Takehiko Machida

A New Method to Eliminate AC Harmonic Currents by Magnetic Flux Compensation-Considerations on Basic Design

A new method of eliminating ac harmonic current is proposed, which is based on the principle of the magnetic flux compensation in a transformer core. By means of the new method, abnormal harmonics as well as normal harmonics can effectively be dealt with. Considerations on the basic design of the new method are given.

Improving Transient Stability of AC System by Joint Usage of DC System

Studies of stability problems are expected to be developed in parallel ac-dc systems. Results obtained by the experiment on the artificial ac and dc transmission facilities were: the more the dc power of steady state compared with the ac power, the more the transient stability is improved. The transient stability is improved if the dc power is rapidly increased in case of faults in the ac system. The 3-phase short circuit at the sending ac system results in a serious decrease of the dc power. This decrease causes the generator to accelerate at the sending end. Two control methods for the countermeasure are presented.

Study of the Effect of the DC Link on Frequency Control in Interconnected AC Systems

This paper presents a control effect of automatic frequency ratio control (AFRC) on an HVDC transmission to the AFC on ac systems when AFRC is applied to a random load disturbance in a steady state. The analysis of dynamic response of an ac-dc transmission system has been made by an analog computer. The frequency-improving and reduction effects of the output power of regulating power stations by AFRC are statistically analyzed by a digital computer.

A Method to Detect the Deionization Margin Angle and to Prevent the Commutation Failure of an Inverter for DC Transmission

A method is suggested to detect directly the deionization margin angle and to prevent the commutation failure of an inverter. The deionization margin angle is detected by anode- cathode voltage of a valve and ac phase voltage. The method to prevent the commutation failure, namely the one to hold the critical deionization angle keeps a necessary deionization angle for the alternating voltage drop, thus enabling safer valve operation.

A Method of Automatic Frequency Ratio Control by a DC System

A method of automatic frequency ratio control (AFC) by a dc system is suggested. This control also provides a tie line bias control action (TBC) in ac?dc systems, and can cooperate with the AFC and TBC in ac systems. The operating principle is that the frequency deviations of two ac systems are detected and its controller adjusts the dc power for constant frequency control. A logic circuit is provided in the controller to give the signals to regulate the governors of the generators. By the proper adjustment of the sensitivity of dc power, the dead band of frequency deviations, and the regulation sensitivity of the governors, the frequency control in the ac?dc system can be acheived quite satisfactorily.

Transient Analysis of Harmonic Current Elimination Method by Magnetic Flux Compensation

This paper presents the transient analysis of the new harmonic current elimination method by analog simulation. The analysis has made clear that the new method has the desirable cancellation effect of harmonic currents both in the steady-and transient-state.

Analog Computer Study of Automatic Frequency Ratio Control on an HVDC Transmission System

A method has been developed to simulate an automatic frequency control system in ac-dc power transmission on an analog computer. As an example of an ac-dc system a model of Sakuma frequency changer, between Tokyo Electric Power Co. system (50 Hz) and Chubu Electric Power Co. system (60 Hz), is studied in detail. Three new methods of automatic frequency ratio control (AFRC) by dc transmission are considered and compared. The variation of frequencies in the ac systems and the dc power change due to a step load increase in the Chubu power system are examined. These frequency variations and power change are used to optimize the parameters of the AFRC devices.

Control and Protective System of HVDC Transmission by HVDC Simulator (Thyristor Converter)

Worldwide research and development of the high-voltage thy- ristor converter has been actively promoted recently. In order to apply the thyristor converter to a present-day power system, it is necessary to develop a control and protective system suitable for the system and to study an operating ability when troubles develop in the converter and power system. To solve this problem, we manufactured a HVDC simulator by using a thyristor converter simulating a practical converter and we newly developed the control and protective system.