**What is Voltage Regulation of a Transformer?**

**Voltage regulation of transformer** is defined as the percentage change in the transformer secondary voltage from no load to full load. In other words, the transformer voltage regulation describes the ability of the transformer to provide the constant voltage from no load to full load. The secondary voltage of the transformer should not vary with load when the input supply is constant. The transformer can be treated as a voltage source and the variation in the secondary terminal voltage from no load to full load depends on the voltage drop in the transformer winding.

When current flows through the transformer the voltage drop takes place due to reactance and resistance of the transformer.The variation in the secondary output voltage of the transformer from its no load to full load is called the **voltage regulation of the transformer.**

**Transformer Voltage Regulation Formula**

_{no load}is the no load voltage and V

_{full voltage}is full load voltage.

**Example of Voltage Regulation :**

**What Factors affects the Transformer Voltage Regulation?**

The following factors affects the voltage regulation of the transformer.

**Resistance per phase –**The resistance of the primary and secondary winding cause voltage drop. The more the resistance, the more the voltage drop. Transformer with higher primary and secondary resistance has poor voltage regulation.**Reactance per phase –**The reactance of the primary and secondary winding cause voltage drop. The more the reactance, the more the voltage drop. Transformer with higher primary and secondary reactance has poor voltage regulation.**Leakage Flux –**If leakage flux is more, the leakage reactance X_{L}increases which increases Ia X_{L}voltage drop. Hence regulation becomes poor.**Magnitude of secondary load current-**If load current increases I_{a}R_{a}and I_{a}X_{L}voltage drop increases. Therefore terminals voltage drops which makes regulation poor.-
**Load Power factor :**The load power factor also affects the transformer voltage regulation. The lagging power factor demands more current and it cause more voltage drop in transformer winding. As a result the voltage regulation of the transformer deteriorates. The leading power factor increase the transformer secondary voltage and thus the regulation of transformer improves.

The transformer have primary and the secondary winding. The winding has resistance and reactance. The primary resistance and reactance can be referred at the secondary side or vice versa. The voltage regulation of the transformer depends on the reactance and the resistance of the transformer. The equivalent secondary circuit of the transformer is as given below.

_{2}=0 and the transformer draws only no load current. The voltage drop I

_{2}Z

_{2}across secondary impedance takes place with an increase in the secondary current. The voltage drop in the secondary winding is maximum when transformer operates at its full kVA capacity delivering the rated secondary current to the load.

_{2}

_{2}Z

_{2}

_{2}

E

_{2}= I

_{2}Z

_{2}+ V

_{2}

_{2}– V

_{2}= I

_{2}Z

_{2}

The regulation of the transformer depends on the power factor of the load. Now, we will discuss the regulation of the transformer at lagging, leading and unity power factor.

**Voltage Regulation of Transformer for Lagging Power Factor**

_{2}and secondary current I

_{2}is θ

_{2}. The phasor diagram of the no load voltage(E

_{2}) , full load voltage (V

_{2}) and current (I

_{2})is as shown below.

_{2}

_{ }In triangle DEF,

DC = DE Sinθ_{2}

_{2}= V

_{2}+ AE Cosθ

_{2}+ DE Sinθ

_{2}

_{2}= V

_{2}+ I

_{2}R

_{2}Cosθ

_{2}+ I

_{2}X

_{2}Sinθ

_{2}

**E _{2} – V_{2} = I_{2}R_{2} Cosθ_{2} + I_{2}X_{2} Sinθ_{2}**

**Voltage Regulation of Transformer for Leading Power Factor**

**The phsor diagram of the transformer operating at leading power factor is as shown below.**

_{2}

BC = DE Sinθ_{2}

The angle between OC and OD is very small and OC is equal to OD.

Here, OA = V

_{2}

_{2}= V

_{2}+ AE Cosθ

_{2}– DE Sinθ

_{2}

_{2}= V

_{2}+ I

_{2}R

_{2}Cosθ

_{2}– I

_{2}X

_{2}Sinθ

_{2}

**E**

_{2}– V_{2}= I_{2}R_{2}Cosθ_{2}– I_{2}X_{2}Sinθ_{2}

**Zero Voltage Regulation of Transformer**

The secondary voltage at no load can’t be equal to the secondary voltage at load. The zero voltage regulation of the transformer is an ideal case and practically it is not possible. An ideal transformer has zero voltage regulation which is hypothetical.

**Solved Problem on Voltage Regulation of Transformer**