Start Command of Auxiliary Motors of Gas Turbines

Hello everyone....

I am working in operation of Gas turbine (19.6 MW, Frame-5 with Mark-VIe). My query on staring logic of auxiliary motors was explained in this forum (Thanks CSA..)

Can anyone help me also to make out how the auxiliary motors (AOP & EOP) get the start command and also the working of hydraulic ratchet pump.

thanks and regards
Most Mark VIe turbine control systems use electromechanical relay output contacts to start and stop all auxiliary motors, including the DC Emergency L.O. Pump motor and the hydraulic ratchet Kemp motor. But, somehow, I don't think that's quite what you are asking.... Each motor has its own motor starter contactor which must be energized to send power to the motor. The relay contacts of the Mark* (any Mark*--not only the Mark VIe) close to energize the motor starter contactor and open to stop the motor by de-energizing the motor starter contactor. The motor starter contractors are located in what's usually called the MCC: Motor Control Center.

The Mark* is programmed to know when to start and stop all the auxiliary motors, including the Aux L.O Pump motor the DC Emergency L.O. Pump motor and the hydraulic ratchet pump motor when necessary.

The Operation and Service manuals provided with the turbine-generator have written descriptions of each system. They aren't usually very detailed but are a great starting place to learn about systems and auxiliary operations.

The hydraulic ratchet pump motor runs whenever the turbine-generator shaft needs to turn while on Cooldown (usually every three minutes) AND when the unit is being started. The hydraulic ratchet pump motor helps to start the shaft turning when it is being started from zero spied (this is called breaking the shaft away from zero speed). The pressure and flow from the hydraulic ratchet pump is usually directed to the hydraulic ratchet self-sequencer and that ports the high-pressure oil to the Pistons of the hydraulic ratchet mechanism which is mounted on the torque converter (usually). The pistons of the mechanism are used to turn the turbine shaft approximately 45 degrees of rotation and to retract the mechanism in preparation for the next rotation (called a forward stroke).

During Cooldown, the hydraulic ratchet pump goes through a forward stroke, then a retraction stroke, then a short forward stroke motion and stops--in preparation for the next full forward stroke. The Aux. L.O. Pump runs continuously when on Cooldown (meaning during and between shaft rotations); this is to keep L.O. flowing to the hearings to cool them.

I hope this helps.
Yes this is very helpful indeed. Kindly also help to make out, how actually the control system detects OR which components physically senses that AOP (and EOP) is to be started or stopped. Also Once the component senses that the pump is to started, how it is then transmitted to the control system (Mark-VIe in the control room)? And how the control system energizes the relay enabling the starting of a particular motor?

Sir, tried with the manual and also with the instt person, but could not help myself. thanks for your help..

So, what you <b>really</b> want to know is: how does a control system work? Because a Mark VIe turbine control system is just like many other programmable control systems in many respects. It just so happens that the Mark* series of turbine control systems were developed primarily to operate and protect GE-design heavy duty gas turbines, but the Mark VI and Mark VIe can also be used for DCS applications as well as steam turbines and wind turbines.

A programmable control system uses input modules to detect various operating parameters such as speed and pressure and temperature and vibration and position. The main "processor" of a programmable control system is programmed (configured) to use those input parameters to operate (control) and protect some equipment (such as a gas turbine and auxiliaries). The determinations made by the program in the processor (and there may be multiple, redundant processors) are then directed to output modules to control fuel flow-rate or valve position or. Or the operation of an electric motor or a torque converter or a diesel engine being used as a starting means for the gas turbine. Programmable control systems are very versatile and can generally be used for many different and diverse applications; turbine and auxiliary control and protection is one specialized and complex application of a programmable control system.

Most basic operations of a Mark VIe turbine control system are based on the speed of the turbine shaft, or if it is not spinning (called zero speed). The operation (of many electric motors and solenoid-operated vavkes, for example) are based primarily on turbine shaft speed. Other operations are based on more complex mathematical schemes and calculations--all of which can be configured as necessary to control and protect a turbine and its auxiliaries and its driven device using a programmable control system with input and output modules and one or more processors.

