Turbine speed control

[extremechanical]

Hi, May I understand why Electronic Speed control is provided for Steam Turbines in addition to Hydraulic Governor? Are they not (Hydraulic or Mechanical governors) meant for throttling steam inlet as per set speed? If the function of Electronic Governor is to covert RPM to frequency and throttle the COntrol Valve, then we should be ok only with Electronic Governor?

Please let me know...

 

[JJPellin]

The four main types of governors for single stage steam turbines are mechanical, hydraulic, hydraulic-mechanical and electronic. I have never seen a turbine that required more than one type at a time. But, be cautious. There is a second, separate system to protect the turbine against overspeed. This system can be called an “emergency governor.” The overspeed trip system also has at least two options. It can be purely mechanical or it can be electronic. So, there are combinations of options between the speed governor and the overspeed protection systems. It would not be unusual to have a hydraulic governor with an electronic overspeed protection system. Or, you might have an electronic governor with a mechanical overspeed protection system. But, to your original question, there should be no need for two speed control systems, hydraulic and electronic on the same turbine at the same time.

One other possibility occurred to me. The turbine could be built with a hydraulic governor, but have provisions for a future electronic governor. This might just mean that the rotor already has a toothed wheel and is machined for the speed probes needed for a possible future upgrade to an electronic governor.


Johnny Pellin

 

[extremechanical]

Johnny, Thanks a lot for a very clear reply. ( All your replies are always very clear! ) Right now we have number of steam turbines used as drivers for pumps.

1. All have hydraulic governors with Woodward Electronic Governors. I did not see an "Emergency Governor", But there is a purely mechanical Overspeed trip is provided. I am calling " purely mechanical", since ( my assumption) the shank there goes off and steam inlet to the Turbine is stopped in case there is an overspeed situation.

2. I did check your point, if they provided just an electronic over speed trip, but no, the manual clearly says they have provided Mechanical over speed trip.

3. I also went to the field to verify, the turbine has a Mechanical Governor unit attached, with a WOodward console.

Again , I am just thinking , could electronic governor is provided to control it through DCS? ( I know this is not a good question, even pure mechanical/hydraulic governor could be controlled with DCS)

Thanks a lot Johnny.

 

[JJPellin]

What you are describing sounds to me like an electronic governor that uses a hydraulic actuator to open and close the governor valve. This would still be classified as an electronic governor. The actuator could be hydraulic, pneumatic or electronic. But, that is just the actuator. The actual governor that provides the control signal is purely electronic.

Johnny Pellin

 

[Pumpsonly]

It would be much clearer if you can post the schematic drawing of the control system.