Choosing of Excitation Systems:

Dear Sourav,

From my experience, the earlier generator were provided with a DC generator on the same shaft and the voltage variation was achieved with the rotary amplidyne. As the system started becoming bigger and bigger, the present trend in hydro generators, is to go in for static excitation system with DVR (digital voltage regulator). The performance is extremely good and trouble free. However, for small capacity units (tubular) which has a spped increaser between the generator and turbine, the manufacturers recommend brushless excitation which is also good

For thermal units, the earlier trend was to go in for static excitation systems. The present trend with Indian, European and Japanese manufacturers is to go in for brushless excitation, which are very good. But Chinese manufacturers supply only static excitation with DVR

Samuel Chelliah

Debate on choice of excitation system is going on since last so many years and will continue. Each manufacturer has a philosophy and sticks to it. Each one giving advantages of the philosophy followed by them. For the size of generator you are referring, you should first decide as to what response ratio you are looking for. There is no need to go for some thing which is more than what you need.

With the introduction of digital Automatic Voltage regulators (AVR) both the system can give the response required for most of the systems to which generators are connected.

With static excitation, you will have to change the brushes as and when required, spot machine the slip rings after their normal wear and may have to replace them after some number of spot machining has been done. Spot machining and replacement of slip ring requires longer shut down.

Brushless excitation would be costly but with less of maintenance. But off course with a lesser response as compared to static excitation (but would meet your requirement in all probability).

So have your response requirement worked out and then may make your final choice.

I have observed in cases that excitation system voltage excitation system voltage response time during forcing not more than: 0.05 second.

What does this mean?

sks

This means that in less than 0.05 second the excitation system would raise the excitation voltage to a value that is required to force the excitation current to maintain generator terminal voltage under fault conditions.