selection and operation, but is also a useful aid to fast and efficient testing.

All of the features mentioned and many other benefits usually only found on more advanced insulation testers are embodied in Megger’s latest MIT400 family of testers.

The entry level MIT400 provides insulation testing at 250 V, 500 V and 1,000 V, together with continuity testing and voltage measure-ment to CAT IV 600 V protection levels. The MIT410 adds 50 V and 100 V insulation tests, as well as fully automatic (DAR) and (PI) testing, while the MIT420 will measure up to 200 GΩ and adds insulation pass-band settings and also internal storage of test results. At the top of the range is the MIT430, which not only stores test results but also allows them to be transferred to a PC via a Bluetooth wireless connection.

Dave MooreProduct Manager

Safety and convenience in insulation testing

4 GUIDED INNOVATION SPECIFIED TO MISLEAD! 5

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“Innovation is the key to success” is a good maxim for any company, and it is particularly appropriate for companies in the technology sector. However, it is also very apparent that not all innovation leads to success.

In fact, it’s disconcertingly easy to come up with instances of innovations that have led to resounding failure – the Sinclair C5, for example, that was going to revolutionise urban transport or, going a little further back in history, the Hughes H-4 Hercules aircraft that was intended to be the world’s first “jumbo” scale passenger carrier, but ended up flying just once – and then only just.

So what is it that separates successful innovation from potentially disastrous innovation? The answer has two components – in order to be successful, the innovation must lead to a product or service that the marketplace wants, needs and can afford, and it must also respect the limitations of the available technology.

The logical way to satisfy the first requirement is to ask potential customers what they want. It’s acceptable to offer them suggestions, of course, if only to keep the process on track, but the real essential is to listen to what those customers have to say. This may sound completely obvious, but companies have time and time again placed on the market products that have flopped, simply because they thought they knew what their customers wanted better than the customers themselves.

To satisfy the second requirement – respecting the limitations of technology – companies need to have access to genuine and well-proven expertise. The kind of experts needed are those who are not afraid to push the limits of what current technology can dependably deliver, but know their field well enough so that they never allow their enthusiasm to take them beyond those limits.

It is taking heed of these requirements that has helped Megger and its predecessors to remain in the vanguard of successful electrical test instrument innovation for well over a century.

The company’s approach to innovation is well illustrated in the recent development of its new range of portable appliance (PAT testers). The first step was to talk to users in general terms. What did they most want from a PAT tester?

It was interesting to note that speed and ease of use were the top items on the list, but perhaps this shouldn’t have been surprising given that PAT testing is a very competitive business and that making a good profit depends on being able to carry out tests quickly and efficiently. It’s also worthy of mention that, for most users, having the instrument offer a wide range of functions, most of which would be rarely used, didn’t figure on their wish list at all.

Pages of features may be exciting for the members of the marketing team who love all of those bullet points and for the product engineers who can’t wait to add in a few more extras, but what the vast majority of PAT testing customers really want is a simple instrument that’s easy to use!

After the users had discussed general require-ments for PAT testers, they were asked about more specific issues and it soon became apparent that two common problems were causing a lot of annoyance and aggravation.

The first was the time that it takes the testers to start up. This doesn’t really matter for the first

Mark HadleyProduct Manager

Guided innovation

time it’s used on a particular site, but it matters a lot when the instrument has only been switched off briefly to allow the user to move, say, from one desk to another or between rooms. Since someone carrying out PAT tests on a large site may have work in tens of rooms, having to wait even a minute or two for the PAT tester to reboot after each move soon becomes very annoying!

The second problem that users were having was PAT testers that regularly shut themselves down. It wasn’t hard to trace the root of the problem. For high current bond tests, the instruments are required to deliver a current of up to 25 A. All can do this once in a while but when called upon to carry out several of these tests sequentially, a lot of testers overheat, and are forced to shut themselves down to cool off and prevent damage.

Megger addressed the boot up time issue by adding a back-up battery to its new instrument, which keeps it ticking over for up to five minutes after the power has been switched off. The result, instant restart when moving from room to room. No it wasn’t rocket science, but it was genuine innovation and it makes users very happy!

To address the shutdown issue it was necessary for the development engineers to look to the latest technology in power supply components, and to choose devices that would enable them to build a compact, lightweight power section into the instrument, which was, nevertheless continuously rated. Users could now carry out any reasonable number of high-current bond tests sequentially, and their test set would just keep on going.

The more general issues that had been identified for PAT testers were addressed with equal care. The new testers were equipped with full colour displays to show the test data and results clearly and unambiguously, and with clearly identified pushbuttons to initiate test sequences.

The testers were provided with a pass/fail with user-defined limits that makes testing for standard assets very quick and easy, and arrangements were made for them to be supplied pre-pro-grammed for automatic operation so they are ready to go straight from the box.

None of these innovations stands out on its own as earth shattering but, in combination, they represent a big step forward for PAT testing instruments. They are a response to genuine customer requirements, and they make good use of the latest technology. Megger believes that it is innovations like this that are the true key to success, and the company’s enviable track record over the last 100+ years suggests that it may just be right.

IEC 61850, the new standard for substation data networks, is creating a lot of interest and excitement. It’s also creating more than a few challenges, not least for substation control engineers who spend their lives creating and working on interlocking schemes. And one of the biggest challenges they face is not how to implement interlocking schemes based on IEC 61850, but how to test them. The problem is particularly acute, because at present IEC 61850 is being more widely used for interlocking than it is in protection applications.

