1. Following the Minute Lecture ‘Four analogies to explain reactive power’, we received many reactions. Several writers suggested further analogies
This inspired us for making a sequel to this minute lecture, with four more analogies worked out
When explaining reactive power to lay persons, you can pick any analogy of your choice, according to your target audience

2. What does the analogy needs to explain?
Remember: these analogies are didactic tools; none of them are 100% correct
They elucidate the difference between active power (W), reactive power (VAR), and apparent power (VA)
Some of them also explain why reactive power limits the capacity of the lines in the grid, why reactive power increases energy losses in the grid, or other related phenomena

3. I. The beer analogy (1/2)
Suppose you want to quench your thirst by a cool beer. This beer is the active power (W)
Along with your ale comes a bit of foam, which doesn’t quench your thirst. This is the reactive power (VAR)

4. I. The beer analogy (2/2)
The total content of the glas, is the apparent power (VA)
The more foam, the bigger glas you need (= you need a line with a higher capacity)

5. II. The marble-in-a-tube analogy (1/3)
Suppose your goal is to push marbles out of one end of a horizontal pipe
You accomplish this by pushing marbles into the pipe

6. II. The marble-in-a-tube analogy (2/3)
The first ten marbles will give you no result, they will just fill the tube
Only the 11th marble will result in a marble coming out of the other end of the pipe

7. II. The marble-in-a-tube analogy (3/3)
The ‘marbles in’ can be compared to apparent power (VA), the ‘marbles out’ to active power (W) and the length of the pipe to reactive power (VAR)
The longer the length of the pipe (more reactive power), the more marbles are needed (apparent power) for the same result (active power)

8. III. The cash flow analogy (1/2)
Suppose you are running a business. You have to spend an amount of money C (cost) on one day, for earning a larger amount of money E (earnings) one month later. Your profit will be P = E - C
C is not lost money. However, without spending C, you will not be able to make the profit P
The profit P can be compared to the active power. The earnings E are the equivalent of the apparent power. The cost C is the reactive power

9. III. The cash flow analogy (2/2)
To bridge the time between the spending of C and the earning of E, you will need some money. You could borrow this money (take reactive power from the power grid). That will however cost interest (reactive power penalty)
A better solution would be to have some cash money available at your business (= a capacitor bank at your site).

10. IV. The water tower (1/7)
Suppose a water tower and men that have to bring water to the tank by climbing ladders. After emptying their bucket, they return by another ladder.

11. IV. The water tower (2/7) The climbing ladder = the electricity line
The number of men on the ladder = the voltage
The amount of water each man carries = the current
The amount of water added to the tank per time interval = the frequency

12. IV. The water tower (3/7) Energy = voltage x current
The active power = the height of the tower.
If the tower is high (high power), there are two solutions to keep the frequency: using more men (higher voltage) or increasing the amount of water each man carries (higher current)

13. IV. The water tower (4/7)
There are three ladders = three phases

14. IV. The water tower (5/7) Width of the tower = reactive power
Consequence: the length of the ladder (apparent power/voltage) depends on the height of the tower (active power) and the width of the tower (reactive power).
The higher the reactive power, the longer the ladder. So if the same voltage is kept (same amount of men on the ladder), each man has to carry more water to keep up the same frequency.

15. IV. The water tower (6/7)

16. IV. The water tower (7/7)
If a man is carrying more water (higher current), he will lose some along the way. So more reactive power means more losses.
If the reactive power is so high that the men have to carry really a lot of water, one of the men could collapse  the other men have to carry even more water  if no support from new men is given, the system risks to experience a complete breakdown

17. Round-up
Another four analogies represent the idea of active and reactive power in an electric system:
The beer analogy
The marble-in-a-tube analogy
The cash flow analogy
The water tower analogy
Some people prefer one or another analogy
We hope they will increase the reader’s insight in the phenomenon, or help explaining the phenomenon to others

18. Links and references P Sauer, What is Reactive Power?, PSERC, Sep 2003
Minute Lecture: 4 analogies to explain reactive power