Ken Nagakura

Circulating Currents in Stator Coils of Large Turbine Generators and Loss Reduction

Stator coils transposed by 540deg are widely used as one of the solutions to reduce the circulating current loss in the coil strands of turbine generators. However, the difference of the leakage fluxes in the two coil end parts, which is possibly caused by the coil end length deviation, the winding pitch, and the presence of the connection rings, may induce unbalanced voltage in the stator coil strands, which increase circulating current loss even in the transposition coils. This paper describes the mechanism and the analysis results of the circulating current increase in the coil strands due to the coil end flux difference. Then, some new schemes to reduce the circulating current loss are proposed and discussed.

Eddy current analysis in the stator end structures of large capacity turbine generators

In the stator core end region of the large capacity turbine generators, the leakage magnetic flux induces eddy current loss in the metal structures. In this paper, the results of three-dimensional electromagnetic field analyses of the stator end structures are described. It is demonstrated that the eddy current loss dependency on the power factor can be explained with the phasor diagrams on the magnetic flux. Then the relationship between the end structure and the current source is discussed.

Development of world's largest hydrogen-cooled turbine generator

Simple generator systems are preferred for thermal power generation because of their better operability and maintainability, and their lower cost. Hydrogen-cooled generators of up to 600 MVA have been developed to meet these customer requirements. Development of this generator was achieved mainly by optimization of the cooling gas flow distribution and high thermal conducting insulation of the stator winding. A 500 MVA turbine generator applying these key technologies has been designed and manufactured, and has shown satisfactory results in a shop test.

Development of the world's largest hydrogen indirectly cooled turbine generator

Water-cooled stator-winding generators are widely used for large capacity turbine generators of thermal power plant. However, simpler stator cooling system is preferred considering easy operation and maintenance and lower cost. Hydrogen indirectly cooled generator is one of the solution with expansion its capacity. TOSHIBA has developed, manufactured and tested 670MVA hydrogen indirectly cooled generator.

Technologies for high efficiency large capacity turbine generator

For large capacity turbine generators of thermal power plants, water-cooling system has widely been applied to stator windings. TOSHIBA has developed generators using hydrogen indirectly cooled windings, which are more suitable for high efficiency and easy to maintain, with capacity of 670MVA and efficiency of 99.1%. As the bars of stator windings are cooled with hydrogen gas through the insulation surrounding the bars, it is important to suppress the temperature rise. In this paper, some technologies to realize high efficiency turbine generators, such as multiple parallel circuit winding to reduce current per single bar and ventilation system optimization are described.

Analytical study on generator load rejection characteristic using advanced equivalent circuit

This paper describes the analytical study on generator load rejection characteristic using the advanced equivalent circuit model. The authors have studied the synchronous machine equivalent circuit model and transient phenomena, by simulation with the electromagnetic transients program (ATP-EMTP), and compared the results with the experimental data

Current progress in high thermal conducing insulation technology for large capacity turbine generator

We have enlarged the capacity of indirectly hydrogen-cooled turbine generators to improve the efficiency, simplify the machine structure and save the maintenance cost over the past decade. The one of the key technologies is the heat transfer from a stator bar conductor to iron core, because indirectly hydrogen-cooling performance is inferior to directly water-cooling one. So, we have developed High Thermal Conducting (HTC) insulation technology and achieved twice of thermal conductivity compared to conventional epoxy-mica insulation [1]. Recently, we have achieved further improvement in thermal conductivity of HTC insulation. The progress of HTC insulation technology is reported in this paper.

Effect of reactance saturation on transient and stability for cylindrical synchronous machine

This paper presents the influence of reactance saturation in transient and stability phenomena for cylindrical synchronous machine. For this purpose the authors have examined various equivalent circuit models using electromagnetic transients program (EMTP-ATP).

A study on quadrature equivalent circuit model in large synchronous machine

This paper describes a study on equivalent circuit model in a large synchronous machine. In this study, the authors studied the quadrature axis transient reactance xpsilaq, not only the influence of the operational impedance , but also the difference of transient and dynamic characteristics using finite element method (FEM) and EMTP.

Study of saturation characteristic of equivalent circuits for cylindrical synchronous machine

The authors have studied the saturation characteristic of equivalent circuit of cylindrical synchronous machine. Using the measured data, the authors have studied the effect on the saturation characteristic of equivalent circuits by the finite element method (FEM) and the electromagnetic transients program (ATP-EMTP).