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- Wass, Torbjörn, 1971-
(författare)
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Studies of high-temperature superconducting tapes and their application in power apparatus
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Intensive development in the field of high-temperature superconductors (HTS) has resulted in long length HTS with high current carrying capacity. The performance of HTS in the form of multifilamentary silver sheathed Bi-2223 tapes is close to the requirements for power application. Several power apparatus prototypes based on HTS have been and are being demonstrated. Recently the first commercial order for a HTS power apparatus was placed. Tennessee Valley Authority ordered two 12 MVA synchronous condensers with HTS rotor windings for reactive power compensation.In most power devices the conductor is carrying an AC transport current while it is exposed to an AC magnetic field transverse to the current path. In certain applications such as multi-layer power transmission cables or the control winding in a controllable reactor, the conductors are exposed to a magnetic field component longitudinal to the tape axis that is parallel with the current path. In this thesis, the losses in HTS tapes in longitudinally applied magnetic field are investigated and a single phase small scale controllable reactor with a loss optimized HTS control winding is designed, constructed and tested.An experimental setup to measure the losses in tapes exposed to longitudinal magnetic fields, transport currents, frequencies, and temperatures is presented. The system is based on a calorimetric loss measuring method where the losses are determined by the temperature response of the conductor when exposed to magnetic field and/or carrying transport current.Semi-empirical loss models are developed from the results of the loss measurements of non-twisted multifilamentary Bi-2223 tapes. The losses when the sample is carrying transport currents and is exposed to longitudinal magnetic fields are found to consist of hysteresis, flux flow, and eddy current losses. The hysteresis losses can be modeled with the critical state model. The flux flow losses can be described with a power law dependent current voltage characteristic.The loss models are well suited for the design of power devices in which HTS is exposed to longitudinal magnetic fields. Based on the knowledge of the losses a single phase small scale controllable reactor with a loss optimized HTS control winding is designed, constructed and tested. A simple model of the magnetic circuit of the controllable reactor is presented. Calculations from the model are compared with experimental measurements. The feasibility to design controllable shunt reactors with large linear dynamic range, low losses and limited harmonic distortion is demonstrated. Compared to a copper control winding the HTS control winding increases the dynamic range and reduces the size due to the high current density and reduces the losses of the control winding.
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| 2. |
- Wass, Torbjörn, et al.
(författare)
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The design and construction of a controllable reactor with a HTS control winding.
- 2006
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Ingår i: 7TH EUROPEAN CONFERENCE ON APPLIED SUPERCONDUCTIVITY (EUCAS'05). - : IOP Publishing. ; , s. 873-876
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Konferensbidrag (refereegranskat)abstract
- Reactive power compensation is vital for obtaining efficient operation of long transmission power lines or cables. The need of reactive power changes with the load of the transmission line. Discrete units of conventional reactors are therefore switched in and out in order to obtain more efficient reactive power compensation. A continuous reactive compensation will reduce the transmission losses and increase the transmission capacity of active power. We have designed and constructed a one phase small scale prototype of a controllable shunt reactor with a high temperature superconducting control winding. The reactor consists basically of two windings and an iron core. The control winding is placed so that it generates a DC magnetic field perpendicular to the main AC magnetic field. Thus the DC current in the control winding can control the direction of the magnetization of the iron core and thereby the reactance of the reactor. Such a control winding will have low losses and give the reactor a large dynamic range. For this small scale reactor we found that the reactive power could be varied with a factor six. We have demonstrated the feasibility to design large scale controllable shunt reactors with large dynamic range and low losses utilizing a control winding made of a high temperature superconductor.
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| 3. |
- Wass, Torbjörn, et al.
