HIGHLIGHT | Quarterly Magazine
INTELLIGENT SWITCHGEAR NEEDS AN INTEGRAL TEST APPROACH
SAFER, SMARTER, GREENER
SHORT-CIRCUIT TESTING OF LARGE POWER TRANSFORMERS
No. 69 | July 2017
80% OF PREPAID METERS INITIALLY FAIL CERTIFICATION
DNV GL IN ENERGY
Highlight is the quarterly newsletter of KEMA Laboratories. KEMA Laboratories are part of DNV GL – Energy. Our expertise spans from proficiency in onshore and offshore wind power, solar, conventional generation, transmission and distribution, smart grids, and sustainable energy use to innovative involvement in the energy markets and regulations. Our 2,500 energy experts support clients around the globe in delivering a safe, reliable, efficient, and sustainable energy supply. We have over 90 years of experience in testing, inspections and certification – and the KEMA brand is renowned globally as the gold standard for quality. Our Testing, Inspections and Certification (TIC) activities are internationally recognised for their quality and integrity. Our main product is the KEMA Type Test Certificate, which is issued if a component successfully passes an internationally recognised type test program in our laboratories. For our customers, the award of a KEMA Type Test Certificate is a respected indicator of the reliability and safety of their products. KEMA Laboratories are located in the Netherlands, USA, and the Czech Republic. Editorial department DNV GL – Energy KEMA Laboratories P.O. Box 9035 6800 ET Arnhem The Netherlands T +31 26 356 32 22 E firstname.lastname@example.org I www.dnvgl.com/kemalaboratories Editorial staff Angela de Geest Photography DNV GL Fotostudio Alain Baars
Pleasure in South America Last month some of the KEMA Laboratories team members had the pleasure of travelling in South America visiting both old and new customers. It was interesting to meet so many enthusiastic and passionate engineers working on grid expansion and working to improve the reliability of the grids. During talking about component testing we had some interesting discussions, particularly on testing of large power transformers (LPT). A recurring topic (also in other parts of the world) is that many people cannot believe that test objects that have been subjected to so many short-circuit tests, can still be installed in the grid.
replace short-circuit testing. Furthermore, discussions within the standard committees seem to indicate that large power transformers should be designed to frequently withstand regular short-circuit currents as they may occur in the field, many times over the life of the transformer. As anecdotal evidence indicates that many short-circuit faults in power transformers occur after overhauls with maintenance earthing accidentally still left in place – it makes sense that LPT’s are designed to frequently handle these (large) short circuit currents without deterioration of their performance. We would be happy to hear your views and I encourage you to let us know!
Although in industry some technical experts used to argue that short-circuit testing of power transformers was not necessary at all as verification by calculation would be sufficient. It is clear that the industry at large is coming to the conclusion that calculations are not sufficient enough and cannot
Executive Vice-President KEMA Laboratories
Intelligent switchgear needs an integral test approach
Short-circuit testing of large power transformers
80% of prepaid meters initially fail certification
Introducing James Mack KEMA Laboratories - 90 years, a lifetime in testing Events
Testing activities Powergear Voltamp
metal-enclosed bus tested according to IEEE standards
India sets record by testing a tap-off isolated phase bus
Energy Oman successfully tested transformers at
KEMA Laboratories in Arnhem Succesful GE
testing of circuit breaker for Siemens AG
receives type test certificates for circuit breakers
INTELLIGENT SWITCHGEAR NEEDS AN INTEGRAL TEST APPROACH
The latest grid components are more and more required to have real-time controllability to be directly able to respond to rapidly changing grid conditions. Intelligent electronic devices (IEDs) are the gateways that communicate through ‘big data’ to the outside world. Digitalization of equipment therefore is the drive to protection, telecontrol, monitoring, metering, automatic grid restoration etc. and the data must be trusted. Transformers, circuit breakers and even cables will feature embedded sensors that are in constant communication with the network operations center. In other words, grids will join the celebrated Internet of Things – and in a big way. From KEMA Laboratory’s experience, electronic components with IED functionality, have a failure rate up to 80% in a test environment. Whist there are already standards for electromagnetic compatibility, many in the power industry question how well these apply given the abnormal system conditions often facing the electronics in primary equipment. New standards are needed that more accurately reflect standard operating and, especially, abnormal conditions within a substation. Recently, KEMA Laboratories, in cooperation with Liander, a major DSO in the Netherlands, tested an “intelligent” MV substation in an integral approach. This implies that a complete ring main unit, including transformer, IED and switchgear is submitted to a number of switching tests in full power conditions.
The idea is to verify the integrity of the electronics and its output, during switching operations, the arcs, sparks and transients of which might jeopardize the micro-electronics. A realistic test environment was created, including a long cable to reproduce actual transients. There were some interesting lessons to learn. First of all, the switchgear had no classical control, but could only be remotely operated through the DSO’s wireless network. This caused some synchronization issues leaving the test-engineer outside his comfort zone of accurate control of the test-object. Also, some unexpected effects of the switching operations could be observed in the power supply chain of the electronics, which needs further study. This is a real challenge for components that typically operate at very low voltage levels. Unprotected Internet of Things devices simply will not survive. We will need more robust devices and these will need to be thoroughly tested under realistic conditions, preferably in an integrated approach together with the primary equipment they are controlling.
