Overvoltage of shunt capacitors

I am reading book about voltage stability, it mentions that overvoltage will happen at the stable part of the system as voltage
collapse results in system breakup.
Any one know why?
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On 6/25/07 2:32 PM, in article snipped-for-privacy@e9g2000prf.googlegroups.com, "kelfookf"

gobbledegook
Bill
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I am reading book about voltage stability, it mentions that with applie of shunt capacitors, overvoltage will happen at the stable part of the system as voltage collapse results in system breakup.
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Gobbledegook.
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Cheers .......... Rheilly P



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The whole purpose of such capacitors is to produce reactive required by the load. In the case of loss of load, there can be overvoltages due to these capacitors. Look at a line with inductive impedance and a load at the end. Put reactive compensation at the load end and look at the voltage. Now drop the load and keep the reactive compensation and see what happens to the voltage. In some cases it can be quite drastic- near series resonance.
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This is mention in a book that I don't quite understand how it happens
"There are several disadvantages to mechanically switched capacitors. ... If voltage collapse results in a systems in a system breakup, the stable parts of the system may experience damaging overvoltages immediately following separation. "
Cheers,
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As Don pointed out, having capacitors at the end of an inductive line is a common practice to compensate for any inductive loads placed on the line. (having an inductive load on an inductive line results in pretty severe voltage drop without any compensation)
Mechanical switches that are automatically controlled to maintain line voltage at the load end will switch caps in/out as load increases/decreases. But they react rather slowly, they are designed to 'follow' with normal load fluctuations.
When a system starts to trip lines and 'break up', the inductive load can be lost much faster (like a single breaker tripping). The mechancial switch won't disconnect the caps fast enough and the large capacitance at the end of an inductive line can result in very high voltages.
daestrom
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