(författare)
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The magnetic circuit of a controllable reactor
- 2006
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Ingår i: IEEE transactions on magnetics. - 0018-9464 .- 1941-0069. ; 42:9, s. 2196-2200
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Tidskriftsartikel (refereegranskat)abstract
- Reactive power compensation is vital for obtaining efficient operation of long transmission power lines or cables. A controllable shunt reactor that controls the transmission of power by continuous reactive power compensation will reduce the transmission losses and increase the transmission capacity of active power. We show that the saturation phenomena of iron and the high current density of a high-temperature superconductor can be utilized to design controllable reactors with large dynamic range, low losses, and limited harmonic distortion. We have designed and constructed a small-scale prototype of a controllable shunt reactor with a high-temperature superconductor control winding. We present a simple model of the magnetic circuit of the controllable reactor and we compare alculations from the model to experimental measurements on the controllable reactor.
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| 4. |
- Schönborg, Niclas, et al.
(författare)
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Impact of DC components in transport current and external magnetic field on hysteresis losses in an HTS tape
- 2004
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Ingår i: IEEE transactions on applied superconductivity (Print). - 1051-8223 .- 1558-2515. ; 14:3, s. 1955-1958
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Tidskriftsartikel (refereegranskat)abstract
- The high-temperature superconductor (HTS) development is presently intensive, and one can expect that HTSs will be used in different electric devices in the future. In some of these devices, e.g., a magnetostrictive actuator, the conductor will be exposed to both ac and dc transport currents and external magnetic fields. One of the most important parameters in the design of electric devices is the power loss. It is, therefore, of importance to develop models that are able to predict the power loss in devices based on HTSs. In this paper, we present an experimental characterization of the hysteresis losses in an HTS tape exposed to ac or dc transport currents in combination with external magnetic fields. The experimental results are compared to some existing models based on the critical state model. The power loss was measured on a multifilamentary Bi-2223 tape at constant temperature (70 K) and frequency (50 Hz).
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| 5. |
- Wass, Torbjörn, et al.
(författare)
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AC losses in applied longitudinal magnetic fields at variable temperatures
- 2004
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Ingår i: IEEE transactions on applied superconductivity (Print). - 1051-8223 .- 1558-2515. ; 14:1, s. 22-27
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Tidskriftsartikel (refereegranskat)abstract
- In most power devices, the conductor is carrying anac transport current while it is exposed to an ac magnetic fieldtransverse to the current path. In certain applications, such aspower cables or a control winding in a controllable reactor, theconductors are exposed to a magnetic field component longitudinalto the tape axis that is parallel to the current path. To createan improved base for the design of such power devices it is ofinterest to study the losses in high-temperature superconductortapes due to longitudinal field in detail. We have investigated thelosses at several temperatures of a nontwisted multifilamentaryBi-2223 tape when it was exposed to a longitudinal magnetic field.The losses were measured with a calorimetric method and theresults were compared with the critical state hysteresis loss model.The hysteresis losses are dominating at power frequencies (50,60 Hz) in the investigated field range 2–200 mT and are accuratelydescribed by the critical state hysteresis model.
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| 6. |
- Wass, Torbjörn, et al.
(författare)
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Experimental set-up for calorimetric AC loss measurements on HTS tapes in applied longitudinal magnetic fields carrying transport currents at variable temperatures
- 2004
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 75:1, s. 99-103
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Tidskriftsartikel (refereegranskat)abstract
- In most power devices, the conductor is carrying an ac transport current while it is exposed to an ac magnetic field transverse to the current path. In certain applications, such as multilayer power cables or the control winding in a controllable reactor, the conductors are exposed to a magnetic field component parallel with the current path that is longitudinal to the tape axis. An experimental setup to measure the losses at a different longitudinal magnetic field, transport currents, frequency, and temperature is presented. The system is based on a calorimetric measuring method. Examples are given of power loss measurements on multifilamentary Bi 2223 tapes at different longitudinal ac magnetic fields 0-250 mT peak value, frequencies 0-1000 Hz, ac transport currents 0-70 A peak value, and temperatures 55-85 K. The calorimetric technique presented is fast, accurate, and capable of measuring losses between 0.5-100 mW/m. The data obtained from the apparatus can provide an improved base for the design of power devices.
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