Numerical Analysis of Rotating Pumping Flows in Inter-Coil Rotor Cavities and Short Cooling Grooves of a Generator

Wei Tong

doi:10.1155/s1023621x01000112

Abstract

An important characteristic of wall rotating-driven flows is the tendency of fluid with high angular momentum to be flung radially outward. For a generator, the rotor rotating-driven flow, usually referred to as the rotating pumping flow, plays an important role in rotor winding cooling. In this study, three-dimensional numerical analyzes are presented for turbulent pumping flow in the inter-coil rotor cavity and short cooling grooves of a generator. Calculations of the flow field and the mass flux distribution through the grooves were carried out in a sequence of four related cases Under an isothermal condition: (a) pumping flow, which is the self-generated flow resulted from the rotor pumping action; (b) mixing flow, which is the combination of the ventilating flow and pumping flow, under a constant density condition; (c) mixing flow, with density modeled by the ideal gas law; and (d) mixing flow, with different pressure differentials applied on the system. The comparisons of the results from these cases can provide useful information regarding the impacts of the ventilating flow, gas density, and system pressure differential on the mass flux distribution in the short cooling grooves. Results show that the pumping effect is strong enough to generate the cooling flow for rotor winding cooling. Therefore, for small- or mid-size generators ventilation fans may be eliminated. It also suggests that increasing the chimney dimension can improve the distribution uniformity of mass flux through the cooling grooves.

Highlights

The increasing demands for power supply have accelerated the design of reliable, high-powered, high-efficiency, and cost-effective modern generators with state-of-the-art technologies.Among many design parameters, thermal capability and insulation are recognized as two major items to limit the generators’ rating and size
Direct cooling is implemented in two different ways: (a) Radial flow cooling uses the rotor rotation to create a pressure differential between the subslot and the stator-rotor air gap, and to force gas radially outward through rotor slots into the rotor winding. (b) Diagonal flow cooling uses the rotor surface velocity to force gas through the rotor winding turns
Radial flow cooling can be achieved by machining ventilating grooves on the copper conductors

Summary

INTRODUCTION

The increasing demands for power supply have accelerated the design of reliable, high-powered, high-efficiency, and cost-effective modern generators with state-of-the-art technologies. Indirect cooling was the first method developed to cool the field winding It relies on heat conduction from the copper conductors through the insulation to the relatively cooler rotor core. Direct cooling is implemented in two different ways: (a) Radial flow cooling uses the rotor rotation to create a pressure differential between the subslot and the stator-rotor air gap, and to force gas radially outward through rotor slots into the rotor winding. (b) Diagonal flow cooling uses the rotor surface velocity to force gas through the rotor winding turns. As a more effective and efficient cooling method, direct cooling is widely used in rotor windings to attain a relative uniform temperature along the conductor length. (b) Mixing flow, which is a combination of the pumping and ventilating flows in dual cooling In this case, constant density is assumed. The rotor winding consists of a number of coils, separated by wedge blocks along the rotor axis and

D CONDUCTOR

RESULTS AND DISCUSSION

CONCLUSIONS