Electrical Computer Engineering

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    DISTRIBUTION SYSTEM RELIABILITY IMPROVEMENT USING DISTRIBUTED GENERATION AND NETWORK RECONFIGURATION
    (Hawassa University, 2021-10-28) MEKLIT GIRMA
    Power supply reliability is the basic issue for economic and technology development of the country. The sufficient or adequate and secure supply of power will assure the reliability of the system. Unreliability of the system occur due to high outage frequency and duration, system overload and unsecure system or protection system. When the distribution system is reliable, it has capacity to meet the demand of customer and operate under adverse condition. Arbaminch distribution system has encountered frequent power interruption and power quality problem. The interruptions are mainly caused by system overload and short circuit fault. The reliability of the distribution system is assessed based on the data from Ethiopian Electric Power Corporation. Arbaminich substation of feeder -05 is selected as case study, which has high rate of interruption. Feeder -05 has SAIDI value of 236.8386 Hr./cust. /yr. and SAIFI of 221.6338 f/cust. /yr. The reliability indexes values of feeder -05 are not within the ranges of bench marks of reliability requirement. This thesis focused on reliability improvement of distribution system with better placement of distributed generation and network reconfiguration. Particle swarm optimization algorithm is used for placement of DG, size and network reconfiguration. The algorithm is done using MATLAB 2016 software. Based on the availability in the area, efficiency, cost and emission level, Solar and Microturbine sources are used as distributed generation. The suitable site and size of DG are found at bus 10 with suitable size 4.5 MW. For network reconfiguration sectionalizing switch is used. Before reconfiguration the switch was placed at bus 20, 21, 22,23 and 24. During network reconfiguration switch changed to bus 3, 4,12,24 and 31. The reliability indices SAFI, SAIDI and EENS value improved by 82.81%,78.89% and 78.10% respectively after DG with reconfiguration used. Expected interruption cost before applying the proposed method is 9,758,852$ /year. After the proposed method used expected interruption cost reduced to 2,995,270$ /year. This indicates that, 6,763,582 $/year is saved after using the proposed techniques
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    MODEL REFERENCE ADAPTIVE SYSTEM BASED SPEED CONTROL OF SENSOR-LESS FIVE PHASE INDUCTION MOTOR
    (Hawassa University, 2020-10-17) MELAKU TESFAYE SHIFERAW
    This paper presents, rotor flux based model reference adaptive system speed estimator used for closed loop speed control of five phase induction motor without mechanical speed sensor. Multiphase motor drives with phase number greater than three phase leads to an improvement in the medium to high power drives application. The multiphase induction motor find application in special and critical area where high reliability is demanded such as Electric vehicles, aerospace application, ship propulsion and locomotive traction and in high power application. In principle, control methods for multi-phase machines are the same as for three-phase machines. Variable speed induction motor drives without mechanical speed sensors at the motor shaft have the attractions of low cost and high reliability. To replace the speed sensor, information of the rotor speed is extracted from measured stator currents and voltages at motor terminals. Vector controlled drives require estimating the magnitude and spatial orientation of the fundamental magnetic flux in the stator or in the rotor. In this thesis, rotor flux based model reference adaptive system speed estimator is used for closed loop speed control of five phase induction motor without mechanical speed sensor with hysteresis current control. Model reference adaptive system designed to correct parameter variation to estimate the motor speed. As result the induction motor sensor-less control can operate over a wide range including zero speed. The sensor-less vector control operation has been verified by simulation on MATLAB. FOPI and PI controller was used for speed controller. The performance of two controllers has been verified through simulation results. It is seen that execute of the induction motor has improved when FOPI controller is used in place of classical PI controller
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    IMPROVING VOLTAGE SAG AND VOLTAGE SWELL OF DISTRIBUTION SYSTEM WITH INTEGRATION OF ULTRA CAPACITOR AND DYNAMIC VOLTAGE RESTORER
    (Hawassa University, 2018-08-26) MEKONNEN SOLOMON
    Power Quality (PQ) problem is an occurrence manifested as a nonstandard voltage, current or frequency that results in a failure of end use equipments. The supply status of electrical services required for case study of Agro Processing Industry illustrates this concept. The voltage sag and swell are the most frequent PQ problems that mainly occur in the distribution systems because of it causes circuit breaker tripping, failure of drive systems, shutdown for domestic and industrial equipment. The Dynamic Voltage Restorer (DVR) connected in series has magnificent dynamic capabilities and is a flexible solution for PQ problems. Ultra-Capacitors (UCAP) has ideal characteristics such as high power and low energy density essential for the mitigation of voltage sag and swell. In this proposed research voltage sag and voltage swell problem are improved by using the method of integration of Ultra Capacitor and Dynamic Voltage Restorer device. In this study UCAP was used as energy storage as it provides excessive power in a short time interval of time. Integrated DVR into Ultra Capacitor via bidirectional DC-DC converter which supports in presenting a rigid dc-link voltage and helps in compensating temporary voltage sag and voltage swell. The integrated UCAP-DVR is implemented at low voltage side of distribution transformer. PI Controller was used in DVR for power quality enhancement. The simulation results carried out by Matlab/Simulink verify the performance of the proposed method. In the proposed system the voltage sag is mitigated from 0.304 p.u to 1p.u and the voltage swell is compensated from 1.125p.u to 1p.u