• 200 jobs to go at South Wales Transformers

    Almost 200 jobs will be lost when South Wales Transformers closes and its operations are moved to larger premises in Loughborough.
    FKI Transformers, the parent company, hopes the move will reduce costs and allow it to compete more favourably in the UK and overseas. It says competitors in countries where it costs less to produce transformers have greater flexibility with prices and have profited in the UK market at the expense of SWT.
    The decision to relocate was totally unexpected by the union Amicus, which says a 90-day consultation period will begin in the hope of securing the factory from closure.

  • New high quality ring-type current transformers save installation time

    New high quality ring-type current transformers save installation time

    A range of high quality ring type Crompton Instruments Current Transformers with one metre flying leads, suitable for primary currents from 60 up to 2500A with 5A secondaries, has recently been released by Tyco Electronics.

    The cost-effective and versatile tape wound DB series current transformers are easily and quickly installed where conventional foot/busbar mount devices are not practical due to space or location. Long flying leads can easily be terminated wherever convenient and provide a consistent and versatile connection to any measuring/indicating equipment in applications such as switch gear, distribution systems, generator sets and control panels.

    Featuring Class 3 accuracy and Class E insulation, DB series current transformers aren’t liable to vibration issues when fitted in an alternator box and can withstand an overload of 1.2 times rated current continuously. Designed for an operating temperature range from +20 up to +70 degrees Celsius, the devices are compliant with IEC44-1 EN60044-1.

  • Test & Measurement - Complete health check for power transformers

    Test & Measurement - Complete health check for power transformers

    Liam Warren of ABB’s UK power service operation explains how the latest state-of-the-art diagnostic techniques can help to predict potential transformer faults well before they become a problem

    Power transformers are mission-critical elements in many industrial, utility and power generation installations. Should an unexpected failure occur, it can result in a lengthy downtime, with consequent loss of operating revenue, and expensive repairs. Planned maintenance is the best insurance against transformer failure and that’s where advanced diagnostic techniques come in. They offer an efficient, cost-effective way of assessing the overall condition of a transformer fleet so areas of potential concern can be flagged and action taken well before a potential failure develops into a serious fault.

    Furthermore, if an operator has a transformer that is already causing concern, then diagnostic tests can establish the severity of the problem, locate the fault and help the service team to provide expert advice on what action to take. For example, with regular testing it might be possible for the transformer to continue in service, while operating under a safe, reduced load, until a planned service interval is reached.

    ABB’s transformer diagnostic service utilizes four main techniques – SFRA (Sweep Frequency Response Analysis), FDS (Frequency Domain Spectroscopy, winding resistance measurement and oil sampling.

    The SFRA (Sweep Frequency Response Analysis) test, carried out by a Pax FRAX-101 system, is an important tool for identifying potential winding geometry changes. It consists of a low-voltage, off-line, measurement of the impedance of the transformer windings as a function of frequency. The test is performed by injecting a variable frequency AC voltage into each individual transformer winding and plotting the responding current as a curve.
    We recommend SFRA reference curves should be captured in the factory to provide a baseline ‘finger print’ of the windings in an as-new condition. However, for installed transformers, a field test can provide the baseline curves. SFRA testing should be performed periodically during the service life of the transformer, or after a specific incident that has caused significant fault currents. An alternative approach is to utilise a type-based comparison between sister transformers with the same design. Under certain conditions, a construction based comparison can be used when comparing measurements between windings in the same transformer.
    When interpreted by an expert, comparison of the SFRA test with the transformer’s original baseline curves is an excellent method to check for movement or displacement of windings or winding circuits that could affect its ability to withstand faults. It is much more definitive than low-voltage impedance tests routinely performed on transformers, it helps avoid catastrophic failures and can even locate the exact position of a fault.
    Figure 1 shows a typical SFRA analysis in which the pronounced dip in the frequency response curve of one of the transformer phases indicates a potential fault – most probably due either to a winding failure or core movement.

    FDS (Frequency Domain Spectroscopy), carried out by a Pax IDAX-206 system, is used to assess the integrity of a transformer’s insulation system. The test determines the volume of moisture and presence of contaminants in the solid insulation, as well as the conductivity and power factor of the oil. This is an extremely useful tool in an overall condition assessment programme as standard power factor tests alone do not yield this type of information.

    The FDS test measures the dielectric properties (capacitance, loss and power factor) of the transformer’s insulation as a function of frequency, This off-line test utilizes the same type of connections as a standard (Doble) mains frequency insulation power factor test . However, by covering a much wider frequency range – typically 1 mHz to 1000 Hz – the test offers increased sensitivity to insulation issues.

    An important primary use of the FDS test is to determine the moisture content of the cellulose insulation structure of power transformers. It is difficult to obtain a reliable assessment of moisture content by oil sample tests, as the water is transferred between the solid insulation and the oil as the temperature changes. An oil sample has to be taken at relatively high temperatures, when the transformer is in equilibrium. But this is a relatively rare state for a transformer and can result in unreliable assessments.

    An illustration of the advantages of FDS is provided by an exercise in which a customer provided ABB with a list of seven suspect transformers. In each case, moisture in oil test results had indicated the need for oil processing and drying. By carrying out FDS tests we were able to show that only two units actually needed drying. So our recommendation was to dry these two, while keeping the other five under careful surveillance. The customer not only made a very significant saving in operational and maintenance costs, preventing unnecessary drying operations on five transformers also reduced the risk of over-drying and loosening of windings.

    Winding resistance measurement
    Winding resistance measurement tests are carried out by an Omicron CPC 100 system. This is used to inject a DC current of up to 2kV through the transformer windings and it then measures the voltage drop across that winding - enabling the resistance to be calculated.

    The main purpose of this test is to check for significant differences between the windings, which could indicate field damage or deterioration, and also to ensure that the transformer connections are correct and that there are no severe mismatches or open circuits.

    Oil sampling
    Just as a blood test can provide a doctor with a wealth of information about their patient, a sample of transformer oil can tell an engineer a great deal about the condition of a transformer, enabling them to effectively manage the asset for extended life and enhanced reliability.
    The role of the oil in the transformer is to both cool it and insulate the internal components, and in doing so it bathes every internal component. As a result, the oil contains around 70 per cent of the available diagnostic information for the transformer and laboratory analysis can provide an early indication of a developing condition such as tap changer arcing.
    The data generated from an oil sample is only as good as the sample itself. It is vital to obtain a clean uncontaminated sample to BS 5263. This includes taking the sample while warm, and measuring the temperature so that the laboratory can then adjust the results for moisture content, preflushing the sample leg and running the sample quietly into a clean glass vessel to minimise degassing and sealing the sample securely.
    We recommend that the best information can be obtained from oil sampling by viewing trends. So it is useful to take a bench-mark sample when a transformer has been energized or an oil treatment performed and to then take further samples at regular intervals so that any variation in quality can be measured in order to monitor developing faults.
    Typical tests carried out in the laboratory analysis of the oil sample include:
    - Breakdown voltage (dielectric strength)
    - Moisture content
    - Dissolved gas analysis (DGA)
    - Oxidation
    Each of these parameters impacts on the other parameters, and they all work together to affect the condition of the transformer.