The exact details of how the Mark VIe operates to sense the various parameters of a GE-design heavy duty gas turbine are very technical and can be very confusing and complicated--especially to an inexperienced person or someone who has had little or no training. I know, having worked on GE-design heavy duty gas turbines around the world for more than 35 years, that there are Operations and Service Manuals provided for each and every site (which may have more than one turbine). And that there are many people at many sites who do not use the manuals to educate themselves about turbine operation and systems. I also know that at too many sites there are people who do not allow others at the site to access or use the manuals to learn and educate themselves.

There is also the very real problem with the manuals that things are not presented in a readable manner. Or in a manner that is understandable to a new, or even a novice, person. BUT, there is still a lot of good information in the manuals that, while not well-presented, is very valuable.

To understand what a turbine control system does one really needs to know how a turbine works. And to understand how a turbine works one needs to study and understand the P&ID's (Piping & Instrumentation Diagrams); GE usually calls them Piping Schematic Diagrams, or Schematic Piping Diagrams. They are the graphical representation of the various systems and show most of the I/O (Inputs and Outputs) that are connected to the Mark VIe. Most people resist trying to study and learn these drawings--but you can be assured that if will you study and learn them you will be on the best path to learning and understanding how the Mark VIe programmable turbine control system works.

So, the best places to start learning are the System Descriptions and P&IDs in the Operations & Service Manuals.

If you have questions we will try to answer them here. But, you have to be motivated and do your own research and learn to use the available documentation. We can only teach so much from here, and we know nothing about your knowledge and experience, which doesn't seem like much at this point. Know that a well-intentioned key-stroke or mouse-click will not harm the turbine. But lack of knowledge and experience can--and will.

It's great you have got this opportunity, but it's unfortunate that you aren't getting any formal training and are not getting much from the manuals or the instrumentation technician. Many people only know what they know and aren't good at explaining things to other people. But, get thee a manual and a set of P&IDs and start studying! LOTS of people have done more with less!

Best of luck.
Thanks again CSA,

Also please inform how many P&ID will be there for a gas turbine? I knew recently that aux motors P&ID is one of them. I am trying to find copies of all for our turbine.


Let's list most (I don't have a comprehensive list of every P&ID for every turbine):

Hydraulic Oil
Trip Oil (sometimes called Control Oil)
Fuel Gas
Liquid Fuel
Liquid Fuel Forwarding (if provided by the turbine packager)
Fuel Purge (if the unit burns more than one fuel)
Cooling Water
Cooling & Sealing Air
Heating & Ventilation
Starting Means
Water (or Steam) Injection (for NOx emissions control, if so equipped)
Atomizing Air (if unit burns Liquid Fuel)
Inlet & Exhaust

These are the most common for most GE-design heavy duty gas turbines. Some units have liquid fuel reliability systems, and nitrogen purge systems. Units which burn naphtha may also have an additional system or two.

Depending on the age and packager of your turbine you may find all of the P&IDs (called Schematic Piping Diagrams, or "Piping Schematics") in Vol. III of the Operations & Maintenance Manuals. Some packagers put the P&IDs in each System Description section of the Manuals.

You want to make your own copies of the P&IDs, and make them as large as your photocopier will make. Then you want bind them together, and as you study them you want to make notes on them for future reference.

Another document you will find VERY useful is the Device Summary drawing. Most packagers provided one; it lists the settings for each device like pressure switches and temperature switches and pressure transmitters and limit switches and level switches and so forth. It also gave descriptions of device numbers (such as 88QA, or 88QA-1). 88 is a device number for an AC electric motor; QA stands for Auxiliary L.O. pump. 88QA is the Aux. L.O. Pump motor. Most devices on the P&IDs are identified by device number, so having the Device Summary is also very helpful when trying to determine what each device is. If GE packaged the turbine at your site, and it's an older machine (pre-2000 or so), you will probably also find the Device Summary in the same section of Vol. II of the Operations & Service Manuals.

Finally, another good document to have (which can also sometimes be found in Vol. III of the manuals provided by GE if GE was the packager of the unit) is the Piping Symbols drawing. It is very useful in helping to understand the various symbols on the P&IDs. Most are pretty common, but some are kind of unique. Having the Piping Symbols drawing can be very useful.

If you have questions, you can ask here on We should be able to help with most questions.