Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Steam Turbine Oscillating Working

Steam Turbine Oscillating Working

Steam Turbine Oscillating Working


I have a question regarding the above subject as below:
There is a single stage steam turbine that is connected to a gear box and a pump.The rated BHP of turbine is equal to 1200 hp.But when we need lower BHP (near to 950 hp),we try to reduce the turbine RPM.But we face to big oscillation in throttle valve opening and consequently in turbine RPM and therefore in pump discharge pressure.
Would you please send me your answer to the followings:
1)What is the criteria for oscillating working of a steam turbine?
2)Is the above subject(oscillation in low bhp at a steam turbine)usual or not?
3)Are there any margin (in percent of rated bhp)for preventing the oscillation working of a steam turbine?
4)What are your suggestions and comments for eliminating of the mentioned oscillation?

RE: Steam Turbine Oscillating Working

The situation that you have described is not "USUAL", by which I mean "expectable" or "acceptable".  The situation that you have described is rather common, especially when commissioning a turbine driven equipment string, but should be solvable.  

The turn-down that you have described - from 1200hp to 950hp is not severe.  The turbine and controls should be able to handle this.  

There are too many variables that you have not described for anyone to be absolutely certain of the problem based only on your post, but it is a good guess that the control system is not properly functioning at the part-load condition.  This is sometimes called "hunting" - the control system is "hunting for the set point".  It might be necessary to change the control system settings (proportional range, sensitivity, reset) to try to improve the behavior.  

Certain mechanical conditions can also contribute to the problem: loose valve and/or control system linkage, or the governing valve settings are two examples.  If the position of one of the governing valves is near to its seat at the part-load, the sensitivity of the entire "turbine system" might be higher at part load than at full load, and thereby make the equipment string more vulnerable to "hunting".  Loose linkage is something that, by itself, will not cause hunting, but might contribute to it when it begins.  There is likely to be some hysteresis - asymmetry of the oscillations if the linkage is loose.

Control system settings should be reviewed - preferrably with the OEM.
At the part-load point you could try to slightly throttle the steam upstream of the turbine; either at the trip&throttle valve, or farther upstream.  DO NOT DISABLE ANY OF THE SAFETY SYSTEMS IN ORDER TO DO THIS.  If the steam pressure to the turbine is changed (reduced), the governing valve(s) must move to try to hold the load.  If the oscillation is reduced by throttling the inlet steam, the governing valve is "bouncing" around on its seat at unthrottled part-load.  Governor valve settings might be modified so as to improve the part-load response.

It is also possible - very unlikely, but possible - that there is some sort of flow oscillation in the process side, and the pump load is actually oscillating.  Rule out the turbine control system first.  Check turbine mechanical systems next, then look at the process flow.

RE: Steam Turbine Oscillating Working

Sir Poetix is absolutely right.  99% it is a control system problem.  

His suggestion to throttle the steam flow upstream of the throttle valve at partial load operation is the best (if possible).  This would shift the throttle valve operation away from unstable region and it should be again able of handling the whole system automatically.

Folks, Merry Christmas and Happy New Year to all of you.  

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


eBook - Integrating the Engineering Ecosystem
Aras Innovator provides multiple options for integrating data between systems, depending on the scenario. Utilizing the right approach to meet specific business requirements is vital. These needs range from authoring tools, federating data from various and dissimilar databases, and triggering processes and workflows. Download Now
Research Report - Simulation-Driven Design for SOLIDWORKS Users
In this engineering.com research report, we discuss the rising role of simulation and the paradigm shift commonly called the democratization of simulation. In particular, we focus on how SOLIDWORKS users can take advantage of simulation-driven design through two analysis tools: SOLIDWORKS Simulation and 3DEXPERIENCE WORKS. Download Now
White Paper - Industry 4.0 and the Future of Engineering Education
With industries becoming more automated, more tech-driven and more complex, engineers need to keep their skills and knowledge up to date in order to stay on top of this wave—and to be prepared for the Industry 4.0 future. The University of Cincinnati offers two online Master of Engineering degree programs designed specifically for practicing engineers. Download Now
eBook - The Design Gridlock Manifesto
In this eBook, you’ll learn 6 ways old CAD technology slows your company down and hear how design teams have put those problems to rest. “The Design Gridlock Manifesto” shares first-hand modern CAD experiences from 15 companies around the world. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close