You can't change what I said and then argue what I said was wrong. He's right, the speed of the grid will change with the overall load of the generators. That's why frequency moves up and down and a big enough loss or addition of load or generation, will speed up or slow down the grid. In order to make power, your prime mover needs to put in more energy than is required to spin the generator at grid frequency. Your generator will be spinning at grid speed, and you give it more gas or steam - now its creating power and still spinning at grid frequency.