Page 311 - Basic Electrical Engineering

Figure 3.17 Phasor diagrams (a) resistive circuit; (b) purely inductive circuit; (c) purely capacitive
circuit

3.2.2 L–R Series Circuit

Let us consider a resistance element and an inductor connected in series as
shown in Fig. 3.18. A voltage, V of frequency, f is applied across the whole

circuit. The voltage drop across the resistance is V and across the inductor is
R
V . Current flowing through the circuit is I.
L

Figure 3.18 (a) R–L series circuit; (b) phasor diagram

V = IR, V = IX where X = ωL = 2πfL
L
L
L
R
We have to add V and V to get V. But these are to be added vectorially as
R
L
they are all not in phase, i.e., these vectors are not along the same direction.
To draw the current and voltage phasor we take the current I as the reference
phasor as shown in Fig. 3.18 (b), since current I is common to V and V ,
R
L
i.e., since the same current is flowing through both resistance and inductance.