Of course, options do exist for testing IEC 61850 interlocking schemes. However, these almost always involve the use of protective relay test set that supports IEC 61850. This approach, however, is far from ideal. The first concern is that, in most cases, control engineers are not protection engineers. They are unlikely, therefore, to be familiar with the operating a protective relay test set. They could, of course, learn, but that’s a pretty steep learning curve for something that is not central to their work.

Another issue is that protective relay test sets are necessarily costly, since they incorporate high-performance precision amplifiers and other elements that are expensive to develop and produce. Yet these are not needed for testing interlocking schemes, so using a relay test set in this application is not only overkill, it also needlessly ties up expensive capital equipment.

It’s clear that there is a pressing need for a

reasonably priced instrument that is simple to use and provides all of the facilities needed for testing IEC 61850 interlocking schemes, but does not incorporate the expensive extras needed for protective relay testing.

It’s not difficult, in principle at least, to imagine how such a test set would work. First of all, it would monitor the GOOSE messages that IEC 61850 installations use to communicate and it would convert them to the ordinary type of on/off binary signal that control engineers are used to working within non-networked installations.

The test set would also be capable of working in the opposite direction. That is, it should take signals from ordinary contacts and convert them into appropriate GOOSE messages. In effect, a test set of this kind is simply an interface between the GOOSE messages on the bus and the electromechanical world of the control engineer.

Romain DouibProduct Marketing Manager

Putting engineers back in control

Of course, there’s rather more to be considered than this very basic overview initially sug-gests. For example, the conversion between GOOSE messages and binary signals must be fast enough so as not to materially affect the timing of the interlocking system. In practice, a conversion time of less than a millisecond, which is achievable with careful design, will be fast enough to satisfy the most demanding of requirements.

Next, it is clearly necessary to be able to associate particular GOOSE messages with specific inputs and outputs on the test set. This is best accomplished with software but, if it is to be intuitive and easy to work with, the software needs to be carefully designed. Further refinements can also be envisaged. For example, LEDs that provide instant visual confirmation of the state of the instruments binary inputs and outputs would be an important benefit for users.

The ideas mentioned in this article have driven the development of Megger’s new GOOSERTM. This embodies a number of unique technical features for which patents are pending, and offers the most efficient and cost-effective solution currently available to the challenge of testing IEC 61850-based sub-station interlocking schemes.

That is, however, by no means the limit of the capabilities of the GOOSERTM. While it may not be particularly interesting to control engineers, the unit can also be used to adapt a conventional protection relay test set so that it can be used to test IEC 61850 protection schemes. This is a big benefit for users that already have protection relay test sets – whether they are units supplied by Megger or by others – as it is offers a very straightforward and cost-effective upgrade path.

It also creates an attractive option for consultants and smaller organisations who can now purchase a GOOSERTM and a modestly priced relay test set, such as the Megger SVERKER, to cover all of their relay and interlocking test requirements for both conventional and IEC 61850 schemes.

Equipment that allows convenient and dependable testing of IEC 61850 interlocking schemes has, until now, been difficult or even impossible to find. This situation has now been addressed by Megger’s Goose Message Interface, a unique instrument that provides the added bonus of facilitating the testing of IEC 61850 protection schemes.

SPECIFIED TO MISLEAD! 5

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A great strength of Megger today is that it builds on the unrivalled expertise of the many innovative businesses that have, over the years, become part of the Megger organisation. One of the most significant of these businesses, particularly in the Americas, is the James G Biddle Company, based in south eastern Pennsylvania. But what is the background of that company, and how did it come to play such an important role in the electrical instrument sector?

James G Biddle founded his business on George Washington’s birthday – February 22nd – in 1895, after having worked for eight years with James W Queen & Company, at the time a leading manufacturer and importer of high-quality scientific instruments, where he managed the scientific and electrical apparatus department.

Originally, Biddle described himself as a “manufacturers’ agent” and, from his office in Philadelphia, he corresponded with overseas

manufacturers to arrange the importation and sale of scientific and electrical equipment.

In 1910, Dr. Arthur J. Rowland, head of the electrical department at Philadelphia’s Drexel Institute of Art, Science and Industry – now Drexel University – told Biddle about a new type of device for measuring megohms that represented a major advance over the techniques that were currently being used for testing insulation quality. This was the insulation tester, invented by Sydney Evershed and manufactured in England by Evershed & Vignoles. It was the first instrument that accurately measured the insulation resistance of all types of electrical circuits, machines and equipment.

As a result of Dr. Rowland’s tip off, Biddle travelled to England, which was no trivial investment of time and money in those days before cheap air travel. There he visited Evershed & Vignoles and, with a gentleman’s handshake, concluded an agreement that made his firm the sole distributor in the USA for Evershed & Vignoles instruments, including Megger insulation testers, Ducter® low resistance testers and earth testers.

On his return to the USA, Biddle ordered five Megger insulation testers. These he sent out on a sale-or-return basis to some of his closest engineering acquaintances in electrical

The Biddle backstory

James G Biddle

Graeme ThomsonVP Americas’ Distribution & Telco

GOOSER

IEC 61850 Test System

▪▪ Allows for re

liable testing of GOOSE relay

functions using any conventional re

lay test set

▪▪ Easy-to-Use

▪▪ Separate LAN ports for su

bstation bus and

PC – Safe Substa

tion Bus A

ccess P

oint

▪▪ Seamless interactio

n between SCL file and

GOOSE “sniffing”

▪▪ GOOSE merge function – S

CL GOOSE vs

captured GOOSE for advanced network

troubleshooting

▪▪ Stand alone functionality

– Download a

configuration and run

▪▪ Patent pending

Descriptio

n

The GOOSER™ is a general p

urpose IEC 61850-8-1 GOOSE

test equipment.

