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Multi-Part Series Circuit with Resistance and Inductance

Author: E.E. Kimberly

When two or more devices with resistance and inductance are connected in series across an alternating voltage, the resistance of the whole is the arithmetical sum of the resistances of all the parts and the inductance of the whole is the arithmetical sum of the inductances of all the parts.

Example 5-4. - A coil having resistance R1 = 20 ohms and inductance L1 = 0.10 henry is connected in series with a second coil having resistance R2 = 50 ohms and inductance L2 = 0.05 henry. It is required to force 10 amperes with 60-cycle frequency through this circuit. What must be the applied voltage?

Solution. - The schematic circuit diagram is shown in Fig. 5-9. The total resistance is


Fig. 5-9. Impedance Coils in Series

Also, the total inductance is


The remainder of the solution follows:


Voltmeter Vi, Fig. 5-9, measures the voltage I(R1+jX1) across the impedance R1+jX1. Voltmeter V2 measures the voltage I(R2+jXz) across the impedance R2+jX2 The readings of these voltmeters may be computed as follows:

ee_001-115.png I

The arithmetical sum of Vi and Vz is greater than 900, the required voltage, but this sum has no significance because Vi and Vz are not in phase. Their vector sum is 900. The impedance diagram is shown in Fig. 5-10.
Fig. 5-10. Impedance Diagram for Example 5-4

Last Update: 2010-10-06