Takaaki Kai

Study for the performance of high speed switchgear for protection of in-house generation system

In large industrial plants and factories, it has become popular to use in-house generation systems connected to utility power systems. Especially, co-generation systems have been introduced to many consumers such as hotels and hospitals. However, when a fault occurs on the transmission line, voltage on the internal power system drops instantaneously until its clearance. To enhance the loads reliability, a new switchgear system has been developed. This equipment consists of static switchgear applying thyristor, disconnecting switches, and a control circuit. This control circuit has functions to detect voltage drops and voltage synchronization. This equipment is installed in series with the circuit breaker which connects the buses of the consumers own power generation system, and executes high speed tripping and reclosing when the voltage on the consumers bus drops instantaneously. In this paper, artificial test results of this equipment is presented. From these results, it is confirmed that this equipment can restrain voltage drop of the important loads within one cycle by means of tripping the short circuit current within one cycle when the voltage drops under the setting value. Then, comparison between measured results and simulated results by EMTP is represented. From this comparison, it is confirmed that verification of this equipments performance using EMTP is effective. Then, influence of voltage drop (20% and 50%) on loads is investigated by simulating transient voltage change of the generator.

A simplified fault currents analysis method considering transient of synchronous machine

The transient fault currents of a synchronous machine fault were mathematically analyzed by using the two-reaction theory, Clarkes components, etc. However, the methods were extremely complicated and the transient fault analysis of synchronous machine with a load was not carried out except for three-phase faults. This paper proposes a simplified fault currents analysis method considering synchronous machine transients. The method is based on the symmetrical components scheme. The advantages of the method are that the transient analysis is able to be accomplished more easily than the conventional method when the fault point is a synchronous machine terminal or a transmission line. The accuracy of the method is confirmed by comparing the analysis results with Electro-Magnetic Transient Program (EMTP) digital simulations.

Analysis of an adjustable speed rotary condenser for power system stabilization

Over the last five to ten years, significant progress has been made in high-power semiconductor devices and in their practical applications to power systems. This comes not only from sophisticated semiconductor technology but also from the demand for a higher degree of frequency and voltage stability, and for greater reliability in power systems. This paper deals with an adjustable speed rotary condenser capable of not only reactive power control but also active power control based on a flywheel effect of the rotor. The behavior of a power system consisting of the adjustable speed rotary condenser, a synchronous generator, and a transmission line is subjected to a set of nonlinear differential equations. The set of nonlinear equations can be linearized by limiting attention to small perturbations around a reference state, thus leading to the so-called Heffron–Phillips model of the power system. The Heffron–Phillips model derived is effective in analyzing effects of the adjustable speed rotary condenser on power system stabilization. The validity of the analysis is confirmed by computer simulation based on EMTDC. Finally, it is discussed how well power system stabilization is achieved by the rotary condenser. As a result, the rotary condenser has the function of decoupling reactive power control from active power control, thus producing a good effect on power system stabilization which would not be achieved by a conventional inverter-based static var compensator.

New Balance Ground Relaying With Countermeasure Against Zero-Phase-Sequence Circulating Current

In Japan, both untransposed low voltage two circuit lines (L1 and L2) and higher voltage two circuit lines (H1 and H2) are frequently mounted on a common tower.

A study of thyristor controlled series capacitor models for power system stability analysis

The thyristor-controlled series capacitor (TCSC) is promising as a powerful device to increase power transfer capability and transient stability. The basic configuration of the TCSC consists of a series of capacitors connected antiparallel with thyristor-controlled reactors, so that firing angle control of the thyristors makes the TCSC capable of achieving impedance control in a wide range with quick response. It is important to clarify the relationship between the fundamental reactance of the TCSC and the firing angle of the thyristors, thus leading to practical applications of the TCSC for enhancement of power transfer capability and transient stability in transmission lines. Two relationship equations for the TCSCs fundamental reactance have already been proposed. One is the relationship equation derived from a TCSC circuit whose source is a voltage. The other is the relationship equation derived from a TCSC circuit whose source is a current. For TCSC installed in a transmission line, it is clear which equation is more adequate for analyzing power system stability. In this paper, the authors determine whether either of the equations is valid for analyzing a power system stability. 1. In the steady state, the TCSC fundamental reactance is analyzed and compared with the two equations and EMTP. It is clear that the TCSC reactance based on current source is adequate. 2. The swing angle of a generator when the firing angle is stepped up is analyzed with EMTP and an analytical model using the TCSC model based on current source. It is shown that the proposed model is effective for power system stability analysis.