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A New Tool for Live, On-site, HV Instrument Transformers Accuracy Check

pubblicazioni - Articolo

A New Tool for Live, On-site, HV Instrument Transformers Accuracy Check

Metering accuracy is of essence in interconnections between Distribution and Transmission networks, in order to ensure market correctness; all components of measurement chains, from instrument transformers to meters, must therefore be calibrated.

Instrument transformers role is crucial, since even tiny errors in voltage or current measurements, accumulated over a long period, will lead to a significant financial unbalance in energy trading. Up to now, instrument transformers are usually calibrated at the Manufacturer’s along their operation range, keeping into account a wide range of standard conditions; after service installation no more accuracy checks are usually carried on, due to both technical and economical reasons: traditionally available calibration equipment and methodologies require service removal of instrument transformers. Recent studies and test campaigns however demonstrated that instrument transformer accuracy may deteriorate with ageing; moreover, as happens for meters, to all Parts involved should be granted at any moment the right and the possibility of verifying the accuracy of all components of measurement chains. Thanks to improvements in transducer technologies, appropriate metrological and live-line working procedures, new equipment tools purposely developed, in Italy was developed a methodology allowing a live, on-site verification of instrument transformer accuracy. This check can be performed without service outages and intervention on the busbar configuration, by means of live insertion of standard transducers; signals coming from standards and from equipment to be checked are compared, using a purposely developed software tool, keeping into account and getting round the possible presence of harmonics, random noise and other harsh environment disturbances. This approach is a powerful tool for on-site evaluation of the transformer accuracy, allowing identification of the voltage and current transducers ,including burdens and signal cables, which no longer comply with the prescribed accuracy requirements and thus must undergo further laboratory investigations

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