Hi,

In MS 6001b datasheet there is a "MANUAL SPEED CHANGER, RPM" data in Governor section. What is this used for? Is it the definition of speed limits of the gas turbine while giving raise or lower command from HMI?

Thanks.
Hsirab

 

It's difficult to comment without seeing the document, or at least the relevant portion of the document, you are quoting from.

Can you post the document, or the relevant portion of the document, to a file-sharing site and then post the URL of the location here so that we could review the information? (Some people have used www.tinypic.com; others have used www.speedyshare.com; there are many file-sharing sites which can be used temporarily for this purpose for no cost (i.e., free).)

If the turbine is driving a generator, then speed control is not something an operator is normally interested in, because in most parts of the world when the generator breaker is closed and the unit is operating in parallel with other generators and their prime movers on a grid the speed of the generator is usually fixed and doesn't very much, if at all.

It's only during acceleration (during starting), and shutdown, or during off line testing that speed control is of concern to operators of turbine-generators.

So, if you would provide more information, at least about the type of device the turbine is driving, and more specifically about your desire to understand speed control of the turbine (and driven device), we could, perhaps, provide a better answer.

 

Sorry for the late answer.
In relevant section of the data sheet below data is supplied.
*GOVERNOR (5.4.3)
*MRF'S STD
*MAKE - GE
*MODEL - MARKVie
*REMOTE SHUTDOWN SIGNAL - ELECTRIC
*MANUAL SPEED CHANGER, RPM -150%MAX 95% MIN
*MAINTAIN TURBINE SPEED UPON FAILURE OF CONTROL SIGNAL OR ACTUATOR.

There are three turbines running on a island, not connected to a grid. One is in ISO mode, the other two in droop mode. Is manual speed changer related with iso mode?

 

"Data sheet" is still a confusing term for me; I'm not familiar with a "data sheet" that's provided with any GE-design heavy duty gas turbine. Control Specifications, yes; "data sheet", no. I would venture to say from the information provided this looks like a sales and marketing document.

Manual speed control is only going to be active when the generator breaker is open--regardless of whether or not the unit is being operated in Droop or Isochronous Mode, islanded, or on a grid of any size.

When you change the turbine speed reference in Isochronous mode, you are effectively changing the frequency reference for the load the machine--and any machines operating in parallel with the Isochronous machine. (Turbine speed is directly proportional to generator frequency, which dictates that when frequency is constant speed is constant. And it's desirable for the frequency to be constant on an AC system of any size.)

You can't increase the load being supplied by the Isochronous machine with any command issued to the Speedtronic, because the Isochronous control mode is only responding to changes in frequency that are caused by changes in <b>EITHER</b> the number of motors and lights and computers which are being driven by the machine(s), <b>OR</b> a change in the load being carried by a turbine-generator (or turbine-generators) being operated in parallel with the Isochronous machine.

When you change the turbine speed reference of a Speedtronic turbine control panel of a GE-design heavy duty gas turbine being operated in Droop speed control/governor mode you are effectively changing the load of the machine (by changing the amount of fuel going into the turbine's combustors). Most operators don't realize that even though they are watching the MW meter or the MW value on the HMI display when they clicking on RAISE- or LOWER SPD/LOAD targets they are really changing the turbine speed reference, not the load setpoint. Pre-Selected Load Control is just a "special" case of Droop Speed Control and in general should NOT be used for machines being operated in Droop speed control in islanded operation. (If there is any bobble in the system to which the Isoch machine can't respond, any machine in Pre-Select Load Control will not assist with load control and will actually make the frequency excursion worse.)

In general, the manual speed range of GE-design heavy duty gas turbines when the generator breaker is open is set to 95% to 107% of rated speed. GE doesn't want the speed of the unit to be controlled by the operator below 95% of rated speed (because of the potential of operation at one of two critical vibration speeds), nor do they want the unit to run unloaded at speeds above 107% of rated for any extended period of time <b>EXCEPT</b> during on-line (running) overspeed testing. During on-line (running) overspeed testing, the 107% upper speed limit is adjusted to be slightly higher than the expected overspeed trip setpoint to allow the machine speed to be increased to the overspeed trip setpoint.

The upper- and lower speed limits are usually defined by Control Constants TNKR3 and TNKR4, the "High Speed Stop" and "Low Speed Stop", respectively. Have a look at the Control Specifications, or the running Control Constant values of the machines at your site to be certain about the values of the Stops at your site.

So that bit about 150% of (rated) speed is, well, dubious. GE does not allow their designs of single-shaft heavy duty gas turbines to ever go above 113.5% of rated speed. There is a hard-coded electrical overspeed trip at 113.5% of rated speed to ensure they are never run above that speed. Ever. (It's typically the "Maximum Search Speed", the 113.5% value, but it's No-Man's Land as far as shaft speed. The turbine and driven devices usually will fly apart at speeds in excess of 113.5% of rated so it's just not allowed, even for test purposes.)

There have been MANY threads on (Speed)control.com about Droop speed control/governor mode, and indirectly about Isochronous speed control/governor mode on Speedtronic turbine control systems used on GE-design heavy duty gas turbines.

For (lots) more information about speed control modes of Speedtronic turbine control systems, use the 'Search' feature of control.com (NOTE: preface each word of a search term with a + character!). You can combine words into a specific term with double quotation marks, but it must still be proceeded with a + character, for example

+"droop speed control"

would be a valid search term for the exact words "droop speed control"). There is Help available for the 'Search' function if necessary.