Nomorecatering, I was hoping someone else would pad up and answer your questions but I will have a crack at it for you.
Firstly let me tell you I have never worked in a power station but have worked with co generators in Hospitals and the like that work in unison with the grid. I will make this as simple as I can as I have no intension of writing a 100 page thesis or would anyone want to read it.
Imagine you had 2 petrol engines. 1 a v8 running at say 1200rpm and 1 a 4cyl doing 2300rpm but both producing the same hp at those revs. Now say through some clutch mechanism you suddenly joined them together as one. The result would be catastrophic at the very least,with broken crankshafts and bent con rods as a minimum. Now hold that thought. While joining 2 generator outputs together is totally different the end result is similar. For two or more generator supplies to run in unison 4 things have to match up. Voltage magnitude, Phase sequence, Frequency and Phase angle.
Large generators produce 3phase power. In Australia we call these, red phase,white phase and blue phase. All are 120 electrical degrees apart (phase angle). To see this on a scope it looks something like the ABC logo only 3 of them all intermingled but rotating 120deg apart.
The best way to describe how this works is look at the basic 3phase motor.
Around the stator of the motor are sets of winding in groups connected to each phase. Unlike a single phase motor where the current comes in on the active runs around the winding and then out the neutral (return) a 3phase motor has 3 actives but at any given time 1 of those actives is acting as the return.(without a return you would have no flow so no motion)In Australia this changes 50 times/second and is what we call the frequency and measured in Hertz. The rotation direction of that motor is determined by the sequence of each phase supplying the motor and return. eg RWB sequence might result in a clockwise direction. By simply swapping 2 phases at the motor to produce say RBW sequence will cause the motor to rotate counter clockwise.
Now can you imagine the result if we put 2 supplies together that were in opposite sequence or different frequencies ,voltages etc? we are back to our petrol engine senario.Motors would stall,reverse (or try to)burn out, not to mention what it would do to appliances with electronics and also destoy the generators supplying it all. Fortunately this cant happen as there are numerous protection devises installed at different points in the network to monitor and switch off if some event outside the set parameters happen. I use it only as a simple explanation as to why it take such a long time to get it all up and running again once the grid goes off line.
Will continue as time permits with your other questions
Last edited by mostlytossas; 8th Oct 2016 at 04:43.