HIGH FLUX DENSITY ROTATIONAL CORE LOSS MEASUREMENTS

Energy conversion processes involve losses. Specifically core losses, which are a result of the magnetization process in cored electrical energy conversion and storage devices. The cores are made of soft ferromagnetic materials that are easily magnetized and demagnetized. These soft magnetic cores, allow a reduction in size, higher energy storage density, and a reduction in magnetizing current, when compared to non-cored devices. The characterization of soft ferromagnetic materials is traditionally done under unidirectional pulsating fields, which is sufficient for single-phase transformers and inductors, where the cores are under pulsating fields. However, T-joints of three phase transformers and teeth-roots of rotating machine stator cores are exposed to two-dimensional rotational fields of higher core loss. Pulsating measurements are therefore insufficient in the characterization of soft ferromagnetic materials used in rotating electrical machines or in three phase transformers. In two-dimensional fields, the magnetization direction changes with time, tracing a flux density locus. This requires the measurement of tangential magnetic field and flux density components, hence the associated loss. This study proposes a two-dimensional rotational core loss tester for high flux density measurements up to about 2 T, at 60 Hz. Its frequency measurement range is from 60 Hz to 1 kHz. The initial sizing was done analytically, then implemented in three-dimensional finite element analysis, prototyped and experiments performed to verify its capability. It was validated by testing two 0.35 mm and 0.65 mm thick samples. Very high flux densities in the range of 2 T at 60 Hz were achieved in both samples. For the thinner sample, flux densities of 1.8 T and 1.6 T were measured at 400 Hz and 1 kHz, respectively, while for the thicker one, the range reduced to 1.7 T and 1.4 T, at 400 Hz and 1 kHz, respectively. The magnetizer also reproduced non-sinusoidal flux density waveforms, for flux densities less than or equal to 1.0 T, without any waveform control. The proposed rotational core loss setup will find application in the characterization of electrical steels, and generation of pulsating and rotational core loss data. This data can then be applied in core loss models, uprating of megawatt (MW) rated machines, transient and hotspots analysis, and in the design of higher power density machines, such as high-speed machines

The importance of measurement of transmission losses and associated measurement uncertainty on the cross-border energy exchange

U početnoj fazi istraživanja napravljen je pregled znanstvene literature vezano za procjenu mjerne nesigurnosti. Utvrđeno je da je najzastupljenija metoda sukladno međunarodno prihvaćenom dokumentu „Guide to the expression of uncertainty in measurement“, tzv. GUM metoda. Ova metoda sadrži određene nedostatke te je izdana dopuna istog dokumenta koja preporuča uporabu Monte Carlo metode. Nadalje, u disertaciji je prikazan trenutno zastupljeni način za utvrđivanje razmijenjene energije kod prekogranične razmjene električne energije uključujući metode izračuna gubitaka prijenosa. Utvrđeno je da niti jedna metoda ne uključuje mjernu nesigurnost odnosno sistematske pogreške obračunskog mjerenja. Naime, uslijed velikih količina prenesene energije mali postotci sistematskih pogrešaka mogu rezultirati značajnom krivo raspodijeljenom energijom između operatora prijenosnih sustava odnosno potencijalnom financijskom štetom za sudionike razmjene. U okviru disertacije proveden je postupak izračuna mjerne nesigurnosti otpora prijenosnog voda i gubitaka s pomoću GUM i Monte Carlo metode. Za potrebe potonje metode proveden je postupak procjene razdiobe izlazne veličine. Također je razvijen je način utvrđivanja mjerne nesigurnosti razmijenjene energije i gubitaka prijenosa što uključuje metodu za ispravak razmijenjene energije i gubitaka za iznos sistematskih pogrešaka čime je smanjena ukupna mjerna nesigurnost te metodu za raspodjelu razmijenjene energije i pripadajućih gubitaka. Praktični rezultati pokazuju da je mjerna nesigurnost smanjena nakon ispravka sistematskih pogrešaka čime je potvrđena hipoteza disertacije. Može se zaključiti da ova metoda predstavlja pravedniji način za utvrđivanje razmijenjene energije i gubitaka prijenosa kod prekogranične razmjene energije.In the initial phase of the research process, a review of scientific literature was performed regarding the measurement uncertainty calculation methods. It is found that the most commonly used method is according to the internationally accepted document "Guide to the expression of uncertainty in measurement", i.e. GUM method. However, this method contains certain deficiencies and has been followed by the Supplement 1 which recommends using the Monte Carlo method. Furthermore, the dissertation presents the current method for determining the exchanged energy on the cross-border energy exchange as well as methods for calculation of the transmission losses. It is found that the actual methods do not involve measurement uncertainty nor systematic errors in the calculation procedure. Namely, due to large amounts of exchanged energy small percentages of systemic errors can result in significant erroneously associated energy to the transmission system operators, i.e. potential financial damage for energy exchange participants. A method for calculating the measurement uncertainty of transmission line resistance and transmission line losses using the GUM and the Monte Carlo method is developed. For the purpose of the latter method, the procedure for estimating the distribution of the output value is performed. A method for determining the measurement uncertainty of the exchange of energy and the transmission losses, including the method for correcting the exchanged energy and transmission losses for the amount of systematic errors is developed, thus reducing the total measurement uncertainty. A method for allocating the exchanged energy and the transmission losses between transmission system operators is developed as well. Practical results show that the measurement uncertainty is reduced after correcting systematic errors, thus confirming the hypothesis of the dissertation. It can be concluded that this method represents a fairer way to determine the exchanged energy and the transmission losses on the cross-border energy exchange

Processing Dependent Systematic Contributions to Measurement Uncertainty

In the measurement field, the correlation of two uncertainty contributions is a form of probabilistic association that can significantly affect the final uncertainty associated to the measurement result. The Guide to the expression of uncertainty in measurement recommends a mathematical approach to deal with correlated random contributions to measurement uncertainty. A similar kind of association, or dependence, can characterize also different systematic contributions to uncertainty and should be taken into account when evaluating their effect on the final measurement uncertainty. This paper discusses a new approach to handle such systematic contributions when they are represented by symmetric possibility distributions (PDs) of the same shape. This method allows one to build the joint PD of two systematic contributions, both dependent and independent, and propagate them through a generic measurement function