The GOOSER can convert a GOOSE messag

e received on

its rear E

thernet port into a binary output activation, and it

can convert a binary input activation into a G

OOSE message

published (sent) at its r

ear Ethernet port. T

he conversion time is

typically 0.6 ms.

The GOOSER is equipped with 10 binary inputs an

d 10 binary

outputs. Using these it can convert si

multaneously up to 20

GOOSE messages.

Binary inputs of the GOOSER can react on DC-voltage presence

(voltage sense or “wet” contact mode) or can independently detect

an applied closed/open contact (contact sense or “dry” contact

mode).

For high speed operation the binary outputs of the GOOSER are

solid state, fu

lly protected against incorrect connections an

d short

circuits. These have a st

rong breaking capacity to drive inductive

loads like auxiliary

relays.

The GOOSER has two physically isolated Ethernet ports: r

ear

and front. The GOOSE messages are

transferred by the firmware

from the rear port to

the front port where the messag

es can be

visualized using the provided PC-GOOSER software or with

any third party network analyzer. This functionality

allows the

GOOSER to act as a secure and safe

substation access p

oint.

With the 6.4” color touch screen on the front panel the

GOOSER can be used without the need for a PC. The GOOSER

configuration files are

read from a memory stic

k inserted in the

USB port on the front panel.

The software PC-GOOSER provides mapping of the binary

inputs and outputs of the GOOSER to the desired GOOSE

messages. The GOOSE messag

es are read from availab

le SCL

(Substation Configuratio

n Language) files or may be automatically

GOOSER

IEC 61850 Test Syste

m

detected by scanning the substation network in search

of available

published GOOSE messages. This process is

known as GOOSE

“sniffing”.

The PC-GOOSER also provides ad

vanced network

troubleshooting tasks such as c

omparing the GOOSE messages

available on the network with the GOOSE messag

es described on

the SCL files (GOOSE Merge functionality

).

The specifications contained in data sheets and product literature for test instruments are only in rare instances actually incorrect, but far more often they are misleading. Paul Swinerd of Megger explains.

The specifications given by the manufacturer for an instrument should give a clear picture of its true performance. Indeed, this is essential if users are to be able to choose the most appropriate and safest instrument for their own particular application. Unfortunately, specifications are not always as easy to interpret as they ought to be, and the reason is not hard to find.

These days, buying decisions are often made by purchasing staff who are neither engineers nor instrument specialists. Small wonder then, that they base their decisions, at least in part, by comparing a product’s specification with a pre-defined list of criteria that must be equalled or exceeded. This makes it very tempting for instrument manufacturers to “massage” their specifications to push their products to the top of the list.

Note that there’s no suggestion that the figures contained in a “massaged” specification are actually untrue, they are simply presented in such a way that they are misleading or open to misinterpretation. There’s also no suggestion either that purchasing officers are falling down on the job, simply that they can-not be experts in every technology with which they are involved.

Let’s look at a few examples of specifications that are not quite what they appear to be at first sight, starting with earth testers. Many companies specify the output current as either

Specified to mislead!

Paul SwinerdProduct Manager

200 mA or 250 mA into a short circuit. But short circuit conditions never occur in earth testing. For this reason, conscientious companies like Megger specify the current that will flow under actual test conditions.

For Megger instruments, this is 0.45 mA. This is not a figure chosen at random; it has been selected to meet the requirements of IEC 61010-1, which states that when the test voltage is greater than 33 V rms, the test current must not exceed 0.5 mA. For lower test voltages, it is true that the standard places no limit on the current, but using high currents brings no benefits but will almost certainly shorten the life of the instrument battery.

Sticking with earth testers, let’s now consider noise rejection. Some manufacturers specify this in decibels (dB). This is, of course, a ratio rather than a limit – it doesn’t actually tell the user the level at which noise will start to affect readings. A far better approach, adopted by enlightened manufacturers, is to quote a maximum noise voltage – for example, 40 V peak to peak, as this is something that users can actually measure, should they wish to.

Another ploy is to state in the user guide for an earth tester that the instrument’s operating error is quoted in line with the requirements of IEC 61557-1. This means that the error figure relates to the instrument operating with only 3 V rms interference present. In practical applications, however, the interference levels may well be far higher.

The interpretation of general accuracy state-ments is another area where great care is needed.

If a digital insulation tester reads 50 GΩ, for example, and its accuracy is specified as ± 5% of the reading, it’s not hard to work out that the actual value being measured must lie somewhere between 47.5 GΩ and 52.5 GΩ.

But what if the accuracy of the instrument had been specified as ± 5% ± 3 digits? Now the accuracy depends on the instrument’s resolution – that seemingly innocuous ± 3 digits could increase the potential error in the measurement by 0.3 GΩ or even 3 GΩ!

At this point, it’s necessary to sound yet another word of caution. An apparently good specification may be the result of “specmanship” where the figures have been carefully chosen and massaged in the way we have already discussed. Or, of course, it may be that the specification really is good, and the instrument to which it refers is an excellent product!

A good illustration of this is provided by Megger’s 5 kV and 10 kV insulation testers, where accusations have sometimes been made that the specification has been designed to “tick all the boxes” in a buyer’s purchasing requirements, rather than to reflect the actual needs of users. Let’s look at why these accusations don’t stand up.

