Dear Mr. Jacob,

your guess is correct: voltage regulators (reactive power control) and speed governors (active power control) have very different time constants. The first has settling time in the order of hundreds of milisseconds, usually under 400ms for static excitation or 800ms for rotating. And governors have settling time of some seconds, depending too much on the type of prime mover. Values from 4 to 10 seconds being very common.

Dear Erick Alves,

thanks for your answer. A popular proceeding to this topic is

Stefan STERPU: Robustness margins in electric power systems; Power and Energy Society General Meeting - Conversion and Delivery of Electrical Energy in the 21st Century; IEEE pp.1 - 6, 20 - 24 July 2008.

You can it download from

http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=4596197

or I can send you a copy. In page 5 chapter V. (CASE STUDY) last section will be advice to agreement between performance und robustness!

The DPMA in Germany (http://www.dpma.de) pointed this proceeding in accounting of investigation procedure at the patent specification

https://www.researchgate.net/publication/235343232_Verfahren_und_Vorrichtung_zur_Spannungs-_und_Blindleistungsregelung_der_elektrisch_erregten_Synchronmaschine_mit_einer_besonders_robusten_Anpassung_an_ihren_nichtlinearen_Magnetkreis .

I think performance und robustness is not a contradiction. My experience is, the voltage regulators should be preventing reactive power oscillations. In the parallel operation of flywheel generators (in IPP Garching) reactive power oscillations cause active power oscillations. Active power oscillations abbreviate the life time of flywheel generators.

Are in the parallel operation of synchronous machines in 380-kV-grid similar problems?

Best Regards

Christian Jacob

Patent Verfahren und Vorrichtung zur Spannungs- und Blindleistungsr...

Dear Mr. Jacob,

sorry for the late reply.

I would highly appreciate if you can send me the text from PES General Meeting.

My practical experience with both AVRs (automatic voltage regulators) and governors shows me there is a close relationship between robustness and performance.

AVRs with high gains are usually necessary to have low rise and settling times. Nevertheless, AVR with high gains causes transient active power oscillations in the 2Hz range (local mode). The peak of these oscillations usually are in the 2-3% of the apparent power of the unit. But specially in long transmission lines or weak grids, these oscillations can reach 5-6% of the apparent power.

A PSS (power system stabilizer) in the excitation system is usually necessary to damp these oscillations as governors are too slow to damp them. However, the use of a PSS increases reactive power oscillations.

The book Power System Stability and Control from P. Kundur (http://www.amazon.com/books/dp/007035958X) explains in detail these correlations, in special chapters 8, 11 and parts of 15.

If you would like to have some reference papers about the subject, I can also post the links.

Best regards,

Erick Alves.