The energy problem has assumed a central role in research activity owing to its economic impact. The demand is for an "electrical energy" product of high quality and low cost, possibly obtained from sustainable sources and continuously flowing to the user with negligible deterioration in its quality. Measurements are necessary in all these processes.
In energy production the measurement of active and reactive power is crucial for the improvement of generation and transmission efficiency. Precision energy metering is necessary in international and national links and for the calibration of verification instruments. Measurements of synchronization and of the efficiency of generating, transforming and converting systems are necessary for integrating the different sources of electrical energy. Furthermore, grid control needs distributed measurements of voltage, current, instantaneous power, and phase distributed territorially and as a function of time for identifying pre-critical, critical and fault conditions and for automatically taking suitable actions (smart grid) to avoid service discontinuity.
A recent written standard (IEC-61000-4-30) sets out the requirements for the quality of electrical energy, defining a set of parameters such as number of interruptions, distortion, voltage variation and transients, which take account of the difference between the real and the "ideal" supplied waveforms. The lack of power quality has a significant impact on the correct working of electrical and electronic devices and systems, or on the cost of filtering and protecting them from unwanted effects. The power quality standard also tries to set a limit between supplier and user responsibilities and measurements are necessary not only for monitoring the unwanted effects but also for identifying their source.
For the measurements of electrical power and energy traditional techniques are employed alongside new ones and many aspects are integrated, ranging from voltage and current transducers, shunts, phase characterization, sampling, algorithms, the construction of traceability from the national standards.
At INRIM there has been growing activity in the field of power measurements. The former measurement systems, based on the analogic processing of current and voltage signals, have been replaced by new ones based on digital sampling. The new primary standard for power participated in the CCEM (Consultative Committee for Electricity and Magnetism) international comparison CCEM-K5, where it was validated at the highest level. This system is based on simultaneous sampling of both voltage and current and on an asynchronous algorithm which reconstructs the two waveforms and computes the power. For calibration purposes, two other systems were subsequently set up: one for the direct comparison of wattmeters and power converters and another, more recent, for the measurement of tri-phase power and energy. The laboratory for power measurement is shown in fig. 1.

Fig. 1 Laboratory for the measurement of electrical power and energy at INRIM.

A further related field is the development of shunts, which are used both for current measurements [1] by improving the AC-DC transfer reference of current, and for power measurement. A new system for the precision measurement of the shunt impedance phase has been designed and will be applied to the characterization of these devices.
When measurements on the high voltage grid are concerned, further uncertainty components, introduced by the voltage and current transducers have to be considered. As an alternative to current and voltage transformers, a new generation of converting devices with low power output has recently been developed. INRIM activity is focused on the set-up and the characterization of measuring systems which include non-conventional transducers, to be used as references for on-site measurements [2]. Work is in progress to develop a reference divider for on-site calibration on the medium voltage grid. As to the high current measurements, in collaboration with the Electrical Engineering Department of Politecnico di Torino, a 3D numerical model has been worked out, which allows analysis and optimization of actual Rogowski coil behavior under non-ideal measurement conditions (fig. 2).

Fig. 2 3D model of a split-core Rogowski coil (coil radius 150 mm) with non uniform pitch winding and normalized mutual inductance with optimized turn distribution. The values in brackets refer to the simulation performed with uniform turn distribution when the primary conductor gets nearer to the coil gap.

For power quality measurements, where acquiring and processing voltage and current signals is important, systems for static and dynamic calibration of DACs and ADCs and for producing calibrated signals with periodical and non periodical alterations have been experimented. The reconstruction of the harmonic distortion has been studied and asynchronous algorithms have been developed and analyzed.
INRIM work on power and power quality measurements has recently taken advantage of cooperation with other European national metrology institutes in the framework of the EU supported iMERA Plus project "Next generation of power and energy measuring techniques". By means of all these activities INRIM is trying to provide a better metrological infrastructure to national users for the measurement of power, thus responding to what is today a novel challenge for the metrological laboratories.

[1] U. Pogliano, G.C. Bosco, D. Serazio: "Coaxial shunts as AC-DC Transfer Standards of Current", IEEE Trans. on Instrum. and Meas., Vol. 58, n. 4, pp. 872-877, April 2009.
[2] G. Crotti, A. Sardi, N. Kuljaca, P. Mazza, G. de Donà: "Set up and characterization of reference measuring systems for on-site live verification of HV instrument transformers", in Transverse Disciplines in Metrology, Wiley-ISTE, 2009.