1. Which of these: a) loss of excitation at full load (induction generator operation), or b) inadvertant energisation (Asynchronous motor operation), is more detrimental to rotor of 2-pole synchronous generator?

2. Why the speed of rotor increases (super synchronous) in induction generator?

3. MarkVguy - I appreciate your article on end-winding heating. How does the reactive power flow and what is the correct convention of naming it? Is it lagging/leading reactive power or "generator absorbing/supplying" reactive power? Does generator really "absorb" reactive power? I also had a look at the following website http://eknowledge.pjm.com which has explained about the reactive power flow.

I shall be grateful for help in this regard.

 

markvguy has been told that his understanding of reactive power flow is actually a misunderstanding. Apparently, leading VArs don't flow INTO an under-excited synchronous generator running in parallel with other generators on a large or infinite grid.

This author is still researching the explanation which has been offered, but it seems that synchronous generators only export VArs, they aren't capable of receiving or being a VAr load on the grid. This is counter to his understanding, so it's going to take some research. As we all know, there isn't a lot of (understandable) writing on VArs. It's NOT rocket science, and this author FAILS TO UNDERSTAND why any explanation of the topic MUST ALWAYS begin or end with vector diagrams, which are absolutely useless to operators (who are an extremely difficult group of people to talk- or work with to begin with).

This author has always considered that when a synchronous generator being operated in parallel with other generators on a large/infinite grid is operated in an over-excited condition that it was "exporting" VArs to the grid (known as Lagging VArs). He has also considered that a synchronous generator being operated in parallel with other generators on a large/infinite grid in an under-excited condition was a VAr "load" on the grid, receiving VArs from the grid (known as Leading VArs)--which is what has been questioned and said to be false. Research is under way, but engineering library access won't be available for another couple of weeks.

As for which condition would be more detrimental, this author has seen the aftermath of inadvertent energization--and the unit was rendered useless. The turbine rotor was bent, the load coupling was broken!, the generator rotor was bent, and the rotor coils were electrically open and bulging out of the slots. If a unit were to be operated at full load and a loss of field condition occurred, this author has always been told that induction would cause the rotor to heat up very quickly. It is believed the generator wouldn't operate in this condition for "very long", and if allowed to would probably require major maintenance or replacement.

This author has no experience with super synchronous induction motors or generators.

markvguy