    In general, power transformers are very reliable devices and will provide excellent service for many years if maintained and serviced regularly. Failures, when they occur, are usually very serious and require costly repairs and inconvenient downtime. The best insurance against failure is a planned monitoring and testing regime. The new generation of high-technology, non-invasive, diagnostic techniques can play a vital role in this regime.

  • Test and Measurement - Power transformers – are you covered?

    It's easy to assume the substation on your site belongs to the power utility, but are you absolutely sure? If you get it wrong, says Damon Mount of Megger, and you're unlucky enough to suffer a transformer fault, you could find yourself landed with a bill for tens or even hundreds of thousands of pounds

    In the substation, the power transformers are probably the most expensive items. And that's not the worst of it - the delivery time for a replacement transformer is typically months - or even years for the largest types. The direct and indirect costs associated with a transformer failure can, therefore, be enormous.

    But there's surely no need for concern. All of the power transformers on your site are the responsibility of your energy supplier, aren't they? It may be a very good idea to check again. In a surprisingly large percentage of installations, the power transformers belong to the owner of the premises, and not to the power utility.

    Of course, there's still no reason to worry, because transformer failures will certainly be covered by insurance, won't they? The answer is possibly not. Because of the huge costs involved, insurers are understandably cautious about making payouts relating to transformer faults and failures. If there is a claim, they will certainly ask for evidence to show the transformer has been regularly tested and maintained.

    Since many companies are not even aware they are responsible for the power transformers on their sites, it's not too much of a surprise there are a lot of transformers that most certainly don't get the regular attention they need.

    This is a special concern with the many transformers currently in use that have long exceeded their design lives. Although they may apparently still be working well, it is inevitable some of the materials used in their construction - in particular the insulating materials - will have started to deteriorate.

    If an unmaintained transformer fails, whether it is old or new, it's perfectly possible that the insurers will contest the claim or refuse to pay. Let's take a look at what needs to be done to avoid this potentially devastating situation.

    The first and most obvious step is for maintenance departments to check which of the transformers on their site are their responsibility. The next step is to implement a regular testing programme for these transformers.

    But what form should the testing take? There are, of course, many types of conventional tests that can be applied to power transformers to check, for instance, the performance of the tap changers or the windings.

    This means to build up a reasonably complete picture of the transformer's condition, a whole battery of tests is needed, which will take a considerable time to perform. During this time, the transformer will be out of service, which can be very inconvenient.

    There are, however, two tests that between them can provide a wealth of information, not only about the presence of faults but also, in many cases, their type and location. These tests are sweep frequency response analysis (SFRA) and frequency domain spectroscopy (FDS).

    Electrically, a transformer is made up of multiple capacitances, inductances and resistances. It is, in effect, a very complex circuit that produces a unique ‘fingerprint' when test signals are injected over a range of frequencies and the results plotted as a curve. In particular, the capacitances in the transformer are affected by the distance between conductors.
    Movement of the windings, which can be caused by electrical overloads, mechanical shocks or simply by ageing will, therefore, alter the capacitances and change the shape of the frequency response curve.

    The SFRA test technique for transformers is based on comparisons between measured curves, which allow variations to be detected. An SFRA test involves multiple sweeps and reveals whether the mechanical or electrical integrity of the transformer has been compromised.

    SFRA tests are used to capture a ‘fingerprint' reference curve for each winding when the transformer is new or when it is known to be in good condition. These curves are subsequently used as the basis for comparisons during maintenance or when problems are suspected.

    The best way to use SFRA testing is to take regular measurements on the same transformer over a period time, and to compare the results. However, it is also possible to use type-based comparisons between transformers with the same design. Finally, a construction-based comparison can be used in some circumstances, when comparing measurements between windings in the same transformer.

    A single SFRA test can detect winding problems that would otherwise require multiple tests with various kinds of test equipment, as well as problems that cannot be detected at all by tests of other kinds.

    As a general guide, magnetisation and other problems relating to the core alter the shape of the SFRA curve at the lowest frequencies, up to around 10 kHz. Medium frequencies, from 10 kHz to 100 kHz represent axial or radial movements in the windings, and high frequencies above 100 kHz correspond to problems involving the cables from the windings to bushings and tap changers. In modern SFRA test sets, built-in analytical tools simplify comparisons between curves.

    While SFRA tests provide a lot of information about the condition of a transformer, they do not give an accurate indication of the presence of contaminants - in particular water - in the transformer insulation. Standard tests, such as the widely used Karl Fischer test, are, of course, available for accurately assessing the moisture content of transformer oil, but this is not the whole story.

    In fact, it is usual for a much greater percentage of the moisture in a transformer to be held in solid insulation such as paper than is held in the oil. To further complicate matters, the moisture moves between the solid insulants and the oil in a way that is influenced by many factors including, in particular, temperature. 

    Measuring the moisture content of the oil may not, therefore, provide dependable information about the moisture content of the transformer's solid insulation. This is a serious concern, as moisture in the insulation significantly accelerates the ageing process in transformers and, in addition, it can cause bubbles between windings that lead to sudden catastrophic failures.

    To establish the moisture content in the transformer, the second of the tests mentioned earlier - frequency domain spectroscopy (FDS) - can be used. Initially, this may sound a lot like SFRA, as it involves measuring transformer characteristics at over a range of frequencies. This time, however, it's the dielectric properties of the insulation (capacitance, loss and power factor) that are measured over a range of frequencies, typically from one millihertz to one kilohertz.

    These are, in essence, the same dielectric tests that are often carried out at power frequency, but testing at a single frequency provides far less information than is revealed by FDS testing. Unlike spot-frequency testing, FDS can, for example, reliably distinguish between a transformer that is dry but has bad oil, and one that is wet but has good oil. In the first case, the oil needs refurbishing or replacing; in the second the transformer only needs drying out.

    FDS testing also has other benefits - it can be performed at any temperature, and the test can be completed quickly. Software can be used to calculate the water content in percentage terms, and modern FDS test sets typically provide accurate and detailed results in less than 20 minutes.

    As we have seen, regular testing using the SFRA and FDS test techniques provides a reliable insight into the condition of power transformers, but how can this information best be used by the transformer owner?