One of the main applications for high voltage insulation testers is predictive maintenance, which relies upon a series of measurements being made over periods of months or even years, so that the results can be trended. For the trend to be valid, the readings must be directly comparable, and this means that the instrument must meet tough requirements in all of the following areas:

• test voltage accuracy and stability• test current capability• guard terminal performance• operating temperature range• operating humidity range• noise immunity• measuring range – an infinity reading is useless for trending

In other words, every area of the specification is important. Achieving good results in all areas is, therefore, most definitely not a case of specmanship – it truly does reflect real user requirements.

In the light of this, there is one final question that needs to be addressed. How can a “massaged” specification be distinguished from a specification that is genuinely good?

The first part of the answer is to look at the specification very carefully and to ask the instrument manufacturer for an explanation of any areas that appear vague or confusing. The second part is to choose instruments from a well known and respected supplier that has a strong and well-established reputation for offering products that do exactly what they are claimed to do.

Bear these thoughts in mind, and you will be well placed to avoid the undoubted perils of misleading instrument specifications.

TM1800

Circuit B

reaker Analyzer Syste

m

TM1800

Circuit B

reaker Analyzer System

▪ Stand-alone functionality

– one toolbox

for all breaker te

sting

▪ Expandable modular concept

▪ Safer testin

g – DualGround™, te

st circu

it

breakers with

both sides g

rounded

▪ Designed for off-l

ine and on-line

measurement

▪ Rugged and reliable for field use

Descriptio

n

The TM1800™ is the instru

ment platform for circuit breaker

maintenance, based on more than 20 years’ experience of over

4,000 delivered breaker analyzers. T

he modular constru

ction makes

it possible to configure the TM1800 for measurements on all

known types of circuit breakers in operatio

n on the world market.

The robust design contains powerful technology that streamlines

circuit breaker testing. Sophisticated measurement modules enable

great time savings as

many parameters can be measured sim

ultane-

ously, eliminating the need for new setup each tim

e.

The patented DualGround™ testing using the new DCM module

makes the testing safe and tim

e saving, by keeping the circuit

breaker grounded on both sides throughout the test. The DCM

module uses a measuring technology called Dynamic Capacitive

Measurement.

Timing M/R is using the patented Active Interference Suppression

to obtain correct timing and accurate PIR (Pre-Insertion Resisto

r)

values in high voltage substations.

An adaptive, easy-to-use software suite supports activities fro

m

timing, simply turning a knob without the need for presetting, to

advanced help functions for hooking up to the test object. A full

keyboard and 8” color screen is the front end of the high-level

user interface. The Select-Connect-Inspect workflow guides yo

u

to fast results in

three steps. Testing is made easier to learn and

perform.

The system also offers fu

ll connection capability to the local net-

work, printers etc.

Testing with

DualGround

Electricity deregulation changes the business environment for utili-

ties, switchgear owners an

d service companies. Deregulatio

n has

been shown to lead directly to increased emphasis on efficiency of

operations, m

aintenance and service levels. Internationalization of

business brings new challenges: su

bstantial i

nvestments by global

corporations will bring with them sharper or new requirements fo

r

increased emphasis on health, saf

ety and environmental compli-

ance. Experience has al

so shown demands for shorter time periods

for testing, while the switchgear is less an

d less availab

le to be

taken out of service.

The safety aspect

Network operators an

d service companies need to maintain and

develop their industry safe

ty record. Eminent International bod-

ies including the IEEE® and IEC®, National Safety agencies

and Trade Unions increases the demands on safety. D

uring the

deregulation applicable safe

ty regulations have been clarifi

ed and

the application of existing rules has ti

ghtened. Keeping a good

safety record is b

ecoming a crucial asset in attr

acting investors and

customers.

In all substati

ons the capacitive coupling from live high voltage

conductors induce harm

ful/lethal currents in all p

arallel conduc-

tors. Grounding both sides of the test object will le

ad the induced

current to earth and provide a sa

fe area for the test personnel. See

figures below.

Both sides g

rounded

The best way to provide safe

ty in circuit breaker testing is to keep

both sides of the circuit breaker grounded throughout the test.

This will al

so make the test faster an

d easier.

Minimum time shall b

e spent in the substation and focus sh

all be

on the test rather than the equipment.

The DualGround™ testing method is availab

le for all tests o

n all

circuit breakers.

manufacturing and public utility companies. Four out of the five elected to keep and pay for the instruments they had been sent, providing immediate confirmation that Biddle had made a good business decision in becoming the distributor for Evershed & Vignoles.

His business expanded and developed, and in 1936 it was incorporated as the James G Biddle Company. In 1940, largely because of his failing eyesight, Biddle retired but in 1945 he was appointed Chairman of the Board.

As it was impossible to import instruments from England during the years of the Second World War, the company started manufacturing Evershed & Vignoles products under licence in the USA. From that point on the Biddle organisation made products of its own and in 1989, using ideas put forward by the Common-wealth Edison Company of Chicago, it started development work on a range of instruments for evaluating the condition and performance of large battery systems, such as those used in electrical substations.

This work ultimately led to the introduction of the BITE (Battery Impedance Test Equipment) range of products. For the first time, these instruments allowed the condition of a battery installation to be accurately assessed without the need for a full discharge test. This concept was so successful that the descendants of the original BITE range are still on sale today, albeit now as Megger products.

Through the years, the James G. Biddle Compa-ny has had a number of other “firsts” in specific

types of test equipment that are now standards in the electrical industry. Among these instruments are the first transformer turns ratio test set, the first commercially available cable fault locator, the first partial discharge (corona) detection system and the first automatic 10 kV insulation power factor test set. The descendants of these products still have an important place in the Megger line up.

