# electrical grid

## transmission lines

Transmission lines on big towerslike those in the opening photo abovecarry high-voltage electric current from power plants to electric substations. Smaller towers and individual power poles carry lower-voltage current from electric substations to homes and businesses.

## electric substations

Electric substations have several functions. Many substations distribute electricity from a few high-voltage lines to several lower-voltage lines. They have electric transformers, which use electromagnetic induction to change the voltage of the current. Some transformers increase the voltage; others decrease the voltage. In the Figure 1.2, you can see how both types of transformers are used in an electrical grid. A step-up transformer increases the voltage of the current as it leaves the power plant. After the voltage has been increased, less current travels through the high-voltage power lines. This reduces the amount of power that is lost due to resistance of the power lines. A step-down transformer decreases the voltage of the current so it can be distributed safely to businesses and homes. A high-voltage power line may have 750,000 volts, whereas most home circuits have a maximum of 240 volts. Therefore, one or more step-down transformers are needed to decrease the voltage of current before it enters homes. Q: Assume that a home needs a 14-volt circuit for a light and a 120-volt circuit for a microwave oven. If the main power line entering home has 240 volts, what can you infer about the homes electrical system? A: The homes electrical system must have step-down transformers that lower the voltage for some of the homes circuits.

## what is an electrical grid

An electrical grid is the entire electrical system that generates, transmits, and distributes electric power throughout a region or country. A very simple electrical grid is sketched in the Figure 1.1. The grid includes a power plant, transmission lines, and electric substations, all of which work together to provide alternating current to customers.

## power plants

Electricity originates in power plants. They have electric generators that produce electricity by electromagnetic induction. In this process, a changing magnetic field is used to generate electric current. The generators convert kinetic energy to electrical energy. The kinetic energy may come from flowing water, burning fuel, wind, or some other energy source.

## instructional diagrams

No diagram descriptions associated with this lesson

## questions

electrical grids include

``````a) power plants.

b) transmission lines.

c) electric substations.

-->  d) all of the above
``````

the voltage of current that leaves a power plant is increased

``````a) after the current has been transmitted to homes.

b) near the power plant by step-down transformers.

-->  c) for the purpose of reducing current in transmission lines.

d) two of the above
``````

electric transformers use electromagnetic induction to change the resistance in electric lines.

``````a. true

-->  b. false
``````

the main function of electric substations is generating additional electricity.

``````a. true

-->  b. false
``````

electric substations may distribute electricity from a few high-voltage lines to several lower-voltage lines.

``````-->  a. true

b. false
``````

## diagram questions

No diagram questions associated with this lesson