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SHORT-CIRCUIT TESTING OF LARGE POWER TRANSFORMERS Power transformers are the most expensive pieces of equipment in power sytems. Interruption of service of transformers need to be avoided at all time, given the enormous consequences. International studies have indicated that the failure rate of transformers is around 0.6%, with converter transformers failing up to 5%. In depth study reveals that a major portion of these failures (up to 20%) is directly related to short-circuits. During a short-circuit, the large currents involved lead to severe mechanical forces and stresses in the transformer windings, which may become deformed when the structural design of the transformer is not adequate. Two methods in order to verify whether a transformer survives a short-circuit are practiced today. The first one is “design review”, in which third-party consultants check calculation results of forces and stresses and compare these with critical values based on tests or based on internal manufacturer’s rules. Design review is based on calculation results of idealized, homogeneous structures, it does not cover transient phenomena, it excludes a number of key subcomponents and it is not embedded in a strict quality surveillance system. The second verification method is “short-circuit testing”, in which the complete transformer is subjected to real short-circuit current and thus to the same stresses as would occur in service.
Short-circuit testing is the only complete verification method of shortcircuit withstand capability of power transformers. In the last few years, KEMA laboratories was extended significantly, among others to deal with the increasing request for transformer short-circuit tests. Having now six 2250 MVA short-circuit generators and ten short-circuit test transformers (making in total 550 kV), we are now ready to test power transformers with rated voltage up to 800 kV and power up to 1000 MVA (based on three-phase transformer banks). By the time of writing, already several 800 kV class power transformers have been tested. In spite of the wide application of advanced calculation methods, still around 20 – 30% of the transformers submitted to a short-circuit test, fail to pass the standardized short-circuit tests. The results suggest a tendency of the highest initial failure rates for the highest ratings: the failure rate of the largest transformers (> 300 kV or > 200 MVA), around 100 tested, is in the range of 30%. These statistics are based on a population of 320 power transformers of 25 MVA and above in a 21 year time span. Mostly, the reason for failure is a reactance increase beyond the limit set by the IEC 60076-5 standard, which indicates an unacceptable internal deformation.
In a number of cases, however, unexpected events are triggered by short-circuit current which are outside of the “usual” failure modes, like breaking of a bushing, oil spill, internal flashover etc. The rate of failure to pass a shortcircuit tests hardly changes over time, which may be related to the high pressure on costs that lead to design close to the margin. Short-circuit tests are recognized to be non-destructive. A key asset of KEMA Laboratories is the avoidance of major damage in case of a malfunction inside the transformer. High-speed protection combined with very fast circuit breakers guarantee survival of the transformer and the possibility to identify the root cause of a failure in a test. In case of grid-supplied test stations, switching has to be done by slow circuit breakers that allow a fault inside the transformer to become fatal for the equipment. In the past, utilities mainly relied on the selection of trusted manufacturers to secure short-circuit capability of their transformers. However, in recent times the situation has changed, with more and more users asking for tests on critical units or prototypes of series of identical units. This may be because a long term relationship between purchaser and a single manufacturer is less and less achievable because of increasing deregulation.
The high failure rate in service due to poor short-circuit performance before the year 2000 (0.4% in France, 0.35% in Italy, 1.2% in Turkey, China: 84% of all internal failures was due to short-circuit, India: over 80% of the failures were caused by winding displacement) led to the adoption of short-circuit testing as a method for quality improvement. By now, it is generally understood and supported by CIGRE that “short-circuit testing is the most comprehensive solution because all parts are verified”. The experience achieved through tests, and sometimes even if the test result is negative, turns out to be a precious source of information and knowledge. Critical spots can be detected and simple measures be set up, often with negligible impact on costs, which result in being highly beneficial also with respect to long term reliability. For further reading go to our recent in-depth articles “Short-circuit withstand capability of power transformers-Part I and Part II” in Transformers Magazine, Volume 4, Issue 2 and 3 (2017), as part of DNV GL’s story line on the lifecycle of transformers.
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80% OF PREPAID METERS INITIALLY FAIL CERTIFICATION In 2005, a new industrial standard for testing prepaid electricity meters was introduced. But test results at KEMA Laboratories suggest around 80% of prepaid meters initially fail to meet that standard. The IEC 62055-31 standard for prepaid meters covers all the requirements for static electricity meters laid down in the IEC 62052-11 and IEC 62053-series plus additional requirements specific to prepaid meters. These include factors such as timekeeping under various conditions and how to check payment functionality during environmental conditions tests. Special tests are included to ensure long-term operation of the keypad interface and token carrier (card) interface. Another area of testing specific to prepaid meters is the load switch utilization that cuts off the electricity supply when the customer’s credit is exhausted. This must switch under heavy duties – for instance, during load conditions with different power factors. And it is the load switch that is responsible for the vast majority of failures we see during certification.
