Letters

Squeaky grease

Editor:

“Grease: what it is; how it works” in the April EA brought back memories of long ago in the San Francisco Bay area.

A friend, Chet Gutleben, was a sales engineer for G.E. when I worked for the Standard Oil Co. of California and later Chevron Chemical Co. One day, Chet mentioned a peculiarity of a grease that G.E. had been using in their motors, [called] something like BRB-2. Chet observed that it was fine grease that kept bearing water low and lasted a long time, but that it had an odd feature: the grease itself squeaked!

He said that one could hear the squeaking and that G.E. had pulled bearings apart to see that was happening. There was no wear or damage to the bearing, but the grease squeaked.

I guess the moral was: “The squeaky grease gets the wheel.” Sorry ….

Reid C. Allen, PE. Senior Electrical Engineer

Roberts & Schaefer Salt Lake City, Utah Over the years, a great many different grease formulations have been used by motor manufacturers, but this is the first time we’ve heard of a grease that announced its presence. Has any other reader encountered this?-Editor

Early warning system?

Editor:

We are currently overhauling a 5,650 kW Siemens slip ring motor. The stator voltage is 6.6 kV, while the rotor is 3.4 kV The motor speed is 1,470 RPM. A “flashover” had occurred between the slip rings, causing a fire in the immediate area. However, neither the rotor nor stator windings were affected. We’ve been asked by our customer to suggest an “early warning system” to prevent this eventually occurring again. Is there such protection available?

Derry Sheehan

Technical Director

Avonmore Electrical Co. Ltd.

Roskeen, Mallow

County Cork

Ireland

Flashovers between slip rings normally result from surface tracking caused by moisture or dirt contamination. This motor operates at an usually high rotor voltage, which makes matters worse.

For service in areas subject to such contamination, collector assemblies often include added barrier plates or disks between adjacent rings. That, plus frequent cleaning, is the only preventive measure we know of. No protective device attached to the collector or in the rotor circuit can be relied upon to give an early warning.-Editor

Copyright Barks Publications May 2002

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