Voltage Regulation of a Transformer

Definition: At a constant supply voltage the change in the secondary terminal voltage from no load to full load with respect to no load voltage is called as Voltage Regulation of a Transformer.

When the Transformer is loaded with a constant supply voltage, the terminal voltage changes depending upon the load and its power factor. The algebraic difference between the no-load and full load terminal voltage is measured in terms of voltage regulation.

VOLTAGE-REGULATION-EQ1
where,
E2 – secondary terminal voltage at no load
V2 – secondary terminal voltage at full load

When all the quantities are referred to the primary side of the transformer, the voltage regulation equation becomes
VOLTAGE-REGULATION-EQ2
Let us understand the voltage regulation by taking an example explained below

If the secondary side of the transformer is open circuited meaning, no load is connected to the secondary side of the transformer then I2 = 0 that means the secondary current will not flow in the circuit.If there is no secondary current flowing the circuit, there will be no voltage drops across the resistive and reactive components of the secondary side of the transformer. The primary side voltage drop is almost negligible.

Now if the transformer works on full load, that means the load is connected to the secondary side of the transformer, the voltage drop appears, but the value of the voltage regulation from no load to full load should be less for the better performance of the transformer.
volltage-regulation-ckt--diagram

From the circuit diagram shown above, the following conclusions are made

  • The primary voltage should always be greater than the induced emf on the primary side of the transformer. V1>E1
  • The secondary terminal voltage at no load is always be greater than the secondary voltage at full load. E2>V2

Considering the above circuit diagram the following equations are drawn
VOLTAGE-REGULATION-EQ3
The approximate expression for the no-load secondary voltage for the different types of load is

  1. For inductive loadVOLTAGE-REGULATION-EQ4Where,
    VOLTAGE-REGULATION-EQ5

    • For Capacitive loadVOLTAGE-REGULATION-EQ6

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