The meter fails during the test Testing brings confidence This is a major issue for the electricity industry. Unreliable or inaccurate meters could lead to energy retailers losing revenue, or consumers losing their electricity for no reason. Certification is currently optional for this type of meter. For instance, it isn’t yet covered by the European Union’s Measuring Instruments Directive (MID) (but this could change). However, certification does provide confidence that the meter will be accurate and reliable under all conditions. So energy providers and consumers know they are getting what they pay for, and manufacturers have a more saleable product.
KWh meter in test
KEMA Laboratories is unique in being able to carry out the complete IEC 62055-31 type test program at our own premises, having invested in specially adapted facilities for tests such as the load-switch test. Combined with our independence and in-depth technical expertise, this “one-stop shop” approach streamlines testing and time to market, and gives all parties even greater confidence in the certified meter.
Introducing James Mack KEMA Laboratories is committed to growing market awareness and developing business opportunities within the utility segment in North America. We warmly welcome James Mack who has joined KEMA Laboratories as a Sales Executive based in Chalfont, Pennsylvania, USA. James has a Degree in Mechanical Engineering and has held various sales roles calling on utilities and power generation plants for the past 15 years. James can be reached at the DNV GL - KEMA Laboratories in Chalfont at email@example.com, +1 215-822-4270.
KEMA Laboratories 90 years, a lifetime in testing In 1927, KEMA was born to verify the safety and compliance of electrical components in the Netherlands. 90 years later, the world and industry in which we operate may have changed beyond recognition, but our commitment to ensuring quality and reliability through independent testing is the same as ever. Our history is full of highlights and milestones: from commissioning our first short-circuit laboratory in 1927 to performing the worldâ€™s first ultra-high voltage component tests earlier this year. Over the coming months, we will be reliving that history through a series of videos and articles covering different periods of our life in our webpages. You can discover a new chapter of our story every 2-3 weeks, so donâ€™t forget to come back regularly. For more info please visit www.dnvgl.com/kema90years
European Utility Week 3 - 5 October 2017 RAI Amsterdam, the Netherlands Singapore International Utility Week (SIEW 2017) 23 - 27 October 2017 Sands Expo and Convention Centre Marina Bay Sands, Singapore INMR World Congress 5 - 8 November 2017 Sitges - Barcelona, Spain EP China 20 - 22 November 2017 Shanghai New International Expo Center Shanghai, China
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TESTING ACTIVITIES SUCCESSFUL TESTING OF CIRCUIT BREAKER FOR SIEMENS AG
SUCCESSFUL ACCEPTANCE TESTS FOR ROYAL SMIT TRANSFORMERS
Siemens AG from Berlin, Germany successfully tested their 1100 kV - 63 kA - 50 Hz circuit breaker for short-time current withstand ability and capacitive current switching at KEMA Laboratories Arnhem.
Royal SMIT Transformers successfully tested a 405/240/21 kV 600/600/65 MVA three-phase three-winding autotransformer for short-circuit performance. These acceptance tests were performed for RTE, France.
GE RECEIVES TYPE TEST CERTIFICATES FOR CIRCUIT BREAKERS GE successfully performed the type tests on their FKGA8 generator circuit breaker for short-circuit, switching and dielectric performance at KEMA Laboratories Arnhem. The generator circuit-breaker is rated 33 kV - 50.000 A - 210 kA - 50/60 Hz for generators above 801 MVA. For this achievement type test certificates, per IEC/IEEE 62271-37-013 have been issued.
POWERGEAR INDIA SETS RECORD BY TESTING A TAP-OFF ISOLATED PHASE BUS
Powergear Limited (Chennai, India) pushed the testing facilities to its limits by setting a record. A tap-off Isolated Phase Bus (IPB) was successfully tested based on IEEE standard C37.23 for a momentary withstand current of 1071 kApeak at KEMA Laboratories in Arnhem. The short-time withstand current test equivalent to 391 kA - 1s was performed at KEMA Laboratories in Prague.
THREE-PHASE METAL-ENCLOSED BUS TESTED ACCORDING TO IEEE STANDARDS Thee-phase Metal-Enclosed Bus (IPB), rated 36 kV, 25500 A, 50 Hz, manufactured by Electrobudowa SA (Tychy, Poland) has been tested in accordance with IEEE Std. C37.23 for: dielectric performance (AC: 80 kV and LI: 170 kV) temperature-rise performance (continuous current: 25500 A, 50 Hz, 3-phase) short-circuit performance (short-time withstand current: 492 kA peak - 143 kA - 1 s) All tests have been passed with satisfactory results.
VOLTAMP ENERGY OMAN SUCCESSFULLY TESTED TRANSFORMERS AT KEMA LABORATORIES IN ARNHEM Voltamp Energy SAOG, Oman, has successfully tested 2 transformers at KEMA Laboratories in Arnhem. The 125 MVA - 132 kV large power transformer has been tested and certified in accordance to IEC 60076-5 (2006). The 315 kVA - 33 kV three phase earthing transformer in accordance to IEC 60076. Both transformers are tested per the stringent criteria specified by the Electricity Transmission Company of Oman. This is the first ever earthing transformer to be tested at KEMA Laboratories for both short-circuit and for neutral fault current.
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