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Published by Megger
February 2009 |
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| The industry's recognised information tool |
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ELECTRICAL
TESTER |
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In this issue |
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Filling the regulatory void |
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Testing multi-ratio CTs |
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EMC for a change |
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Filling the regulatory void |
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| Dr Andrew Dodds |
| Director of Group Development |
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| A recent report issued by the McKinsey Global Institute, one of the world’s most respected economic research organisations, proposes that after years of successful operation, the price cap mechanism in the Performance Based Rate (PBR) regulatory framework, which effectively controls the income and profitability of many European deregulated electricity distribution companies, is fast approaching the end of its useful life. |
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| The PBR regime attempts to align the motives of the utilities with those of the regulator and consumer and was originally devised to provide an ongoing incentive for power companies to improve productivity, quality and reliability of services while simultaneously increasing efficiency through cutting costs. To achieve this, the PBR regime requires the regulator to set lower rates each year. Until now, says the McKinsey report, this arrangement has worked well and has yielded much improved efficiencies amongst the distribution companies along with far fewer supply disconnections. |
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| The problem is that the distribution companies now have nowhere left to cut. It simply isn’t possible for them to make further significant efficiency increases without major investment, but the PBR regime, which dictates continually falling prices for their services, makes investment very difficult if not impossible. In fact the regime not only militates against investment for the future but also against essential investment to replace existing plant and cables that are at the end of their working life. As a consequence, the transmission companies are increasingly being forced to rely on life-expired equipment, particularly transformers. This is a serious threat to the reliability of their networks, and puts at risk the efficiency gains that have been among the most notable successes of the PBR regime. |
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| The regulators around Europe are aware of this problem and most are working toward regulatory regime change. Indeed, the bulk of the McKinsey report is devoted to recommendations on the form that this change might take. However, even if change is coming, they will take years to formulate and implement, especially given the four- and five-year review cycles built into most implementations of the current PBR regime. |
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| The question therefore remains how can transmission and distribution companies bridge this investment gap and not penalise earnings until the regulatory regime changes? |
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| There is no completely satisfactory answer, but a damage limitation strategy at least, is possible. This requires further extending the life and maintaining performance of existing plant, even though much may have already exceeded its original design life. |
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| One solution to implementing this strategy is predictive testing – essentially regular testing of key items of plant to detect signs of performance deterioration that indicate the need for further investigation or action. In many cases, this early warning of an incipient fault will allow remedial measures to be put in place to eliminate the risk of a complete failure. |
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| A good example relates to power transformers, where testing to manage transformer life can lead to timely recognition of defects. |
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| The transformer life can be extended through reduced loading (if possible), prior to attempts to improve the transformer condition through remedial action. This may include in field drying out techniques to remove excessive moisture, replacement of contaminated oil or mechanical maintenance which may extend the useful life of the transformer by years. This will most certainly be less than that needed to source a replacement transformer given manufacturers are quoting delivery times in excess of two years for new power transformers. |
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| Advances achieved through modern test equipment are now providing powerful predictive maintenance test techniques. These include swept frequency analysis (SFRA) for power transformers enabling detection of mechanical and electrical changes of the core and winding assembly, similarly Dielectric Frequency Response measurements on transformers are useful to determine moisture content in oil/paper insulation systems. High moisture content in transformers curbs the loading capability whilst accelerating the aging process and is of vital importance for decisions on maintenance or load restriction. |
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| To support justification for investments into new test equipment, it is worth considering the costs in relation to the potential for savings. If the new equipment eliminates the need to replace just one transformer, it will have paid for itself many times over. Even the best of predictive testing programmes cannot of course, indefinitely prolong the life of ageing electrical plant. A change to the PBR regime that facilitates investment in new equipment is essential. Until this change occurs however, it is incumbent on the transmission and distribution utilities to make best possible use of the plant they have. Predictive testing, with modern test equipment is without doubt the key. |
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Testing multi-ratio CTs |
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| David Milner |
| Product Manager |
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| Current transformers are crucial to the operation of a substation protection system and are therefore subject to thorough testing during commissioning of the system. However the time taken to perform the associated tests has in the past been both cumbersome and time consuming given the manual test sets available, especially when faced with multi ratio secondaries. |
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| In order to overcome these problems Megger recognised the need for a new automated test set. The design brief was to provide a portable test set where pressing just one button initiates an automated test sequence that covers ratio, saturation knee point, burden, polarity and phase deviation tests. |
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| The result is the Megger MCT1600 current transformer test set. Speed of test for a CT is now only a few minutes in automated mode. The test set uses the latest DSP and Power amplifier technology to ensure accuracy and speed and is suitable for testing both single- and multi-tap CTs either in manual or automated mode depending on the operator’s practice. |
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| Tests are performed at the mains rated frequency as required by the relevant standards to IEEE C57.13.1, IEC 60044-1 and IEC 60044-6. A 1kV insulation test is provided along with automatic demagnetization of the CT on completion of testing. Test results are shown on a 6.5-inch fullcolour daylight viewable LCD screen, which is capable of displaying up to ten saturation curves simultaneously. A full QWERTY keypad allows rapid entry of data such as site and equipment identification data, and the instrument automatically generates reports, which are stored internally. Test results may be transferred to a standard USB stick for later processing with a PC. |
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EMC for a change |
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| Test equipment being EMC tested at Megger’s Dover site |
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| Graham Heritage |
| Technical Director |
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| Things are changing in relation to EMC and test equipment but, perhaps surprisingly, the reason for the change is not the introduction of the new European EMC Directive! It’s true that, from 20 July 2009, it will no longer be permissible to declare compliance against the old Directive (89/336/EC). Instead, compliance will have to relate to its replacement – 2004/108/EC. For users and manufacturers of test equipment, however, this makes almost no difference. The changes in the new Directive relate mostly to systems and are, therefore, much more important in fields like process control. |
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| In fact the changes that affect test equipment relate to a new and updated version of the product standard IEC 61326-1. Meeting the requirements of this EMC standard carries a presumption of conformity and is the normal means of compliance with the EMC Directive. |
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| The new version of IEC 61326-1 differs from the old in two key areas. The first is the frequency range for field immunity testing has been extended from 1 GHz to 2.7 GHz. This is to take into account the increasing use of equipment that operates at the higher frequencies. |
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| The second important change is that minimum immunity pass criteria have been set, whereas previously the manufacturer was allowed to choose any one of three criteria. |
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| Radiated and conducted RF immunity must meet the requirements for Criteria A pass. In effect this means that the product must remain within its published specification while being tested. All other tests, except for those involving mains supply interruptions for mains powered equipment, must at least meet the requirements for a Criteria B pass. This allows the equipment under test to go out of specification while being tested. |
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| Tests involving mains supply interruptions must meet at least the requirements for a Criteria C pass, which means that user intervention may be needed to restore the equipment to its normal state. |
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| Suppliers of test equipment like Megger have to test not only new products, but also existing products that they intend to continue selling, to ensure that they meet the new standard. In order to do this, it is likely to that those suppliers will need to purchase additional equipment to extend the scope of their test installations up to 2.7 GHz. |
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| Although the suppliers will undoubtedly do all they can to absorb these additional costs, it is almost inevitable that a proportion will be passed on to their customers. In summary, therefore, the changes to the EMC test regime arguably mean that customers will get a better product, but almost certainly at a higher price. |
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