Electrical Power Systems Technology

44 Electrical Power Systems Technology

Sample Problem:
Given: resistive current = 125 amperes, and reactive current = 65 am-
peres.
Find: total current.
Solution:

IT= IR^2 + IX^2

IT= 125^2 + 65a^2

IT= 5625 + 4225

IT= 99.25 A

A similar method of vector diagramming can be used for voltages in
RL and RC series circuits. This method may also be used for currents in
RL and RC parallel circuits. RLC circuits were used in the examples to il-
lustrate the method used to find a resultant reactive voltage or current in
a circuit.

IMPEDANCE IN AC CIRCUITS

Another application of the use of vectors is determining the total
opposition of an AC circuit to the flow of current. This total opposition is
called impedance (Z) and is measured in ohms.

Impedance in Series AC Circuit
Both resistances and reactances in AC circuits affect the opposition
to current flow.
Impedance (Z) of an AC circuit may be expressed as:

VT

Z = —

I

or

Z = R^2 + XL– XC

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