| 1. |
- Akke, Magnus, et al.
(författare)
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An object-oriented transformer model in OMOLA
- 1997
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Ingår i: Proceedings of the world congress - International federation of Automatic Control. - 0080429262 ; , s. 259-264
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Konferensbidrag (refereegranskat)
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| 2. |
- Akke, Magnus
(författare)
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Frequency estimation by demodulation of two complex signals
- 1997
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Ingår i: IEEE Transactions on Power Delivery. - : Institute of Electrical and Electronics Engineers (IEEE). - 1937-4208 .- 0885-8977. ; 12:1, s. 157-163
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a method for frequency estimation in a power system by demodulation of two complex signals. In power system analysis, the αβ-transform is used to convert three phase quantities to a complex quantity where the real part is the in-phase component and the imaginary part is the quadrature component. This complex signal is demodulated with a known complex phasor rotating in opposite direction to the input. The advantage of this method is that the demodulation does not introduce a double frequency component. For signals with high signal to noise ratio, the filtering demand for the double frequency component can often limit the speed of the frequency estimator. Hence, the method can improve fast frequency estimation of signals with good noise properties. The method loses its benefits for noisy signals, where the filter design is governed by the demand to filter harmonics and white noise. The method has been previously published, but not explored to its potential. The paper presents four examples to illustrate the strengths and weaknesses of the method.
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| 3. |
- Akke, Magnus, et al.
(författare)
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Improved estimates from the differential equation algorithm by median post-filtering
- 1997
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Ingår i: Sixth International Conference on Developments in Power System Protection (Conf. Publ. No. 434). - : IEE. - 0537-9989. - 0852966725 ; :434, s. 235-238
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Konferensbidrag (refereegranskat)abstract
- Fast line relaying algorithms are motivated by the need to keep the fault clearing time as short as possible. Fast fault clearing reduces the risk for transient instability, thermal stress on equipment and risk for personnel injuries. There exists, at least, three different themes in transmission line protection: impedance algorithms differential equation algorithms (DEA); and travelling wave algorithms. This paper focuses on the differential equation algorithm. The paper presents the equations used in the differential equation algorithm. Both the continuous-time and the discrete-time equations are given. The very poor estimates are explained by the equations determinant. At some isolated points the determinant approaches zero and the equations become singular. This results in useless, often extreme, estimates. A simulation shows that a linear post-filter is unsuitable for this problem. To solve the problem we suggest a median post-filter. This filter type totally rejects the extreme values, and therefore produce fast and accurate estimates.
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| 4. |
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| 5. |
- Akke, Magnus
(författare)
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Some Control Applications in Electric Power Systems
- 1997
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents some control applications in electric power systems. The work consists of the four parts: interaction between DC cables and ship steering autopilots; frequency estimation; computer relaying; field tests using load switching to damp power oscillations. The first three parts are based on four papers that are given in Appendix A-D. The thesis presents supplementary text to these papers. The last chapter is more self contained and presents field tests from a small hydro power station. These tests show that load switching is an excellent method to damp power oscillations. A proof used in stochastic analysis of fault locators is presented in Appendix E. The first paper presents novel results on interaction of DC cables and ship steering autopilots. Simulations with a non-linear model show that a ship using steering autopilot with a magnetic compass can be captured by a DC cable, i.e, the ship tracks the cable. A full scale experimental study has been performed at the Kontiskan HVDC link. Good agreement was obtained between measurements and computer sinulations. The second paper presents a method for frequency estimation in power systems by demodulation of two complex signals. The third and fourth paper presents some improvements of the differential equation algorithm (DEA) that can be used for transmission line protection. The third paper uses the determinant to explain why isolated estimates from the DEA can be very poor. A median filter is proposed to reject these poor estimates. The fourth paper suggests the followinmg improvements to the DEA: fault classification; intermediate filtering and a new algorithm for three phase faults. Simulation results indicate a nominal operation time of 5-7 ms for three phase faults and slightly longer for other fault types
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| 6. |
- Akke, Magnus, et al.
(författare)
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Some improvements in the three-phase differential equation algorithm for fast transmission line protection
- 1998
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Ingår i: IEEE Transactions on Power Delivery. - 1937-4208. ; 13:1, s. 66-72
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents some improvements of the differential equation algorithm for transmission line protection. The improvements are: fault classification; new filtering; new algorithm for three-phase faults. Simulation results indicate a nominal operation time of 5-7 ms for three-phase faults and slightly higher for other fault types.
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| 7. |
- Hiskens, I A, et al.
(författare)
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Analysis of the Nordel power grid disturbance of January 1, 1997 using trajectory sensitivities
- 1999
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Ingår i: IEEE Transactions on Power Systems. - : Institute of Electrical and Electronics Engineers (IEEE). - 0885-8950. ; 14:3, s. 987-994
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Tidskriftsartikel (refereegranskat)abstract
- This paper uses trajectory sensitivity analysis to investigate a major disturbance of the Nordel power system which occurred on January 1, 1997. The Nordel system is described, and the details of the disturbance are presented. Background to trajectory sensitivity analysis is also provided. Results of the investigation indicate the usefulness of trajectory sensitivities for exploring the influence of various system parameters on the large disturbance behaviour of the system. The trajectory sensitivities provide a way of judging the relative importance of various factors which affected behaviour.
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| 8. |
- Samuelsson, Olof, et al.
(författare)
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On-off Control of an Active Load for Power System Damping - Theory and Field Test
- 1999
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Ingår i: IEEE Transactions on Power Systems. - : Institute of Electrical and Electronics Engineers (IEEE). - 0885-8950. ; 14:2, s. 608-613
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Konferensbidrag (refereegranskat)abstract
- Controlled resistive loads can contribute to damping of electro-mechanical oscillations. This paper presents an on-off damping controller for a single machine system. It was used at a field test in Southern Sweden to damp oscillations of a 0.9 MW hydro power generator. The controller used estimated machine frequency as input and controlled a 20 kW resistive load via thyristor switches. The field measurements are compared to time simulations and a systematic procedure for tuning the controller is given. The results indicate that on-off control of active loads is effective in terms of added damping and that it is simple to tune and implement
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