• Nuclear Engineering and Technology
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• v.50 no.1
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• pp.190-202
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• 2018

Maintaining the integrity of the major equipment in nuclear power plants is critical to the safety of the structures. In particular, the soundness of the piping is a critical matter that is directly linked to the safety of nuclear power plants. Currently, the limit state of the piping design standard is plastic collapse, and the actual pipe failure is leakage due to a penetration crack. Actual pipe failure, however, cannot be applied to the analysis of seismic fragility because it is difficult to quantify. This paper proposes methods of measuring the failure strain and deformation angle, which are necessary for evaluating the quantitative failure criteria of the steel pipe elbow using an image measurement system. Furthermore, the failure strain and deformation angle, which cannot be measured using the conventional sensors, were efficiently measured using the proposed methods.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.45 no.3
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• pp.352-357
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• 1996

Recently, Permanent Magnet Synchronous Motor(PMSM) drives are widely used for industrial applications due to its high efficiency and high power factor control strategy. PMSM generally have two classifications such as the SPMSM(Surface Permanent Magnet Synchronous Motors) and IPMSM(Inter Permanent Magnet Synchronous Motors). IPMSA has economical merits over SPMSM in higher speed range, mechanical robustness, and higher power rate by the geometric difference. The maximum torque operation in IPMSM is realized by the current angle control which is to utilize additional reluctance torque due to a rotor saliency. In traction, spindle and compressor drives, constant power operation with higher speed range are desirable. This is simply achieved in the DC motor drives by the reduction of the field current as the speed is increased. However, in the PMSM, direct control of the magnet flux is not available. The airgap flux can be weakened by the appropriate current angle control to demagnetize. In this paper, the control method of optimal current vector in IPMSM is described in order to obtain the maximum torque or maximum output with the speed and load variations. The applied algorithm is realized by the proto system with torque and speed control Experimental results show this approach is satisfied for the high performance servo applications. (author). 6 refs., 9 figs., 1 tab.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.54 no.7
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• pp.345-351
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• 2005

An out-of-step condition results from the loss of the synchronism of the generators. A disturbance in a power system causes the generator angle to oscillate. When there is a severe disturbance such as a heavy current fault loss of major generation or loss of a large block of load, the oscillation can be severe and even increase largely and finally the out-of-step condition may un. During the power swing and out-of-step conditions, the apparent impedance at a relay location changes, and the power flow also changes as the angle difference is varied. This paper presents a method to analyze the trajectory of complex power during a power swing and out-of-step condition. The trajectory of the complex power is analyzed when a power swings and a fault occurs. Moreover, the complex power is analyzed when the ratios between the voltages at both sides and the line impedances are changed. These methods are verified through simulation using the ATP/EMTP MODELS.

• Journal of Power Electronics
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• v.10 no.1
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• pp.85-90
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• 2010

In this paper the effects of a Static Synchronous Series Compensator, which is constructed with a 48-pulse inverter, on the power demand from the grid are studied. Extensive simulation studies were carried out in the MATLAB simulation environment to observe the compensation achieved by the SSSC and its effects on the line voltage, line current, phase angle and real/reactive power. The designed device is simulated in a power system which is comprised of a three phase power source, a transmission line, line inductance and load. The system parameters such as line voltage, line current, reactive power Q and real power P transmissions are observed both when the SSSC is connected to and disconnected from the power system. The motivation for modeling a SSSC from a multi-pulse inverter is to enhance the voltage waveform of the device and this is observed in the total harmonic distortion (THD) analysis performed at the end of the paper. According to the results, the power flow and phase angle can be controlled successfully by the new device through voltage injection. Finally a THD analysis is performed to see the harmonics content. The effect on the quality of the line voltage and current is acceptable according to international standards.

• The Transactions of the Korean Institute of Power Electronics
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• v.14 no.4
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• pp.278-284
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• 2009

This paper presents a firing angle controller of a thyristor converter for DC power supply using PID controller with parallel data loop to improve the dynamic response. The proposed parallel data loop for firing angle controller of 3-phase semi-converter, generates pre-measured firing angle according to reference voltage and load current. With the approximated firing angle according to operating conditions, the output voltage can fast keep the reference value with small voltage error. And the PID controller compensates the output voltage error from the firing angle of parallel data loop. In order to reduce the sudden changing of the data from current ripple, a simple digital low pass filter is used to determine the output data. The proposed control scheme is verified by the experimental test of a practical 50[A] grade thyristor converter system.

