Power grid scavenger hunt (student document)

Your assignment is to find as many of the following “pieces” of the power grid as you can. If you think you’ve found one of them, take your own photograph of it and note the location. Many of the pieces you can find by walking around your neighborhood, but some of the pieces you might only see while traveling around in a vehicle.

1) Transmission line2) Subtransmission line3) Distribution line4) Pole-mounted transformer5) Pad-mounted transformer6) Fuse7) Static wire8) Ground wire9) Guy wire10)Electric meter11)Circuit breaker panel12)Substation

Power lines

The most obvious parts of the power grid are power lines, which consist of cables hanging high above the ground, strung between wooden poles or steel towers.

You will notice different sizes and shapes of power lines. The largest ones are steel lattice towers called “transmission lines.” They carry electricity from power plants to cities over long distances. The electricity is transmitted at very high voltage (for example, 345,000 volts), because higher-voltage transmission is more efficient. Medium-sized power lines, called “subtransmission lines,” carry electricity through a city or to large industrial consumers. They can be made of steel or wood. A typical voltage might be 69,000 volts. The smallest power lines (and the ones most commonly seen near your home) are called “distribution lines.” They carry electricity through neighborhoods. They are most often made of wood. A typical voltage might be 12,000 volts.

Try to find one type of transmission line, one type of subtransmission line, and one type of distribution line. The ones you find in your city might not look exactly the same as the ones shown in the diagram, but try to classify the lines you find as best you can. Some poles might carry multiple types of power lines (for example, a subtransmission and a distribution line, or two distribution lines). Poles might also carry fiber optic, cable TV, or telephone lines farther down on the pole, which makes them even more confusing!

Questions to consider about power lines:1) As you look at power lines from lower voltage to higher voltage (from right to left)

in the diagram above, you should notice some trends. As the voltage of a power line increases, what else changes about it? Given what you know about electricity and voltage, can you think of a reason each trend exists?

2) What are some similarities you notice among most (or all) power lines?3) The majority of power lines are NOT insulated. What might be some possible

reasons for this? Do you think leaving power lines uninsulated is worth the risk?4) If power lines are not insulated, how can birds sit on them without being shocked?

Pole-mounted transformer

Pole-mounted transformers are found on distribution lines. They lower the voltage of the electricity coming from the distribution line to 120 volts, so that it can be safely used in homes and businesses.

Questions to consider about pole-mounted transformers:1) How many of these can you find? Are they rare or common?

Pad-mounted transformer

Pad-mounted transformers are usually green metal boxes that sit on a concrete pad. They will have lots of warning signs, like “Danger: High Voltage,” so don’t get too close! Pad-mounted transformers fulfill the same exact role as pole-mounted transformers: they lower the voltage of the electricity so that it can be used in homes and businesses. However, they are used in areas with underground distribution lines.

Questions to consider about pad-mounted transformers:1) Can you find the transformer (it might be pole-mounted or pad-mounted) that

supplies electricity to your home? Does this imply that your home is powered by overhead or underground power lines?

Fuse

A fuse is a safety device that will melt if too much current passes through it, which might happen if lightning strikes the power line or if the line touches a tree.

Questions to consider about fuses:1) Why do you think fuses are designed to melt when too much current passes

through them?

Static wire Ground wire

A static wire is the highest wire on all types of power lines. It usually does not carry electric current, but it does serve a very important role: it will intercept lightning strikes so they don’t hit the power line itself.

A ground wire runs the length of a power pole. It is connected to the static wire and will carry current caused by lightning strikes safely into the ground.

Questions to consider about static wires and ground wires:1) What might happen if power poles did not have static wires and ground wires?

Guy wire

A guy wire runs from high on a power pole to the ground at an angle. Guy wires are not meant to conduct electricity at all. They are sometimes, but not always, covered by a bright yellow plastic tube.

Questions to consider about guy wires:1) Can you figure out the purpose of guy wires?2) Can you think of a reason for the bright yellow plastic tube?

Electric meter

An electric meter is a device that measures how much electrical energy is being consumed by a building or apartment.

Questions to consider about electric meters:1) Can you find the electric meter that is measuring the energy used by your home?

Circuit breaker panel

Circuit breaker panels provide a homeowner access to all the circuit breakers for different circuits in the building. (For example, the furnace, air conditioner, kitchen outlets, bedroom outlets, etc. may all be on different circuits in a house.) A circuit breaker is a switch that will open (thereby stopping the flow of current) whenever too much current is flowing. Circuit breakers are similar to fuses but they don’t need to be replaced entirely when they trip. A person can simply reset the circuit breaker to restore electricity to the circuit. If you find the circuit breaker panel for your house, don’t touch it without your parents’ permission!

Substation

You might have to search around to find a substation… you probably won’t find one in your neighborhood. A substation will have lots of electrical equipment contained in a fenced enclosure. You might see large power lines on one side of a substation and smaller power lines on the other side. Substations can fulfill a variety of different functions, but consider two types of substations: transmission substations, which increases the voltage from power plants so it can be transmitted long distance along transmission lines, and distribution substations, which decreases the voltage from transmission lines so it can be distributed through a city.

Below is a diagram of the power grid to help you put together all of the “pieces” you’ve discovered in this scavenger hunt.