I'm curious to know if there is a distinction between 'rolling blackouts' and 'cascading power outages.' The terms sound like they are similar, but I'm not sure. I would be interested to know the differences, if there are any. Thank you.

-- Anonymous, September 10, 1998

Answers

Cascading Outages is a known phenomenon in power transmission parlance. I can throw more light on Cascading Outages. Cascading Outage is a phenomenon where one transmission line disturbance (faults, lightning stroke, line breaks) or generator disturbance propagates into multiple disturbances in a wide area.

On August 10, 1996, a major failure occurred in the Western Systems Coordinating Council (WSCC) system resulting in break-up into four islands with loss of around 30,000 MW of load affecting 7.4 million customers in western North America. This grid disturbance started with a 500 kV line sagging close to a tree and flashing over. The line was tripped (opened) following unsuccessful single-pole reclosure (attempting to close a line after a transient fault).

On July 2, 1996, a short circuit on a 345 kV line (flashover to a tree) in Wyoming started a chain of events leading to a breakup of the western North American power system. July 2 was the third and, until the August 10 failure, the most serious of western system breakups. The first disturbance in Western US was caused by the January 17, 1994, Northridge California earthquake. The second breakup occurred on December 14, 1994, and like July 2, originated in southern Idaho and Wyoming.

The North American Reliability Council (NERC) and WSCC regularly post disturbance summaries on their web sites. The final disturbance reports may be downloaded from the WSCC web site. The NERC annually publishes a report describing major power outages in North America.

Rolling blackouts could be an emergency load shedding exercise carried out to prevent any large scale grid outage.

-- Anonymous, September 10, 1998

A Cascading power outage is when a problem in one part of the transmission or generator system affects another system causing it to fail. Example: generator fails, load on other generators rises until they are overloaded and the safety system trips shutting them down. The shutdown places greater burden on adjacent generating systems which could experience the same overload/shutdown sequence.(a cascacde) A rolling blackout is something a power producer or distributor does on purpose in order to reduce the load on an overburdened system. (Example: Customers served by various substations are taken off line one or more substations at a time for a predetermined amount of time before being turned back on and another group of customers being blacked out.)This enables the power company to "ration" available power and prevent a total shutdown due to overload Hope this helped Keith

-- Anonymous, September 15, 1998