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Power in Symmetrical Components – Understanding Symmetrical Components Power Systems

This post gives a brief about power in symmetrical components. Let us take a look at symmetrical component transformation in time-dependent form used in electric-machine theory, with the help of few mathematical equations, and vector diagrams. Here’s more about symmetric power in 3 phase.

Charles Legeyt Fortescue proved that any set of unbalanced phasors or polyphase signal can be represented as the sum of N symmetrical sets of balanced phasors where N is a prime number. These phasors represent only a single frequency component.

One of the sets of phasors has the same phase as the underlying system, second set has a reverse phase and in the last set all individual phasors are in phase with each other.This forms three independent sources which makes the analysis of asymmetric faults easy and tractable.This technique can also be extended to higher order phase systems.This analytical technique has been accepted and progressed by engineers at General Electric and Westinghouse.

In a 3 phase winding a positive sequence set of currents produce normal rotating field, a negative sequence set produces a field with the opposite rotation, and the zero sequence set with all phasors in phase with each other produces an oscillating field and not a rotating one. These effects can be detected physically. This mathematical tool has become the basis for the design of protection relays. In such cases negative-sequence voltages and currents are used as a reliable indicator of fault conditions.

Symmetrical component transformation application in the time-dependent form is used in electric-machine theory. In the field of power systems this transformation is applied to steady state sinusoidal phasors for fault corrections. Although they were formulated for 3-phase phasors, they are fundamental to the transformation of random instantaneous variables.

The use of time-dependent symmetrical components in network calculations is advantageous in several ways. Firstly Network-component data are available in these coordinates mostly and the simple relation with their steady-state phasors supports the interpretation of results that are calculated by the other popularly used steady-state phasor theories like in case of asymmetric faults.

Moreover, the power transformation of symmetrical components can be extended to m-n winding machines and the unitary form was used, which is advantageous since power and torque need no back transformation, since unitary transformation is power invariant. What’s more, the aiee paper aircraft symmetrical components are also based on the following equations, and you can understand everything about the symmetric components power systems in detail by visiting the following link.

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