Print this page Calculating Currents in Balanced and Unbalanced Three Phase Circuits
Joseph E. Fleckenstein, P.E.
Course Outline
This course presents the methods and means for calculation currents in both balanced and unbalanced three phase circuits. The course includes an initial, brief review of the electrical principles that are germane to the course content. Next, the course reviews the methods and formulas commonly used to calculate currents in balanced delta and wye three phase circuits. With an understanding of these principles, the course moves into the subject of unbalanced three phase circuits. The course introduces the commonly used phasor diagrams to provide a visual picture of the currents and voltages of three phase circuits. The course also provides in cookbook fashion the mathematical equations for calculating currents in all of the possible forms of three phase circuits. To illustrate the principles involved, the course includes a total of 43 detailed illustrations and 17 examples of typical calculations. Since calculations of power and power factor are a common use of current calculations, these subjects are also treated in the course.
To facilitate future use of the course material the course includes a summary of the symbols and equations used in the course.
This course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of the course materials.
Learning Objective
Upon completing the course, the student will:
- Be able to recognize the differences between rms, instantaneous and peak voltages and currents applicable to both single phase and three phase circuits;
- Be able to recognize the types and features of the types of three phase circuits: balanced and unbalanced, delta and wye;
- Be able to understand the concept of three phase voltage sequence;
- Be able to understand the concept of current lead and lag and power factor in three phase circuits;
- Be able to understand and construct phasor diagrams for single phase circuits;
- Be able to construct phasor diagrams for three phase delta circuits;
- Be able to construct phasor diagrams for three phase wye circuits;
- Be able to represent a phasor by its abscissa and ordinate vector components;
- Be able to calculate line currents and line the lead/lag of line currents, given the phase currents of a balanced three phase delta circuit;
- Be able to calculate line currents and the line lead/lag of line currents, given the phase currents of a balanced three phase wye circuit;
- Be able to select and apply the correct equation to determine three phase circuit current values;
- Be able to calculate the sizing of a capacitor bank to provide power factor compensation;
- Be able to calculate the line currents and power factor in three phase lines serving a mix of three phase delta and wye users that might be balanced or unbalanced;
- Be able to convert line current lead or lag to power factor; and
- Be able to calculate phase power and total power of a three phase service that delivers current to a mix of three phase users.
Intended Audience
This course is intended primarily for electrical engineers who periodically find a need to determine currents in three phase circuits.
Benefit for Attendee
The primary benefit of this course is that it provides a simple and easily understood means to calculate three phase currents. This benefit can be especially helpful to those who need to correctly determine three phase currents since most available texts on the subject can be very confusing and befuddling.
Course Introduction
The equations pertinent to currents and voltages in single phase circuits are relatively straightforward and, compared to three phase circuits, easily performed. Three phase circuits, on the other hand, can be more challenging. Nevertheless, three phase circuits are very common and engineers frequently find a need to calculate currents in these circuits. This course describes in simple terms the principles involved in calculating currents in three phase circuits.
Course Content
The course content is contained in the following PDF file:
Calculating Currents in Balanced and Unbalanced Three Phase Circuits
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Course Summary
This course teaches the methods for calculating currents in three phase circuits. Any engineer who is concerned with calculations pertinent to electrical circuits, and in particular three phase circuits, will find the course of value.
Related Links
The following links provide supplementary information on subjects related to the content of this course:
Quiz
Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.
DISCLAIMER: The materials contained in the online course are not intended as a representation or warranty on the part of PDH Center or any other person/organization named herein. The materials are for general information only. They are not a substitute for competent professional advice. Application of this information to a specific project should be reviewed by a registered architect and/or professional engineer/surveyor. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.