In 1991, Biddle and MultiAmp, another major force in the USA test equipment market, came together with Megger to form the organisation that was then known as AVO Megger Instruments. Today, the whole organisation is known as Megger and it continues, as always, to lead the way in innovative test instrumentation that sets the highest standards for performance, usability and value. The company still follows the vision that James G. Biddle used to make his company successful over 100 years ago, “A firm belief in personal relationships, and an intensive desire to perform a special service not elsewhere available.”

Checking DC motor armatures with aMegger insulation tester - 1930s style!

■ Simple manual or automatic testin

g

■ 230 V and 110 V operation

■ Bond testing at 25 A,10 A and 200 mA

■ Differential, to

uch and substit

ute leakage

testin

g

■Full c

olour display

■ Tests porta

ble RCDs and extension leads

PAT300 SERIES

Portable Appliance Testers

PAT300 series

Portable appliance teste

rs

DESCRIPTION

An easily portable desktop appliance tester for te

sting the

safety of portable electrical equipment to

meet health and

safety regulations. The PAT300 series are fully featured

testers with dedicated test b

uttons for direct access t

o tests.

They are designed for customers who do not re

quire the

complexity of a fully confi gurable database of clients and

results within the tester but do need a complete range of

functions to allow automatic or m

anual testing of th

e

widest range of electric

al assets. There are two products in

the range – the PAT320 and the PAT350. The PAT350 is

identical to the PAT320, with the additio

n of fl ash-test

capability for use in environments s

uch as manufacturing,

production or tool-hire shops.

Simple push-button operation make the PAT300s fast a

nd

intuitive in use. All regulatory test re

quirements are supported,

including Class I and Class I

I, IEC power le

ads, extension

leads and full tests

for portable RCDs. An automatic mode is

available for Class I and Class I

I testin

g. In automatic mode,

the tests proceed sequentially through bond, insulation

and operation, indicating a pass or fail at each test.

If a fail

occurs, testin

g is stopped. When manual testin

g, each test is

preceded by a selection screen where the test parameters a

re

selected, such as bond test c

urrent, insulation test v

oltage

or leakage test ty

pe. These diagnostic buttons provide direct

access to any test in

dividually, allowing sin

gle tests to be

performed following repair or a suspect re

sult.

Accessories su

pplied with all models in

clude a combined

earth-bond and insulation test lead, an adaptor fo

r testin

g

extension leads, and a carry-case convenient product and

lead storage.

APPLICATIONS

There is a legal re

quirement for any landlord, employer or

owner of a place of work or public place, to ensure that all

electrical equipment accessib

le by tenants, employees or th

e

public is maintained in a safe conditio

n, and an acceptable

method of ensuring this is by routine electric

al testing. This

can be performed by electrical contractors, s

pecialist PAT

testing organisations, m

aintenance departments, o

r facilities

management companies.

The PAT300 range is suitable for performing portable

appliance testing in locations su

ch as hotels, public houses,

schools, colleges, n

urseries, shops, o

ffi ces, theatres, b

anks,

restaurants, cafés, sp

orts and leisure facilitie

s, cinemas,

factories and hair salons etc. The PAT350 is s

uitable for use in

tool-hire shops where equipment is

routinely tested prior to

hire, and will perform a fl ash test in

addition to sta

ndard PAT

tests.

6 OIL TESTING WITHOUT SLICKS! HOW SAFE ARE MAGNETIC FIELDS? 7

The industry’s recognised information tool

ELECTRICALTESTER

Testing the quality of insulating oil is an invaluable guide to the condition of many kinds of large electrical plant, including power transformers. However, oil testing is frequently seen as a messy and inconvenient procedure that all to often produces results of dubious accuracy. These problems, how-ever, have their roots not in the testing techniques themselves, but in the shortcomings exhibited by many of the oil test sets currently in use.

Let’s take a look at the most important of these shortcomings, and see what might be done to address them. One of the most common complaints from users of oil test sets is that they are messy. In most models, for example, any oil spilled in the instrument is retained – which is good, because oil that finds its way onto the floor is a definite safety hazard.

The problem comes when its time to clean the instrument and remove the oil from its spill container. Almost invariably, the only way to do this is to use paper towels or similar absorbent material to soak up the oil, a procedure that can hardly be described as convenient. Might not a better solution be a built in drain tube, which can be used to transfer the spilled oil to a suitable container for disposal or recovery?

Then there are the test vessels themselves. Traditionally, these have been made of glass, to ensure freedom from interaction with the oils under test. Glass vessels are, however, expensive to produce and easy to break. Today, however, glass is not the only material that’s suitable for use in oil test vessels. New moulded materials are now available that will not react in any with insulating oils, and these are a far better option.

These moulded vessels are relatively inexpensive, which means, for example, that testing laboratories can easily afford to keep separate vessels for each different type of oil that they test, as many prefer to do. Moulded vessels are also much more robust than their glass counterparts – they’re not guaranteed to bounce if they’re dropped, but there’s a very good chance that they will.

The use of these new moulded materials also allows much more freedom in the design of the vessel. This means that an effective pouring lip can readily be incorporated, allowing the vessel to be emptied conveniently without dripping hazardous oil every-where. The vessels can also be produced in a shape that makes them quick and easy to clean. On the subject of cleaning, another common complaint about current oil test sets is the difficulty of accessing the electrodes to allow thorough cleaning. This is purely a matter of design, of course, and there are no intrinsic reasons why machines can’t be produced that allow unhindered electrode access.

