• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2007.11a
• /
• pp.1066-1071
• /
• 2007

This case study refers to turbine-generator with retrofitted turbine rotor. Vibration problem occurring after the retrofit was mainly due to high vibration from exciter side. However, repeated test run and operation during scheduled maintenance caused high vibration from generator bearing, and post-overhaul test run before turbine vibration correction caused oil whip on the bearing. This case study shows how to analyze vibration condition of high turbine generator vibration detected during the post-overhaul test run and vibration condition of offline and online data to reflect it on establishing maintenance schedule and overhaul correction procedure. Vibration data could be acquired during steady load operation or even with varying speed and load. Each data is important for machinery condition evaluation. This case study shows that the vibration data during extreme condition is the key factor in analysis, which helps to find the machinery problem.

• Journal of KSNVE
• /
• v.8 no.6
• /
• pp.1062-1068
• /
• 1998

This paper describes the vibration characteristics of a high head pump-turbine runner. with nine blades and an outer diameter of 4.410 mm. of the pumped storage power plant. Mode shapes and natural frequencies were obtained by means of both the finite element analysis and modal testing. both in air and in water. The natural frequencies in air were calculated using the finite element method by ANSYS software. In order to confirm calculation results. the natural frequencies and mode shapes of the runner were measured using a hydraulic exciter both in air and in water. Natural frequencies of the pump-turbine runner were found at 174. 310 Hz in air, and at 107. 184 Hz in water. The first mode shape is flat plate mode with two nodal diameter and the second one is also flat plate mode with three nodal diameter. It can be shown that the natural frequencies of the pump-turbine runner in water is reduced approximately 40 ％ due to additional mass effect. Natural frequencies in air predicted by ANSYS software are in good agreement with test results.

• International Journal of Safety
• /
• v.4 no.2
• /
• pp.18-23
• /
• 2005

There are many electrical connections in the electric apparatus and most fires due to a fault contact result from a failure or misuse of electric apparatus and installation. The fault contact happens between electrical connections by the loose and the mechanical vibration. In this paper, we have investigated thermal and electrical properties of screwed electric contacts due to the mechanical vibration. The exciter was connected to a signal generator and power amplifier that provided the vibration frequency and amplitude. The vibration, temperature and voltage data were sent to a data acquisition system (DAQ). In the case that fault contact took place, the arc happened between the screwed electric contact and electric wire, heat due to the arc was transmitted to the adjacent insulators, for which the oxide could be generated more. In addition, a spark was generated and the insulator began to melt. Thus, the possibility of electrical fire became the highest in this case. Finally, when the fault contact takes place due to vibration, the hazard of an electric accident is very high.

• Proceedings of the KIPE Conference
• /
• 2008.06a
• /
• pp.136-138
• /
• 2008

The output voltage of synchronous generator is regulated constantly by field current control in excitation system. Most of ship generator exciter system uses the thyristor phase controlled rectifier. However this rectifier is difficult to realize that the speed control system because its control period is slower than MOSFET and IGBT type converter. Therefore, this paper deals with PMG(Permanent Magnet Generator) type digital excitation system using MOSFET for ship synchronous generator. The organization of this excitation system is very simple. When the generator is under the short circuit accident, the output voltage becomes zero state and AVR can not operate. Thus generator requires the function for flowing output current through CBS. The performance of the proposed system is evaluated on a 10kVA experimental prototype circuit in place of real ship generator.

• Journal of the Korean Society for Railway
• /
• v.9 no.2 s.33
• /
• pp.160-168
• /
• 2006

The major objective of this study is to investigate the effects and application of external post-tensioning method far steel plate girder bridge. It analyzed the mechanical behaviors of steel plate girder bridge with applying external post-tensioning on the finite element analysis, field test and laboratory test fur the lateral dynamic characteristics. As a result, the reinforcement of steel plate girder bridge the external post-tensioning method are obviously effective for the lateral dynamic response which is non-reinforced. The analytical and experimental study are carried out to investigate the post-tension force decrease lateral acceleration and deflection on steel plate girder bridge for serviceability. And the external post-tensioning method reduce dynamic maximum displacement(about $10{\sim}24%$), the increase of dynamic safety is predicted by adopting external post-tensioning method. From the dynamic test results of the servicing steel plate girder bridge, it is investigated that the change degree of natural frequency is very low with applying the external post-tensioning method The servicing steel plate girder bridge with external post-tensioning has need of the reasonable reinforcement measures which could be reducing the effect of lateral dynamic behavior that degradation phenomenon of structure by an unusual response characteristic and a drop durability.