    A short-circuit fault on the transformer may cause unseen damage inside, and a damaged transformer put back into service could fail catastrophically. An SFRA test can be done before re-energising and compared to a reference trace taken while the transformer was in good working order. If the two traces match, nothing has changed and the transformer can be safely returned to service. Carrying out this test takes less than an hour, reducing outage time and saving money.

    Ageing, mechanical damage and moisture content can be seen as a change in the frequency response of the transformer over time and may indicate that remedial action, such as drying out the transformer, is needed to guard against future failures. In other cases, it may show that the transformer is inevitably coming to the end of its useful life, but even then the information is invaluable.

    In this situation, it may be possible, for example, to minimise the load on the transformer so it can continue in service until a replacement is obtained. And even in the worst case, there is at least a warning that failure is imminent, which can allow time for contingency plans to be made and put into place.

    There is also another very valuable aspect of regular testing, which we touched on earlier. Insurance companies are more likely to honour a claim for failure of a power transformer that's been regularly tested and properly maintained so as to remedy any issues identified by the tests. Such a transformer is, of course, less likely to fail, but if it does there is at least the consolation that the insurers will foot the bill!

    Even for those who are aware of their responsibilities in looking after power transformers, regular testing may appear as something of a burden. However, tests with modern instruments can be performed quickly and easily, and they yield dependable informative results. And, if the test regime eliminates just one unforeseen transformer failure that would otherwise have occurred, the effort involved in testing and the cost of the instruments used will have been repaid many times over.

  • Transformers - Transformer transformations

    John Clarke, of Zucchini EdM Transformers, discusses the environmental and cost-saving effects of cast-resin transformers

    A transformer is a device that transfers electrical energy from one circuit to another through a shared magnetic field. A key application is to ‘tap off' 11,000 volts (11 kv) of electrical power from the national grid and step it down to 415 volts, which is the normal 3-phase electrical power system used in the UK for commercial, institutional or industrial applications. A transformer therefore makes raw electricity ‘usable', as well as allowing it to travel through cables. In fact, most of the world's electrical power has passed through transformers by the time it reaches the consumer.

    Large, high-power transformers, in particular, need to have a built-in cooling facility to transport heat from the interior. Thus, one of the numerous ways of classifying transformers is according to cooling type. For example, for power transformers rated up to a nominal kVA, natural convective air-cooling, often fan-assisted, is adequate. Traditionally, oil transformers relied on highly refined mineral oil as a cooling medium, while the latest generation cast-resin transformers, the transformer core is insulated by a thin coating of inorganic material.

    Over the last decade, remarkable advances in materials technology and manufacturing methods have fostered the popularity of cast resin transformers, particularly in fire-sensitive locations such as high-rise structures, hospitals, and public buildings where the transformer is located indoors and a fire outbreak would be particularly hazardous because of the high density of people.

    Safety is high on the list of benefits provided by cast resin transformers. The advanced epoxy mixture used in EdM transformers is a non-hazardous material, which is both fire-resistant and self-extinguishing. Even when the material is exposed to arcing, no toxic gases are produced, and the transformer can be safely situated close to the load, saving on cabling, civil works and transmission loss.

    Another key benefit is the fact that cast resin transformers require no maintenance during their lifetime.

    Compare all these benefits with the disadvantages of traditional oil transformers with their relatively low fire point, pollution potential, higher installation costs (due in part to the fire-protection and containment measures often needing to be installed along with the installation), and a high maintenance requirement.

    Oil-cooled transformers are not, it has to be said, a favourite with insurance companies. Oil, of course, is a non-renewable resource, while EdM transformers are insulated in a sustainable material, which has been developed and refined over 15-years to comply fully with European Union and national directives on the protection of the environment. Indeed, they do not pollute the environment where they are installed and are therefore recommended for all ISO locations, a standard that helps organizations minimise the negative effects of their operations on the environment.

    As well as protecting the environment, the high quality epoxy resin filled with silica and trihydrate alumina, that have developed to encapsulate transformers, stops moisture  ingress, thus preventing electrical breakdown under load, as well as inward pollution from the environment. This not only makes the transformers ideal for damp or dirty conditions, but extends the life of the transformer's working parts and eliminates maintenance. EdM transformers are also coated in high-vacuum chambers to reduce air and other gases in the resin that could produce partial earth discharges. In effect, they thermetically seal the transformer's core. As a result, consultants and specifiers looking for standard transformers with power outputs in the range of 100 to 3,500 kVA (and up to 16,000 kVA for specific projects), get complete peace of mind.

    Another point is cast resin transformers do not have the noise and vibration problems associated with oil-based machines.

    Cast resin transformers are now available in different specifications to meet the needs of the climate or hazardous and unforgiving environments, exceptionally cold ambient temperatures and environments with high fire risk.

    One of the most gratifying outcomes of installing environmentally friendly technology in recent years has been the realisation by individuals and companies that saving the environment  - can also save money! As well as being favourably priced, cast resin transformers are exceptionally energy-efficient, producing a high transformation yield and thus consuming less input energy.

    At Zucchini EdM, we have developed ‘mathematical models' highlighting the savings that can be made by the user of a given electrical item on a case-by-case basis. For example, a 1,000 kVA energy-efficient transformer can produce savings of  €30,000 over a 20-year period, the equivalent of 20 MWh per year. The European Commission has assessed if equipment such as this were brought into general use, emissions of 11 million tonnes of carbon dioxide - equivalent to the electrical power used by 5 million homes - would be avoided.

  • Transformers - Oil sampling – the comprehensive transformer health test

    In the same way a blood test can provide a doctor with a wealth of information about  their patient, taking an oil sample enables service engineers to learn a great deal about the condition of a transformer. This can play a key role in the effective management of a vital network asset for extended life and enhanced reliability. Liam Warren, ABB's general manager power service explains

    The oil in a transformer acts as both a coolant and insulation for the internal components. In doing this it bathes almost every internal part. As a result, the oil contains around 70%  of the available diagnostic information for the transformer. The challenge is to access this information and analyse it effectively to provide an early indication of a developing condition such as tap-changer arcing.

    Obtaining a representative sample
    The data generated from an oil sample is only as good as the sample itself. A poorly drawn or contaminated sample can invalidate the test results or even lead to a misdiagnosis. At ABB we have recently upgraded our sampling procedure to use the TFSS (Turbulent Flush Sampling System). This compact, self-contained system provides several benefits including:
    - promoting turbulent flush
    - standardizing flush volumes
    - producing a representative sample
    - preventing sample contamination
    TFSS ensures the sample is representative of the oil inside the transformer, rather than any contaminates that might have settled into the valve.

    Transformer condition assessment (TCA)
    Traditional oil-testing programmes utilise only a few diagnostic parameters, leaving a vast amount of potential oil-based information unexplored. Yet surveys of failed transformers reveal many failures can be attributed to problems that could have been properly managed with an early diagnosis through a more detailed analysis of the insulating fluid.

