Air-cooled Generator Research Articles

Numerical Calculation of Fluid Heat Transfer in Rotor of Large Air-Cooled Generator Based on Global Ventilation Network Model

Numerical Calculation of Fluid Heat Transfer in Rotor of Large Air-Cooled Generator Based on Global Ventilation Network Model

Thompson-Lampard Theorem for Dielectric Characteristics Detection of Generator Stator Insulation

The insulation of large generator stator winding will be gradually aging in the long-term operation process. The traditional aging test method cannot accurately locate the non-penetrating local defects of winding. Interdigital electrode is widely used in the fields of environmental monitoring and food detection because of its excellent characteristics such as self-closing and unidirectional penetration, but it has not been popularized in the identification of generator insulation aging. The paper proposes an interdigital electrode structure based on the Thompson-Lampard theory. The electrode suitable for dielectric characteristic detection of stator winding, and the electrode structure is optimized by using the finite element method from the parameters of signal strength, sensitivity and penetration depth. With the help of optimising, the measuring accuracy of the electrode can reach 0.1 level. Then, the different moisture conditions of water-cooled generator and air-cooled generator are simulated to verify the feasibility that interdigital electrode can detect insulation moisture which is an important factor in accelerating insulation aging. Finally, the moisture depth detection results show that the electrode combination based on the Thompson-Lampard theory can be used to locate moisture depth accurately, it is of great significance for the prevention of insulation aging and the pre-diagnosis.

Flow Behavior and Heat Transfer Characteristics Between Outer and Slotted Inner Cylinders

Abstract The performance of air-cooled generators can be improved only if they have efficient system designs for heat removal. An air-cooled generator is composed of a pair of coaxial cylinders, namely, a fixed outer cylinder (stator) and a rotating inner cylinder (rotor); the rotor has axial slits. In this study, we experimentally and numerically clarified the flow behavior and the heat transfer characteristics of rotating coaxial cylinders by simulating a salient-pole rotor in an air-cooled generator. The flow behavior in the slit between the salient poles was observed by using a high-speed video camera. We measured the temperature on the slit walls to investigate the heat transfer. The velocity fields and the heat transfer coefficient between the rotor and the stator were obtained via a numerical simulation. From the results, we experimentally and numerically observed the vortex structure in the slit. The local Nusselt numbers on the front-side wall of the slits near the impinging flow were higher than those on the back-side wall near the separated flow. The local Nusselt numbers on the front-side wall were high because the gap flow between the cylinders impinged on the front-side wall and promoted heat transfer. By contrast, the local Nusselt numbers on the back-side wall were low because a separated flow appeared near the back-side wall, where the hot fluid was retained, thereby causing the separated flow to disturb the heat transfer on the back-side wall.

Heat transfer coefficient distribution in inner surface of stator ventilation duct for large capacity air-cooled turbine generator

The stator ventilation duct is the main path for fluid flowing to cool the stator bar and the core. Considering the complexity of the ventilation system, the investigation on the relationship between the air motion law in the ventilation duct and its surface heat transfer coefficient is crucial for the accurate calculation of the temperature field. Therefore, this paper takes the 150 MW air-cooled turbo-generator as a research object. Firstly, a new calculation model of the stator taking the air gap under rotor rotation state, and the yoke back into account is proposed to calculate the heat transfer coefficient in inner surface of stator ventilation duct. The relationship among the velocity vector, temperature of fluid and heat transfer coefficient in the ventilation duct is analyzed. Secondly, the temperature field of the new model calculated by finite volume method is compared with the measured values to verify the accuracy of calculation method. Finally, the influence of the varied rotational velocity on the heat transfer coefficient is investigated. The correction coefficient of the heat transfer coefficient related to the velocity is proposed. The calculation of the heat transfer coefficient and the correction of the fitting formula can provide theoretical guidance for the ventilation design of generators.

Treatment of abnormal vibration at the end of large air-cooled generator --The reference of operation and maintenance fault diagnosis of new type phase modifier

This paper introduces the abnormal natural frequency at the end of a large-scale air-cooled generator in a power generation company, analyzes the abnormal vibration frequency data at the end of the generator, and solves them successfully, which provides a reference for the state analysis of new high power phase modifier.

Influence of a Novel Stator Teeth Internal Ventilation Structure on Air-Cooled Turbo-Generator Parameters and Stator Temperature

In order to solve the problems of severe heating and cooling difficulty in the stator of air-cooled turbo-generator, a novel stator teeth internal ventilation structure with axial vents in the generator stator teeth is proposed. Based on this structure, global two-dimensional electromagnetic field models of 150MW air-cooled turbo-generator with different stator tooth internal ventilation structures are established to study the influence of the axial vents of the internal ventilation structure on air gap magnetic flux density of the generator, magnetic flux density of stator teeth, stator core loss, and synchronous reactance. Furtherly, flow network models of the ventilation system with different internal ventilation structures and fluid-heat transfer numerical models of stator with half axial and one tooth pitch of generator are established to calculate the effects of the structure on the temperature of stator winding, insulation and teeth. It can provide a new research idea for the ventilation structure of large air-cooled generator.

Structural Design of Air-Cooled Large Generator by Utilizing Topology Optimization

Structural Design of Air-Cooled Large Generator by Utilizing Topology Optimization

Thermal Analysis of Hybrid Excitation Generator for Distributed Generation Applications

This paper presents a general thermal calculation method to analyze the thermal behaviors of hybrid excitation generators for distributed generation applications. The three-dimensional (3D) finite element method was adopted to calculate the temperature field of the air-cooled generator. The steady-state heat transfer mathematic and physical models were established, and hypothetical conditions were presented, together with boundary conditions and loads were calculated. The temperature field distributions under different operation conditions were achieved. The temperature field of a 12kW, 100rpm prototype was calculated, and the calculation results were compared with experimental data to verify the accuracy of the thermal calculation results.

