| 1. |
- Abdulahovic, Tarik, 1976, et al.
(författare)
-
Vacuum Circuit-Breaker Parameter Calculation and Modelling for Power System Transient Studies
- 2017
-
Ingår i: IEEE Transactions on Power Delivery. - : Institute of Electrical and Electronics Engineers (IEEE). - 0885-8977 .- 1937-4208. ; 33:3, s. 1165-1172
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, a black-box vacuum circuit-breaker model is developed and its parameters are calculated. The developed model is deterministic and does not include the stochastic behavior of arc interruption. The phenomena, such as the current chopping, high-frequency current quenching capability, and rate of rise of dielectric strength are treated as deterministic and calculated using mean values. The vacuum breaker model is verified using a laboratory test setup, and simulation results show good agreement with the obtained measurements. The withstand voltage of the breaker during appearance of the voltage restrikes shows good agreement with the measurements. Moreover, the magnitude and repetitiveness of the high-frequency transients obtained in simulations are within a 10% margin when compared with measurements.
|
|
| 2. |
- Abdulahovic, Tarik, 1976, et al.
(författare)
-
Voltage Stress in a Transformer Winding During Very Fast Transients Caused by Breaker Closing Event
- 2014
-
Ingår i: IEEE Transactions on Power Delivery. - 0885-8977 .- 1937-4208. ; 29:4, s. 1946-1954
-
Tidskriftsartikel (refereegranskat)abstract
- Transformers connected at the medium-voltage level in cable grids, such as wind park collection grids and industrial grids, are exposed to the stress of very fast transients. These electric transients are mainly generated during breaker switching operations and the rise time of the transient voltage in such systems is much shorter compared to the rise times of transients generated in transmission systems at a high-voltage level. In this paper, the internal voltage stress is studied during very fast transients generated during transformer energization. Instead of using a breaker, the energizing tests are performed using a low-impedance pulse generator that can generate lightning impulse-shaped waveforms and voltage steps with rise times varying between 35 and 500 ns. Experiments show that during very fast transients with a 35-ns rise time and 1-p.u. magnitude, the interturn voltage exceeds the level obtained with a lightning impulse-shaped voltage waveform of 4.4 pu. Furthermore, during a specific switching scenario with delta-connected transformers, where the winding is excited from both ends, the same 1-p.u./35-ns voltage step generates an interturn voltage that exceeds the 1-p.u. level, which is more than 2.5 times higher voltage stress than during a lightning impulse test.
|
|
| 3. |
- Abeywickrama, Nilanga, 1976, et al.
(författare)
-
Exploring Possibilities for Characterization of POwer Transformer Insulation by Frequency Response Analysis (FRA)
- 2006
-
Ingår i: IEEE Transactions on Power Delivery. - 0885-8977 .- 1937-4208. ; 21:3, s. 1375-1382
-
Tidskriftsartikel (refereegranskat)abstract
- This paper explores the possibility for using frequencyresponse analysis (FRA) technique to characterize thequality of transformer insulation. For this purpose, a single-phase and a three-phase lumped parameter circuit models were developed.The single-phase model represents a transformer without a laminated core, whereas the three-phase model represents a real transformer with core. Calculations of frequency dependent circuit parameters are presented and the effects imparted on the frequency response by different loss mechanisms (in insulation, inwindings and in core) are discussed. The simulations are compared with results of measurements on real objects. It is shown that FRA could be used for insulation diagnostics if the measurements were of high enough quality.
|
|
| 4. |
- Abeywickrama, Nilanga, 1976, et al.
(författare)
-
High-frequency modeling of power transformers for use in frequency response analysis (FRA)
- 2008
-
Ingår i: IEEE Transactions on Power Delivery. - 0885-8977 .- 1937-4208. ; 23:4, s. 2042-2049
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents an advanced model of the frequencyresponse of a three-phase power transformer for usein conjunction with diagnostic measurements by the method offrequency response analysis (FRA). The model includes high frequency behavior of the laminated core and the insulationthrough taking into account the frequency dependencies of the complex permittivity of insulation materials (paper, pressboard, and oil) and of the anisotropic complex permeability of magnetic core and conductors. A lumped parameter circuit model is used to simulate the frequency response of open-circuit impedance,short-circuit impedance, and impedance between primary and secondary windings, in which the characteristics of circuit elements are calculated by means of the finite-element method. Theeffect of correct representation of each circuit element on the FRA response is analyzed and discussed in comparison to measurement results on a real transformer.
|
|
| 5. |
- Accoto, Nadia, et al.
(författare)
-
Bayesian Hidden Markov Models for Performance-Based Regulation of Continuity of Electricity Supply
- 2010
-
Ingår i: IEEE Transactions on Power Delivery. - 0885-8977 .- 1937-4208. ; 25:3, s. 1236-1249
-
Tidskriftsartikel (refereegranskat)abstract
- A fundamental aspect in the regulation of the continuity of electricity supply is the identification of faults that could be caused by an exceptional event and, therefore, that are outside the utility control and responsibility. Different methods have been proposed during the years: the interpretation of the observed faults as a signal of an underlying system naturally leads to the analysis of the problem by means of a hidden Markov model. Thesemodels, in fact, are widely used for introducing dependence in data and/or for modeling observed phenomena depending on hidden processes. The application of this method shows that the model is able to identify exceptional events; moreover, the study of the estimated model parameters gives rise to reality-linked considerations.
|
|
| 6. |
- Ahmed, Noman, et al.
