| 1. |
- Manyahi, M. J., et al.
(författare)
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Simplified model for estimation of lightning induced transient transfer through distribution transformer
- 2005
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Ingår i: International Journal of Electrical Power & Energy Systems. - : Elsevier BV. - 0142-0615 .- 1879-3517. ; 27:4, s. 241-253
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Tidskriftsartikel (refereegranskat)abstract
- In this work a simplified procedure for the formulation of distribution transformer model for studying its response to lightning caused transients is presented. Simplification is achieved by the way with which the model formulation is realised. That is, by consolidating various steps for model formulation that is based on terminal measurements of driving point and transfer short circuit admittance parameters. Sequence of steps in the model formulation procedure begins with the determination of nodal admittance matrix of the transformer by network analyser measurements at the transformer terminals. Thereafter, the elements of nodal admittance matrix are simultaneously approximated in the form of rational functions consisting of real as well as complex conjugate poles and zeros, for realisation of admittance functions in the form of RLCG networks. Finally, the equivalent terminal model of the transformer is created as a pi-network consisting of the above RLCG networks for each of its branches. The model can be used in electromagnetic transient or circuit simulation programs in either time or frequency domain for estimating the transfer of common mode transients, such as that caused by lightning, across distribution class transformer. The validity of the model is verified by comparing the model predictions with experimentally measured outputs for different types of common-mode surge waveform as inputs, including a chopped waveform that simulate the operation of surge arresters. Besides it has been verified that the directly measured admittance functions by the network analyser closely matches the derived admittance functions from the time domain impulse measurements up to 3 MHz, higher than achieved in previous models, which improves the resulting model capability of simulating fast transients. The model can be used in power quality studies, to estimate the transient voltages appearing at the low voltage customer installation due to the induced lightning surges on the high voltage side of the transformer. The procedure is general enough to be adapted for any two-port devices that behaves linearly in the frequency range of interest.
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| 2. |
- Manyahi, M.J., Thottappillil, R., Scuka, V.
(författare)
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Transient Response of Equipment Transformers
- 1999
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Ingår i: proceedings. - : 1999 International Conference on Electrical Engineering and Technology, Dar Es Salaam, Tanzania.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 3. |
- Manyahi, M. J., et al.
(författare)
-
Transient response of transformer with XLPE insulation cable winding design
- 2005
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Ingår i: International Journal of Electrical Power & Energy Systems. - : Elsevier BV. - 0142-0615 .- 1879-3517. ; 27:1, s. 69-80
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Tidskriftsartikel (refereegranskat)abstract
- Significant advances in XLPE insulation cables that have higher electric field strength withstand capability have made it possible to apply these high voltage (HV) cables as windings in generators and transformers. Therefore, the recent advent of HV generator (Powerformer) that can be connected directly to the power transmission line has motivated the design of HV transformer (Dryformer) that performs one step transformation from transmission to distribution voltage levels. Since the dryformer will be connected directly to transmission lines, they will be subjected to transients resulting from direct and indirect lightning strikes as well as fast switching surges from Gas insulated circuit breakers. This paper presents the results of experimental studies on the cable winding power transformer (Dryformer) to study its response to various transients. Experimental investigations have been carried to obtain the transformer model parameters based on terminal measurement of admittance functions using Network Analyser, and hence for comparing the model predictions with experimentally obtained responses. The model has been successfully used in estimating the dryformer transient responses at its terminals due to surge application of various front times and peak amplitudes that are representative of lightning and switching caused transients. Experiment and simulation results show that there are considerable differences in the transient response characteristics of dryformer windings as compared to that of transformers with traditional winding design. These differences on transient responses are discussed in perspective of their basic difference in winding design features.
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