A new joint research project (JRP) integrating metrology institutes and universities from nine countries is aimed at realization of a new generation of standards for quantum resistance metrology. The project exploits graphene's properties to simplify operation of standards without compromising the unprecedented precision delivered by semiconductor quantum Hall devices. Higher operating temperatures (above 4.2 K, and up to 8 K) and together with lower magnetic fields (below 5 T, and potentially down to 2 T) will lead to a significantly improved and cost-saving dissemination of intrinsically referenced resistance standards to all end-users relying on electrical measurements.

The high power medium frequency transformer (HPMFT) is one of the key elements of an isolated, bi-directional DC-DC converters in applications such as future all-DC offshore wind farms, traction and solid state transformers. This paper describes a design methodology taking into account the loss calculation, isolation requirements and thermal management. Incorporating this design methodology, an optimization process with a wide range of parameter variations is applied on a design example to find the highest power density while the efficiency, isolation, thermal and leakage inductance requirements are all met.

High power isolated DC-DC converters are likely to provide solutions for many technical challenges associated with power density, efficiency and reliability in potential applications such as offshore wind farms, inter-connection of DC grids, MVDC in data centers and in future solid state transformer applications. The high power medium frequency transformer (HPMFT) is one of the key elements of such a converter to realize the voltage adaption, isolation requirements, as well as high power density. This paper describes a design and optimization methodology taking into account the loss calculation, isolation requirements and thermal management. Incorporating this design methodology, an optimization process with a wide range of parameter variations is applied on a 50 kW, 1 / 3 kV, 5 kHz transformer to find the highest power density while the efficiency, isolation, thermal and leakage inductance requirements are all met. The optimized transformers are then manufactured and will be presented in this paper.

The medium-frequency power transformer (MFPT) is one of the key elements of an isolated bi-directional dc-dc converters in applications such as future all-dc offshore wind farms, traction, and solid state transformers. This paper describes a design methodology taking into account loss calculation, isolation requirements, and thermal management. Incorporating this design methodology, an optimization process with a wide range of parameter variations is applied on a design example to find the highest power density while the efficiency, isolation, thermal, and leakage inductance requirements are all met.

23 May 2012

HVDC power transmission is now being considered not only for point-to-point interties, but also as true grids where several operators may tie into the grid, each having its own economic sphere. In this new situation, it is important that transmitted energy be distinguished from losses incurred in the converter stations, to enable a fair distribution of costs for grid operation. To this end, a metrology infrastructure is needed where high-current and high-voltage transducers must be possible to calibrate traceably, and where dc electricity meters can be calibrated and approved. A research project is currently working with these questions in a concerted European research effort, funded by the European Commission. The present publication highlights important aspects of this work.

We present a novel method of generating an ac voltage using a programmable Josephson voltage standard. The ac voltage is generated by Δ-Σ (Delta-Sigma) modulation of multiple Josephson levels. Compared with an ac voltage generated by stepwise approximation, the Δ-Σ method reduces the low frequency harmonics of the generated signal. We demonstrate this method by generating a 90 Hz sine wave and measuring the spectrum with a digitizer.

We have developed methods to characterise voltage dependence of the phase response in voltage dividers. The voltage dependence is a combination of two parts, a linear dependence and a power dependence due to voltage and temperature dependence in capacitors respectively. The standard uncertainty of the phase at 240 V and 100 kHz is estimated to be 20 μrad.

The design, evaluation and commissioning of a high voltage reference testbed for pulsed applications to be used in the precision testing of high voltage dividers is described. The testbed is composed of a pulsed power supply, a reference divider based on compressed gas capacitor technology and an acquisition system which makes use of the fast measurement capabilities of the HP 3458 DVM. Results of the evaluation of the reference system are presented.

We report on the performance of a simple method, known as the Reference Step Method, to build up the dc voltage scale of a source. The key advantages of this method are that it relies on equipment that is readily available in most high-level laboratories and can be fully automated. The Type A uncertainties achieved by this approach can be less than 0.1 μV/V. This performance is achieved because of the excellent differential linearity of the DMM used in the method. We are validating the accuracy of the method by directly comparing this approach with more traditional resistive divider techniques.