    ABB bridges this gap by working with a leading test laboratory to provide TCA (transformer condition assessment). TCA offers a comprehensive assessment of the dielectric and mechanical state of the transformer including:
    - Dissolved gas analysis (DGA)
    - Insulating fluid quality analysis
    - Particle analysis
    - Furan analysis

    DGA - a view of operational condition
    Hydrocarbon (mineral base) oils are frequently used as insulating fluids in high voltage power equipment such as transformers because of their favourable dielectric strength and chemical stability. Normal degradation of the oil usually occurs due to oxidation. This is generally a slow process. However, under the influence of an electrical or thermal fault, the oil can degrade to form a variety of low molecular weight gases that dissolve in the oil (such as methane, ethane, ethylene, acetylene, hydrogen, carbon monoxide and carbon dioxide).
    The composition of the breakdown gases depends on the type of fault, while the quantity depends on its duration. Hence by dissolved gas analysis (DGA) it is possible to distinguish such transformer fault processes as partial discharge (corona), overheating (pyrolysis) and arcing.

    DGA involves two steps - extraction and chromatographic analysis. In the first step, the gases are extracted by subjecting the oil sample to high vacuum. The volume of the extracted gases is measured and a portion of the gas is transferred to a gas chromatograph.

    The great sensitivity of the chromatographic process enables low detection limits for each gas - at the parts per million level. The remarkable sensitivity and precision of this method ensures a high measure of reliability for the diagnostic interpretation of DGA data.
    Based on the dissolved gases in the transformer oil it is possible to indentify faults such as corona, sparking, overheating and arcing.

    Corona - is a low energy electrical fault that results from the ionization of the fluid surrounding the fault. Typically, this is characterised by an increased level of hydrogen without a concurrent increase in hydrocarbon gases.

    Sparking - is an intermittent high voltage discharge that occurs without high current. It is characterised by increasing levels of hydrogen, methane and ethane without a concurrent increase in acetylene.

    Overheating - can arise from a variety of causes, such as overloading, circulating currents, improper grounding and poor connections. It is characterised by the presence of hydrogen together with methane, ethane and ethylene.

    Arcing - the most severe fault process, involves high current and high temperatures and may occur prior to short circuit failures. It is characterised by the presence of acetylene.
    Faults involving cellulose insulating materials, such as impregnated paper, wood and pressboard, result in the formation of carbon dioxide and possibly carbon monoxide. In load tap-changers, thermal problems are characterised by elevated levels of ethylene.
    Interpretation of DGA data can be a complex process because of the large number of equipment parameters and operating conditions that affect gas formation. It is important to take into consideration the operating philosophy and past history of the transformer. Establishing baseline values for a transformer against which future DGA tests can be compared is a very effective diagnostic testing procedure. Monitoring the rate of gas generation makes it possible to assess the progress of the fault process.
    Insulating fluid quality analysis - a view of how the transformer is being managed
    There are a number of routine tests on the insulating fluid that provide a useful indication of how well the transformer is being managed in service. They cover a number of key parameters including PCBs, moisture, acidity and dielectric strength.

    PCB content
    Although not related directly to the transformer performance, it is still important to identify the presence of the chemicals known as Polychlorinated Biphenyls (PCBs) in the insulating fluid. PCBs were very popular in the late 1950s/early 1960s as an alternative to mineral oil thanks to their excellent insulating properties. They are however highly toxic and have been outlawed for many years. Unfortunately, PCBs were in service for long enough to cause some cross-contamination with mineral oil stocks and it is relatively common to find some background traces in older transformers. No immediate action is required at levels below 50 ppm. At levels between 50 to 500 ppm the transformer needs to be taken out of service when possible so that it can be flushed and re-filled with fresh oil. At anything greater than 500 ppm immediate action is required.

    An increase in the oil's moisture content can degrade its insulating properties and result in dielectric breakdown. This is especially important when a transformer is subjected to fluctuating temperatures, possibly when in intermittent operation, as the cooling down process causes dissolved water to come out of solution, reducing the insulating properties. In addition, cellulose-based paper is in common use as insulation for the transformer windings and the presence of excess moisture can damage this paper.

    Increased acidity not only cause the oil to attack the many copper components in the transformer as well as corroding the steel tanking, it also degrades the paper insulation. Acids can also cause the formation of a sludge that blocks ducts and cooling galleys, resulting in less efficient cooling - resulting in further degradation of the oil. As a general rule, the oil must be replaced when the acidity exceeds 0.5 mg/g KOH.

    Dielectric strength
    The dielectric strength of the transformer oil is a measure of how effective an insulator it is. Factors that can cause a significant reduction in dielectric strength include the presence of contaminants that result in an increased content of free-ions and ion-forming particles, such as water, oil degradation products and cellulose insulation breakdown products.

    Particle analysis
    One of the major advances in extracting a higher level of diagnostic information from transformers has come from the identification of suspended and sedimented  particles found in the oil. When the DGA analysis indicates the presence of a possible fault, particle analysis will provide corroboration and pinpoint its location. For example, in one analysis the DGA results suggested that heating gases and carbon oxide gases were present, indicating a hot spot. The microscopic analysis confirmed the hot spot condition with the presence of charred paper in the oil.

    Furan analysis - a view of remaining life
    In general, the life of a well maintained transformer with no serious operating defects will be determined by the condition of its insulating paper. As the paper degrades it produces organic compounds known as Furans. There is a direct relationship between the amount of Furans produced and the strength of the paper insulation. Furan analysis can therefore provide a useful estimate of the transformer's remaining service life.

    Oil sampling becomes most useful when carried out on a regular basis so trends may be identified. So it is useful to take a benchmark sample when a transformer has been energised or an oil treatment performed and to then take further samples at regular intervals so that any variation in quality can be measured in order to monitor developing faults.

    The battery of sophisticated analysis techniques available to monitor the quality of the oil form a valuable diagnostic tool that provides an indication of the general condition of a transformer, how well it is being managed and how long it can be expected to function before requiring a major service or replacement. Perhaps most importantly, it can be used to anticipate severe faults, enabling preventive action to be taken before they occur.

  • Advertisement feature - Diagnostics and condition assessment for transformers

    Long before most electrical apparatus fail, signs of trouble appear and can be detected  by oil tests!

    The condition of generation, transmission or distribution transformers can be determined by the analysis of electrical insulating oil. These fluids circulate as a dielectric and coolant and can be sampled, in most cases, while the equipment is energised. With outages minimised in modern times, this is a key attribute.

