Replacing magnetic - carbon steel 2-pole turbogenerator retaining rings with Cr18Mn18.

[jt2001]

Hi All,

What are the risks of replacing carbon steel magnetic retaining rings with non-magnetic 18-18 forged rings?

Is there a significant difference in flux generatation ? Are there any possible risks in replacing the rings with the modern standard?

18-18 is the unanymous material of choice for this application. I would be tentative to fit a ring made of anything else.

Kind regards,

Jack

 

[Gr8blu]

The effect may be different depending on where - exactly - the retaining rings lie with respect to the stationary core iron when the machine is operating on magnetic center. In some (rare) cases, the rings are intended as part of the magnetic circuit. Most often, the reason behind the use of magnetic (ferrous) material was either: 1) not understanding that non-magnetic materials were an option, 2) relative cost between materials based on physical size and/or machining/fabrication tolerances, and 3) required strength of material (i.e. how much hoop stress is required at both operating and overspeed conditions).

In general - the use of 18-18 should reduce some of the eddy effect losses by some amount. Whether that will be noticeable in your equipment is up for discussion, in part because of other variations in the magnetic circuit of the machine). The machine should generate the same amount of total flux, regardless - you're not changing the core iron or (presumably) the winding by any appreciable amount. As a result of the reduced eddy loss, the coil itself (in the area of the exposed end head region) should run a little bit cooler at any given line current. However - if the nonmagnetic material is either wider (i.e. requires more surface contact) or needs to be thicker, the net cooling effect can be the opposite (i.e. more heat in the coil).

Converting energy to motion for more than half a century

 

[jt2001]

Hi Gr8blu,

Is there any obvious difference in design with the rotors where the rings are intended as part of the magnetic circuit as you mention?

I would not anticipate a larger ring would be required or any major mechanical changes would be required in using the 18-18 ring - Although I have not completed a mechanical comparison yet.

I would assume that ferrous rings were installed on this unit on basis of cost or more likely the machine was manufactured before the event of the cold formed 18-18 material being available.

I am investigating completing a calculation in Ansys to observe any possible changes in performance. I cannot find any research papers explicity addressing this topic.

Regards,

Jack