We report on the performance of a simple method, known as the reference step method, to build up the dc voltage scale of a source. The key advantages of this method are that it relies on equipment that is readily available in most high-level laboratories and can be fully automated. The Type A uncertainties achieved by this approach can be less than 0.1 μV/V. This performance is achieved because of the excellent differential linearity of the DVM used in the method. We have validated the overall accuracy of the method by directly comparing this approach with more traditional resistive divider techniques and have established that the expanded uncertainty is better than 0.2 μV/V up to 1000 V, limited only by the performance of the instruments used.

We describe high accuracy low-frequency ac-dc transfer determinations performed with a programmable Josephson voltage standard. The ac-dc difference characteristic of a planar multijunction thermal converter is determined indirectly by comparison via a high input impedance thermal transfer standard at 0.8 V in the frequency range 10 Hz to 110 Hz. 

This paper describes the selection and characterization of resistors for a 1000 kV HVDC divider. One thousand 10 MΩ resistors will be connected in series in the final design. Due to the large number of resistors only a randomly selected set has been characterized. The measured temperature and voltage coefficients of the resistors are around 1 μΩ/Ω/K and -10 μΩ/Ω/kV respectively, which make them very suitable for reaching the overall desired divider uncertainty of better than 100 μV/V.

This paper describes the results of a bilateral three-phase power comparison between SP, Sweden and MIKES, Finland. A three-phase precision electricity meter was used a transfer reference. Both active and reactive three-phase power measurements were compared.

The project suggests appropriate methods for quality assurance of measurement processes and measuring equipment used for condition monitoring of power transformers, specifically for selection of on-line monitoring systems for: • Temperature • Partial discharge (PD) • Sound and vibration The developed methods can be developed further in subsequent projects to cover the quality of other types of measurement processes and measuring equipment as part of maintenance planning activities.

SP has experience in the field of fiberoptic communication and expertise in research in the field. Also, SP has expertise in the high-voltage field and there is currently a large interest in developing the high-voltage network in order to accommodate new small producers of electric power (wind mills, solar power, etc.) In this report we describe efforts to find areas of interest to develop fiberoptic sensors for offshore monitoring of high-voltage equipment. A large number of research papers and review articles have been collected and reviewed in order to investigate what possibilities are at hand for SP to provide support for development of new or existing fiberoptic sensor technologies.

An HVDC reference voltage divider has been designed for high accuracy and wide-band measurements up to 1000 kV. To maintain wide-band characteristics, field distribution must be optimized in order to minimize the response time of the divider. To compensate the stray capacitance, a capacitive path that surrounds the resistive reference divider is added to function as a shield. Optimal capacitance values producing a matched distribution are obtained using 3D FEM simulations. Factors affecting the performance of the divider are assessed by simulating multiple scenarios representing different practical considerations in real-life applications.

Josephson voltage standards are well established for use at dc and low-frequency ac voltages. The increasing demand i) to provide traceability for arbitrary waveforms, ii) to extend the range of use to higher frequencies, and iii) to improve the accuracy is being addressed in the project Q-WAVE, which is jointly funded by the European Union and the participating countries within the European Metrology Research Programme (EMRP). Here, sampling measurements and procedures using binary-divided 1 V and 10 V arrays are investigated. In addition, a quantum-based analogue-to-digital converter for direct measurements of arbitrary waveforms is under development. It will contain several Josephson arrays in series biased by a pulse drive based on opto-electronics, in order to increase the output voltage.

We demonstrate reversible carrier density control across the Dirac point (Δ n∼ 1013cm-2) in epitaxial graphene on SiC (SiC/G) via high electrostatic potential gating with ions produced by corona discharge. The method is attractive for applications where graphene with a fixed carrier density is needed, such as quantum metrology, and more generally as a simple method of gating 2DEGs formed at semiconductor interfaces and in topological insulators.

Recently, IEC and IEEE have published a number of revised and new standards for high-voltage and high-current testing. Significant changes and additions have been introduced to these revised and new standards. CIGRE WG D1.35 has developed a guide to give high-voltage test engineers a broader knowledge of how to apply the latest high-voltage and high-current testing standards. The guide presents a brief account of the history of these standards with the aim to allow readers to gain a better appreciation of the technical background followed by sections summarize the major changes made to the standards in their latest revisions to provide a general picture of the revisions. Finally, some discussion is given on the practical implications of these changes. Practical examples are provided to illustrate some of the new techniques and new procedures. The guide also lists areas of possible improvements to the standards for future revisions.