Page 238 - Electrician - TT (Volume 1)

ELECTRICIAN - CITS

Power triangle
A power triangle identifies three different types of power in AC circuitsTrue power in watts[P] Reactive power in
vars [Pq]Apparent power in VA[Pa]Pa = P + Pq 2
2
2
The power triangle graphically shows the relationship between real (P), reactive (Q) and apparent power (S).

2
S P Q 2
S = P + JQ L

S = S<q V I
I
V
m m (Sin2ωS m m Sin2ω V I Sin2ω
2 2 2 RMS RMS

The power triangle also shows that we can find real (P) and reactive (Q) power.
S = IV (VA)
P = Scosq (W)
Q=S sinq (VAR)

Related problem
Calculate the power taken by an incandescent lamp rated 250v when it carries a current of 0.4A if the resistance
is 625 ohms

P= VR x IR =250 x 0.4 = 100Watts
P = I2xR =0.4 x 0.4 x 625 =100 Watts
P = E2 / R =2502 /625 = 100Watts

225

CITS : Power - Electrician & Wireman - Lesson 38-40