Many existing oil test sets also have operational shortcomings. Precise setting of the electrode spacing is, for example, essential if reliable test results are to be obtained. But precise setting alone is not enough – provision must be made to ensure that the setting is not accidentally altered during testing. Test sets often fail in this respect by providing the facilities needed to set the electrode spacing accurately, but no option to lock the electrodes in place after the spacing has been set.

Then there’s the question of test options. Portable oil test sets capable of testing at up to 80 kV are few and far between, as are instruments with the option of carrying out tests that detect breakdown by monitoring current, as required by IEC standards, or by monitoring voltage, as required by ASTM standards.

Of course, there are many other features that would be useful to some, but not necessarily all users. These include, for example, an integral printer or, for portable models, a choice of battery types. Rather than increase costs by building these into every instrument, why not build the instruments to order, to the exact specification required by the customer?

In the design of its new range of oil test sets, Megger has addressed all of the points raised in this article. The new testers are easy to use, easy to clean and employ the same robust test vessel for every model. In addition they all have a locking mechanism on the electrode adjusters to prevent the electrode gap from moving.

The OTS range includes five models. The OTS60AF, OTS80AF and OTS100AF are primarily intended for use in fixed locations, such as laboratories, and offer maximum test voltages of 60 kV, 80 kV and 100 kV respectively. The OTS60PB and OTS80PB are compact lightweight instruments for portable use and offer maximum test voltages of 60 kV and 80 kV respectively.

All models feature a colour display with straightforward menu navigation, which makes them fast and easy to use. In addition, the laboratory models have a large keypad to facilitate rapid data entry. A configure-to-build service is offered across the complete range.

Oil Testing without slicks!Paul SwinerdProduct Manager

Throughout the UK and Europe, appliance testing is becoming more common to ensure electrical equipment is safe to use. Tests that are usually performed include a visual inspection, earth continuity or earth bond test and an insulation resistance test. Also an operations test and an earth leakage test are often performed to gain further information.

Earth leakage measurements are performed when the equipment is running in its normal operating mode. For appliances that have different settings, e.g. hair dryers, the appliance should be set to its highest setting and be switched on. Earth leakage tests are often performed in place of an insulation test if there is doubt an insulation test could damage the equipment under test.

There are various earth leakage tests that can be performed:

Differential Earth Leakage Tests (IDIFF)

This measures the difference in current between the live and neutral conductors. The difference is displayed as the leakage current. The measured value is adjusted to reflect the worst leakage current at the upper operating voltage limit.

Touch Current Test (IF)

Where no earth return path exists, (Class II) one has to be provided to simulate the equip-ment being held in the hand. The measured value is adjusted to reflect the worst leakage current at the upper operating voltage limit.

Earth leakage tests on Portable Appliances

Substitute Leakage Test (IPE)

This measures the leakage current in the earth conductor using a low AC voltage (typically 40 Vac).

This reduces the risk of electric shock and prevents the equipment from running during the test, where this would otherwise be considered dangerous. The test socket is optional since this test is independent of the supply voltage. The measured value is adjusted to reflect the worst leakage current at the upper operating voltage limit.

Megger manufactures a range of PAT testers that have the ability to test earth leakage, along with earth bond, insulation, operation and flash tests. Visit www.megger.com for more information.

HOW SAFE ARE MAGNETIC FIELDS? 7

The industry’s recognised information tool

ELECTRICALTESTER

We are all surrounded by magnetic fields emanating from the Earth and from various electro-magnetic devices: motors, transformers, relays and even such common items as fridge magnets. But do we know how strong these fields are? And are they safe? As engineers and electricians, should we be worried when working in a “magnetised” area? Read on for some interesting answers.

High frequencyHigh frequency magnetic fields (GHz upwards) are capable of producing ionisation. The health implications of some types of field, such as those associated with mobile phones, are still being debated, whereas for the other types of field, like X-rays, the harmful effects are much better understood.

From a health and safety point of view, ionising fields are treated almost as radioactive sources and are subjected to special rules and working restrictions. Their use is strictly controlled so there is generally a much smaller chance of dangerous exposure. For example, the radiated power of mobile phones is limited even though, after several years of research, there is no clear and conclusive evidence that the high frequency electromagnetic field that phones generate in normal use is dangerous. Nevertheless, the higher the frequency, the lower are the limits of safe exposure.

Low frequencyLower down the spectrum, the mains frequency of 50/60 Hz produces electromagnetic fields of very long wavelength (over 6000 km) and therefore their influence is confined to the so-called “near field” region, where Faraday’s law of magnetic induction applies. The International Com-mission on Non-Ionizing Radiation Protection (www.ICNIRP.de) has published exposure guide-lines, based on the current densities induced by time-varying fields. The safe DC field values are much higher, because a stationary field is not capable of inducing a current.

Levels of magnetic field Magnetic fields are generated around electric currents. In air, gases and vacuum the field is directly proportional to the value of the current. The immediate implication is that for the same power, lower voltage systems will generate higher fields because the currents will be higher. For instance, a 20 V, 500 W battery operated drill will require 25 A DC. Similar drill supplied by mains of 230 V will consume only around 2 A. Thus the magnetic field in the first case will be over 10 times greater, but it will also have different influence on health because it is a DC current. (For the sake of simplicity, we are neglecting issues like electric field, arcing, etc.)

Let us calculate the fields for the four simple configurations shown in Fig. 1: a single wire, two wires, a transformer and a very large coil that could surround the whole human body.

