STATISTICAL ANALYSIS OF TEMPERATURE RISE TEST FOR INCREASED ACCURACY ON X- AND Y- EXPONENTS

On a large number ( > 50 ) of identical large power single-phase autotransformers ONAF temperature rise test have been performed as part of the customer specification. Part of the 24 hour test is a 125% overload for 8 hours. Based on this data one can statistically evaluate aspects as average value, standard deviation and correlation on many parameters. Measurement tolerances have a large influence on the top oil exponent x and the winding exponent y. The calculation of x and y is determined by the ratio of two temperature differences due to a load difference, which can result in larger errors than expected. In two transformers fibre optic ( FO ) sensors were installed in the common winding to measure the hot-spot, not only during steady state, but also during transient conditions. For ONAF cooling, a step increase of load takes a relatively long time before the oil flow reaches a steady state, as is described in the loading guide. The overshoot in the gradient between the hot-spot temperature and the top oil temperature is demonstrated and can influence the hot-spot gradient exponent z. Based on the test results and a statistical simulation one can conclude that the normal tolerances in the temperature- and resistance measurements, result in a large standard deviation in the exponents x and y. Use of the exponents x and y, based on a heat run of one single transformer, should be handled with extreme care. In case of doubt, the use of the exponents given in the loading guide result in a safe margin when determining the overload capabilities of a transformer

STATISTICAL ANALYSIS OF TEMPERATURE RISE TEST FOR INCREASED ACCURACY ON X- AND Y- EXPONENTS

On a large number ( > 50 ) of identical large power single-phase autotransformers ONAF temperature rise test have been performed as part of the customer specification. Part of the 24 hour test is a 125% overload for 8 hours. Based on this data one can statistically evaluate aspects as average value, standard deviation and correlation on many parameters. Measurement tolerances have a large influence on the top oil exponent x and the winding exponent y. The calculation of x and y is determined by the ratio of two temperature differences due to a load difference, which can result in larger errors than expected. In two transformers fibre optic ( FO ) sensors were installed in the common winding to measure the hot-spot, not only during steady state, but also during transient conditions. For ONAF cooling, a step increase of load takes a relatively long time before the oil flow reaches a steady state, as is described in the loading guide. The overshoot in the gradient between the hot-spot temperature and the top oil temperature is demonstrated and can influence the hot-spot gradient exponent z. Based on the test results and a statistical simulation one can conclude that the normal tolerances in the temperature- and resistance measurements, result in a large standard deviation in the exponents x and y. Use of the exponents x and y, based on a heat run of one single transformer, should be handled with extreme care. In case of doubt, the use of the exponents given in the loading guide result in a safe margin when determining the overload capabilities of a transformer

An optimized BSCCO/Ag resonator coil for utility use

AC coils made with BSCCO-2223/Ag tapes and operating in liquid nitrogen have a potential for power related applications, e.g., inductors, transformers and current limiters. High-Tc tapes are available from several producers, while access to the coil building know-help is still rather limited, The relevant knowledge and technology suitable for making HTS coils for 50-60 Hz operation is being developed as a part of the current project. To verify the technology, several test solenoids and a first full-scale sub-coil have been manufactured. Electromagnetic, thermal and mechanical analysis of the coils is performed. The electromagnetic analysis focuses on the reduction of the radial magnetic field component in the windings. Voltage-current characteristics and the AC loss data obtained from relevant short sample measurements are applied. A good agreement between calculated and measured V-I curves and losses of the coils is found. A remarkable increase of the critical current and the reduction of the AC loss at the coil edges are predicted and confirmed experimentally. With the losses defined, thermal analysis and optimization of the coil structure are performed numerically followed by measurements for verification. The paper reports on the series of coils developed and explains the features of the projec

Construction and test of a 1 MVA class BSCCO resonator coil

A high quality factor, superconducting resonator coil is developed in cooperation with the Dutch companies SMIT Transformers and SMIT DRAAD. The coil system is manufactured in industry, using industrial tooling. It has a design reactive power rating of 1 MVA at a frequency of 50 Hz and the operating temperature is 64 K. The system consists of four concentric but separate coils, made of 2 km of Bi-2223 conductors from two different manufacturers. The coils are optimized by shaping the magnetic field around the coil edges with ferro-magnetic C-cups to reach a design electrical quality factor of 1000. The system is operated in a glass-epoxy cryostat at 64 K and 77 K. The resonator coil design demonstrates all the superconducting elements that are essential for manufacturing superconducting transformers. A numerical model has been developed to predict the DC and AC behavior of the system based on measurements of short samples and test coils. A comparison is made between the experiment and model calculations

Performance test results of a low-loss 1 MVA BSCCO resonator coil system

A high-quality superconducting resonator coil system has been developed in the Netherlands in cooperation with the companies SMIT Transformers and SMIT Draad. The coil system was manufactured in industry, using industrial tooling. It has a reactive power rating of 1 MVA at a frequency of 50 Hz and a temperature of 64 K. The system consists of four concentric solenoidal coils, including 2 km of Bi-2223 conductors from two manufacturers. The coil performance has been optimized by shaping the magnetic field around the coil edges with laminated ferro-magnetic C-cups to reduce the AC loss to about 1 kW at 1 MVA reactive power. The system is operated in a glass-epoxy cryostat at either 64 or 77 K. The resonator coil demonstrates all superconducting elements that are essential for manufacturing superconducting transformers. The construction of the system is finalized and the total system has been tested in various operational configurations. The results of the system test at full power are presented and analyzed.\ud \u

An optimized BSCCOIAg resonator coil for tility USC

AC coils made with BSCCO-2223/Ag tapes and operating in liquid nitrogen have a potential for power related applications, e.g., inductors, transformers and current limiters. High-T/sub c/ tapes are available from several producers, while access to the coil building know-help is still rather limited, The relevant knowledge and technology suitable for making HTS coils for 50-60 Hz operation is being developed as a part of the current project. To verify the technology, several test solenoids and a first full-scale sub-coil have been manufactured. Electromagnetic, thermal and mechanical analysis of the coils is performed. The electromagnetic analysis focuses on the reduction of the radial magnetic field component in the windings. Voltage-current characteristics and the AC loss data obtained from relevant short sample measurements are applied. A good agreement between calculated and measured V-I curves and losses of the coils is found. A remarkable increase of the critical current and the reduction of the AC loss at the coil edges are predicted and confirmed experimentally. With the losses defined, thermal analysis and optimization of the coil structure are performed numerically followed by measurements for verification. The paper reports on the series of coils developed and explains the features of the project