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COMMERCIAL FEATURE ® TAPSCAN VAM – THE STETHOSCOPE FOR TAP-CHANGERS The doctor’s stethoscope is a diagnostic tool for evaluating acoustic noise. TAPSCAN ® VAM – the new vibroacoustics service from Maschinenfabrik Reinhausen (MR) – has a very similar function. W ith people, the stethoscope evaluates the state of health and with transformers it evaluates the state of the on-load tap- changer (OLTC), which is responsible for regulating power transformers. This complex electro-mechanical component is of critical importance for operators, since it is indispensable for supplying energy free of malfunctions and interruptions. VIBROACOUSTICS ARE IDEAL FOR THE JOB MR is the world market leader in regulating power transformers using on-load tap-changers and, in addition to offering numerous innovative transformer-related products, also provides comprehensive asset management solutions. Optimising asset management is becoming increasingly important as the requirements placed on transformer service lives continue to increase the world over. Evaluating the state of on-load tap-changers is therefore indispensable and vibroacoustics are ideal for the job. The benefits include quick, reliable and detailed evaluations without needing to disconnect the transformer from the network. HOW DOES THE VIBROACOUSTIC MEASUREMENT WORK? Each on-load tap-changer has a specific profile – its ‘heartbeat,’ so to speak – which is recorded and transmitted using acceleration sensors. The sensors are attached to suitable measuring points depending on the design of the transformer. They are attached with either screw or cap nut adapters or using an adapter glued or magnetically attached to the transformer tank. The best possible connection to the tap- changer is usually obtained on the tap-changer cover. The sensors are then connected to the measuring device 20 via a measuring cable. Additionally, a self-powered current clamp is attached to the motor-drive unit to trigger the measurement. This is used to determine when the motor is running or the OLTC is being driven and when the next tap- change operation is imminent. All noises from an on-load tap- change operation are recorded and the data is evaluated using a time frequency domain analysis. Special software is used to compare the analysed and processed data with stored reference data from the type of tap-changer measured. The expertise and experience from more than 80 years of developing and manufacturing on-load tap-changers are incorporated into the detailed recommendation for action that the operator receives after the measurement is completed. Specialists at MR know exactly which noise belongs to which point during the tap-change operation. The combination of in-depth data evaluation and expert knowledge allows explicit statements to be made about the on-load tap-changer assemblies involved in the tap-change operation. THE ADVANTAGES ARE CONVINCING: • The transformer does not have to be switched off • The measurement can take place during normal operation • It is safe and reliable, and can be used to minimise risks • Service and maintenance activities can be prioritised and coordinated efficiently DETAILS OF THE OPTIONS PROVIDED: Population measurement A fleet of tap-changers is measured in the field to detect differences between the individual tap-changers and deviations. A reference value is required for this which can either be obtained from a characterisation of on-load tap-changers at MR or by calculating an average from the tap-changers in the field. The fleet of transformers awaiting analysis can, for example, be used for this purpose. Creation of fingerprints An acoustic profile of an installed tap- changer (regardless of manufacturer or tap-changer type) is produced at the transformer manufacturer’s plant or at the installation site to enable comparison measurements at a later date. Comparison measurements may become necessary after maintenance work by external staff, repairs or movement of the transformer or after earthquakes et cetera. Checking a tap-changer in the field An individual tap-changer in the field is measured to produce a statement about its mechanical condition. The vibroacoustic profile is compared with an existing reference profile and a recommendation for action is given. IN CONCLUSION TAPSCAN ® VAM improves the safety and reliability of equipment and minimises risk. Service and maintenance work can be better coordinated and prioritised at reduced cost – which is especially important for fleet management. TAPSCAN ® VAM is a quick and reliable way of producing a qualified evaluation of the condition of on-load tap-changers in the field. What makes the vibroacoustic measurements from MR unique is the level of detail provided by the special software and the time frequency domain analysis. ESI ESI AFRICA ISSUE 4 2014