Fig. 1. The magnetic field was calculated for four simplified cases (at 5 m distance) in relation to the body centre: single wire, a transformer (1 m high), two wires (separated by 0.5 m) and also for the whole body placed inside a 2 m coil

The intensity of the field (flux density) reduces with the distance from the source. For a single wire the flux density values are as shown in Fig. 2. We can see that if the distance increases by a factor of ten, the field decreases by the same factor.

Because the space between the source and the human is, in practice, filled mostly by air, the resulting flux density values are relatively small when compared, for example, with values inside magnetic cores. Low DC current (below 10 A) does not generate fields that are greater than magnetic field of the Earth. Such values are, therefore, perfectly safe.

Fig. 2. Magnetic field levels around a single wire at various currents

The ICNIRP guidelines for safe levels of static and time-varying electromagnetic fields were based on many research reports, including data from World Health Organisation. It was recommended that for the general public the safe level of DC magnetic field is up to 400 mT. As can be seen from Fig. 2, very large electric currents at short distances would be required to generate this level of field in air. Such fields can be generated with the help of permanent magnets and magnetic cores, but their range will be limited so that only fingers and, at worst, limbs will be affected. Of course for special cases, like for people with heart pacemakers, the safe limits are much lower – a value of 0.5 mT is mentioned.

For AC fields the values are much lower and they depend inversely on frequency – the higher the frequency the lower the limit. For continuous exposure at 50/60Hz the recommended safe limits are 100 nT for the general public and 500 nT for professionals (occupational). Much lower AC currents are sufficient to generate these levels of magnetic field.

A hand-held mains-supplied drill with a 2A current in the worst case of very close proximity to operator’s hands can generate field, which is slightly above the limit. However, such a tool would not be used all the time and the real exposure should be calculated as the average value over time. Much higher peak values can be safely tolerated if the exposure time is short.

For instance, if the field is 10 times the safe limit, then as a rough approximation it can still be tolerated safely if the exposure is limited to a tenth of the time, e.g. six minutes in an hour. So it will be still perfectly safe to walk slowly past a 100 A busbar, provided that the exposure time is suitably limited, whereas touching such an energised high- or medium-voltage conductor would cause almost certain death, but for electrical rather than magnetic reasons.

Magnetic field at a 5 m distanceLet us look again at the fields from various sources as shown in Fig. 1. The 5 m spacing was chosen here arbitrarily, but engineers and electricians often work at this sort of distance from overhead lines, cables, transformers, etc. while still remaining safe from an electrical point of view. Even if the spacing were reduced to 2.5 m, the fields would simply double.

Almost the worst-case scenario for normal circumstances is the magnetic field generated by a single wire (or a single busbar) as shown in Fig. 3. The magnetic field around a transformer will be significantly lower. This is because the field will be contained mostly in the magnetic core and the oil tank will provide further shielding. In fact, the highest magnetic field can be expected at the lower voltage bushings of the transformer – where the currents are highest.

With a single phase supply the current flows in one wire and returns in another. The magnetic fields from the wires cancel to a large extent and so the resulting field is much lower. Similar effect occurs for three-phase supply, because the currents also balance out. The spacing affects the cancelation, but the multi-wire field will be always lower. The most effective cancellation happens in cables, where the wires are placed as close as possible to each other.

Fig. 3. Magnetic field levels for the configuration from Fig. 1

In order to expose the body to a static field of over 2 T, the person would have to be INSIDE a large coil with 50 turns and over 50 kA current. Under such unreal conditions, the mechanical dangers (we are not even considering the electrical hazards) are actually much greater than the magnetic ones. The surrounding magnetic field will magnetise any tool made of iron or steel and this will cause a mechanical force proportional to the square of flux density and the area of the tool. For example a 10 mm cube made of steel can be magnetised up to 2 T, which can result with a force of 160 N. Imagine what effect would have on a spanner in your pocket …

This is exactly the reason that a person undergoing magnetic resonance imaging (MRI) has to strip almost naked and cannot have any metal parts on or in their body (e.g. implants). The MRI scanner can generate fields up to 7 T, which could potentially rip those metal bits from human flesh.

Because of the lower exposure limits for AC fields, the situation is slightly different for alternating currents. Nevertheless, at a 5 m distance a three-phase overhead line carrying 30A is roughly within the safe limits, whereas the 1000 A cable is well within limits. And as mentioned above, much higher currents can be safely tolerated if the exposure is limited in time.

So the conclusion has to be that low frequency magnetic fields are quite safe from magnetic point of view. They can also be extremely dangerous, of course, but for mechanical or electrical rather than magnetic reasons!

How safe are magnetic fields?

5m

single wire

two wires

transformer

0.5m

1m

2m coil

Dr Stan ZurekMagnetics Technical Specialist

8 THE FLYING FLASHOVER

The industry’s recognised information tool

ELECTRICALTESTER

In this issue, experts from the Megger Technical Support Group supply answers to the questions they most frequently receive about the testing of insulating oils.

Q: Sometimes when I’m carrying out break-down tests on a sample of oil, the results I obtain are inconsistent. Why is this and what should I do about it?A: Some of the standards for testing insulating oils recommend that if the standard deviation divided by the mean for the test results is greater than 0.1, the test should be repeated and the mean taken of all the results. There

Q&Aare, however, steps that can be taken to help reduce the problem of inconsistent results. Variable results are often caused by particles in the oil lining up between the electrodes. To minimise this effect, the oil should be left to settle for a few minutes before it is tested. Another problem occurs when an oil sample is tested several times – carbon particles may be formed by the successive breakdowns, and these will lead to lower test results. Megger OTS oil test sets have been designed to limit energy dissipated in the breakdown spark to reduce this from happening. Finally, if the oil sample is left in the test chamber for too long, it is likely that it will become warmer and drier, leading to higher test results.

