WhyPower PowerLine Map

Below you'll see an overhead map of a Power Grid for part of Whyville and Myville. Notice there are 3 towns; each town is supplied electricity by a dedicated power plant and power lines. Town B and Town C also have electrical substations between the town and power plant.

Your job in this game is to understand how the power plants, substations and power lines work together to provide electricity for a town. Interesting points along the power lines have been marked with red dots. Measuring the voltage and the current in the wires at those points will help you understand how the Power Grid works.

To start, you should earn your Powerline Technician badge. Pick up the meter and drag and drop it onto the colored boxes attached to each square dot on the power lines.

After you have measured the voltage and current at each location, you need to compute the Power at each of those locations. Click the colored boxes and enter the power values.

When you have finished, you'll have earned your Technician badge, and you can move on to earning your Engineer badge.

Great! Now that you have measured all the voltages and currents and computed all the power values, see if you can answer these questions for your Engineer level badge.

What value remains the same in Circuit A?

Voltage
Current (amps)
Power (watts)

Around Circuit A, what values decrease in the direction of the arrows? Check all that apply.

Voltage
Current (Amps)
Power (watts)

The difference between the voltage going into and coming out of a Town is always how many volts?

volts

The difference between the power going into and coming out of a Town is always how many watts?

watts

Those 1,152 watts of power you just computed above across each Town represents the useful amount of energy supplied by the power plant, that can be used to cool homes, light streets, run the dishwasher, etc.

The total power generated by the power plant is shown in the top left box of each circuit. So the power plant in Circuit A generates 10,464 watts.

Compare the power generated by Power Plant A and the useful power used by Town A:

The Town uses more power than the Power Plant generates
The Power Plant generates just about the same amount of power as the Town uses
The Power Plant generates a little more energy than the Town uses
The Power Plant generates much more power than the Town uses.

Where does all the missing power go?
It just magically disappears
The wires that carry the electricity to the Town heat up, and that wastes the electricity
The energy is recycled by the Power Plant and used again

So, now we see mostly how a power grid works. Electrical power is generated in the Power Plant, and sent along wires to the towns where it will be used. Along the way, power is lost in the wires as heat and other excess radiation.

That means the goal of a Power Grid Engineer is to reduce the energy lost in the power lines as much as possible.

Let's compare the three circuits below to see which does the best job of reducing power lost.

Complete this table:

	Town A	Town B	Town C
Power generated by the Power Plant	watts	watts	watts
Power used by the Town	watts	watts	watts
Power wasted:	watts	watts	watts

Which circuit wastes the least power?

Circuit A
Circuit B
Circuit C

Yes, Circuit C loses only 182 watts out of the 1334 watts it generates. In other words, only 14% of the energy is wasted. Circuit A wastes a whopping 89% !

What are the differences between Circuit A and Circuit C? Check all that apply.

Town C is closer to the power plant, so the wires are shorter.
Town C uses less power than Town A
The wires between the power plant and Town C go through two electrical substations

Great, yes, shorter wires and substations must explain the difference.

Let's examine the shorter wires. Circuit B and Circuit C are almost identical, except that the distance between the Circuit B substations is twice the same distance in Circuit C.

So, if we can investigate the differences in those circuits, we can see how longer or shorter wires affect the power loss.

Let's compute the power lost in each wire. Complete the table below:

Circuit B					Circuit C
Watts generated in the Power Plant:		Watts entering first substation:		Power lost in wire:	Watts generated in the Power Plant:		Watts entering first substation:		Power lost in wire:
	–		=			–		=
Watts leaving the first substation:		Watts entering second substation:		Power lost in wire:	Watts leaving the first substation:		Watts entering second substation:		Power lost in wire:
	–		=			–		=
Watts leaving the second substation:		Watts entering Town:		Power lost in wire:	Watts leaving the second substation:		Watts entering Town:		Power lost in wire:
	–		=			–		=

Total power lost in wires (add up boxes above):					Total power lost in wires: (add up boxes above)

Compare the power losses computed above, and check all that apply:

Most of the power lost is in the long stretch between the two substations
The wires between the substations in City B lose about twice the power as the same wires in City C
The voltage drops in the wires between the substations are about the same in the two Circuits
The current in the wires between the substations are about the same in the two Circuits

YES! So, the shorter the power line, the less electricity it wastes.

