I am investing ideas for converting a GE Frame 6B unit from a Diesel Start Engine to an electric motor start. Any information would be helpful.

The installations consist in a diesel (Detroit V12, 600HP) start engine, for the start up of the gas turbine GE MS 6B. Is needed to change it for an electrical equipment.

 

Changing the starting means is possible, not inexpensive, but possible.

You should start your investigation by looking at the electrical supply system at your site. This is often the limiting factor when considering such a change. How much will the 'auxiliary' electrical supply system have to be modified to support an electric motor of the size required to replace the diesel starting means? Again, this is usually the most costly part of the change as most sites with diesel starting means aren't built with the electrical supply capability to support an electric starting means.

But, I would like to understand why you want to replace the diesel starting means. Are you experiencing problems with the diesel or the diesel governor?

This is not a simple change-out, it can be and has been done before. But, again, the replacement of the diesel with an electric motor is possible, but usually the most work involved is in readying the electrical supply system to provide the power for the electric motor.

 

>Changing the starting means is possible, not inexpensive, but possible>

we are also looking for this because of multiple problems with start up diesels at our frame 5 gas turbine. Is there a package available? What kw size motor do we need?

 

Most diesel starting problems can be traced to some very simple issues. I've seen sites where adding a block heater to the diesel and keeping the diesel warm when the unit was not operating was all that was required to eliminate starting problems.

I've seen older units with worn fuel racks and deteriorated hydraulic actuators be miraculously restored to trouble-free operation simply by having a qualified diesel mechanic in to replace the fuel rack and hydraulic actuators.

In some cases, cleaning or replacing injectors also greatly improved starting--at the recommendation of a knowledgeable diesel mechanic brought in to analyze the problems and make recommendations.

At a couple of sites, the position of the gravity dampers on the Accessory Compartment doors allowed cold air (at -5 to -15 deg C during winter) to be drawn in from the outside across the diesel when the turbine was running. The diesel would reliably start the turbine when the turbine was cold and the compartment vent fans weren't running, but if the unit tripped while running the diesel wouldn't start because it was very cold.

The gravity dampers had originally been installed in the wrong doors and were relocated to the proper door (actually the doors were swapped to different locations) to prevent the cold ambient air from being drawn in "across" the diesel and starting reliability improved dramatically. A block heater was eventually added and all the problems of almost many years went away.

At another site, the shut-off solenoid was mis-adjusted and caused starting reliability problems. A simple readjustment was all that was required.

One of my favorite recollections was the site that continually complained over several years about diesel starting problems. During a site visit, when the diesel failed to start one of the operators went out and reset the air box damper (the emergency diesel stop damper that is held in place with a latching mechanism) to the open position. The unit started on the next attempt. The plant supervisor turned to me and said, "We have to reset that damper almost every time we try to start the unit. That diesel is just totally unreliable!"

After a couple of minutes of discussion, it came out that every time the diesel failed to start if someone went out and reset the damper it always started on the next attempt. Sometimes the diesel would start and then suddenly stop during acceleration. Resetting the air box damper would result in the diesel starting on the next attempt. But the solution to the starting, and even the nuisance shutdowns, always seemed to be resetting the air box damper.

When I asked what happened if someone checked the damper prior to starting the unit and reset it if necessary, I was told that they had never tried that.

We removed the filters to access the air box and emergency shut-off damper and found the bolts holding the damper's latch were loose. We used some thread-locking liquid on the bolts and put the same latch back in place. In some twenty (20!) start attempts in the next couple of days the diesel never failed to start and never shut down unexpectedly. And the air box emergency shut-off damper was never found to be unlatched.

But the Customer still demanded a quote for an electric starting means, and absolutely choked when they saw the cost, and never bought the electric starting motor. And I think GE spent about six man-weeks of effort, including sending people to site to assess the electrical system, to produce a quote for a completely unnecessary quote for something they never sold. (I know most won't cry for GE's loss!)

Oh, and let's not forget the torque converter. They do degrade over time and sometimes it's not the diesel's inability to accelerate the unit, it's the torque converter's inability to transmit the torque from the diesel. I've seen people complain that the diesel is operating at rated speed but not producing sufficient torque, but the fuel rack wasn't even at 60% of rated stroke and the problem was traced to the torque converter.

Lastly, I've seen poor quality fuel and water in the fuel cause lots of problems for diesels. In one case, simply checking the fuel filters revealed water in the diesel fuel, and in another case one site had never replaced the diesel fuel- or air filters in more than 20 years of operation!

Best to get someone out and go over the diesel from stem to stern and refurbish it to like new condition. Pay attention to the details like block temperature and Accessory Compartment cooling air flow patterns.

If you know the HP rating of the diesel on your unit, you can approximate the KW requirements of a starting means. The biggest problem with converting a starting means from diesel to electric is the electrical power supply. Be aware that most electric motors are usually "overloaded" during starting, so the electrical supply must be adequately sized to provide the necessary current. Usually, a new transformer has to be added to accommodate the power requirements of the electric starting motor. That requires a power system study and relay coordination and lots of new electrical system work. It really is a very involved procedure, not just simply changing the physical device that provides the torque to accelerate the unit during starting.

I would have to believe that a full refurbishment of the diesel would be less than 25% of the cost of converting to an electric starting motor.

 

Currently, the general trend on the starting means is to use electric motor (or steam turbine, if steam is available) starter. Diesel is required on turbines with black-start capability. We had the experience of replacing diesel starters with electric motors (350 - 400 HP) on a few MS5002A units. The package was supplied by GE, and it was helpful. However, the logic changes required in the Mark IV Speedtronic system had errors.

If your unit has the older "jaw-type", starting clutch, it will be worthwhile to have them replaced with the newer type - self synchronizing clutch. The "jaw-type" clutches, over period of time' are likely to give problems.

In spite of all these hiccups, still it is worth the troubles you have to take.

To summarize, get GE involved. With out the support from GE, it will be extremely difficult.