Recently, the energy demand and supply situation in the Republic of Korea (ROK) has been largely affected by the fluctuations in the energy markets around the world. Such a situation has provided a basis for requiring improvements to power plant facilities. The automatic generator voltage control systems in large-scale power plants are adopting a rapid-response static excitation method to improve the transient stability. A domestic commercially developed large-scale triple-redundant excitation system is currently operated by the 1000 MW-class nuclear power plant and its efficiency has been verified at the same site. However, such a system is too costly for smaller power plants so that a reliable and low-cost redundant digital excitation control system was developed and introduced in this study to resolve the cost problem. The system has improved its stability and reliability at the same time through double (redundant) configuration. Additionally, the system's performance was put to the test by conducting a series of control function tests after applying it to the gas turbine used in a thermal power station. This study includes the development of system hardware, simulations as well as on-site experiments and each element was validated as a result. Also, the study discusses and validates the method used for replacing the protective relays at the Kanudi power plant operating in Papua New Guinea. The replacement of 27 and 81 protective relays at the existing power plant was carried out as they did not function properly. New relays were installed after removing the power supply in the existing panel. The individual power output sections of new relays were connected in parallel with the existing properly functioning relays, as previous protective relays had only allowed monitoring without outputting the contents. Thus, the new protective system was designed to enable both existing and new relays to carry out the detection function. It was validated that the replacement was successful. The new system with the new relays is performing properly by protecting its power generator and preventing further accidents.

Since modeling and simulation are the two most effective tools that can be used in the design or analysis process, they play a vital role in developing such system. In many cases, they are the only possible means of making a safe engineering decision for a new concept of process for a large-scale system. Elsewhere, they are used as a critical element in the analysis of energy systems or to suggest a method of developing a novel and effective energy system model. Thus, in this study, simulations and test bed experiment were carried out to assess a low-power digital excitation system in order to validate its effectiveness. The excitation systems currently used by most of the power stations in the Republic of Korea were installed during the 1970s or 1980s. Unfortunately, it is difficult to seek technical assistance for them as they depend on foreign technologies, requiring a large sum to be paid when requesting one or more engineers to be dispatched. As such, technical updates have always been made by foreign companies, since it is not easy to make modifications to the system without the help of the original system developer. The technology developed in this study was designed to address such problem. The inability to conduct a test for an actual system can be solved by using a power system analysis program to analyze the characteristics of the controller. The study confirmed the system’s effectiveness, and the Test Bed was proven to be flexible and adequate for the experiment. The proposed excitation system is expected to increase the stability and economic effect of the system by optimizing existing systems. In the future, the authors plan to focus on student education by establishing an education system that allows students to learn about the digital excitation system and its simulation.

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In this paper an excitation system which is effective for improving the start-up characteristic of synchronous motors has been discussed in this study. Excitation system is a system that maintains/controls the voltage of an output terminal(s) by supplying direct current to a field coil. The excitation control system of synchronous motor should be able to achieve stabilization (i.e., power factor 1) as rapidly possible by controlling excitation current in accordance with the control mode applied. When a direct current is passed through the field winding of the rotor, the rotation is restrained in the rotor. When the