Air-cooled Generators Research Articles

An experimental study of noise reduction of portable generator using local made acoustic enclosure

Portable generators are now widely used in shops, offices, and homes to provide electrical power during power outages in Iraq. However, these generators produce a lot of noise emitted from rotating mechanical parts and fuel combustion inside engine chamber. This noise has a negative impact on the neuroendocrine, cardiovascular, respiratory, and digestive systems. The reduction of generator noise still attracts the interest of many researchers. In this work, the reduction of generator noise under the use of an acoustic enclosure, made from local materials, is investigated experimentally. Experimental work is conducted using a 2kW generator and compares the sound intensity for two cases: a generator without enclosure and one with enclosure. The enclosure is made from plywood, galvanized sheet, glass wool, cork, and a compressed sponge. The results include the measurement of sound intensity at day and night, at zero to full load, and at two different distances. The findings depicted that generator noise reduction reaches 10.3 dB at night and 9.6 dB during the day. In addition, the engine temperature, in case of using the enclosure, is kept within the allowable range of air-cooled generators which is 300 °C. The maximum temperature at 100% load measured inside the enclosure was 77.86 °C during the night time and 91.75 °C at day time.

Improving Combined Flow and Thermal Network Accuracy for Radially Air-Cooled Generators by Considering the Nonlinear Resistance Characteristics of T-Junction Flow

This work aims to improve the combined flow and thermal network (CFTN) accuracy for radially air-cooled generators by investigating the possible error stemming from the flow part. The nonlinear resistance characteristics of the T-junction dividing flow are first time considered for such cooling arrangement, which is achieved by employing the Gardel equations and the blend equation as the governing equations. Compared with the CFD model results as the benchmark, the nonlinear CFTN predicts an accurate flow rate in the radially extended airducts, making only 9% root mean square (rms) error for all the airducts. On the contrary, the linear CFTN fails to obtain a reliable flow distribution, as the rms error is as large as 34%. As a result, the nonlinear CFTN improves the accuracy of the maximum winding temperature by 6.4% over the linear CFTN and gives a more reasonable temperature gradient in the axial direction. Furthermore, the relative difference between the linear and nonlinear CFTNs is found to be even larger in the following conditions: large cooling air flow rate, wide airgap, low slot fill factor, and large airduct number. The proposed nonlinear CFTN modeling approach is also validated against experimental measurements for a prototype. The modeled temperatures match well with the measurements at different axial positions. According to the aforementioned findings, the nonlinear CFTN modeling approach is considered to be a reliable thermal analysis tool for the radial air-cooling arrangement.

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.

Построение трехмерной тепловой модели статора турбогенератора с учетом газодинамики

The construction of a thermal model of a fully air cooled turbine generator stator with taking into account gas dynamics is considered. The complete mathematical model includes various physical subsystems with multiphysical relationships. The study is based on accurate 3D models with the use of the modern and proven COMSOL Multiphysics software, in which the finite element method is used for calculation. The equivalent thermal conductivity of the gap between the winding bar copper conductors and stator iron is studied. The gap in question consists of the winding bar main insulation and a gap filled with additional semiconducting gaskets or similar materials. The above-mentioned physical parameter has a strong influence on the temperature distribution, because the main part of the heat releasing in the bar is transferred to the stator core through these elements. The optimal minimum equivalent thermal conductivity coefficient is analyzed and selected. A model of a turbine generator stator symmetric element together with a turbulent cooling air flow is developed and analyzed. The development of such integrated models will make it possible not only to simplify the design process, but also to analyze various insulation systems. For example, air-cooled turbine generators initially use the Global VPI insulation system; however, after replacing---for economic reasons---the stator winding, another insulation system is used, namely, the Resin Rich system. For correctly making a transition to another insulation system, integrated calculations, including thermal ones, should be carried out. In practice, after changing the insulation system, which may entail certain thermal limitations, it may be necessary to decrease the turbine generator rated power output for its further operation without overheating the stator winding, which can be obtained on the basis of simulation. In this regard, the equivalent thermal conductivity coefficient also plays an important role; its value can be preliminarily analyzed to select the necessary materials in terms of their thermal properties, and their filling factor to retain the turbine generator nominal parameters after its rewinding.

Ventilation Cooling Design for a Novel 350-MW Air-Cooled Turbo Generator

Herein, we successfully designed a ventilation system for a new 350-MW air-cooled turbogenerator based on a reasonable lectotype choice and optimization analysis. Fluid field and thermal analysis based on computational fluid dynamics were performed to guide the optimization of cooling structures and ensure temperature rise under the limit of insulation grade B. The measured values obtained from recent factory assembly-type testing were found to coincide with the design expectations for generator efficiency and temperature rise. The results confirmed the feasibility of a multi-chamber forward-flow cooling path for 400-MVA-class air-cooled generators.