    Oil testing can detect developing apparatus problems such as, local overheating at a loose connection or electrical discharge between turns, so problems can be managed and catastrophic failures prevented. Oils and other insulating materials degrade during their life as a result of heating, oxidation, and in more serious cases, from discharge activity. Accelerated or excessive degradation of the oil can be detected, but more important is to detect abnormal conditions or faults that can result in failure of the apparatus.

    There are a variety of tests that can help detect problems with the insulating materials and the apparatus. Because diagnostics from oil data is so good today, condition-based maintenance is possible. With good knowledge of the condition of transformers, attention can be focused on problems so they are managed to minimise out of service time while reducing risk of a catastrophic failure. By understanding the true condition of transformers and how they age, proper maintenance can be used to extend the life of such important assets. To use oil tests effectively requires accurate data, background information as to where the sample was taken, nameplate information, and a good understanding of the diagnostics.

    Oil Quality Testing
    Colour (ASTM D 1500, ISO 2049): Insulating liquids darken with the presence of oxidation byproducts and foreign materials and are an indicator of ageing.
    Dielectric Breakdown Voltage (ASTM D877 or 1816, IEC 60156): A low value indicates the presence of contaminants such as water, dirt or other conducting particles in the insulating liquid.

    Interfacial Tension (ASTM D 971, ISO 6295):  Monitors the progression of oxidation and detects contaminants such as soaps, paints, varnishes and byproducts of insulation ageing.
    Acidity / Neutralization Number (ASTM D 974, IEC 62021-1): Monitors the progression of oxidation by detecting acidic compounds which accelerate deterioration of the solid insulation and are precursors to sludge formation.

    Visual (ASTM D 1524, IEC 60296): Visual inspection identifies foreign material in the insulating liquid, which may lower its dielectric strength.
    Power Factor or Dissipation Factor at 25°C (ASTM D 924, IEC 60247): High values indicate the presence of contaminants like carbon, polar compounds, metal soaps and byproducts of oxidation.

    Water Content (ASTM D 1533, IEC 60814):   Excessive moisture is one of the primary causes of low insulating liquid dielectric breakdown strength. High water content may be detrimental to the transformer under a variety of conditions. Reporting results in concentration (ppm) and percent relative saturation gives more effective interpretation of results
    Specific Gravity or density (ASTM D 1298, IEC ISO 3675): Helps identify different types of insulating liquids.

    Diagnostic Testing
    Dissolved Gas Analysis (ASTM D 3612, IEC 60567): The single most important test you can perform to detect problems and head-off potential transformer failures. It monitors gas generation in transformers for advance notice of developing faults to properly manage risk. It's a good way to detect thermal and electrical problems and determine their severity.
    Furanic Compounds (ASTM D 5837, IEC 61198): Since the paper is the most important dielectric component of the transformer, having the ability to assess its condition is a must. When the cellulose breaks down, furanic compounds are generated and can be used to detect accelerated ageing and localized problems.

    Metals-In-Oil (Various methods): Dissolved and particulate metals such as copper, iron, zinc, and lead can be detected and can be indicators of incipient-fault conditions, potential bearing wear from pumps or other wear metals from vibration of components.

    Keep up to Date
    Corrosive Sulphur - There are sulphur compounds in oil that can be corrosive resulting in the formation of copper sulphide on conductors and in insulating paper. On conductors the copper sulphide is too resistive and causes overheating. In the paper copper sulphide is too conductive and can results in a dielectric failure. Copper sulphide particles can bridge insulation gaps resulting in dielectric failure in the oil.

    Paper Quality Testing
    Degree of Polymerization of Paper (ASTM D 4243, IEC 60450): This test provides a measure of paper ageing, and correlates with important physical properties like resistance to tearing and bursting. This is a critical factor in estimating the real ageing of the main transformer insulation. This test does require a paper sample so is used opportunistically when internal inspections are needed.

    Doble Engineering Company
    For accurate and reliable oil testing and professional diagnostics by a team of chemists and engineers come to Doble Engineering Company. We can help with creating a cost-effective test programme and diagnostic services. Specialised testing is available to analyse problems beyond the typical tests. When transformers develop problems Doble is there to help with you with the testing, assessment, and action plan.

    Email: This email address is being protected from spambots. You need JavaScript enabled to view it.

    Tel: 01483 514120


  • Transformers - Transformer oil testing: here or there?

    Most engineers would agree breakdown testing provides the most reliable indicator of the condition of the oil in a power transformer. There is, however, far less agreement about whether the testing should be carried out on site or in the laboratory. Paul Swinerd of Megger looks at the arguments for and against each of these options

    The condition of the oil in a power transformer is a major influence on the transformer's reliability, operating life and even safety. A dependable and convenient method of assessing oil condition is, therefore, an essential adjunct to transformer operation and maintenance.
    Various options are available to meet this requirement including, for example, the Karl Fischer coulometric titrimitry method that can be used to quickly determine the moisture content of the oil. This test is used frequently as water contamination is the most common cause of oil degradation. The most direct measure of the oil's ability to perform adequately as a dielectric medium is, however, given by breakdown testing.

    In breakdown testing, a sample of oil taken from the transformer is transferred to a test vessel, which is then loaded into the breakdown tester. Typically the instrument will then carry out a series of tests in a pre-programmed sequence determined by the oil testing specification appropriate to the application.

    In addition to the application of test voltages - usually in the tens of kV range - to electrodes immersed in the oil, the test sequence will also include predetermined stirring and standing times.

    Breakdown test sets that operate in the way described are available in laboratory versions, and in portable versions that are designed for convenient use in the field. Some manufacturers, including Megger, also offer instruments that are equally well suited to use on-site and in the laboratory. But which is preferable - laboratory testing or field testing?
    In order to understand the arguments for and against each approach, it is first necessary to appreciate contamination of the oil sample has a large effect on the accuracy of the results obtained in a breakdown test, with even a tiny amount of contamination making the results unreliable and, therefore, unusable.

    Some engineers argue this means it is best to carry out testing on site. Their rationale is that, for laboratory testing, the oil sample has to be bottled and sent to the laboratory, and there will always be doubt about whether the bottle was adequately cleaned before use, and whether it was sufficiently well sealed to guard against contamination in transit.

    There are other engineers, however, who will point out the sample is at most risk of being contaminated while it is being collected, and that the contamination risks associated with bottling and transportation are, by comparison, relatively small. Their conclusion is there is no significant difference between the overall contamination risks for on-site and laboratory testing.

    Proponents of laboratory testing will also argue, once the oil sample reaches the laboratory, it will almost certainly be tested by a skilled technician who will fully understand the procedures and precautions involved, and will follow them carefully to ensure accurate results are obtained.

    On the other hand, tests on site are frequently performed under less than ideal conditions, and there is often pressure to complete the testing process as quickly as possible. These factors are conducive to error, especially if the person performing the tests carries out breakdown testing only infrequently.