(författare)
-
Efficient Modeling of an MMC-Based Multiterminal DC System Employing Hybrid HVDC Breakers
- 2015
-
Ingår i: IEEE Transactions on Power Delivery. - : IEEE. - 0885-8977 .- 1937-4208. ; 30:4, s. 1792-1801
-
Tidskriftsartikel (refereegranskat)abstract
- The feasibility of future multiterminal dc (MTDC) systems depends largely on the capability to withstand dc-side faults. Simulation models of MTDC systems play a very important role in investigating these faults. For such studies, the test system needs to be accurate and computationally efficient. This paper proposes a detailed equivalent model of the modular multilevel converter (MMC), which is used to develop the MTDC test system. The proposed model is capable of representing the blocked-mode operation of the MMC, and can be used to study the balancing control of the capacitor voltages. In addition, the operation of the MMC when redundant submodules are included in the arms can also be studied. A simplified model of a hybrid high-voltage dc breaker is also developed. Hence, the developed test system is capable of accurately describing the behavior of the MMC-based MTDC system employing hybrid HVDC breakers, during fault conditions. Using time-domain simulations, permanent dc-side faults are studied in the MTDC system. In addition, a scheme to control the fault current through the MMC using thyristors on the ac side of the converter is proposed.
|
|
| 7. |
- Akke, Magnus
(författare)
-
Frequency estimation by demodulation of two complex signals
- 1997
-
Ingår i: IEEE Transactions on Power Delivery. - : Institute of Electrical and Electronics Engineers (IEEE). - 1937-4208 .- 0885-8977. ; 12:1, s. 157-163
-
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.
|
|
| 8. |
- Almas, Muhammad Shoaib, et al.
(författare)
-
RT-HIL Implementation of Hybrid Synchrophasor and GOOSE-based Passive Islanding Schemes
- 2015
-
Ingår i: IEEE Transactions on Power Delivery. - : IEEE. - 0885-8977 .- 1937-4208. ; 31:3, s. 1299-1309
-
Tidskriftsartikel (refereegranskat)abstract
- Real-time hardware-in-the-loop performance assessmentof three different passive islanding detection methodsfor local and wide-area synchrophasor measurements is carriedout in this paper. Islanding detection algorithms are deployedwithin the phasor measurement unit (PMU) using logic equations.Tripping decisions are based on local and wide-area synchrophasorsas computed by the PMU, and trips are generated usingIEC 61850-8-1 generic object-oriented substation event messages.The performance assessment compares these islanding detectionschemes for the nondetection zone and operation speed underdifferent operating conditions. The testbench that is demonstratedis useful for a myriad of applications where simulation exercises inpower system computer-aided design software provide no realisticinsight into the practical design and implementation challenges.Finally, different communication latencies introduced due tothe utilization of synchrophasors and IEC 61850-8-1 GOOSEmessages are determined.
|
|
| 9. |
- Alvehag, Karin, et al.
(författare)
-
A Reliability Model for Distribution Systems Incorporating Seasonal Variations in Severe Weather
- 2011
-
Ingår i: IEEE Transactions on Power Delivery. - 0885-8977 .- 1937-4208. ; 26:2, s. 910-919
-
Tidskriftsartikel (refereegranskat)abstract
- In distribution system planning and operation, accurate assessment of reliability performance is essential for making informed decisions. Also, performance-based regulation, accompanied by quality regulation, increases the need to understand and quantify differences in reliability performance between networks. Distribution system reliability performance indices exhibit stochastic behavior due to the impact of severe weather. In this paper, a new reliability model is presented which incorporates the stochastic nature of the severe weather intensity and duration to model variations in failure rate and restoration time. The model considers the impact of high winds and lightning and can be expanded to account for more types of severe weather. Furthermore, the modeling approach considers when severe weather is likely to occur during the year by using a nonhomogeneous Poisson process (NHPP). The proposed model is validated and applied to a test system to estimate reliability indices. Results show that the stochasticity in weather has a great impact on the variance in the reliability indices.
|
|
| 10. |
- Anatory, Justinian, et al.
(författare)
-
A broadband power-line communication system design scheme for typical Tanzanian low-voltage network
- 2009
-
Ingår i: IEEE Transactions on Power Delivery. - USA : IEEE. - 0885-8977 .- 1937-4208. ; 24:3, s. 1218-1224
-
Tidskriftsartikel (refereegranskat)abstract
- Information and communications technologies (ICTs) are gaining importance in developing countries. Power-line network is a potential infrastructure for ICT services provision. Power-lines are highly interconnected network with stochastic variation in number of branches. Under such distributed network conditions the design of a broadband power-line communication (BPLC) system is a challenge. In this paper a case study of an actual power-line network, representative of a low-voltage BPLC channel in Dar es Salaam, Tanzania is considered. We shall investigate the performance of such a low-voltage channel that uses orthogonal frequency division multiplexing (OFDM) technique with binary phase shift keying (BPSK) modulation scheme for communication. For sensitivity analysis, three different transmitter locations were chosen and receiver points were varied to identify the possible degraded performance scenarios. Analysis show that in the frequency bands of 100 MHz, the channel delay spread for such networks is about 4 s, giving a maximum number of subchannels 4096 with 512 cyclic prefix. To improve the degraded performance scenarios, the concatenated Reed Solomon outer code with punctured convolution inner code was applied to the network. It was found that when the branches were terminated by its corresponding characteristic impedances the performance is improved by 10-20 dB compared to a corresponding uncoded system. On the contrary for a coded system when the branches were terminated either in low or higher impedances compared to branch characteristic impedances the improvement was greater than 2-15 dB. This study demonstrates that the specification proposed by IEEE-802.16 broadband wireless access working groups can be used for performance improvement of distributed low-voltage systems.
|
|
