Browsing by Author "Jayatunga, JVUP"

Now showing 1 - 3 of 3

item: Conference-Abstract
Analysis of the performance of three phase induction motor under supply source unbalance
Sudasinghe, SPM; Jayatunga, JVUP; Wadduwage, D. Prasad
Presence of voltage unbalance adversely affects the operation of three phase induction motors. Influence of unbalanced supply voltages on the adverse performance of the motor is intensified by the fact that a small unbalance in phase voltages can cause a disproportionately larger unbalanced phase currents. Thus, the additional heat produced in both the stator and the rotor windings lead to a reduction in the motor efficiency, demanding motor de-rating which was established to depend on the voltage unbalance factor. This study investigates the effects of varying unbalanced voltages which lead to the same voltage unbalance factor, on the operation performance of an induction motor and the effect of positive sequence voltage on it. Statistical analysis is carried out to identify the possible variation range for the performance parameters of induction motors of different scales for different unbalance voltage conditions.
item: Thesis-Abstract
Fault localization using wavelet transforms in electric power netwoorks
Jayatunga, JVUP; De Silva, N; Karunadasa, JP
Determination of fault location in electric power systems is very vital for economic operation of power systems. Conventional distance protection schemes provide sufficient information for fault isolation and those are not satisfactory for accurate fault location and identification. This study focuses on developing an observer model for the distance relay through fault transient analysis which provides more useful information related to fault localization. Using the theory of wavelet singularity detection as a powerful signal processing tool, travelling wave behavior of faulted signals is investigated to build up the fault location algorithm. Fault transients are discriminated from other types of power system transients using Daubechies-4 mother wavelet. The principle of proposed scheme is based on the identification of successive high frequency voltage waves arriving at the substation end in modal domain. Clarke transformation matrix is used to obtain modal quantities which eliminate significant electromagnetic coupling between three phase quantities. The resulted fault transient voltage graph provides basic information for fault distance calculation with the help of power network's physical characteristics. Surges originated from different discontinuity points of the network including the fault point are analyzed by their magnitude, polarity and timing to incorporate them into the proposed fault location technique. New scheme is capable of locating faults irrespective of fault types, once the appropriate mode is selected from the modal domain. Fault characterization by modal analysis is based on the trial and error approach at the time of fault simulation. Extensive simulation studies carried out using MATLAB/SIMULINK Simpower control block set show that the proposed algorithm provides an accepted degree of accuracy in fault location under different conditions and validity of proposed technique to a branched network is also investigated during the study.
item: Thesis-Full-text
Feasibility study on distribution transformer based urban grid connected energy islands with distributed generation
Amarasinghe, HPP; De Silva, PSN; Jayatunga, JVUP
Sri Lanka’s distribution network has been facing drastic changes during recent past due to the continuous addition of distributed renewable generation into the network. Addition of rooftop solar PV into the low voltage distribution feeders has significantly increased during 2016-2017, due to the government initiative “Surya Bala Sangramaya” on promoting rooftop solar generation. As a result, in highly populated urban areas, some distribution transformer service areas now have more than 50% of installed solar rooftop capacity, compared to the connected transformer capacity. These transformers export power to the medium voltage network from low voltage side during daytime due to high solar generation and low energy usage inside these service areas. An increasing number of transformers will experience such reverse power flow in near future with the acceleration of promoting rooftop solar programs. Operating with higher density of rooftop solar in distribution transformer service areas will result in numerous power quality issues and higher distribution losses in spite of the advantages of utilizing household rooftops for solar PV generation. In this study, a futuristic solution is proposed to effectively utilize the daytime solar PV generation in a single distribution transformer service area itself with the formation of smart grid type operation. Distribution transformer based smart grid, which operates with controlling mechanisms, loads, rooftop solar and battery storage systems is discussed in this report. This system can be developed and operated as a community-based smart grid that is formed inside the distribution transformer service area with the contribution of the electricity customers. Other than operating as individual energy customers and energy producers, public can become procumers who operate and control their loads and PV generation together to optimize load flow, power quality and economics in this proposed smart grid. This research is a preliminary study to identify the possibility of such distribution transformer based smart grid for Lanka Electricity Company Private Limited operation area. Extensive simulations were carried out using Matlab Simulink by modeling the three phase four wire LV network for a single transformer area to identify the present behavior of the LV Network. Then the model was upgraded to proposed future smart grid arrangement. Results on the customer behaviors, load flows and power quality on both normal and smart grid type scenarios are presented for several case studies including the present situation, future expected situation and for the proposed smart grid. As the outcome of this research, simulated results were obtained for smart grid arrangement inside an actual transformer service area and technical compatibility of the concept is presented to the Sri Lankan urban distribution transformers.