Now, let's see what the substations are doing, because Circuit B still wastes less power than Circuit A, and their wires are exactly the same length. Compare the voltages entering (293 volts) and leaving (2032 volts) the first substation in Circuit B.

The voltage leaving the substation is about 5 times the voltage entering
The voltage leaving the substation is about 6 times the voltage entering.
The voltage leaving the substation is about 7 times the voltage entering.
The voltage leaving the substation is about 8 times the voltage entering.

Ok, so the voltage increases a lot inside the first substation. What about the current?

Compare the current entering (4.8 amps) and leaving (0.68 amps) the first substation in Circuit B.

The current leaving the substation is about 5 times less than the voltage entering
The current leaving the substation is about 6 times less than the voltage entering
The current leaving the substation is about 7 times less than the voltage entering
The current leaving the substation is about 8 times less than the voltage entering

Lastly, what about the power? How does the power change as the electricity passes through the first substation?

The power drops a lot in the substation
The power mostly stays the same in the substation, maybe dropping just a bit
The power increases a lot in the substation

It turns out that an electrical substation is mostly just a big transformer. A transformer is an electrical device that can easily increase or decrease the voltage in a wire, while leaving the power mostly unchanged. If it doubles the voltage, it cuts the current in half.

So, Circuit B might lose less power than Circuit A because the first substation drastically increases the voltage and drastically decreases the current in those long wires.

Can we understand why? The reason these wires lose energy is because they have some Resistance. Resistance is complicated, but everything (except maybe a Superconductor) has some Resistance, and it drains energy from your circuit.

A scientist named Jeorg Ohm figured out the relationship between Voltage, Current, and Resistance, so there's a rule called Ohm's Law that says:

Voltage = Resistance x Current

A little algebra rewrites that as:

Resistance = Voltage ÷ Current

We measure Resistance in Ohms, in honor of Jeorg Ohm.

Use the equation above to compute the resistance in the wires.

Circuit A	Voltage leaving Power Plant:	–	Voltage entering town:	=	Voltage lost in wire:	÷	Current Flowing in wire:	=	Resistance of wire:
		–		=		÷		=
Circuit B	Voltage leaving Power Plant:	–	Voltage entering first substation:	=	Voltage lost in wire:	÷	Current Flowing in wire:	=	Resistance of wire:
		–		=		÷		=
Circuit B	Voltage leaving first substation:	–	Voltage entering second substation:	=	Voltage lost in wire:	÷	Current Flowing in wire:	=	Resistance of wire:
		–		=		÷		=
Circuit B	Voltage leaving second substation:	–	Voltage entering Town B:	=	Voltage lost in wire:	÷	Current Flowing in wire:	=	Resistance of wire:
		–		=		÷		=

Let's analyze our results above. Compare the resistance of the wires in Circuit B to the resistance of the single long wire in Circuit A:

Circuit A has a lot less resistance
Both circuits have about the same resistance.
Circuit B has a lot less resistance.

So, the wires in the two circuits are pretty much the same. So, why does Circuit A lose so much more power? Let's do a bit more algebra, and combine the two equations that we know:

Voltage = Resistance x Current
Power = Voltage x Current

If we re-arrange them a bit, we see that:

Power = Resistance x Current x Current

That means that the Power lost in a wire depends on the resistance of the wire but also, more importantly, on the Current in the wire. If we double the current in the wire, we quadruple the power lost!

Now, finally, we understand why Circuit A loses so much more power than Circuit B.

Circuit B loses less energy in the long wires between the substations because the current in those wires is much less than the current in the wires in Circuit A.

One final question: if you are designing a power grid, how would you best minimize power losses in your circuits? Check all that apply.

String long wires straight from your Power Plant to the town, to minimize Resistance in your circuit
Add substations to your circuits to get the current as low as possible in your wires, since lower current means less power wasted to resistance
Keep your Power Plants as close as possible to the towns they are serving, since the power loss in a wire increases as the wire gets longer.

Measurements Needed: 0 | Power Computations Needed: 0

Drag the meter on top the colored boxes to measure the voltage and current at each location.

Drag and drop the meter here to measure the voltage and current at this point in the wire.

Click to enter the power present at this point in the wire...