Four analogies to explain reactive power
Minute Lectures
Why an analogy?
Reactive power is an essential aspect of the electricity system, but one that is difficult to comprehend by non-experts
By presenting four different analogies, we hope the reader will • For non-experts: develop insight in the phenomenon• For experts: acquire ideas to explain the phenomenon
Of course, none of these analogies are 100% correct
Four analogies to explain reactive power
Minute Lectures
The difference between active power (W), reactive power (VAR), and apparent power (VA)
The idea of compensating reactive power
Why reactive power increases energy losses in the grid
Why reactive power limits the capacity of cables and lines in the grid
What does the analogy need to explain?
Four analogies to explain reactive power
Minute Lectures
I. The bicycle analogy (1/3)
Power stations, producing electrical energy, are represented by bikers
At the backseat of the bike there are passengers, the consumers of electrical energy (the loads)
Four analogies to explain reactive power
Minute Lectures
I. The bicycle analogy (2/3)
A reactive load can be represented by a passenger leaning to one side
The fact that the passenger is leaning to one side, does not influence directly the work that the biker has to deliver, but without compensation, the bike might fall over
Four analogies to explain reactive power
Minute Lectures
I. The bicycle analogy (3/3)
The biker compensates the movement of his passenger by leaning in opposite direction (= by generating inductive power)
Consequences:• A pedalling figure leaning to one
side cannot work as comfortably as before ( limiting capacity)
• The bike catches more head wind ( extra losses)
Four analogies to explain reactive power
Minute Lectures
Take a boat on a canal, pulled by a horse at the bank
II. The horse-and-boat analogy (1/4)
Four analogies to explain reactive power
Minute Lectures
The fact that the horse is not walking straight in front of the boat, does not influence the work it has to do to pull the boat. But without compensation by the rudder, the boat will be pulled towards the bank of the canal.
Consequences:• The turned rudder leads to extra losses• The fact that the rope is pulling at the flank of the
horse and not straight behind it, limit’s the horse’s capacity to deliver work
II. The horse-and-boat analogy (2/4)
Four analogies to explain reactive power
Minute Lectures
II. The horse-and-boat analogy (3/4)
Four analogies to explain reactive power
Minute Lectures
The vector representation of the force to pull the boat, is similar to the vector representation of power in an electric system:
II. The horse-and-boat analogy (4/4)
Four analogies to explain reactive power
Minute Lectures
Suppose men have to push a large ball from one side of an inclined plane to another (A to B)
III. The inclined-plane analogy (1/4)
Four analogies to explain reactive power
Minute Lectures
The active power needed is the same as if the plane were flat, but a man needs to keep the ball up on his path.
Consequences:• A loss of capacity (this man cannot be used for
pushing)• Extra friction losses (since this man will have to
touch the ball)
III. The inclined-plane analogy (2/4)
Four analogies to explain reactive power
Minute Lectures
III. The inclined-plane analogy (3/4)
Four analogies to explain reactive power
Minute Lectures
Vector representation:
III. The inclined-plane analogy (4/4)
Four analogies to explain reactive power
Minute Lectures
Suppose someone has to run from point A to point B
The harder the surface, the less the runner will jump up during his sprint, the faster he will be able to run
IV. The trampoline analogy (1/4)
Four analogies to explain reactive power
Minute Lectures
But now suppose he has to move to a platform B from A using a series of trampolines
He will start at the same height A, compensating for the height (reactive load) of B
IV. The trampoline analogy (2/4)
Four analogies to explain reactive power
Minute Lectures
His work to go from A to B will be the same
But the trajectory has some consequences:• Since the surface is a trampoline, he can’t use all
his force to go full speed forward• He will encounter increased resistance of ground
and air
IV. The trampoline analogy (3/4)
Four analogies to explain reactive power
Minute Lectures
Vector representation:
IV. The trampoline analogy (4/4)
Four analogies to explain reactive power
Minute Lectures
Round-up
Four analogies represent the idea of active and reactive power in an electric system:
• The tandem analogy• The horse-boat analogy• The inclined-plane analogy• The trampoline analogy
All analogies convey the same idea, but depending on the person, one analogy might work better than another
We hope they will increase the reader’s insight in the subject, or help experts to develop ideas to explain it to others
Four analogies to explain reactive power
Minute Lectures
Links and references
• The Electricity System as a Tandem Bicycle>>
• What are VARs?>>
• Capacitors in Harmonic-Rich Environments(technical application note)>>