• Journal of Power Electronics
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• v.15 no.1
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• pp.288-297
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• 2015

This paper presents a novel approach to diagnose interturn insulation faults in three-phase transformers that operate at different loading conditions. This approach is based on the loci of instantaneous symmetrical components and requires the measurement of three input primary winding currents and voltages to diagnose faults in the transformer. The effect of unbalance supply conditions, load variations, constructional imbalance, and measurement errors when this methodology is used is also investigated. Wing size or length determines the loading on the transformer. Wing travel and area determine the degree of severity of fault. Experimental results are presented for a 400/200 V, 7.5 kVA transformer to validate this method.

• Proceedings of the KIEE Conference
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• 2006.10b
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• pp.147-153
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• 2006

Voltage unbalance will be generated by the load unbalance operation such as combination operation of single & three phase load and current unbalance will be more severe by the deteriorated voltage quality. Under the these unbalance conditions, all power electronic converters used in different types of electronic systems can increase harmonic disturbances by injecting harmonic currents directly into the feeder grid of three phase 4-wire. Harmonic current may cause torque to decrease. it may also overheat or become noisy and torque oscillation in the rotor can lead to mechanical resonance and vibration. This paper presents a scheme on the characteristics of induction motor under the combination of linear & non-linear loads at the three phase 4-wire power distribution system by the unbalance and harmonic components. It was able to confirm that the number of torque pulsation decreased and torque ripple values increased by the harmonics that reduction was difficult by five harmonics filters at additional driving time of single-phase non-linear load.

• The Transactions of the Korean Institute of Power Electronics
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• v.6 no.6
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• pp.514-524
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• 2001

Conventional average power theory has been used to design and control active power filters But compensating reference currents of active power filters calculated by conventional average power theory are definitively influenced by three phase source voltage conditions such as unbalance or distortion. This paper presents a new average power algorithm for active power filters which can detect symmetrically equally active or fundamental reactive currents in each phase based on decomposition of fundamental reactive component and harmonics under unbalanced power conditions. The effectiveness of the proposed algorithm is demonstrated by MATLAB/SIMULINK simulation and experimental results for a three wire distribution system with 15% unbalanced source voltages.

• Journal of Power Electronics
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• v.13 no.5
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• pp.884-895
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• 2013

In this paper, the Fourier-based PLL (Phase-locked Loop) is introduced with a new structure, capable of selective harmonic detection in single and three-phase systems. The application of the FB-PLL to harmonic detection is discussed and a new model applicable to three-phase systems is introduced. An analysis of the convergence of the FB-PLL based on a linear model is presented. Simulation and experimental results are included for performance analysis and to support the theoretical development. The decomposition of an input signal in its harmonic components using the Fourier theory is based on previous knowledge of the signal fundamental frequency, which cannot be easily implemented with input signals with varying frequencies or subjected to phase-angle jumps. In this scenario, the main contribution of this paper is the association of a phase-locked loop system, with a harmonic decomposition and reconstruction method, based on the well-established Fourier theory, to allow for the tracking of the fundamental component and desired harmonics from distorted input signals with a varying frequency, amplitude and phase-angle. The application of the proposed technique in three-phase systems is supported by results obtained under unbalanced and voltage sag conditions.

• Journal of Power Electronics
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• v.16 no.5
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• pp.1869-1883
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• 2016

In recent years, some converter structures and analyzing methods for the voltage regulation of stand-alone self-excited induction generators (SEIGs) have been introduced. However, all of them are concerned with the three-phase voltage control of three-phase SEIGs or the single-phase voltage control of single-phase SEIGs for the operation of these machines under balanced load conditions. In this paper, each phase voltage is controlled separately through separated converters, which consist of a full-bridge diode rectifier and one-IGBT. For this purpose, the principle of the electronic load controllers supported by fuzzy logic is employed in the two-different proposed converter structures. While changing single phase consumer loads that are independent from each other, the output voltages of the generator are controlled independently by three-number of separated electronic load controllers (SELCs) in two different mode operations. The aim is to obtain a rated power from the SEIG via the switching of the dump loads to be the complement of consumer load variations. The transient and steady state behaviors of the whole system are investigated by simulation studies from the point of getting the design parameters, and experiments are carried out for validation of the results. The results illustrate that the proposed SELC system is capable of coping with independent consumer load variations to keep output voltage at a desired value for each phase. It is also available for unbalanced consumer load conditions. In addition, it is concluded that the proposed converter without a filter capacitor has less harmonics on the currents.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.53 no.7
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• pp.375-381
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• 2004

