These are known as aero derived turbines. Google advanced on the words AERO DERIVED TURBINE ELECTRIC. You will get about 39000 hits.
The difference is well described by this cut and paste:
>Aero-derivative unit
The aero-derivative type of gas turbine is more adaptable to variable loads than the heavyweight unit and is therefore widely used for gas and oil pumping, as well as for electrical power generation. The turbine may contain more than one concentric shaft to obtain optimum performance from different stages of gas expansion and air compression.
>Heavyweight unit
The heavyweight gas turbines are used mainly for electrical generation. They are often built as a single shaft machine where the compressor, turbine and power turbine are on a single shaft. On start-up the complete rotor has to be accelerated to a self-sustaining speed, usually by a diesel engine or electric motor. For power generation they can maintain good speed control in the event of loss of electrical load.
I worked for a utility that had some aero derived units. When I ran the generation desk, responsible for meeting load, I loved those units. When called on they could be on line at full load in less than 10 minutes. We had 4 of these units with each unit having 2 aero derived (747) engines. Each unit was good for 50 megawatts, 70 megawatts if it was cold out, denser air is good.
The heavy units took 20 minutes to get on line. All of them could run on gas or light fuel oil.
On our aero units the engine was not direct coupled to the generator. The generator had an power turbine on each end that was spun by the exhaust of the aero engine. The line up had the generator in the middle and a jet engine on each end. In an emergency the unit could run with just one engine but there was a power penalty from spinning the unpowered turbine.
Our heavy units were single shaft. All compressor turbines, exhaust turbines and the generator are on the same shaft and revolve at the same speed, 3600 rpm. The heavies only had one burner chamber and it was perpendicular to the shaft.
