Electric Power Transmission:

[MrPickins]

Our electricity went out last night, and I woke up at 2am when my fan shut off. I always sleep with a fan on, so there was no chance I'd fall back asleep. Power didnt come back for about 2 hrs, so I had plenty of time to think.

Anyway, my question is: How does the power company avoid having a huge load when they switch service back on? I'm sure it would be less of an issue that late at night, but yesterday it hit 107F and I know 75% of the a/c's in the outage area tried to kick on within a few seconds of restoration. That has to be a massive load.

I heard today that the outage was caused by a fire in a sub station, and that they got the power back in 2 stages, 1 hr apart. That cuts load in half, but the report said "over 10k people" lost power. That still has to be a ton.

Anyone in the know that can give me a rough idea?

 

[Bassyhead]

I don't know about distributing the power slowly as to not overload the system, but as to supply, power companies can supply more power than they can produce as their grid is connected to other grids and can obtain power from them.

 

[The Boston Dangler]

They activate small sections at a time. Turning a whole town on at once is asking for a meltdown.

 

[PowerEngineer]

As you have correctly surmized, not all electrical appliances are running all the time. Many of the largest users of electricity (e.g. space heaters, air conditioners, water heaters, refrigerators, etc.) are continually cycling on and off. Electric utilities often take this load diversity into account when sizing the equipment in their their distribution systems. This works fine most of the time. When there's an outage (over maybe 30 minutes in length), there's a understandable tendancy for all those big appliances to switch on as soon as power is restored. We call this the "cold load pick-up" problem. To overcome this problem, we often end up segmenting a feeder (usually 500-1000 residential customers), restoring the first segment and waiting 20 minutes for all their appliances to start cycling again, and then the next segment, and the next...until everyone is back in service.

 

[MrPickins]

Originally posted by: PowerEngineer

As you have correctly surmized, not all electrical appliances are running all the time. Many of the largest users of electricity (e.g. space heaters, air conditioners, water heaters, refrigerators, etc.) are continually cycling on and off. Electric utilities often take this load diversity into account when sizing the equipment in their their distribution systems. This works fine most of the time. When there's an outage (over maybe 30 minutes in length), there's a understandable tendancy for all those big appliances to switch on as soon as power is restored. We call this the "cold load pick-up" problem. To overcome this problem, we often end up segmenting a feeder (usually 500-1000 residential customers), restoring the first segment and waiting 20 minutes for all their appliances to start cycling again, and then the next segment, and the next...until everyone is back in service.

That is exactly the answer i was looking for. Thanks a ton. 🙂

 

[Howard]

Originally posted by: PowerEngineer

As you have correctly surmized, not all electrical appliances are running all the time. Many of the largest users of electricity (e.g. space heaters, air conditioners, water heaters, refrigerators, etc.) are continually cycling on and off. Electric utilities often take this load diversity into account when sizing the equipment in their their distribution systems. This works fine most of the time. When there's an outage (over maybe 30 minutes in length), there's a understandable tendancy for all those big appliances to switch on as soon as power is restored. We call this the "cold load pick-up" problem. To overcome this problem, we often end up segmenting a feeder (usually 500-1000 residential customers), restoring the first segment and waiting 20 minutes for all their appliances to start cycling again, and then the next segment, and the next...until everyone is back in service.

Awesome. 🙂

 

[gbuskirk]

Thanks PowerDude, I was wondering about this just a few days ago. Here in the Twin Cities we had a storm last week, and it took almost a week for some homes to get power again. Our home's power was only out for 8 hrs or so. It's one of those things we take for granted!

 

[Goosemaster]

Originally posted by: PowerEngineer

As you have correctly surmized, not all electrical appliances are running all the time. Many of the largest users of electricity (e.g. space heaters, air conditioners, water heaters, refrigerators, etc.) are continually cycling on and off. Electric utilities often take this load diversity into account when sizing the equipment in their their distribution systems. This works fine most of the time. When there's an outage (over maybe 30 minutes in length), there's a understandable tendancy for all those big appliances to switch on as soon as power is restored. We call this the "cold load pick-up" problem. To overcome this problem, we often end up segmenting a feeder (usually 500-1000 residential customers), restoring the first segment and waiting 20 minutes for all their appliances to start cycling again, and then the next segment, and the next...until everyone is back in service.

cool