• Proceedings of the KSR Conference
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• 2008.06a
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• pp.2035-2039
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• 2008

This paper described an on-line condition monitoring device for rotating machines by measurement of unbalance current due to insulation deterioration. The device consists of a zero-phase current transformer (ZCT), a low-noise amplifying circuit, and a microprocessor unit. The prototype device measures current of $500\;{\mu}A\;{\sim}\;30\;mA$ in frequency ranges from 10 Hz to 3 kHz. An application experiment was carried out on 3-phase induction motors and we could measure current changes caused by a short-circuited turn.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.27 no.5
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• pp.26-32
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• 2013

The LED has the proportional characteristic between the flux of light and its current and has caused voltage-current deviation on production process. Thus the unbalancing of each LED strings current occurred by its characteristic deviation. This unbalancing reduce a uniformity of the flux of light. Therefore, we researched to design method the LED driver based on DSP and the balancing transformer for a LED current balancing. These are applied to 50W LED module consist of 4 parallel strings. We analyzed the reduction of LED currents unbalance by experimental result from each method.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.54 no.3
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• pp.134-140
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• 2005

Most of the loads in industrial power distribution systems are usually balanced and connected to three power systems. However, in the user power distribution systems, partial loads are single & three phase and unbalanced, generating voltage unbalance by the impedance mismatching. Voltage unbalance has detrimental effects on three-phase induction motors, including over heating, line-current unbalance, derating, torque pulsation, low efficiency, etc. This paper presents a scheme on operation states of a three-phase induction motor under the unbalanced voltages with harmonics components. Three-phase voltages applied to the stator winding of the studied induction motor are controlled by respectively adjusting not only fundamental but also harmonics components. Harmonic components at the voltage unbalanced factor(VUF) of the three-phase source voltages can then be examined the different values of VUF on machine's operation characteristics.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.52 no.10
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• pp.491-500
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• 2003

Most of the loads in industrial power distribution systems are balanced and connected to three wires power systems. However, in the user power distribution systems, most of the loads are single & three phase and unbalanced, generating a large amount of non-characteristic harmonics. With the advent of power electronics and proliferation of non-linear loads in industrial power applications, power harmonics and their effects on power quality are a topic of concern. Harmonics by the unbalance voltage and non-linear loads, cause the increase of machine loss and heating. In order to allow current harmonic compensation, a filter must be installed. This paper describes the performance of passive filter under the voltage unbalance and non-linear load.

• Proceedings of the KIEE Conference
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• 1997.07c
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• pp.787-789
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• 1997

This paper presents an algorithm to estimate voltage unbalance which is due to railway demand, and which is most troublesome to polyphase motors. For the sake of accuracy, a circuit analysis procedure is introduced in this algorithm. The circuit analysis procedure enables the algorithm to produce a voltage and current profiles as well as unbalance indices. The proposed algorithm is applied to the test system(standard AT fed system) for the analyses of unbalance phenomena. The result shows that the algorithm is useful in the field of railway system planning.

• Proceedings of the KIEE Conference
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• 2005.10a
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• pp.184-190
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• 2005

The railway characteristic, which is concerned, as most utilities is unbalance produced by the large single-phase loads. Here are two theoretical concerns associated with unbalanced loads. First, generator rotor heating resulting from unbalanced current flow, Second, there is the possibility of motor overheating in industrial plants, due to the unbalanced voltage. Therefore, the exact assessment of the voltage unbalance must be carried out preferentially as well as load forecast at stages of designing and planning for the electric railway system. This paper proposes a new analysis model to more effectively estimate voltage unbalance. Numerous distributed circuits in the electric railway system are composed by components. The entire system can be easily modeled by the combination of four-port representation of each component in parallel and/or series. Simulation results using the model are compared with field data, and it verifies the accuracy of the proposed model.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.53 no.2
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• pp.58-64
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• 2004

Most of the loads in industrial power distribution systems are balanced and connected to three power systems. However, in the user power distribution systems, most of the loads are single & three phase and unbalanced, generating voltage unbalance. Voltage unbalance is a condition in a polyphase system in which the rms values of the line-to-line voltages or the phase angles between consecutive line-to-line voltages, are not all equal. Slight voltage unbalance generates a disproportionately high current unbalance at the motor stator winding. This paper presents a scheme on operation states of a three-phase induction motor under unbalanced voltages. The three-phase voltages applied to the stator winding of the studied induction motor are controlled by respectively adjusting the magnitude and phase angle of each phase. The voltage unbalanced factor(VUF) of the three-phase source voltages can then be varied to examine the different values of VUF on machine's operation characteristics.

• Proceedings of the KIPE Conference
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• 2001.10a
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• pp.586-590
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• 2001

In this paper, a novel control scheme compensating source voltage unbalance and harmonic currents for hybrid active power filters is proposed, where no low/high-pass filters are used in compensation voltage composition. The phase angle and compensation voltages for source harmonic current and unbalanced voltage components are derived from the positive sequence component of the unbalanced voltage set, which is simply obtained by using digital all-pass filters. Since a balanced set of the source voltage obtained by scaling the positive sequence components is used as reference values for source current and load voltage, it is possible to eliminate the necessity of low/high-pass filters in the reference generation. Therefore the control algorithm is much simpler and gives more stable performance than the conventional method. In addition, the source harmonic current is eliminated by compensating for the harmonic voltage of the load side added to feedback control of the fundamental component.

• Proceedings of the KIPE Conference
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• 2004.07b
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• pp.787-790
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• 2004

In this paper, a novel control scheme compensating for source voltage unbalance and current harmonics and power factor correction in unified active power filter systems combined with shunt passive filters is proposed, where no low/high-pass filter are used in deriving the reference voltage for compensation. Using digital all-pass filters, the phase angle and the reference voltages compensating for harmonic current and unbalanced voltage are derived from the positive sequence component of the unbalanced voltage. The amplitude of d-axis current in a series filter is controlled as zero for power factor correction. The validity of the proposed control scheme has been verified by experimental results.

• Proceedings of the KIEE Conference
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• 2004.04a
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• pp.103-105
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• 2004

In this paper, a novel control scheme compensating for source voltage unbalance and current harmonics and power factor simultaneously in unified active power filter systems combined with shunt passive filters is proposed, where no low/high-pass filter are used in deriving the reference voltage for compensation. Using digital all-pass filters, the phase angle and the reference voltages compensating for harmonic current and unbalanced voltage are derived from the positive sequence component of the unbalanced voltage. The amplitude of d-axis current in a series filter is controlled as zero for power factor correction. The validity of the proposed control scheme has been verified by experimental results.