AZOJETE VOL 16 NO 2 by Ifeanyichukwu Onwuka
Papers by Ifeanyichukwu Onwuka
A single-phase nine-level inverter with a novel pulse width modulation (PWM) scheme for R-L load ... more A single-phase nine-level inverter with a novel pulse width modulation (PWM) scheme for R-L load is presented in this paper. Four triangular carrier signals that are identical to each other with an offset that is equivalent to the amplitude of the sinusoidal reference signal were used to generate the PWM signals. The inverter is capable of producing nine levels of output-voltage levels (Vdc, Vdc/4, Vdc/2, 3Vdc/4, 0,−Vdc,−Vdc/4,−Vdc/2, 3Vdc/4) from the dc supply voltage. In this paper the dc supply is obtained from ac supply which is boosted to a higher amplitude of dc voltage using dc to dc converter. In this paper, Matlab/ Simulink software is used for the system simulation. Hence, the output load voltage, current and FFT plots are obtained. This paper is focused on minimizing the number of semiconductors devices, weights, and costs for a higher number of output voltage levels. Index Terms: Boost converter, modulation index, multilevel inverter, pulse width-modulation (PWM), total ...
Zenodo (CERN European Organization for Nuclear Research), Mar 13, 2023
Faults occur in substations and the effects of these faults range from damage of electrical equip... more Faults occur in substations and the effects of these faults range from damage of electrical equipment connected to the substation to electrocution of personnel operating the substations. When protective devices fail in their operations after fault occur, mitigating the fault effects can be the only option of saving the lives of the personnel and equipment around the fault location in the substation. A balanced three phase fault, line-to-ground (LG) fault, line-to-line (LL) fault and double line to ground (LLG) fault at the primary and secondary of the respective transformers in the 80 MVA 132/33 kV Ohia Transmission substation were simulated in Electrical Transient Analyzer Program (ETAP). Ranges of fault current flow into the bus of the primary of the respective transformer causing corresponding arc flash energy in calories/cm2, arc flash boundary in centimeters and arc flash distance in centimeters, appropriate recommendations of respective levels of radiating personnel protective equipment (PPE) amongst levels A, B, and D based on the results were made in accordance with National Fire Protection Association (NPFA) 70E2009/2012. The results recorded show the highest fault current flow of 451.01 kA in the primary of the second transformer as a result a three-phase fault and LG fault causing 8.962 cal/cm2 energy to radiate within an arc flash boundary of 76.50 cm (2.51 ft.) given an arc flash distance of 9.75 cm (3.840 inches) and a corresponding choice level D PPE. Further mitigation of the faults effects can be done with a well-designed earth grid with touch potential of 797.7 volts, step potential of 938.5 volts and earth resistance of 2.9 ohms all being within the IEEE tolerable range. Mitigating faults effects can also be achieved using a well-designed fault current limiter (FCL) with normal operating condition of negligible impedance and maximum impedance during fault as 70 ohms and 1200 ohms respectively for the secondary sides of superconducting fault current limiter (SFCL).
NIPES Journal of Science and Technology Research, 2023
Faults occur in substations and the effects of these faults range from damage of electrical equip... more Faults occur in substations and the effects of these faults range from damage of electrical equipment connected to the substation to electrocution of personnel operating the substations. When protective devices fail in their operations after fault occur, mitigating the fault effects can be the only option of saving the lives of the personnel and equipment around the fault location in the substation. A balanced three phase fault, line-to-ground (LG) fault, line-to-line (LL) fault and double line to ground (LLG) fault at the primary and secondary of the respective transformers in the 80 MVA 132/33 kV Ohia Transmission substation were simulated in Electrical Transient Analyzer Program (ETAP). Ranges of fault current flow into the bus of the primary of the respective transformer causing corresponding arc flash energy in calories/cm2, arc flash boundary in centimeters and arc flash distance in centimeters, appropriate recommendations of respective levels of radiating personnel protective equipment (PPE) amongst levels A, B, and D based on the results were made in accordance with National Fire Protection Association (NPFA) 70E2009/2012. The results recorded show the highest fault current flow of 451.01 kA in the primary of the second transformer as a result a three-phase fault and LG fault causing 8.962 cal/cm2 energy to radiate within an arc flash boundary of 76.50 cm (2.51 ft.) given an arc flash distance of 9.75 cm (3.840 inches) and a corresponding choice level D PPE. Further mitigation of the faults effects can be done with a well-designed earth grid with touch potential of 797.7 volts, step potential of 938.5 volts and earth resistance of 2.9 ohms all being within the IEEE tolerable range. Mitigating faults effects can also be achieved using a well-designed fault current limiter (FCL) with normal operating condition of negligible impedance and maximum impedance during fault as 70 ohms and 1200 ohms respectively for the secondary sides of superconducting fault current limiter (SFCL).
University of Nigeria, Nsukka, 2018
1.0 Introduction In large grinding mills such as the mineral and cement industries where twin mot... more 1.0 Introduction In large grinding mills such as the mineral and cement industries where twin motor drives are used, the two major challenges which limit the use of two synchronous motors connected direct on line and mechanically coupled to the same mill are motor overheating – due to the fact that the two motors do not share the mill load equally, and the increased rate of wear of the gear teeth on the account of non alignment of the rotor positions of the two motors (Hoffmann and Trasky, 1972). The reason for these problems has been attributed to small inaccuracies in tolerances and manufacturing circumferential error, pitch diameter error, or rim face run out on the girth gear. Again, due to manufacturing tolerance or difference in wear, the girth gears do not mesh with the pinions exactly the same way, and so the rotors of the motors are not rotated at the same relative angular positions at the time of starting or during running (Valentine et al., 1977). A similar issue is small...
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AZOJETE VOL 16 NO 2 by Ifeanyichukwu Onwuka
Papers by Ifeanyichukwu Onwuka