This paper describes a three-winding transformer protective relaying algorithm based on the ratio of increments of flux linkages (RIFL). To minimize the approximation errors, the algorithm uses integration approximation. The RIFL of the two windings is equal to the turns ratio for all operating conditions except for an internal fault. For a single-phase and three-phase transformer containing the wye-connected windings, the increments of flux linkages (IFL) are calculated. For a three-phase transformer containing the delta-connected windings, the difference of IFL between the two phases are calculated to use the line currents, because the winding currents are practically unavailable. Their ratios are compared with the turns ratio. The comparative study between the proposed and differential approximation methods was conducted. The test results show that the algorithm can reduce the errors resulting from the conventional methods.

• The Transactions of the Korean Institute of Power Electronics
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• v.25 no.2
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• pp.127-132
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• 2020

In this study, single-phase and three-level boost converters applied to the photovoltaic system were compared and analyzed in terms of efficiency and power density according to the input voltage and load conditions. For accurate analysis of efficiency, the losses in each device of the single-phase and three-level boost converters were derived using mathematical equations and simulations by using the PSIM thermal module. Then, the losses were compared with the efficiency confirmed through the actual experiments. Results confirmed that the efficiency and power density can be improved by applying the three-level boost converter to the system according to the selection of the switching frequency.

• The Transactions of the Korean Institute of Power Electronics
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• v.28 no.1
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• pp.22-29
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• 2023

A grid-connected inverter can be used in grid-connected or stand-alone modes. Generally, a grid-connected inverter operates in a grid-connected mode, but the inverter operates in stand-alone mode if grid faults occur. In the stand-alone mode, the grid-connected inverter must supply electric power to a critical load that needs to receive stable power even though grid faults occur. Generally, three-phase loads are used as critical loads, but a single phase is configured in some cases. In these conditions, the critical load is required to unbalance the load power consumption, which makes the three-phase load voltage unbalancd. This unbalanced voltage problem can cause fatal problems to the three-phase critical loads, and thus must be addressed. Hence, this paper proposes an algorithm to solve this unbalanced voltage problem by the individual phase current control. The proposed method is verified using Psim simulation and experiments.

• Proceedings of the KIEE Conference
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• 2003.11a
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• pp.341-344
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• 2003

This paper proposes a tree-winding transformer protective relaying algorithm based on the ratio of increment of flux linkages (RIFL). The RIFL of the two windings is equal to the turns ratio for all operating conditions except an internal faults. For a single-phase transformer and three-phase transformer containing the wye-connected windings, the increments of flux linkages are calculated. for a three-phase transformer containing the delta-connected windings, the difference of the increments of flux linkages between the two phases are calculated using the line currents, because the winding currents are practically unavailable. Their ratios are compared with the turns ratio. The results of various tests show that the algorithm successfully discriminates internal faults from normal operation conditions such as magnetic inrush, overexcitation and external faults. The algorithm can not only detect internal winding faults, but reduce the operating time of a relay.

• Structural Engineering and Mechanics
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• v.90 no.6
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• pp.569-575
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• 2024

The objective of this study is to investigate the influence of an inclined load, location, and time on the behavior of a fiber-reinforced visco-thermoelastic half-space. The displacement, stress, and temperature distributions are derived from the normal mode analysis. The problem is analyzed using a three-phase-lag model. MATLAB programming is employed to ascertain the physical fields with appropriate boundary conditions and to perform numerical computations. The outcomes are then examined with different inclination loads, time, and location settings.