    Nevertheless, there is one important issue that most definitely favours testing on site, and that is the speed with which results can be obtained - typically within an hour of the sample being taken, and often much faster.

    This almost immediate availability of results has two important benefits. The first is that if an unexpected or obviously incorrect result is obtained, the test can usually be repeated at once. The second benefit is, if the tests confirm the oil is in poor condition, the transformer can be taken out of service straight away, thereby reducing the risk of failure.

    While important, however, these benefits should not be interpreted to mean on-site testing is always to be preferred. There are most definitely cases where on-site testing is impractical, or where the certainty of tests being carried out consistently and with a high degree of precision outweighs the advantage of obtaining immediate results.

    The best advice for those considering the implementation of breakdown testing for transformer oil is, therefore, to consider both the laboratory and on-site options carefully in relation to the application in hand, before making a decision.

    Suppliers of oil test sets will undoubtedly be pleased to provide assistance in making this decision but, to be sure of receiving impartial advice, it is most certainly advisable to choose a supplier, like Megger, that offers both portable and laboratory instruments.

  • 3000 distribution transformers for Polish utility company

    Ormazabal is supplying its low loss distribution transformers to the Polish electrical market after winning a public tender to supply Energa.

    Energa is the third biggest Polish utility, with an annual production of 20 TWh, which represents 17% of the countries production. Energa is also the number one renewable energy producer in Poland, with 13% of its production coming from renewable resources.

    Ormazabal manufactures a wide range of dielectric liquid immersed distribution transformers, compliant with all of the requirements in current international regulations and adapted to a client's own needs with a range of powers from 25 kVA to 2500 kVA and insulation levels up to 36 kV.

  • Transformers - Amorphous metal core to success of transformers

    Ceyhun Sahin of ABB explains how a new range of dry-type distribution transformers can play a vital role in improving energy efficiency in power distribution networks

    Transformers in operation incur two types of losses: no-load loss that occurs in the transformer cores due to hysteresis and eddy current losses - which is always present and is constant during normal operation, and load loss that occurs in the transformer’s electrical circuit, including windings and components, due to resistive loss and is a function of loading conditions. Although distribution transformers are very efficient, there is still a large total loss of energy due to the vast installed bases of distribution transformers. Globally, these losses are estimated to account for around 2-3% of all electric energy production – some 25 GW.  According to a 2008 study by SEEDT (Strategies for development and diffusion of Energy- Efficient Distribution Transformers) in the EU alone, there are some 4.5 million distribution transformers, causing 38 TWh of losses each year – more than the entire amount of electricity consumed by Denmark – and 30 million tons of CO2.

    Load profile – a key consideration
    The growing recognition that transformer losses constitute a significant economic cost is driving programmes to implement energy efficiency standards for distribution transformers. This includes the US, with its DOE (Department of Energy) minimum energy efficiency requirements for liquid-filled and dry-type distribution transformers. The required efficiency is typically quoted for a reference load value – in the case of the DOE this is at 50% of the transformers rating. However the overall efficiency of a transformer in service depends very much on the load profile. Depending on the loading, the effective efficiency can vary significantly from the reference value. This variation requires the selection of transformers to consider the load profile

    Distribution transformers are typically custom designed to meet customer specifications and requirements which are normally in compliance with the technical requirements of national or international standards. In addition, the design reflects an optimisation between the cost of materials and labour used in the production of the transformer and the cost of losses.
    Some customers look for the lowest possible purchase price, ignoring the cost of losses over the transformer lifetime. These customers are usually not responsible for the ownership or operational costs of the transformers. Customers with operational responsibility seek to reduce losses and specify loss capitalisation, or loss evaluation, values. These capitalised losses reflect the cost of energy consumed by the transformer during an expected economical lifetime. Therefore, when comparing transformer designs it is best to consider the TCO (Total Cost of Ownership), which is the summation of the purchase price and the loss capitalisation. Typically, the design with the lowest TCO results in the most desirable unit for each individual customer based on its specific loss capitalisation factors.
    An important option for customers seeking to optimise their TCO by specifying ultra high efficiency distribution transformers is amorphous metal. The use of AMDT (amorphous metal distribution transformers) core technology, combined with optimised coil designs, can provide significant reduction in no-load losses, resulting in higher energy efficiency. Amorphous core technology is at the heart of ABB’s new generation EcoDry ultra high efficiency dry-type transformers.

    Amorphous metal transformer cores
    Historically, there was an initial interest in amorphous core transformers which stemmed from the first oil shock in the mid-1970s when improved energy efficiency in power distribution systems was increasingly desirable. This interest fell away in the mid-1990s when energy costs decreased. Furthermore, the initial costs of an amorphous core transformer are higher than of a crystalline silicon steel core transformer: first, the amorphous material itself is more expensive than crystalline silicon steel and second, the saturation magnetic flux density of amorphous steel is lower than that of silicon steel. This means larger sizes of amorphous core transformers are required, which results in a higher cost per unit. However, the higher initial costs can be compensated by lower operating costs over the lifetime of the transformers due to their increased energy efficiency.
    Nowadays, amorphous metal core transformers have become commercially available and are cost-competitive with conventional core transformers. There has also been significant technical progress in increasing the saturation magnetic flux density of iron-based amorphous alloys, resulting in smaller transformers and reduced material costs.
    The amorphous metal used in transformer cores is a unique alloy of Fe–Si–B (iron, silicon and boron) that is produced by extremely rapid solidification from the alloy melt. This causes the metal atoms to form a random pattern, as opposed to conventional Cold-Rolled Grain-Oriented (CRGO) silicon steel (a Fe–Si alloy), which has an organized crystalline structure. The amorphous structure, usually associated with non-metallic systems looks like glass - which has prompted the name ‘glassy metal’ widely used for such materials.
    The absence of a crystalline structure in amorphous metal allows easy magnetization of the material, leading to lower hysteresis losses. The eddy current losses are also lower in amorphous metal due to a combination of its low thickness and a high electrical resistivity of 130 μΩ-cm compared to the 51 μΩ-cm in CRGO silicon steels. Thus, amorphous metal has a much lower total loss than even the best grades of CRGO steel, by up to 70 percent.
    Amorphous metal cores have a proven track-record of over 20 years in liquid-filled transformers and this technology is now being applied to dry-type transformers.

    Advantages of dry-type transformers
    Dry-type distribution transformers offer significant practical advantages, including: no fire risk; no risk of escape of pollutants or fire-hazardous substances; long lifetime; high mechanical strength; ability to cope with load changes, overloads, short-circuits and over-voltages; and reduced installation footprint. This means they can be installed near their place of use – saving on cabling and reducing losses in cables and terminals on the low-voltage side.