Q: Why is it that, even with new oil of known quality, the test results I obtain are often suspiciously low?A: Problems of this kind usually relate to sampling technique and/or to the cleanliness of the equipment. It is very important to ensure that the sample bottles and all of the other items of equipment that come into

contact with the oil are kept dry and scrupulously clean. In particular, it is recommended that the following procedures should be employed for cleaning, storing and using test vessels:• When not in use, vessels should be store full of clean, dry oil. Vessels should be rinsed with the oil to be tested before they are filled with the test sample• If the oil sample is found to have a lower than expected dielectric strength, the vessel should be cleaned with a suitable solvent• In exceptional circumstances, it may be necessary to heat the empty vessel to re move all moisture• Always use clean lint-free room wipes to clean the vessel

DO NOT use paper towels – they leave behind particles of paper that soak up moisture causing breakdown values to be dramatically lowered.

In addition, it’s important to avoid touching the electrodes or the inside of the vessel. Electrodes should also be checked regularly for

pitting or scratches that may cause oil break-down values to be reduced. Remember that the electrode gap is also critical to accuracy.

Q: Why are the results I get often not comparable when I use various different instruments to carry out tests in line with the ASTM D877 standard?A: ASTM D877 specifies that testing should be carried out using electrodes that have sharp (right angled) edges and the radius of the electrode edge has a big effect on breakdown value. Some oil test set manufacturers supply, as standard, electrodes that have radiused edges, and these give results that are not comparable with results produced by a test set with sharp-edged electrodes. Most test set manufacturers can, however, supply sharp-edged electrodes on request, as an aid to comparative testing.

If you have any questions that you would like to ask Megger’s TSG, please give them a call on +44 (0) 1304 502102 or email uksales@megger.com

To the uninitiated, bird streamers may sound like some delightful form of party decoration. That image, however, is a rather a long way from reality, as the operators of high voltage overhead power transmission lines know only too well. For them, bird streamers are a menace, causing flashovers that trip protection systems and disrupt electricity supplies.

But what exactly are these streamers? Putting it as delicately as possible, they are streams of bird excrement. Of course, the droppings from an ordinary garden bird like a sparrow or a robin are hardly likely to be sufficient to cause problems, even if the bird in question has been a little over enthusiastic at the feeder. No, we’re talking birds with rather more impressive evacuation performance, such as eagles, herons, geese, egrets, storks, crows and buzzards – not exactly common in the UK, even with the effects of global warming, but commonplace in many other parts of the world.

These giants of the avian realm have the unfortunate ability to release excrement in the form of a continuous streamer that is two or even three metres in length. The streamers have been reported as having a resistance between 20 kΩ and 40 kΩ per metre, with the actual value presumably depending on what the bird has had for dinner.

While it’s perhaps best not to enquire too closely about how this suspiciously precise data was acquired, it’s not hard to understand how such streamers could produce flashovers on over-head power lines. On overhead distribution systems troubled by unexplained flashovers, therefore, it may, in certain parts of the world, be advisable to scan the skies before reaching for trusty test set!

THE FLYING FLASHOVER

A host of product innovations, especially in the power testing sector, combined with the cautious return of global business confidence are contributing to the enthusiastic response Megger is seeing to its presence at exhibitions around the world.

In the first quarter of 2010, major exhibitions attended by the company included Elecrama in Mumbai, India; Middle East Electricity Exhibition in Dubai, UAE; IEEE PES Transmission & Distribution Conference and Exposition in New Orleans, USA; and Hannover Fair in Hannover, Germany.

Megger shows off its wares worldwide

For electrical engineers and technicians who wish to further their careers by learningnew testing skills or by refreshing their existing skills, Megger is, during 2010, offering a comprehensive programme of training courses at its modern and well-equipped technology centre in Dover.

All of the courses will be presented by engineers who are not only skilled trainers, but also have in-depth practical experience in the areas they are covering.

While the courses include a clear exposition

Get ahead with training

“We’ve made a big investment in exhibitions this year to give as many people as possible the opportunity of seeing first hand our many new products,” said Nick Hilditch, Megger’s Group Marketing Services Manager. “These include, for example, innovative test equipment for evaluating the condition of power transformers, versatile and readily portable HV insulation testers, and ground-breaking solutions for testing IEC 61850 based sub-station installations.” And this investment has been well rewarded. Our stands have been busy at every single exhibition, with visitors showing a high level of genuine interest in our products and the opportunities that they open up for faster, more reliable and more convenient testing. On the basis of this evidence, we confidently predict that 2010 will be an excellent year for sales growth around the world.”

Elecrama, Mumbai

Hannover, Germany

of the essential theory for each topic, they also have a strong practical bias. Wherever possible, they offer those attending extensive opportunities to gain hands-on experience of using the latest test equipment. All courses include an evaluation of the performance of those who have attended, with successful candidates receiving a certificate of training. In most cases, the courses are recognised for the purposes of continuing professional development (CPD).

Megger’s 2010 training programme at the Dover Technology Centre includes courses on:

n earth testing

n cable fault location

n protective relay testing

n tan delta testing

n battery test and battery ground fault location

n insulation testing

n transformer testing.

Courses on other topics can often be arranged to suit specific customer requirements, and many of the courses can also be delivered at the customer’s own premises.

For a full schedule, details of the course content and costs, information about who should attend and to reserve places, please email tony.wills@megger.com. Note that early booking is advised as these courses are invariably very popular and places are limited.