Transformer on No-Load

A transformer is said to be operated in no-load condition if no electrical load is connected across its secondary winding terminals. In other words, when the secondary winding of a transformer remains open-circuited and no current flows through it, then the transformer is said to be in no-load condition.

When a transformer operates in no-load condition, no current flows in the secondary winding, but a small current called no-load current (I₀) which is around 2% to 10% of the rated current flows in the primary winding.

This no-load current I₀ magnetizes the core of the transformer and results in some core losses (i.e., iron losses and copper losses).

The following figure depicts the circuit diagram of an electrical transformer in no-load condition.

In this circuit, we can see that there is an input voltage of V₁ volts is applied to the primary which forces a no-load current of I₀ ampere through it. The secondary winding is open-circuited, hence the secondary I₂ is equal to zero amperes.

As we discussed that when a transformer is operated in no-load condition, it draws only a small current called no-load current from the input power supply. This no-load current has two components namely,

• Magnetizing component
• Power component

The magnetizing component is also called the reactive component and it is responsible for setting up the magnetic flux in the core. This component of the no-load current lags the supply voltage V₁ by an angle of 90°, as it is due to the inductive effect. This component is usually denoted by I_m.

The power component is also called the active component and it is responsible for supplying core losses i.e., iron and copper losses. The active component remains in-phase with the supply voltage. In other words, the angle between the supply voltage V₁ and the active component of the no-load current. This component is designated by the symbol I_w.

Therefore, we can express the no-load current of the transformer as the phasor sum of the magnetizing component and the power component i.e.,

[Tex]I_0=I_m+I_w [/Tex]

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.