For the design engineers of reactors as well as for the most economical use of that equipment, the temperatures of different parts of reactors should be precisely known so that the thermal losses can be optimized and minimized. Through conventional surface testing methods the exact locations of hot spots inside reactor coils can only be estimated by means of empirical mathematical calculations. Therefore, the ability to directly measure the temperatures inside the coils between the conductors would lead to better design of the reactors, and at the same time would show the exact locations of hottest-spot areas and temperatures. In the IEC and IEEE standards, the test methods for determining temperatures and hot spots are mainly described as surface-temperature measuring methods, since modern dry-type air-core reactors usually employ fully encapsulated windings. Therefore, direct access to the winding is not possible for the measurement of hot spot temperatures during a heat-run test. However, it is possible to measure winding surface temperatures with some degree of accuracy. Such winding surface temperature measurements are essentially a measurement of winding hot spot due to the fact that the winding encapsulation medium is thin compared to the winding conductor cross section. Since energy costs are on the increase, losses are becoming a more significant component of the total operating cost. Further, the correct current distribution between the coils causes even temperatures in each coil and helps to optimize the manufacturing and losses of the whole reactor. For this reason, the research work behind this thesis was started and a test reactor manufactured. During the manufacturing process, several fiber optic wires (instead of fiber optic probes, as mentioned in the IEEE standards) were installed in the middle and at the surface of several cylinder windings, for temperature monitoring purposes. Through these optic wires, it became possible to measure the dynamic temperature changes in several cylinders of the reactor, because the temperatures depend on the location and time. The dynamic temperature behavior could be determined in the middle of the windings for the whole length, from bottom to top. At the same time, with other optic wires, the surface temperatures could also be measured from bottom to top. For comparison, some surface temperatures as well as cooling air temperatures in the air ducts were also measured by means of thermocouples and infrared cameras. In this dissertation, the modeling methods for calculating the temperature distribution and hot-spot temperatures in large multi cylinder air-core reactors are studied and a new method is proposed for thermal loss optimization.
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