Study of Three-Dimensional Temperature Field with Changed Structures of Air-Cooled Turbo Generator Stator

Aimed to ventilation system of large air-cooled turbine generator, using the principle of CFD and following characteristics of the stator cooling system, mathematical and physical models of three-dimensional flow and heat ventilation systems built, and two schemes proposed. One was only changing the thickness of the iron core lamination with stableness total effective length of the core, total ventilating ducts, and every duct constant axial length, the other was changing the number of ducts with stableness total effective length of the core. Corresponding basic assumptions and boundary conditions selected, fluid field and temperature field coupled solutions solved, flow field and temperature field of the original and variation structure and the spatial distribution characteristics of each part of the motor analyzed, as well the performance of the stator under different structure was compared. More effectively Structure selected.

J0510103 空気冷却式発電機における突極型回転子モデルでの流動特性

Toward the improvement of performance of the air-cooled generator, design of the generator appropriate to heat removal is important. An air-cooled generator is composed of the pair of coaxial cylinders with the fixed outer cylinder (stator) and rotating inner cylinder (rotor). The present study experimentally and numerically clarifies the flow characteristics in rotating coaxial cylinders simulated a salient-pole rotor within the air-cooled generator. The flow behavior in the slot between the salient-poles was measured via PIV. The velocity fields were obtained by the numerical simulation. In flow visualization, we proposed a transformation method from absolute coordinate to rotational one in order to obtain the velocity fields in rotational coordinate. The vortex structure was observed in the slot on the rotor wall. In the numerical simulation, the same vortex structure as flow visualization was identified, and the numerical simulation was validated by comparing the velocity profiles obtained numerically and those obtained experimentally.

Research on Identification Model of Stator Core Temperature Rise of a Generator

This paper takes the ship air-cooled AC generator with the radial ventilation system for example, establishes the mathematical model of a generator core and winding temperature by using an equivalent thermal circuit method and the temperature calculation method based on the operating parameters, analyzes the transfer function between the generator stator winding temperature rise and the phase voltage, phase current and reactive power, and finally verifies validity of the mathematical model by the experiment.

Experimental Study of Flow Field of Large Air-Cooled Turbine Generator for Multi-Ventilation Ducts of Stator

To study rotational air flow field of rotor and complicated flow distinction owing to multi-ventilation ducts of stator in a large air-cooled turbine generator, considering axial symmetry of air supply, an experiment setup of ventilation system of semi-machine configuration was built in this paper. At condition of rotating, ventilation is measured by hot-wire anemometer. Firstly, ventilation in 16 different semi-circle radius is got. Measurement shows that ventilation in different radius varies much. Then ventilation of outlet of stator ducts is measured. The result shows that ventilation which is affected by flow back and jet less is higher. The conclusion will provide theoretical references for ventilation cooling of rotor ducts in large air-cooled turbine generators.

Calculation and Analysis of Heat Transfer Coefficients and Temperature Fields of Air-Cooled Large Hydro-Generator Rotor Excitation Windings

In this paper, the electromagnetic and temperature field of a 250-MW air-cooled hydro-generator in the Wuqiangxi hydropower station was calculated. The 2-D electromagnetic field model was built. Through solving the model, the additional loss and its distribution were determined. The rotor 3-D temperature field was then calculated and analyzed. Due to many gas eddies, the inner environment of a large hydro-generator is, therefore, complex. This leads to difficulty in determining the heat transfer coefficients on rotor surfaces. To accurately determine the heat transfer coefficients distributions, a method combining numerical and analytical calculations is proposed based on Fourier's theorem and Newton's heat transfer law. Using this new method, the heat transfer coefficients distributions on rotor surfaces were repeatedly calculated. The rotor temperature distribution was then computed. After comparing the measured values, the calculated temperature with determined heat transfer conditions were more accurate than that from traditional methods. This provides a theoretical basis for calculating heat transfer coefficients of outer surfaces of 1000-MW air-cooled giant hydroelectric generator.

Problems with modern air-cooled generator stator winding insulation

Modern stator winding design and manufacturing methods have been successful in reducing the costs of turbine generators. Problems such as thermal cycling, coil abrasion in the slot and PDs in the endwinding have lead to failures after as little as five years of operation. To avoid premature failures, users of modern air-cooled machines should ensure they have a good purchase specification, are present at the factory for critical phases of machine manufacture, operate the machine within specification, keep the windings clean, and closely inspect the stator winding after about one year of operation. The latter is much more important than it was for hydrogen-cooled machines. Although some problems cannot be corrected, effective means are available to slow down the deterioration process, if the problems are discovered at an early enough stage.

Mechatronical considerations in modern motorcar generators

The generator in use today is the air-cooled claw pole generator. It is highly optimized and has nearly reached its technical limits. However, despite this optimization, the efficiency is not very high. Therefore new kinds of electrical power supplies must be researched. For this, a mechatronic power supply system-consisting of the electric generator with its mechanically accelerated masses and its electronic parts for control-is under development. The various aspects to be considered in the design are discussed, the different kinds of generator losses are summarised and analysed, and the PM excited generator is described. Results for a 3 kW rated generator are discussed.