• Journal of the Society of Naval Architects of Korea
• /
• v.33 no.2
• /
• pp.119-126
• /
• 1996

A hydraulic type active control system has been developed for the purpose of vibration suppression of ship superstructrures. The active mass of the developed system weighs about three tons and is designed to have ${\pm}5mm$ stroke below 10Hz. Thus maximum control force of the system is about 60kN. Performance test of the developed system has been carried out on a 4,400TEU contrainer carrier built in Samsung Heavy Industry Co., LTD. Through the exciter tests, it has been confirmed that the vibration levels of the superstructure can be reduced to about 20% of the uncontrolled levels near resonant frequency.

• 제어로봇시스템학회:학술대회논문집
• /
• 2005.06a
• /
• pp.498-501
• /
• 2005

This paper deals with the design and evaluation of the robust controller for a synchronous generator excitation system to improve the steady state and transient stability. The nonlinear characteristics of the system is treated as model uncertainties, and then the robust control techniques are introduced into the power system stability design to take into account these uncertainties at the controller design stage. The performance of the designed controller is examined by extensive non-linear time domain simulation. It is shown that the performance of the robust controller is superior to that of the conventional PI controller. This paper also proposes an improved digital exciter control system for a synchronized generator using a digitally designed controller with database. Results show that the proposed control system manifests excellent control performance compared to existing control systems. It has also been confirmed that it is easy for the proposed control system to implement digital control.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2006.05a
• /
• pp.98-101
• /
• 2006

As an alternative of conventional prestressed concrete (PSC) girders, various types of PSC girders are being developed and applied in bridge structures. Incrementally prestressed concrete girder is one of these newly developed girders. According to design concept, these new types of PSC girders have considerable advantages to reduce their self-weight and make spans longer. However, dynamic interaction between bridge superstructures and passing trains would be sometimes one of critical issues in these more flexible railway bridges. Therefore, it is very important to evaluate modal parameters of newly designed bridges before conducting dynamic analyses. In the present paper, a 25 meters long full scale PSC girder was fabricated as a test specimen and modal testing was carried out to evaluate modal parameters including natural frequencies and modal damping ratios at every prestressing stage. In the modal testing, a digitally controlled vibration exciter as well as an impact hammer is applied to obtain frequency response functions more exactly and the modal parameters are evaluated varying with construction stages. Prestressed force effects on changes of modal parameters are analyzed at every incremental prestressing stage.

• International Journal of Fuzzy Logic and Intelligent Systems
• /
• v.5 no.1
• /
• pp.83-87
• /
• 2005

This paper deals with the design and evaluation of the robust controller for a synchronous generator excitation system to improve the steady state and transient stability. The nonlinear characteristics of the system is treated as model uncertainties, and then the robust control techniques are introduced into the power system stability design to take into account these uncertainties at the controller design stage. The performance of the designed controller is examined by extensive non-linear time domain simulation. It is shown that the performance of the robust controller is superior to that of the conventional PI controller. This paper also proposes an improved digital exciter control system for a synchronized generator using a digitally designed controller with database. Results show that the proposed control system manifests excellent control performance compared to existing control systems. It has also been confirmed that it is easy for the proposed control system to implement digital control.

• The Transactions of the Korean Institute of Electrical Engineers B
• /
• v.50 no.4
• /
• pp.164-169
• /
• 2001

This paper deals with comparison of characteristics of continuous-sheet type low-Tc superconducting (LTS) power supply and discrete-sheet type LTS power supply. These characteristics have been analyzed through experiments. These power supplies consist of two exciters, a rotor, a stator, and a LTS load. A continuous-sheet type has a single continuous niobium (Nb) sheet attached to the inner surface of on the stator. In the case of discrete-sheet type, four separated Nb sheets are used. this experiment is using 1.81 mH LTS magnet load and maximum 30 A dc exciter current. A discrete-sheet type is expected to produce much better pumping rate than a continuous-sheet type. The experimental observations have been compared with the theoretical predictions. In this experiment, the maximum pumping-current has reached about 926 A.