Direct liquid cooling for an outer‐rotor direct‐drive permanent‐magnet synchronous generator for wind farm applications

Offshore applications, which call for the largest and most powerful wind turbines, demand a higher standard of reliability and maintainability. Direct-drive permanent-magnet synchronous generators (DD-PMSGs) are increasingly being specified for these applications. The major shortcoming to traditional high-powered direct-drive generators is extraordinary size and mass leading to extraordinary cost. To generate higher powers at low rotational speeds, direct-drive generators must either develop greater tangential stresses or be larger in diameter. For traditional air-cooled generators, higher power generally means a much larger diameter. Dramatic cost savings can be realised with the development of a more effective stator windings cooling system that puts further the limit on current density enabling the development of high-power direct-drive generators of substantially smaller diameters. This study presents a direct liquid cooling system design for an 8 MW outer-rotor DD-PMSG. The approach is new for wind turbine generators, so its impact on the thermal behaviour and reliability for the total electrical machine has been evaluated and reported here. Testing of a stator coil prototype (1/72nd of the complete stator) with internal cooling liquid flow is also reported to demonstrate the workability of the designed cooling solution.

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.

Effect of surface degradation on slot partial discharge activity

To improve our understanding of slot partial discharge (PD) mechanisms, an accelerated aging test was initiated two years ago. This long-term experiment is being performed on six stator bars subjected to slot PDs under electrical, thermal and mechanical stresses. It is well known that slot PD activity in air-cooled generators is harmful to the stator winding ground insulation. The degradation induced by slot PDs will modify the physical properties of the surfaces of the cavity where PDs take place and this in turn will influence the slot PD process. To understand the evolution of slot PD activity and the changes in its PRPD (Phased Resolved Partial Discharge) pattern, it is therefore essential to recognize and understand the interdependence between surface modifications and PD signals. This paper presents results of visual observations of stator bar surface degradation, changes in surface conductivity and the effect on the evolution of PD signals in the presence of slot PD activity under conditions of electrical, thermal and mechanical stresses.

Study of slot partial discharges in air-cooled generators

Two laboratory experiments were set up in order to investigate the influence of different parameters on slot partial discharge (PD) activity. The goal of the first experiment was to establish the relative importance of temperature and gap size on slot partial discharges (PDs). The second experiment was used to determine how different stresses (e.g. electrical, thermal and mechanical) influence the discharge mechanisms of stator bars affected by slot PDs. Finally, the results obtained in the laboratory were confirmed when compared with actual field measurements on a generator.

Experimental Study of Fluid Motion in Air Gap Using Scaled Water Model. Winding Efficiency of Rotor Surface Shape of Air-Cooled Generators.

In this study, we investigated the value of the loss coefficient, ζ23, at the exit of the rotor ventilation ducts when air coolant flows from the rotor ventilation ducts to the rotor-stator air gap by measuring the distribution of static pressure on the surface of the rotor and the stator and on the wall of the cooling duct of air cooled generators, by using a scale water model. Protuberant type rotor wedge was proposed and they performed much better than the flat type of rotor wedge for ventilation cooling. From the experimental results, for the protuberant type rotor wedge, the fluid can flow from the exit of the rotor cooling duct into the air gap with a small pressure loss, since the fluid near the rotor surface is separated from the rotor surface by the triangular protuberance and the static pressure above the exit of the cooling duct is less than that in the rotor cooling duct. The experimental results of the pressure loss and the results of numerical analysis which will be reported in another paper(1), were in good agreement.

Slot-discharge activity in air-cooled motors and generators

In large motors and generators, the surfaces of the stator coils and bars are finished with a partially conducting coating to suppress discharge activity between the insulation surface and the core. However, slot discharge activity has been reported in some air-cooled motors and generators where significant areas of this coating have been eroded from the insulation surface at the high-voltage end of the winding. This paper considers how slot discharge damage may develop even where the surface coating is in good electrical contact with the stator core. Although the carbon-loaded paints often used to coat epoxy resin/mica paper insulation have acceptable surface resistivities, they are vulnerable to mechanical damage. It is shown that the removal of even a small area of the coating will initiate discharge activity and lead to the type of damage seen in service. The conditions necessary for slot-discharge activity are calculated and the results compared with measurements on stator coils removed from service.

Fire Detection in Open-Type Hydrogenerators

The tests made by the Aluminum Company of Canada Ltd. to determine the optimum automatic fire-detection system for the open ventilation-type generators at its Chute-a-Caron plant are described. Several detection systems were studied, resulting in smoke detection and fixed-temperature detection systems being tested. The test results indicated that a fixed-temperature detection system was most suitable for this application and probably for most other types of vertically mounted air-cooled generators.

