# Transient and subtransient reactance of alternators

1. Nov 3, 2010

### arun babu

please explain the transient and subtransient reactance of synchronous machines

Last edited: Nov 3, 2010
2. Nov 3, 2010

### chaoseverlasting

I assume you're referring to Fortescu's analysis of 3 phase machines. Its a mathematical representation of 3 phase systems that makes analysis easier in some respects. There are other, more experienced members on this forum who could answer your question better.

As an example, I think the Buccholz relay in transformers measures negative sequence currents within a range to raise alarms. This is only possible because we can measure the negative sequence current accurately. Practically it is useful, so we translate the known quantities to better understand the system. Another example is that zero sequence current interfers with communication lines. Thus, we can attribute that interference to a particular component of electrical power. Sorry if this doesnt help.

3. Nov 3, 2010

### arun babu

oops...that was not what i was looking for...anyways thanks for the info..in fact i hope to get a very down to earth and easy to understand explanation on the said topic ie transient and sub transient reactance of alternators...

Last edited by a moderator: Nov 3, 2010
4. Nov 3, 2010

### Staff: Mentor

Well, you need to start by telling us what you know so far, and what sources of information you have used.

5. Nov 3, 2010

### arun babu

i have learnt that it is concerned with the induced current in damper winding and field winding of synchronous machines..which is divided into transient period and sub transient periods

Last edited: Nov 3, 2010
6. Nov 4, 2010

### m.s.j

Generator fault current is normally discussed in terms of “subtransient,” “transient,” and “synchronous” currents and impedances. These terms refer to various time periods during the decay of the AC component of current. Attached Figure plots the envelope of the AC current for a typical machine. The subtransient current, reactance and related time constant defines the AC current component from the inception of the fault and the following cycle or two. This is the maximum available AC short-circuit current from the generator. Synchronous quantities define the final or steady-state current. The transient parameters define the interim current.

--------------------------------
Creative thinking is breezy, Then think about your surrounding things and other thought products. http://electrical-riddles.com

File size:
21.2 KB
Views:
387
7. Nov 4, 2010

### arun babu

thank you m.s.j. could you please explain how generator fault current arises?????

8. Nov 7, 2010

### m.s.j

9. Dec 20, 2010

### omjai

is there any kind of flux variation during the transient state n in the final steady state ??

10. Dec 21, 2010

### m.s.j

Any emf without flux variation is impossible. Please more explain.

--------------------------------------------------------

Creative thinking is breezy, Then think about your surrounding things and other thought products. http://electrical-riddles.com