Operation of Transformer on No-Load

Here is the operation of a transformer in no-load condition:

• Firstly, the input voltage V₁ is applied across the primary winding of the transformer. It magnetizes the core of the transformer by setting up a magnetic flux (ϕ) in it.
• This magnetic flux induces EMFs in the primary and secondary windings due to electromagnetic induction. These induced EMFs lag the applied voltage by an angle of 90°. Here, we are neglecting the primary winding copper loss and the secondary winding copper loss is zero because I₂ = 0.
• The no-load current I₀ lags behind the supply voltage V₁ by an angle of ϕ₀ which is called the no-load power factor angle.
• It is also important to note that the EMF E₁ induced in the primary winding is equal to the supply voltage V₁.
• There are also some losses in the primary winding (copper loss) and the core (iron losses) of the transformer which are represented by the active component (I_w) of the no-load current. This component is equivalent to the resistive effect and hence remains in-phase with the supply voltage (V₁).
• This is how an electrical transformer operates under no-load conditions.

This complete operation of the transformer on no-load can be illustrated with the help of a phasor diagram which is shown in the following figure.

Phasor Diagram Explanation

• The induced EMF (E₁ and E₂) are out of phase with respect to the supply voltage (V₁) and lags the magnetic flux by 90°.
• The reactive component I_m lags the supply voltage V₁ by 90°.
• The active component I_w is in-phase with the supply voltage (V₁).
• The no-load current I₀ lags the supply voltage V₁ by an angle φ₀ which is the no-load power factor angle of the transformer.

From this phasor diagram, we can derive the important relations of different electrical parameters of the transformer. They are,

(1). The magnitude of no-load current:

[Tex]I_0=\sqrt{I_m^2 + I_w^2} [/Tex]

(2). The magnetizing component of no-load current:

[Tex]I_m = I_0 sin {\phi_0} [/Tex]

(3). The active component of no-load current:

[Tex]I_w = I_0 cos \phi_0 [/Tex]

(4). The no-load power factor:

[Tex]cos\phi_0 = \frac{I_w}{I_0} [/Tex]

(5). The power consumed under no-load:

[Tex]P_0 = V_1 I_0 cos\phi_0 [/Tex]

Hence, this is all about the theory and operation of an electrical transformer in no-load condition.

Let us now study the theory and operation of an electrical transformer under loaded conditions.

In this article, we will study the theory of transformer on load and no load operation. A transformer is a static electrical machine used to increase or decrease the value of voltage and current in an electrical circuit. The transformer operates on the principle of electromagnetic induction and mutual inductance. A transformer typically consists of two copper winding and a magnetic core. The windings are named as primary winding and secondary winding. The input supply is connected to the primary winding and the output electrical supply is taken from the secondary winding. Hence, the secondary winding is one to which the electrical load is connected.

Let us understand the operation of a transformer on load and no-load conditions.