Steel Slip Rings for Synchronous Motor 2

[aolalde]

What is the recommended steel grade for DC field slip rings?
This is a Synchronous motor, 1750HP, GE, 1200 rpm, 60 HZ, 6600 Volts, 149 Amperes, Field DC-Volts 125 and Field DC-Amps 960. The Outside diameter of the rings is 11.5" and the width is 1.125".

 

[electricpete]

I don't know the answer. I haven't heard of steel slip rings. Why use steel instead of copper or bronze?

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

 

[DougMSOE]

There are about 7 different classes of materials (includeing Cu)that have been used for slip rings.

STEEL 0.21%C or 1% C with 1% Cr. This is usually used for turbo alternators where high hoop stress may be encountered.
However oxidation is a problem with this material.

Stainless Steel Following is good for poor atmospheric conditions
18% Cr 8% Ni
or
25%Cr 12%Ni
or
17%Cr 10% Ni
Do not combine with Mo and/or W, not advised.

 

[UKpete]

aolalde, I've looked this up in my Morganite book "Carbon Brushes and Electrical Machines", which states:

"The two steels used are classified as either low carbon (0.21% and known as "20" carbon type) or high carbon (1.0% carbon plus 1.0% chromium)"

- actually this is the same as quoted by DougMSOE.

My older edition of the same book states that nickel steels are used in order to get the necessary tensile strength, and that brush contact and load current distribution is improved by the use of helical grooves in the running surface of the ring.

Incidentally it also says that because the machine operates above critical speed, ring grinding should be carried out at or near running speed.

 

[aolalde]

UKpete & DougMSOE, Many thanks for you for help.

Epete. Due to ambiental contamination which attacks copper alloys.