AC1 Fundamentals Unit 4 – Inductive Reactance
Exercise 3 – Parallel RL Circuits
EXERCISE OBJECTIVE
When you have completed this exercise, you will be able to determine characteristics of parallel
RL circuits by using calculated and measured values. You will verify your results with an
oscilloscope.
DISCUSSION
- Total parallel inductance, like total parallel resistance, is found by taking the inverse of the
sum of the reciprocals. When just two inductors are in parallel, use the product-over-sum
method. - Inductive reactance decreases as the number of parallel inductors increases, causing an
increase in circuit current and a decrease in circuit impedance. - Once the parallel elements have been summed, the circuit is simplified to a parallel RL
circuit that consists of one resistive branch and one reactive branch. - The voltage across each parallel component is the same as the applied voltage.
- Branch currents are determined by using Ohm’s law.
- In parallel RL circuits, total circuit current is not the sum of the branch currents. Total circuit
current is the square root of the sum of the each individual branch current squared. - The circuit impedance is calculated using this formula
Z = (R x XL)/[sqrt(R^2 x X^2 L)]. - A more practical method of finding the circuit impedance is to divide the total current into
the applied voltage. - When inductance is decreased, the inductive reactance decreases, resulting in increased
current flow through the reactive branch. Phase angle between the applied voltage and circuit
current decreases.