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Aviation Maintenance Technician Handbook–General

FAA-H-8083-30B Version 2023
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Chapter 12

Fundamentals of Electricity & Electronics

Since inductive reactance causes voltage to lead the current, the total current, which contains a component of inductive current, lags the applied voltage. If the current and voltages are plotted, the angle between the two, called the phase angle, illustrates the amount the current lags the voltage.

In Figure 12-139, a 112-volt generator is connected to a load consisting of a 2 µf capacitance and a 10,000-ohm resistance in parallel. What is the value of the impedance and total current flow?

Solution:

First, find the capacitive reactance of the circuit:

Formula: 1 ; XC = ; 2πfC

Changing 2 μf to farads and entering the values into the formula given:

Figure 12-136. A circuit containing resistance and capacitance.
Figure 12-136. A circuit containing resistance and capacitance.
Formula: 1 ; = ; 2 × 3.14 × 60 × 0.000002 ; 1 10,000 ; = or ; 0.00075360 7.536 ; = 1,327 XC capacitive reactance

To find the impedance, the impedance formula used in a series AC circuit must be modified to fit the parallel circuit:

Formula: RXC ; Z = R2 + XC 2 ; 10,000 × 1,327 ; = (10,000)2 + (1,327)2 ; = 0.1315 W (approximately)

To find the current through the capacitance:

Formula: E ; IC = ; XC ; 110 ; IC = ; 1,327 ; = 0.0829 ampere

To find the current flowing through the resistance:

Formula: E ; IR = ; R ; 110 ; = ; 10,000 ; = 0.011 ampere

To find the total current in the circuit:

Formula: IT 2 = IR 2 + IC 2 ; IT = IL 2 + IR 2 ; = 0.0836 ampere (approximately)

Resonance

It has been shown that both inductive reactance:

Formula: (XL = 2πfL)

and capacitive reactance: