Page 164 - Electrician - TT (Volume 1)

ELECTRICIAN - CITS

R - adjacent side
X - opposite side
AC Circuits - The impedance Triangle
For a series AC circuit the relationship between reactance, resistance and impedance can be remembered and
resolved through the use of trigonometry.

Impedance (Z) is found by use of Pythagoras theorem, The angle ө is found using the trig identity
X
tan ө =
R
X
or ө = tan ( )
-1
R
The angle ө represent the circuit phase angle.
Circuit containing pure resistance
A pure resistance circuit is that which has no inductance and capacitance

In Ohm’s Law
I = V/Z
Z = Total opposition of the circuit
Z = R Purely resistive circuit

Purely resistive circuit voltage and current are in phase
W = I R
2
= I x I x R = V/Z x I x R
= V x I x R/Z

= V x I x cos ф
W = V x I x cosф
Power when the circuit is falling in the negative half cycle
W = (- I ) R = I R
2
2

151
CITS : Power - Electrician & Wireman - Lesson 26-29