Are the common equivalent circuit models valid for a steady

Are the common equivalent circuit models valid for (a) steady state balanced operation, (b) steady state un-balanced operation, (c) slow transients with periods of many cycles of the power frequency, (d) fast transients with periods much below the cycle of the power frequency?

Explanation would help and be appreciated! Thank you.

Solution

an equivalent circuit refers to a theoretical circuit that retains all of the electrical characteristics of a given circuit. Often, an equivalent circuit is sought that simplifies calculation, and more broadly, that is a simplest form of a more complex circuit in order to aid analysis. In its most common form, an equivalent circuit is made up of linear, passive elements. However, more complex equivalent circuits are used that approximate the nonlinear behavior of the original circuit as well. so option (a) is correct