The supplementary comparisons of national standards of ratio error and phase displacement of AC voltage of power frequency have been performed among the following national metrological institutes (NMIs): VNIIMS, MIKES-TKK, SP, CMI, LCOE, BIM and SE “Ukrmetrteststandard”. Its description and measurement results are presented below. 

A calorimetric measuring system for measuring the ratio between AC and DC resistance, RAC/RDC, of high voltage power cable conductors has been designed and constructed. An uncertainty analysis predicts that the ratio RAC/RDC at 90°C of a 2500 mm2 cable of low loss design can be measured with an uncertainty of 1,0%. But the uncertainty of an actual measurement was larger due to unresolved sources of uncertainty.

The Eco-design directive issued by the European Commission has led to requirements on efficiency of power transformers. In the case of large power transformers used in grid applications, serious problems are encountered in establishing how reliable the loss measurements are. An effort is currently ongoing within IEC to produce a documentary standard on “Rules for the determination of uncertainties in the measurement of the losses of power transformers”. An IEC standard should be clear and easy to understand by all users in the industry. Background theory and material, whilst necessary for understanding, is not required for the day-to-day application of the standard. This paper presents a more detailed background and theory on the measurement of transformer losses and how to quantify precision. The authors are all members of the IEC maintenance team working with the standard. 

The Eco-design directive issued by the European Commission has led to re-quirements on efficiency of power transformers. In the case of large power transformers used in grid applications, serious problems are encountered in establishing how reliable the loss measurements are. An effort is currently on-going within IEC to produce a documentary standard on “Rules for the determination of uncertainties in the measurement of the losses of power transformers”. An IEC standard should be clear and easy to understand by all users in the industry. Background theory and material, whilst necessary for understanding, is not required for the day-to-day application of the standard. This paper presents a more detailed background and theory on the measure-ment of transformer losses and how to quantify precision. The authors are all members of the IEC maintenance team working with the standard.

Losses of HVDC converter stations need to be accurately quantified to support evaluation of bids for such systems and to underpin efforts to reduce greenhouse gas emissions. At present, these losses are estimated, based on loss calculations for individual converter components, and no reliable method exists to measure the actual HVDC converter station loss as difference between power on the AC- and DC-side of the station. The necessary requirements for such a measurement are investigated in this study, and a tentative design of a suitable loss measuring setup is explored. This approach is a useful alternative for those cases where a direct measurement of losses via a temporary connection with two converters operating in back-to-back mode cannot be made.

Modern dielectrics used in power capacitors can exhibit a dissipation factor lower than 0.005 %, which approaches the limits of presently available measurement techniques. This article reviews techniques, apparatus, and available calibration services for dissipation factor with regard to lowest achievable uncertainties. It is shown that further metrological advances are necessary to lower uncertainty in the measurement to levels at least five times less than presently achievable, in order to ensure traceable and quality-assured measurement of modern dielectrics with such low dissipation factors

The effect of the coaxial cable type and length on the lightning impulse parameters is often neglected. However, studies have shown that the coaxial cable length can affect the parameters that are calculated according to IEC 60060-1:2010. This study investigates how different coaxial cables influence the impulse waveforms by measuring the input and output of the cable under test with a 2-channel digitizer. Non-standard lightning impulses were generated using an impulse voltage calibrator. Results indicate that coaxial cables attenuate the test voltage and increase both the front time and time-to-half value.

Traceability of the current ratio is crucial for the measurement of electrical energy in revenue metering. A comparison of the AC current ratio was therefore performed within EURAMET in the time period 2012-2016, using a precision CT as the traveling device. The Czech Metrology Institute (CMI) as coordinator processed the measurement results of the 15 European participating laboratories. The comparison of the results for transformer ratios of (4, 5, 6, 8, 10) kA 5 A at 15 VA burden and (4 and 10) kA 5 A ratios at 5 VA burden indicates good agreement between the participating laboratories. The main differences are found for phase displacement, at least in part due to instability of the traveling standard. .

An effort is pursued by several European National Measurement Institutes to lower the uncertainties in calibration of UHV measuring systems for lighting impulse. To this end, several reference dividers are investigated as regards their accuracy both for amplitude and for time parameters. At SP - RISE Research Institutes of Sweden, a 500 kV resistive reference divider has been in use since 2000. Additionally an 800 kV resistive divider is investigated as a possible reference divider for UHV lightning impulse measuring systems. The best uncertainty for the 500 kV reference measuring system is 1 % for voltage amplitude and 3 % for time parameters. The present work aims at lowering these uncertainties by means of better characterisation and evaluation of the possibilities to apply corrections for known errors. The scale factor and dynamic behaviour of a resistive divider can be conveniently determined at low voltage and frequency. Further experiments such as linearity tests and augmented by scientific work is needed to ascertain the performance at high voltage. Step response plays a major role in the characterisation of dividers, and in this work much effort has gone into gathering step responses and evaluating them for various circuit layouts to characterise the variation of the step response due to circuit dimensions and diverse proximity effects. The step applied to the divider is generated by a mercury wetted relay based step generator with an output voltage of 200 V. The step rise-time is a few ns, and thus appreciably faster than the response of the divider. Apart from inspection of the step response itself, evaluation of measurement errors is performed by convolving an ideal curve with the step response of the divider, including its transmission cable. The convolved signal is evaluated with impulse evaluation software and the parameters compared to the ideal input. The difference is a measure of the errors introduced by the divider. This procedure follows IEC 60060-2: 2010.

Lighting impulse measurements are made as a matter of routine in high voltage testing of high-voltage electrical equipment. The test is often decisive for acceptance of the equipment under test, and consequently proper and precise calibration of the measuring system is needed. The present work centres on the need to quantify the errors of reference measuring systems for lightning impulse. Scale factor determination at low frequency (or DC) is the starting point for this determination. The extrapolation from this frequency domain to the domain where microsecond pulses must be faithfully captured requires application either of methods in the frequency domain or in the time domain. Radio frequency measurements are only well defined for coaxial structures and at impedances in the range of 50 O or thereabouts, making them difficult to apply to the large structures of high-voltage measuring systems. The converse method in the time domain is to apply a Dirac impulse to the system and calculate the response to an assumed input signal by convolution. A true Dirac pulse is not readily available and in practice the applied pulse is a step voltage, which is then derived with respect to time and convolved with the applied signal to obtain the response of the measuring system. The step generator used for this purpose should have very fast front without oscillations. The intent is to achieve a close approximation of an ideal step function, which when derived with respect to time, yields the impulse response of a tested system. A necessary prerequisite is that the step is much steeper than the lightning impulse, and is flat after the step on times much longer than the impulse. The ideal switch element in such a step generator should have infinite resistance and zero capacitance in the off-state, very fast switching to on-state and very low resistance in on-state. The mercury wetted reed switch has often been used for this purpose since it has good characteristics in all these respects. Few, if any, electronic components exhibit competitive advantages compared to the reed switch. The relative lack of parasitic effects means that it is close to being an ideal device. Based on earlier experiences by the authors, a new design has been developed with focus on electrical screening and coaxial design in order to realise a step generator that works into a high impedance instrument. Considerable work has been performed to characterise the new device with regard to steepness of step and most importantly, to voltage stability after the step. The most demanding part of this work has been to separate the performance of the switch from that of the oscilloscope. Findings indicate that the step rise-time is less than 0.5 ns, and settling to within 0.5 % within 10 ns.