Transient Stability in Power System

A transient occurs when connections are made to or interrupted from a power line. These appear as "sparks" or flashes. If the power system is operating at 50 Hz or 60 Hz, the frequency of the rapid connection/disconnection (as contacts bounce or move apart) is brief but composed of high frequency components during the event. This has the effect of being connected to a much higher frequency power source which can wreck havoc on systems designed to operate at 50 or 60 Hz.

Basically, the "stability" is a description of the capability of the power system to absorb those high frequency pulses or noise and dissipate it as heat in the core of some large transformer. If the transients make it into the loads connected at the time, the effect can be devastating.

In the case of my new refrigerator, the control boards are wiped out almost every time there is a glitch on the power line. After several warrantied service calls and even another totally new refrigerator, I decided to protect it with a 2KVA UPS and I haven't had a problem since.

I guess you mean what we call a "Grid" here. Gigawatts of generation and lots of transformers and power lines around a country. A battery and voltage converter in a mobile phone is a "power system". If switching-off the phone transmitter causes the voltage to jump high [transient - short duration event] enough for long enough to damage the receiver before the voltage is restored to normal steady [stable] value, you have a "Transient Stability" problem. In the case of Grids, an example of transient stability questions would be "If the 2GW nuclear power plant at XXX disconnects suddenly will the whole Grid collapse? How much will the frequency fall? How much load is disconnected by under-frequency protection? How long before frequency returns to normal?". Along with the frequency question would be another about what happened to the Grid voltage after the disconnection of XXX plant?

In an electrical system when generators are running in parallel, they remain in synchronism with each other. In the case of large disturbance (severe unclear fault or very large load change) of the electrical system, the generators may loose the synchronism and the system becomes unstable. To maintain the generators stable in such disturbance condition is called transient stability. Generally the massive blackout occurs due to lack of transient stability of the system.

For detail see these links:

http://nptel.iitm.ac.in/courses/Webcourse-contents/IIT-KANPUR/power-system/ui/TOC.htm (click Chapter 9, Click Next etc.)

http://cr4.globalspec.com/thread/51442

- MS

So you know now, Guest, there are many sides to "transient", "stability" and "Power System". Did we help? A reply and "Thank you" would encourage us to continue CR4.