@Ahmed mamdouh,

Unfortunately, we don't know if or how it was resolved.

If you're having a similar issue, PLEASE open a new thread with the details of your situation and machine.

To open a new thread, click on FORUMS on the menu bar at the top of the page, and then click on LATEST. You will be presented with this information at the top of the page:



Clock on the 'Post New Thread' button and choose any forum (Power Generation is a good one, but it doesn't really matter which forum you choose) and provide information as requested below along with a general description of the problem.

Provide any and all alarms that are being annunciated when the problem is occurring--even if you believe they aren't relevant to the situation.

Tell us what control system is being used on the machine.

Tell us how long the problem has been occurring at your site.

Tell us what has been done at the site to try to resolve the problem.

In this thread, the generator had a jacking oil system--where a high-pressure pump is used during starting and shutdown to force the very large, heavy generator rotor up in the bearing to prevent damage to the bearing and shaft during low-speed operation and to help reduce the amount of torque required to break the shaft away from zero speed. Please tell us if the machine at your site is similar, or different.

Please tell us about the starting means system--the motor, the torque converter, if there is or isn't a hydraulic ratchet mechanism to assist with breaking the shaft away from zero speed during starting. The more information you can provide, the more concise your answers will be. Tell us if there is any torque converter guide vane angle position feedback to the turbine control system. Tell us if the starting means and torque converter were recently refurbished or replaced.

I know it sounds like a lot of information, but I can ASSURE you that the more information you provide the better the responses will be. Every GE-design Frame 9E heavy duty gas turbine IS NOT like every other GE-design heavy duty gas turbine; they all compress air and use it to burn fuel to produce hot gases that are expanded as they pass through the turbine section--but the auxiliaries (including the starting means system) can have minor, but important, differences to understand when trying to troubleshoot a problem.

Finally, photographs and electronic files can be attached to posts here on Control.com. Often a picture is worth a thousand words. If you send photos of HMI screens/displays--please be sure they are clear (sometimes HMI monitor photos can be very grainy and difficult to view). If you can send a file of the starting means system P&ID, or even a good clear photo of the P&ID it can be very helpful. Help us to help you.

 

The problem was seemingly resolved when we discovered during a Hot Gas Path Inspection (HGPI) and Generator Major Inspection in 2023, that the generator coupling's alignment run-off readings were not GE's specifications. The same was also identified for the accessory coupling. We therefore corrected both couplings' readings by aligning them as per GE's specifications. This seemed to have corrected the problem, however, during an offline compressor water wash last year, the problem resurfaced.
As indicated earlier, one of the permissive for an offline compressor water wash is for the unit to be at Zero Speed (Standstill). The first stage of the process (i.e. detergent injection stage - for 15 minutes) was successful, however, the rinsing stage was not, because the starting motor was not able to turn the gas turbine shaft in order to crank the unit (which is part of the rinsing process).
My observation is that, in recent times, the three 4-inche pipes (WW4) which are to drain water from the exhaust plenum have not been gushing out large volumes of water as in previous offline compressor water wash sessions. No water comes out of one of the 4-inche pipes, water oozes out of the second 4-inche pipe and the last 4-inche pipe is the only one that water gushes out. My question is "What is the impact on the unit and its performance if water that is trapped within the exhaust plenum area is not drained out of the area?"
My suspicion is that, it may be contributing to the Starting Motor's inability to turn the gas turbine shaft, after admitting water into the unit and not draining it out. I have attached the compressor water wash drawing to this post.
Kindly advice me.
Thank you!

 

The problem was seemingly resolved when we discovered during a Hot Gas Path Inspection (HGPI) and Generator Major Inspection in 2023, that the generator coupling's alignment run-off readings were not GE's specifications. The same was also identified for the accessory coupling. We therefore corrected both couplings' readings by aligning them as per GE's specifications. This seemed to have corrected the problem, however, during an offline compressor water wash last year, the problem resurfaced.
As indicated earlier, one of the permissive for an offline compressor water wash is for the unit to be at Zero Speed (Standstill). The first stage of the process (i.e. detergent injection stage - for 15 minutes) was successful, however, the rinsing stage was not, because the starting motor was not able to turn the gas turbine shaft in order to crank the unit (which is part of the rinsing process).
My observation is that, in recent times, the three 4-inche pipes (WW4) which are to drain water from the exhaust plenum have not been gushing out large volumes of water as in previous offline compressor water wash sessions. No water comes out of one of the 4-inche pipes, water oozes out of the second 4-inche pipe and the last 4-inche pipe is the only one that water gushes out. My question is "What is the impact on the unit and its performance if water that is trapped within the exhaust plenum area is not drained out of the area?"
My suspicion is that, it may be contributing to the Starting Motor's inability to turn the gas turbine shaft, after admitting water into the unit and not draining it out. I have attached the compressor water wash drawing to this post.
Kindly advice me.
Thank you!

