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PDH Online Course Description PDH Units/
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\$199

E251
Short Circuit Current Calculations Using Symmetrical Components

Ralph Fehr, Ph.D., P.E.

In practice, three-phase faults account for less than 5% of the short-circuit faults on a typical power system. The vast majority of short-circuit faults, about 70%, are line-to-ground faults. Line-to-line faults account for about 15% of short-circuit faults, with double line-to-ground faults making up the remainder. Of these fault types, only the three-phase fault is balanced. The asymmetrical voltages and currents produced by unbalanced faults preclude the use of single-phase analysis as can be done under balanced conditions. Fortunately, a powerful tool exists for analyzing unbalanced systems – the method of symmetrical components.

This course explains the theory and origin of symmetrical components, using an intuitive method of derivation which likens the phasor components to force vector components. The mathematics needed to convert between sequence and line quantities are presented in a clear, concise way. A highly-reliable and methodical approach of developing sequence networks is also presented, including a novel approach of producing the zero-sequence network by modifying the negative- sequence network. Circuit models for the four different short-circuit faults that can occur on a three-phase system – three-phase, line-to-ground, double line-to-ground, and line-to-line – are presented, including means of modeling fault impedance. A brief but complete review of the per-unit system is included, including worked examples. The per-unit material is followed by examples of calculating both balanced and unbalanced short-circuit fault currents in the per-unit system, using the circuit models presented earlier.

This course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of the course materials.

NY PE & PLS: You must choose courses that are technical in nature or related to matters of laws and ethics contributing to the health and welfare of the public. NY Board does not accept courses related to office management, risk management, leadership, marketing, accounting, financial planning, real estate, and basic CAD. Specific course topics that are on the borderline and are not acceptable by the NY Board have been noted under the course description on our website.

AIA Members: You must take the courses listed under the category "AIA/CES Registered Courses" if you want us to report your Learning Units (LUs) to AIA/CES. If you take courses not registered with AIA/CES, you need to report the earned Learning Units (not qualified for HSW credits) using Self Report Form provided by AIA/CES.

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