I wrote this, some years ago, for a writing mill looking for an info-ish article to sell to an electrical company. It didn’t get bought, but I had fun writing it, and here it is.
How do electric utility companies get electricity from the power plant to your house? First, they need the raw material – high-voltage electricity. It is useful to think of voltage as a pressure measurement, and current as a flow measurement. At this point you could be forgiven for asking, “Why high voltage when low voltage would be so much safer”? The answer is that at high voltage there is relatively less resistance to the flow (current) of electricity. Attempting to do long distance power transmission at 120 to 240-volts would result in absurd losses, and would require much more copper to get the job done.
For instance, consider a 765,000-volt transmission line versus a lowly 345,000-volt line, both transmitting power over a distance of 100-miles. In the 765kV line, resistance losses can as low as one-percent, in the 345kV line they are likely to be about four times higher. So there’s that. Power plants in the US typically generate electricity at voltages ranging from 2,300-volts to 30,000-volts, truly piddling amounts compared to what is needed for efficient long-distance transmission. So the transmission substations connected to the power plant typically step-up the power to anywhere from 230,000 to 765,000-volts before sending it along. This stepping up is done with transformers – transformers are intriguing stationary devices that we’ll have to gloss over for now.
A transformer, an almost magical device, cannot change the amount of power produced, it only changes the characteristics of that power. When a transformer increases the voltage, the current (or flow) is reduced. Since we define electrical power in terms of Voltage x Current it’s easy to see that if one goes up, the other must go down for a given amount of power. When electrical power reaches your home, it will have been stepped down several times. Each time the voltage is stepped down the current (flow of electricity) is increased. By the time the power reaches your home it a relatively safe 120 to 240-volts with ample current. This wonderful property of electrical power is the key to how power is distributed: step up as needed for efficient transmission, step down as needed for maximum flow and safer voltages.
Our power grid, made up of four interconnected North American grids, is designed so that power can be delivered where and when it is most needed. The power grid operator is a sort of market maker, who ensures that a grid needing electricity can be connected to a grid that has electricity to spare.
Power is transformed at two types of substations: transmission substations, and distribution substations. The distribution substation is closest to your home, and transmits lower (although still very high) voltages. A typical flow might appear as below.
copyright 2018 by Almost Lucid Geezer
san bernardino, ca