 

Kwabena,

As I've written, most people are shocked (no pun intended) to hear of the starting motor drawing 150-160% of rated current during CRANKing and acceleration. And, since your site has been in operation for years and it doesn't sound like there is any past record of the current drawn by the starting motor during CRANKing and acceleration it is probably shocking for you and others at your site to even contemplate this much current on a regular basis. Most of the induction electric motors used as starting motors for GE-design heavy duty gas turbines have very good winding insulation (Class F), and have a high service factor/duty rating. These motors aren't operated at currents like this all day, every day--only during CRANKing and acceleration. Specifically, during purging and acceleration--usually. In fact, usually when the starting motor is "de-coupled" from the turbine-generator shaft (by de-energizing the torque converter fill/drain solenoid, 20TU-1) there is some sequencing that keeps the motor running for a minute or two or three with no load (the ampere draw during this time is around 50-60% of rated) just to cool the motor after acceleration.

So, if you or someone at your site is having heartburn and anxiety over the current values I have posted--it's understandable. But, if you speak with GE and get answers from knowledgeable engineers (not field service people--unless they have many years of experience) you will probably find the values are pretty typical and customary and ordinary.

Many large air-cooled generators use different types of generator rotor bearing--not journal type bearings. AND, since you have confirmed the Brush generator at your site employs bearing lift oil ("jacking oil") to provide a means of ensuring the rotor is NOT in contact with the bearing material during break-away and low speed operation that is a further indicator of the amount of torque required from the starting means to break the turbine-generator shaft away from zero speed.

I can't speak to why your problem of breaking the shaft away from zero speed seems to be more common when performing an Off-Line Compressor Water Wash, but the fact that it also happens during other STARTs as well can certainly indicate the amount of torque being provided by the torque converter to break the shaft away from zero speed is marginal. The torque adjustor mechanisms I have worked on that were provided with Voith torque converters (Siemens and Auma) were German marvels of engineering. They had brakes to make sure the motor STOPPED when it was supposed to stop. They had very intricate adjusting mechanisms (which took some familiarization!) which were extremely precisely adjustable. And, to my knowledge they didn't drift (change setting over time). I'm not saying it can't happen (drift)--I'm saying I've never experienced it AND based on the construction it just didn't seem like it was even possible to happen.

By opening the torque adjustor mechanism "manually" you are increasing the amount of oil flowing through the torque converter (from the hydraulic pump to the hydraulic motor)--which requires more current from the starting motor. Not knowing what was done or how it was done by the torque converter service person it's impossible to say if it could have resulted in lower current draw/reduced torque output. I will say that I have been told--and experienced--that manually CLOSING the torque converter guide vanes (with the hand-wheel and manual engagement mechanism) while transmitting torque (when the starting motor is running AND 20TU-1 is energized) CAN and WILL damage the torque adjustor mechanism (which is like a fragile rack and pinion mechanism) in the torque coverter (not the motor-operated torque adjustor mechanism with the limit switches and position indicator). It bends the rack mechanism, and it doesn't take a lot of force to be bent such that it won't work reliably.

So, I'm NOT saying the application code (programming/configuration) in the Mark VI is right or wrong. But I am saying that based on my personal experience and the current values you have provided that it's entirely possible that the starting motor is not providing sufficient torque to break the shaft away from zero speed because the torque adjustor is not adjusted correctly, or something has changed since it did work correctly, and it needs to be verified for proper adjustment/operation.

Anyway, best of luck! Please continue to write back to let us know what you find. It would also be helpful to know if PRIOR to this break-away problem if it was always necessary to force something to get the Off-Line Water Wash sequence to work properly.

Send CLEAR photos of function blocks ("rungs")--please.

PLEASE.

Hello CSA,
It has been a while.
The problem was seemingly resolved when we discovered during a Hot Gas Path Inspection (HGPI) and Generator Major Inspection in 2023, that the generator coupling's alignment run-off readings were not GE's specifications. The same was also identified for the accessory coupling. We therefore corrected both couplings' readings by aligning them as per GE's specifications. This seemed to have corrected the problem, however, during an offline compressor water wash last year, the problem resurfaced.
As indicated earlier, one of the permissive for an offline compressor water wash is for the unit to be at Zero Speed (Standstill). The first stage of the process (i.e. detergent injection stage - for 15 minutes) was successful, however, the rinsing stage was not, because the starting motor was not able to turn the gas turbine shaft in order to crank the unit (which is part of the rinsing process).
My observation is that, in recent times, the three 4-inche pipes (WW4) which are to drain water from the exhaust plenum have not been gushing out large volumes of water as in previous offline compressor water wash sessions. No water comes out of one of the 4-inche pipes, water oozes out of the second 4-inche pipe and the last 4-inche pipe is the only one that water gushes out. My question is "What is the impact on the unit and its performance if water that is trapped within the exhaust plenum area is not drained out of the area?"
My suspicion is that, it may be contributing to the Starting Motor's inability to turn the gas turbine shaft, after admitting water into the unit and not draining it out. I have attached the compressor water wash drawing to this post.
Kindly advice me.
Thank you!