Thermoelectric generators—Design, performance and application

In the present state of the art the construction of useful thermoelectric generators requires careful planning on the part of the design engineer. He must be aware of the significant factors that influence the performance, reliability, life, and ease of fabrication of the generators. This paper illustrates many of the practical problems that are encountered in building present clay generators. A design procedure for free convection air-cooled generators is described. The performance of power thermocouples as a function of junction temperature is discussed and curves illustrating couple efficiency, power output, heat flux, and voltage as a function of hot junction temperature are illustrated. The effects of varying thermocouple length on generator efficiency and generator specific power are shown graphically and methods of predicting generator performance as the number of thermocouple is varied are illustrated. The paper also discusses free convection heat exchangers and fossil fuel burners. In addition, the thermoelectric generator performance on a watts per pound basis is compared with battery and gasoline engine driven generator performance for specific missions.

Thermoelectric Generator Design, Performance, and Application

Many of the practical problems that are encountered in building present-day generators are illustrated. A design procedure for free convection air-cooled generators is described. The performance of power thermocouples as a function of junction temperature is discussed and curves illustrating couple efficiency, power output, heat flux and voltage as a function of hot junction temperature are shown. The effects of varying thermocouple length on generator efficiency and generator specific power are shown graphically and methods of predicting generator performance are illustrated for thermoelectric materials of equal figures of merit but different values of thermal conductivity. The paper also discusses free convection heat exchangers and fossil-fuel burners. The thermoelectric generator preformance on a watts-per-pound basis is compared with battery-and gasoline-engine-driven generator performance for specific missions.

Reduction of Noise Produced by Small and Medium 2-Pole Turbine Generators [includes discussion

In 1945, a systematic program aimed at reducing the noise level of their small and medium size 2-pole turbine generators was undertaken by the company with which the authors are associated. Factory tests on over 110 air-cooled generators ranging from 1,000-kw to 12,500-kw rating indicate that the average noise level of this line of machines has been reduced over 6 decibels. This noise level reduction has been brought about primarily by reducing sound energy transmission. One of the most important methods of reducing sound transmission is to keep the natural mechanical frequency of any part well away from any of the forcing frequencies. A discussion is given of the analytical work, the design program, the test equipment, and the development of a test procedure for obtaining consistent test results. The methods used in this program are general, and are applicable to the reduction of noise generated by other electrical apparatus.

The hydrogen-cooled turbine generator

HYDROGEN cooling for electrical machinery was first proposed to the industry through an AIEE paper presented in 1925. <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> The first hydrogen-cooled machine to be placed in commercial service was a 12,500-kva synchronous condenser, installed in 1928. <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> This was followed by other machines of this type, and later, the hydrogen-cooled frequency-converter was introduced. There are now in operation in the United States 20 of these two types of hydrogen-cooled machines, with a combined output of over one-half million kva, and their records of performance have been highly satisfactory. Prior to 1937, the application of hydrogen cooling to turbine generators had been confined to developmental machines in the manufacturers' plants, although several air-cooled generators had been built with provision for later adaptation to hydrogen cooling. In October 1937 the first hydrogen-cooled generator built for commercial service was placed in operation at Dayton, Ohio. This was a 3,600-rpm unit, of General Electric manufacture, rated at 31,250 kva at 0.8 power factor. Since then, a total of 10 hydrogen-cooled generators have been placed in service in various parts of the country, and 27 others are in the course of installation or construction. The total capacity of these 37 generators is over 2,000,000 kva, and their sizes range from 17,000 kva to 81,250 kva at 3,600 rpm, and from 75,000 kva to 176,470 kva at 1,800 rpm.

The Hydrogen-Cooled Turbine Generator

HYDROGEN cooling for electrical machinery was first proposed to the industry through an AIEE paper presented in 1925.1 The first hydrogen-cooled machine to be placed in commercial service was a 12,500-kva synchronous condenser, installed in 1928.2 This was followed by other machines of this type, and later, the hydrogen-cooled frequency-converter was introduced. There are now in operation in the United States 20 of these two types of hydrogen-cooled machines, with a combined output of over one-half million kva, and their records of performance have been highly satisfactory. Prior to 1937, the application of hydrogen cooling to turbine generators had been confined to developmental machines in the manufacturers' plants, although several air-cooled generators had been built with provision for later adaptation to hydrogen cooling. In October 1937 the first hydrogen-cooled generator built for commercial service was placed in operation at Dayton, Ohio. This was a 3,600-rpm unit, of General Electric manufacture, rated at 31,250 kva at 0.8 power factor. Since then, a total of 10 hydrogen-cooled generators have been placed in service in various parts of the country, and 27 others are in the course of installation or construction. The total capacity of these 37 generators is over 2,000,000 kva, and their sizes range from 17,000 kva to 81,250 kva at 3,600 rpm, and from 75,000 kva to 176,470 kva at 1,800 rpm.