• The Transactions of the Korean Institute of Power Electronics
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• v.6 no.2
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• pp.132-140
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• 2001

A universal motor is a small dc series machine motor that is designed to operate from an ac machine. The characteristics of universal motors are high no-load and staring torque. Because of the high operating speed, the size of these motors for a given hp rating is typically smaller that other fractional hp ac machine, making it ideal for hand-held tools and appliances where weight, compactness, and speed are importance factors. A phase-angle control with AC drive system gains a high popularity due to their simple implementation, but contains the disadvantage of their poor input power factor, subharmonic current. Pulse width modulation control with DC drive systems increase the power factor as without delay phase angle. This paper analyzed the subharmonic characteristics of the phase angle control system that is controlled by zero voltage crossing similar to traditional method, and the dc chopper system that is used PWM.

• Tribology and Lubricants
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• v.34 no.1
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• pp.16-22
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• 2018

Cylindrical turbine guide bearings (TGBs) with simple plain pads have conventionally been used in vertical hydro-power turbine-generator applications in order to provide turbine runner shafts with smooth rotation guides and supports. To overcome low-load/low-eccentricity performance drawbacks, such as very low film stiffness and lack of design credibility in the stiffness values themselves, of conventional cylindrical TGBs, the introduction of a rotational-directional leading-edge taper to each partitioned pad, simply pad leading-edge taper, has been found to be very effective in enhancing their design-application availability and usefulness. In this study, we investigate the effects of taper angle and length for given taper heights in detail in order to systematically establish the effectiveness of design on the performance improvement of vertical hydro-power application cylindrical TGBs with pad leading-edge tapers. The analysis results with $4-Pad{\times}1-Row$ cylindrical TGBs show that the lubrication performance of the cylindrical TGBs is optimized with an approximate taper angle ratio of 0.8 and taper length ratio of 0.9. We conclude that the introduction of pad leading-edge tapers along with the optimization of taper designs can be very effective in improving the overall operation reliability of cylindrical TGBs and the rotordynamic characteristics of vertical hydro-power turbine-generator rotor-bearing systems as well, to which the TGBs are applied.

• Proceedings of the KIEE Conference
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• 2002.07b
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• pp.1358-1360
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• 2002

This paper presents a modeling and simulation of a utility-connected wind energy conversion system with a link of a rectifier and an inverter. It discusses the maximum power control algorithm for the wind turbine and presents the relationship of wind turbine output, rotor speed, power coefficient, tip-speed ratio and wind speed when the wind turbine is operated under the maximum power control algorithm. The control objective is to extract maximum power from wind and transfer the power to the utility. This is achieved by controlling the pitch angle of the wind turbine blades. Pitch control method is mechanically complicated, but the control performance is better than that of the stall regulation method. The simulation results performed on MATLAB will show the variation of generator's rotor speed, pitch angle, and generator output.

• International Journal of Control, Automation, and Systems
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• v.3 no.spc2
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• pp.346-354
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• 2005

This paper presents a new approach to Thyristor Controlled Phase Shifter (TCPS) control. In this paper we have proposed a nonlinear coordinated generator excitation and TCPS controller to enhance the transient stability of a power system. The proposed controller is able to control three main parameters affecting a.c. power transmission: namely excitation voltage, phase angle and reactance in a coordinated manner. The TCPS is located at the midpoint of the transmission line. A nonlinear feedback control law is proposed to linearize and decouple the power system. The design of the proposed controller is based on the local measurements only. Simulation results have been shown to demonstrate the effectiveness of the proposed controller for the enhancement of transient stability of the power system under a large sudden fault.

• Journal of Institute of Control, Robotics and Systems
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• v.13 no.1
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• pp.1-5
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• 2007

Many nonlinear controllers for the power system are based on nonlinear models involving the power angle as an element of the state, and therefore the reference value for the power angle is needed. As this reference value is not generally available, it is difficult to apply such nonlinear control methods in practice. To deal with this problem, we present an input-output feedback linearizing control scheme by selecting the output as a combination of the squared voltage and the relative frequency. It is shown that the internal dynamics are locally stable with controllable damping, and that the frequency remains bounded for all time. Simulations illustrate the effectiveness of the proposed method.