Speaking in general terms, an equivalent circuit is a theoretical circuit system that helps in retaining of electrical features that are present in a particular circuit. These are generally complex in nature and are called macro models of the actual circuit system.
When a transformer functions in a specific manner, there are high chances that issues associated with voltage and currents have cropped up. This has been dealt with by students in the phasor diagram manner. However, when an equivalent circuit is present, there can be equal equations that help in providing calculations to a direct circuit theory. In such a scenario, equivalent circuit becomes a simple interpretation of the behavior of that device.
When transformer windings are taken into consideration, in case of equivalent circuit, it can be seen as an ideal case. Hence, both leakage and resistance reactance is depicted in circuits as primary and secondary formats. So, on this, there is influence of magnetizing current that further causes a non-inductive resistance.
However, by transferring secondary resistance to primary format and vice versa, this equivalent circuit system can be simplified to a great extent. In the same manner, both resistance and reactance in regards to a loadcan be managed in an ideal manner. There are certain a secondary impediments which after a certain point of time is transferred to the primary side and this winding set does not need depiction when put forth in an equivalent circuit. Quite similarly, primary impediments can also be transferred to secondary side and result will be similar to the previous case.
Such instances are known as approximate circuits, and there is a certain amount of leakage reactance that has helped in analyzing combination factors in a correct manner.
For students, it is of prime importance to have detailed knowledge of functioning of such equivalent circuit for further prospects in this field.