Modeling and Protection of Phase Shifting Transformers

This thesis is mainly focused on the development of (i) phase shifting transformers (PSTs) mathematical and simulation models that can be used for the short-circuit and protection studies, and (ii) new phase shifting transformers protection methods that provide more secure and sensitive solutions than the standard current differential protection. The first part of this thesis describes and presents the modeling of the single-core standard-delta, and two-core symmetrical and asymmetrical PST for protection and short-circuit studies. The models already available for such types of PSTs have limitations and require detailed test report data from the manufacturers. However, winding test data at each tap position is seldom available from the manufacturers. Moreover, they are confined to the balanced system conditions. The proposed modeling approach is based on the development of positive, negative and zero-sequence networks. Derived mathematical relations are further used to develop the relations of winding terminal voltages, currents and impedances as a function of tap position. Accuracy of the presented models is verified mathematically with the manufacturer’s test report data. Furthermore, electromagnetic transients program (EMTP) modeling, in commercially available simulation tools such as PSCAD/EMTDC and RTDS, is done in order to further verify the proposed models. The proposed modeling approach does not rely on the availability of the manufacturer test report data and only requires the nameplate information. It can also be used for both balanced and unbalanced system conditions. The second part of the thesis presents two protection principles: (a) electromagnetic differential protection, and (b) directional comparison-based protection. The main motive behind the development of new protection principles is to develop a solution that is more secure, sensitive and offers high-speed protection. Correct implementation of these techniques for the protection of various kinds of PSTs comes across various problems and hence leads us to the proposed solution of those issues. Both techniques solve the problems of conventional challenges such as magnetizing inrush current, core saturation, non-standard phase shift, external fault with current transformer (CT) saturation, etc. The electromagnetic differential protection principle can only be applied to the PST it represents and it requires tap position tracking. A directional comparison-based approach can be applied to any kind of PST without tracking the tap position

Experimental phase-error extraction and modelling in silicon photonic arrayed waveguide gratings

We present a detailed study of parameter sweeps of silicon photonic arrayed waveguide gratings (AWG), looking into the effects of phase errors in the delay lines, which are induced by fabrication variation. We fabricated AWGs with 8 wavelength channels spaced 200 GHz and 400 GHz apart. We swept the waveguide width of the delay lines, and also performed a sweep where we introduced increments of length to the waveguides to emulate different AWG layouts and look into the effect of the phase errors. With this more detailed study we could quantitatively confirm the results of earlier studies, showing the wider waveguides reduce the effect of phase errors and dramatically improve the performance of the AWGs in terms of insertion loss and crosstalk. We also looked into the effect of rotating the layout of the circuit on the mask, and here we could show that, contrary to results with older technologies, this no longer has an effect on the current generation of devices

Correlation between pattern density and linewidth variation in silicon photonics waveguides

We describe the correlation between the measured width of silicon waveguides fabricated with 193 nm lithography and the local pattern density of the mask layout. In the fabrication process, pattern density can affect the composition of the plasma in a dry etching process or the abrasion rate in a planarization step. Using an optical test circuit to extract waveguide width and thickness, we sampled 5841 sites over a fabricated wafer. Using this detailed sampling, we could establish the correlation between the linewidth and average pattern density around the test circuit, as a function of the radius of influence. We find that the intra-die systematic width variation correlates most with the pattern density within a radius of 200 gm, with a correlation coefficient of 0.57. No correlation between pattern density and the intra-die systematic thickness variation is observed. These findings can be used to predict photonic circuit yield or to optimize the circuit layout to minimize the effect of local pattern density. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreemen

Optimal Partitioning of a Surveillance Space for Persistent Coverage Using Multiple Autonomous Unmanned Aerial Vehicles: An Integer Programming Approach

Unmanned aerial vehicles (UAVs) are an essential tool for the battle eld commander in part because they represent an attractive intelligence gathering platform that can quickly identify targets and track movements of individuals within areas of interest. In order to provide meaningful intelligence in near-real time during a mission, it makes sense to operate multiple UAVs with some measure of autonomy to survey the entire area persistently over the mission timeline. This research considers a space where intelligence has identi ed a number of locations and their surroundings that need to be monitored for a period of time. An integer program is formulated and solved to partition this surveillance space into the minimum number of subregions such that these locations fall outside of each partitioned subregion for e cient, persistent surveillance of the locations and their surroundings. Partitioning is followed by a UAV-to-partitioned subspace matching algorithm so that each subregion of the partitioned surveillance space is assigned exactly one UAV. Because the size of the partition is minimized, the number of UAVs used is also minimized

A Control Architecture for Regulating Voltage and Power Flows in a Networked Microgrid System

This paper presents a unique control system to regulate power exchanges and load bus voltage in a networked microgrid (NMG) system comprising AC and DC microgrids. During the islanding of a microgrid in this NMG system, load voltage and power balance can get disturbed. A control system and associated converter and inverter control methods are presented to rectify these issues. An efficient model predictive control (MPC) method, which gives a tracking error of 50% lower than a conventional proportional-integral (PI) controller, is used to control multiple inverters in the NMG system. Simulation studies are conducted to test the NMG in islanding and load change scenarios. With the help of these studies, it is verified that the MPC-controlled inverters can provide better tracking accuracy in achieving desired power flows in the NMG system

Compact silicon photonics circuit to extract multiple parameters for process control monitoring

We present a compact interferometer circuit to extract multiple model parameters of on-chip waveguides and directional couplers from optical measurements. The compact design greatly improves the accuracy of extraction with fewer measurements, making it useful for process monitoring and detailed wafer-level variability analysis. We discuss the design requirements and illustrate the extraction using the Restart-CMA-ES global optimization algorithm. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreemen

Geographic Routing in Clustered Wireless Sensor Network

A WSN is a network of gadgets that is known as nodes. It consists of sensor nodes distributed over a geographical area. The main task of a sensor node is to sense and collect data from certain domain, process them and transmit it to the sink where the application lies. Clustering provides a productive way to prolong the lifetime of WSN. In this paper, we first propose a distributed technique called energy efficient homogenous clustering technique that selects cluster heads to create a connected backbone network. EHC selects CHs on the basis of their residual energy and utility of sensor to its neighbors. Then we propose a route optimization technique in WSNs to make the best use of routing path among obstacles using Dijkstra’s shortest path algorithm. The simulation results show a reduction in average hop count, packet delay, and energy consumption of WSNs

Factors Affecting Secondary School Principals’ Time Management Practices in Khyber Pakhtunkhwa

This study sought to investigate whether principal’s age, gender, administrative experience, training in time management area, school’s nature, level, location and complexity has any effect on the time management practices. Six time management practices used by secondary school principals i.e. scheduling contacts, managing meetings, delegating tasks, setting priorities, managing paperwork, handling interruptions were incorporated in a questionnaire. A questionnaire was designed, validated and administered to respondents for collecting data having Cronbach Alpha value of 0.864. Data were collected from 344 secondary school principals selected through stratified random sample from seven divisional headquarter districts of Khyber Pakhtunkhwa. Results show that principal’s administrative experience and school’s level have significant effect on principals’ time management practices. Whereas principal’s age, gender, training in time management area, school’s nature, location and complexity have no significant effect on principals’ time management practices. It was recommended that introductory courses, refresher courses, workshops, and seminars on time management practices should be included in in-service training program for principals to equip them with skills, knowledge and attitude on adequate time management practices regardless of their personal characteristics and school’s level, location, nature and complexity