Theory of Transformer on Load and No Load Operation (2023):

We have discussed about ideal transformer theory for a better understanding of the original basic theory of transformer. Now we will go through the practical aspects of electrical power transformer one by one and try to draw a vector diagram of the transformer at each step. As we said, in an ideal transformer; There are no core losses in the transformer i.e. loss free core of the transformer. But in a practical transformer, there are hysteresis and eddy current losses in the transformer core.

Theory of Transformer on No-Load

Having No Winding Resistance and No Leakage Reactance:

Let us consider an electrical transformer with only core losses, which means that it has only core losses but no copper losses and no leakage reactance of the transformer. When an alternating source is applied to the primary, the source will supply current to magnetize the core of the transformer.

But this current is not the actual magnetic current. It is slightly larger than the actual magnetic current. The total current supplied by the source has two components, a magnetizing current used simply to magnetize the core, and a second component of the source current used to compensate for core losses in the transformers.

Because of this core loss component, the source current in the transformer at no-load condition supplied from the source is not exactly 90° lags of the supply voltage, but lags by an angle θ of less than 90o. If the total current supplied by the source is Io then it will have a component in phase with the supply voltage V1 and this component of current Iw is the primary loss component.

This component is taken in phase with the source voltage because it is connected to the active or working losses in the transformers. Another component of the source current is defined as Iμ.

This part provides attractive movement space in the center, so it is low wattage. This means that this transformer is a responsible piece of source current. Consequently Iμ will be in quadrature with V1 and in phase with the motion changing Φ. Thus, the absolute required current in the transformer in no-load condition can be expressed as:


Presently you have perceived that making sense of the hypothesis of transformer in no-load is so basic.

Hypothesis of Transformer on Burden
Having No Winding Opposition and Spillage Reactance:

Now we will examine the behavior of the above transformer on load, which means the load is connected to the secondary terminals. Note, a transformer has core loss but not copper loss and leakage reactance. Whenever a load is connected to the secondary winding, the load current starts flowing through the secondary winding along with the load.

This load current depends entirely on the load characteristics and the secondary voltage of the transformer. This current is called secondary current or load current, here it is called I2. Since I2 is passing through the secondary, a self-MFM will be developed in the secondary winding. Here it is N2I2, where, N2 is the number of turns of the secondary winding of the transformer.

This MMF or attractive force provides the transition φ2 in the optional winding. This φ2 will go against the highly attractive transition and immediately weaken the ground motion and often not reduce the necessary self-induced emf E1. Assuming that E1 falls below the required source voltage V1, an additional current will flow from the source to the required winding.

This additional necessary current I2′ induces an additional motion φ′ in the center which will cancel the optional countertransition φ2. Subsequently the focal attractive motion of the center, Φ, remains unchanged regardless of the stack. So all the output current, this transformer can be divided into two parts obtained from the source.

The first is used to polarize the center and offset the misfortune of the center, for example Io. This is a significant portion of the required current. The other is used to meet the counter current of the auxiliary winding. This is known as the pile fraction of the required current. Then the complete nine-phase required flux I1 of the electrical power transformer is given by no winding resistance and spillage reactance.

where θ2 is the point between the auxiliary voltage and the optional current of the transformer.
For now we will take another step from the bottom of the transformer to the ground.

Theory of Transformer On Load, with Resistivity Winding, but No Leakage Reactance:

For now, consider the winding impedance of the transformer but no spillage reactance. Up to this point we have examined a transformer with ideal windings, i.e. windings with no resistance and no spillage reactance, yet for now we will consider a transformer with internal impedance but with no spillage reactance. There is no action. There is no answer. Since the windings are resistive, there will be a voltage drop across the windings.


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