    EcoDry range
    ABB’s EcoDry range includes transformers that reduce no-load losses by up to 70%, and by more than 30% at full load, when compared with international reference standards such as the European CENELEC HD538 standard and the US Department of Energy energy conservation standard for distribution transformers introduced in 2010.
    For each GW saved, there is the potential for an annual reduction of five million tonnes of CO2 emissions – a single 1,000 kVA unit can save 7 tonnes of CO2  a year. Lower losses also generate less heat, so there is a reduced aging effect on the transformer insulation.
    EcoDry transformers achieve higher efficiency levels through the use of state-of-the-art materials and components, including amorphous metal as the core material, as well as the latest simulation methods for loss-optimized design. They are available in ratings from 100 to 3,150 kVA, with operating voltage up to 36 kV.
    The EcoDry range includes three models, each designed to meet the different needs of applications where losses are either predominantly ‘no-load’ losses (caused by fluctuating magnetization of, and eddy currents in, the transformer core), or ‘load’ losses (which occur in the conductors due to ohmic loss and eddy currents, and increase quadratically with the load), or a combination of the two.

    EcoDryBasic – low-load efficiency for power utilities
    Distribution transformers at power utilities often see only a low mean load in actual operation. With low load profiles, it is the no-load losses that account for the major proportion of total losses and they are three to five times higher than the load losses. This means a significant reduction in no-load losses is one of the paramount considerations for the EcoDryBasic transformer,  a high-tech product, based on 30 years of experience, and developed using the very latest simulation methods for a loss-optimised design.
    The EcoDryBasic transformer is specifically designed to meet the needs of power utilities by providing low-load efficiency that enables losses and CO2 emissions to be reduced by more than 50%.

    EcoDry99plus – full-load efficiency for industrial applications
    In an ideal world, industrial plant is operating at or near full capacity, and mean loading of the distribution transformer of 60% or more is not uncommon. The costs of load losses, and their reduction, can be significant.
    In a typical industrial application, an EcoDry99Plus transformer rated at 1,000 kVA, with 10,000 V primary voltage, would reduce annual power losses by more than 30,000 kWh, and cut CO2 emissions by some 18 tonnes per year. At full load, the transformer operates at over 99% efficiency.

    EcoDryUltra – efficiency across the load range
    EcoDryUltra transformers combine the advantages of the EcoDryBasic and EcoDry99Plus to minimise no-load and load losses simultaneously. This transformer type is ideal for variable loads – such as renewable energy applications – and in applications where the supply is fed through two transformers at the same time (for redundancy) and so each is continuously operated at medium load – such as in pumping or ventilation systems.

    Distribution transformers have a vital role to play in helping power utilities and general industry meet targets for reducing carbon emissions, as well as boosting efficiency and cutting running costs. The next generation of low-loss dry amorphous distribution transformers can effectively reduce overall losses, contributing to energy savings, lower operating costs and reduced environmental impact.

  • Advertisement feature - The Wilson e2 amorphous core distribution transformers: A remarkable two year journey from concept to commercial success

    This is the story of a remarkable product manufactured by a similarly remarkable family-run power engineering company, and how it has made significant inroads into the supply transformer market. From technology to market in under two years the Wilson e2 is now specified by leading commercial organisations and blue chip companies.

    Leeds based Wilson Power Solutions (WPS) is proud to celebrate the success of its e2transformer range - the UK’s most energy efficient distribution transformer. This is the UK’s first and only super low loss amorphous distribution transformer that substantially reduces operating costs and CO2 emissions. As a result the e2 is already delivering significant energy savings to businesses committed to driving down their energy costs and radically improving their carbon footprint.

    The Wilson e2 - the highly efficient transformer brand

    The unique e2 is the result of pioneering technology from WPS, a company that is wholly committed to engineering excellence, product innovation and the provision of cost efficient power solutions aimed at reducing environmental impact. The cause for celebration at WPS is that the e2 is a ‘home-grown’ product borne from the collaboration of a small R&D team with an equally small R&D budget at its disposal! Using proven technology and design the Wilson e2 transformers combine amorphous metal cores with low resistance copper conductors to provide unrivalled savings in both core and copper losses.

    Groundbreaking Energy Savings -Reducing operating costs by up to 15%

    Since its launch just two years ago the Wilson e2 has been able to demonstrate startling
    payback results on the initial investment required. The e2 provides guaranteed savings through reduced transformer losses. These savings can be accurately forecast depending on the size of the unit and typical load. For example a 1000kVA transformer at 70% load will save 28,000 kWh (~£2250) per year through loss savings and achieve payback on the additional investment in just 2.5 years. Significant additional savings can be achieved through in-built Voltage optimization capabilities where site supply Voltage is high and Voltage dependent loads are present.

    Corporate endorsement
    The Wilson e2 transformer is helping numerous customers including NHS hospital trusts such as Whipps Cross University Hospital, the Natural History Museum and leading supermarkets, to reduce their operating costs and lower their carbon emissions. ASDA and Tesco have already recognised the very considerable benefits that Wilson e2 transformers are delivering to their bottom line.

    Daniel Travers from the Tesco Corporate Purchasing team commented: “Tesco is installing the Wilson e2 transformer into its estate as we believe it will assist us to improve our emissions target whilst helping us achieve our commercial constraints. The team at Wilson Power Solutions have shown strong technical expertise and customer service.”

    The smart Voltage Optimisation solution for HV applications
    11-14% kWh reduction

    An additional -5% to +7.5% tapping range is built into the Wilson e2 at no extra cost. This enables the operating company to optimise voltage supply from 415V to 380V according to the needs of an individual site, wherever the incoming supply is at medium voltage. This solution avoids the need to invest in supplementary downstream voltage optimisation equipment and represents an extremely cost effective VO for HV installations with a typical reduction of 12% in kWh consumption. The transformer also integrates smoothly with current installations without the risk of disruption. Endorsing the VO capabilities of e2 for additional savings, the Hilton Hotel in Portsmouth saw a significant kWh reduction of up to 14% after replacing their transformer. Similarly, food manufacturer Cranswick bacon recorded an 11% reduction despite increased production levels.

    Key features
    Lowest combined transformer losses
    Built to IEC76/BSEN60076 standard
    Interchangeable with most existing installations
    Flange heights to EA35-1
    Midel or oil filled
    Available for ratings from 315kVA- 3MVA
    In-built Voltage Optimisation capabilities
    Eligible for an interest free Energy Efficiency loan from Carbon Trust

    New – the Wilson e2 plus
    The new Wilson e2 plus is currently undergoing final trials and is being introduced to provide an ‘intelligent’ Voltage regulation solution where supply to site fluctuates or a constant (+/- 1.25%) output Voltage is required. e2 plus comes with an automatic voltage regulator that operates on load tap changers to provide stabilised site voltage.

