So I learnt about phasors and phasor representation this week in college. I noticed that in every example problem that we did, one phasor was chosen as reference and the angle was taken as 0°. My question is :if we take that the reference not as 0°, but something else, would it be wrong? Why is the reference always 0.


1 Answer 1


Why is the reference always 0.

Because it makes the maths easier.

For voltage measurements we choose some part of the circuit as reference and call it zero. All voltage measurements can be taken with reference to that point.

In the same way a surveyor takes some height reference and all subsequent height measurements are + or - relative to that point. Sea-level is an obvious choice but might not make much sense for a building at 3,000 m above sea level where a local reference can be chosen.

For your phasors you take one as the reference and everything else leads or lags that.

You can, of course, use a non-zero reference if it suits. This might be the case if, for example, the system is referenced to another (such as the mains) by a fixed offset. It may suit to do all the calculations relative to the mains even though it's not relevant to the immediate calculation.

  • \$\begingroup\$ Hey thanks transistor, but there's another problem. When we choose reference as zero, the phase angles are always equal to the angle phasor makes with the horizontal. But when zero is not taken as reference it gets convoluted. I'll try to explain in a better way : let V = Asin(wt) be the reference, and V= Asin(wt + Φ) is leading the reference by an angle Φ. If wt were taken 0, the phasor would be making angles 0 and Φ with the horizontal, but as I assume they are not taken as zero the phasor would be making angles wt and wt + Φ with the horizontal. Will the phasor representations be same now? \$\endgroup\$
    – user406653
    Oct 4, 2017 at 17:55
  • \$\begingroup\$ Exactly. The maths gets more difficult. \$\endgroup\$
    – Transistor
    Oct 4, 2017 at 18:17
  • \$\begingroup\$ Yeah, @user406653, it doesn't makes any difference provided they have same frequency. Phasor diagram shows you phase (time) relationship between different quantities, so its their relative positions which matter. In fact, phasers are rotating anti-clockwise with speed depended on their frequency.. so you can draw them way you want. \$\endgroup\$
    – Deep
    Oct 4, 2017 at 18:17
  • \$\begingroup\$ @user406653 the representation, when drawn in cartesian cooordinates, will not be the same, because it's been rotated from your first diagram by the angle you've chosen for the reference. However, the angles between all phasors, which are the angles that matter, will be the same as before. That's another way of saying that the phasor representation is invariant under any angle rotation. \$\endgroup\$
    – Neil_UK
    Oct 4, 2017 at 18:18
  • \$\begingroup\$ @Neil_UK So if 30° is chosen as reference and another quantity leads the reference quantity by another 30°(Φ), will the phasor representations be A∠ 30° and A ∠ 60° or A ∠ 0° and A ∠ 30°? As you said phasor representations are unaffected by the reference value, I'm guessing it should be the second one. \$\endgroup\$
    – user406653
    Oct 4, 2017 at 18:47

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.