Paper 5: Noise Reduction in the Circulating Water Pumphouse at Blyth ‘B’ Power Station

Abstract

The noise produced by the circulating water pump motors at Blyth ‘B’ power station contained a pure tone and this led to complaints both from the public and from the plant attendants. It was established that the noise was principally magnetic in origin, attributable to an unfavourable combination of numbers of stator and rotor slots, and the noise level was reduced by modifying the design of the rotor to obtain a better slot ratio. The noise level was still undesirably high, however, and an experimental silencer for the cooling air inlets and outlets was designed and a mock-up constructed of timber, hardboard, and mineral wool slab. These combined measures reduced the noise inside the pumphouse to well within the ISO noise rating number 85, which has been taken as the hearing damage risk criterion, and abated the public annoyance outside the pumphouse. This paper describes the basic origin of magnetic noise in squirrel-cage motors and methods for controlling noise levels both by design of motor and silencers within the limits set by electrical and economic design parameters.