    Wilson Power Solutions family business

    • Wilson Power Solutions is the Yorkshire-based home of family owned businesses, Power and Distribution Transformers Ltd and Richard Wilson Dencol Ltd.

    • Now under the direction of the third generation of a remarkable power engineering family, this privately owned group strives to meet and exceed the highest standards of quality, client care, environmental sustainability and social responsibility.  It has a successful and growing export division.

    • Passionate about the environment, Wilson Power Solutions is the first UK power engineering company to be certified Carbon Neutral in 2008.

    • Leading provider of energy efficient and sustainable power distribution products and solutions:
    - Wilson VO – Voltage optimisation equipment for LV applications
    - Chargetec battery chargers
    - Power and distribution transformers up to 150MVA
    - Wilson sustainable: Re-engineered transformers and switchgear
    - Buyback of redundant transformers

    To share in the cost savings and environmental benefits delivered by e2 contact Wilson Power Solutions for an assessment of your company’s energy management strategy, by calling the Sales Engineering team on

    +44 (0)113 271 7588
    For more information about products and services visit

  • Advertisement feature - A new approach for analysing moisture in paper and pressboard of power transformers

    Power transformers are a critical, capital-intensive asset for the utility industry.  As an asset manager reviewing the life expectancy of a transformer, or a substation operator responsible for determining the loading capabilities of a transformer, you should be concerned with the water content in your transformer.

    One of the most important ageing indicators of transformers is the water content in the solid part of the insulation (paper, pressboard).  Accurate diagnostic tools for determining the health of your transformers is critical. The OMICRON DIRANA is a unique and efficient device which determines the water content in the solid insulation.

    Moisture entering in to oil-paper insulation can cause three dangerous effects in transformers: it decreases the dielectric withstand strength, accelerates cellulose ageing (de-polymerization) and causes the emission of gas bubbles at high temperatures.

    Water in transformers comes from four sources: residual water after drying, water from cellulose and oil ageing, water through leaky seals or repairs, and water due to breathing.  Therefore, even in the case of a non-breathing transformer the moisture can reach a critical level.

    The DIRANA measures the dielectric response of solid insulation in equipment. The dielectric response is a unique characteristic of the particular insulation system.  The increased moisture content of the insulation results in a changed dielectric model and, consequently a changed dielectric response.  By measuring the dielectric response of the equipment in a wide frequency range, the moisture content can be assessed and the insulation condition diagnosed.  For the dielectric response, the measurement is performed as a traditional ungrounded specimen test (UST), made from the high voltage winding to the low voltage winding (CHL) in a two winding transformer.  We are most concerned with the CHL test, as this is the measurement which contains the most cellulose insulation material.  The test connections and modes are the same as used in a traditional transformer insulation Tangent Delta (or power fact)test with the difference being that it is performed at a low voltage, up to 200vpp, and the test is performed at frequencies from 1 kHz to 10µHz. 

    The unit combines the polarization current measurement (PDC) method in time domain with frequency domain spectroscopy (FDS) and thus significantly reduces the testing time compared to existing techniques.  Essentially, time domain measurements can be accomplished in a short time period but are limited to low frequencies. The extended measurement range of 5 kHz down to 50 µHz, allows the DIRANA to discriminate between the oil, insulation geometry and paper.  The result is independent from the moisture equilibrium.

    The patented technique combines the advantages of both principles.  It acquires data in the time domain from 10 µHz to 0.1 Hz and in the frequency domain from 0.1 Hz to 5 kHz.  This reduces the measuring duration by up to 75% compared to exclusive frequency domain measurements.

    DIRANA's moisture determination is based on a comparison of the transformer's dielectric response to a modelled dielectric response. A fitted algorithm compares the measured data with the modelled data and calculates the geometry data, the moisture content, as well as the oil conductivity.  The moisture assessment is based on IEC 60422. The software is very easy to use, and the user only needs to enter the oil temperature.

    Aged transformer oils often have increased values of conductivity due to acids and other ageing byproducts. This can lead to incorrect water content results. The insulation model in the DIRANA's software compensates for this influence.

    Excessive water content can be extremely detrimental to the life expectancy of a transformer. The Dirana provides a simple, non-intrusive method of detecting this moisture and alerting the user of the need to take action to alleviate the problem.


    Tel: 01785 251 000

  • Advertisement feature – Assess the health of power transformers to ensure long-term operation

    Power transformers are critical, capital-intensive assets for utilities and industry. Their failure is unacceptable because, as well as the severe damage which can occur to the asset itself the effect of its failure on the network can be disastrous. However, replacing on a time basis is not the alternative since replacement costs for these assets can be enormous and so it is important to keep the transformer in service as long as possible.

  • Testing power transformers – safely

    To ensure the safe and reliable operation of electrical equipment in substations, regular testing and maintenance carried out by professionals is essential. Power transformers are, however, critical assets that cannot always be made readily available for condition assessment, so it’s essential to make the most of opportunities for testing when these do present themselves.

  • Why aluminium wound transformers are cost efficient

    By Lapex Ltd

    Enjoy a longer life from the comparable copper wound units Copper as well as aluminium oxidise over time. Aluminium oxide hinders chemical reaction of the metal with the conductor insulation. Aluminium oxide contributes as a good electrical insulator. However, Copper in contrast oxidises completely over time. Copper also acts as a mild catalyst, accelerates the decay of the insulation around the conductor. Therefore, aluminium wound transformers enjoy typically five years longer life than comparable copper wound units and avoid copper price escalation.

    Download the white paper

  • Transformers & Rectifiers Ltd Sales Engineer

    Transformers & Rectifiers Ltd. has steadily expanded its product range over the years. Mostly this has been achieved by strategic acquisition of key competitors. Indeed, one of the strengths of Transformers & Rectifiers Ltd is that it has such a wide product range, and personnel with a wealth of experience gained with different companies who have served complementary sections of the market place.

  • Lack of knowledge around upcoming Halogen ban

    Nearly two thirds of UK consumers have not heard of the ‘halogen lamp ban’

    With the sixth stage of the ErP Regulation (EC) 244/2009 coming into force on 1 September 2018, prohibiting certain inefficient non-directional Halogen lamps on the market, LEDVANCE conducted a consumer study that has revealed a lack of knowledge about the ban in Europe.

  • Tapchangers: The Fundamentals

    Dr Jonathan Hiscock, managing director of Fundamentals Ltd gives us an insight into why tapchangers are so important in the power grid, how their performance can be enhanced, their reliability extended and what to expect if they’re not properly maintained. 

  • Case study: In perfect harmony

    When transformers on a prestigious diamond mining vessel started experiencing the classic symptoms of harmonic noise related problems, CP Automation was on-hand to help.