Question

How do you calculate the impedance voltage of a transformer?

Answer 1

To calculate the impedance voltage of a transformer, you'll need to determine the voltage drop that occurs when a rated current flows through the transformer's impedance. Impedance voltage is the voltage drop caused by the impedance of the transformer's windings and core when supplying rated current. It is usually expressed as a percentage of the rated voltage.

Here's the step-by-step process to calculate the impedance voltage of a transformer:

Identify the transformer specifications:

Rated power (in kilovolt-amperes, kVA) or rated apparent power.
Rated voltage (in volts) on both the primary and secondary sides.
Impedance (in ohms) on either the primary or secondary side. Transformer impedance is usually provided by the manufacturer and is typically expressed as a percentage of the rated voltage.

Determine the rated current:

Calculate the rated current on either the primary or secondary side of the transformer using the following formula:
Rated Current (I_rated) = Rated Power (kVA) / Rated Voltage (V_rated)

Calculate the impedance voltage:

Determine the voltage drop caused by the transformer's impedance when supplying the rated current. This voltage drop is the impedance voltage.
Use the following formula to calculate the impedance voltage:
Impedance Voltage = Impedance (as a percentage of rated voltage) × Rated Voltage (V_rated)

Let's go through an example:

Suppose you have a transformer with the following specifications:

Rated power (kVA): 500 kVA
Rated voltage (V_rated): 11 kV (on both primary and secondary sides)
Transformer impedance: 5% (expressed as a percentage of rated voltage)

Step 1: Calculate the rated current:
Rated Current (I_rated) = 500 kVA / 11 kV ≈ 45.45 A

Step 2: Calculate the impedance voltage:
Impedance Voltage = 5% × 11 kV = 0.05 × 11,000 V = 550 V

So, in this example, the impedance voltage of the transformer is 550 volts.

Remember that transformer impedance is important for understanding its voltage regulation, efficiency, and performance under different load conditions. The impedance voltage represents the voltage drop that occurs due to the transformer's internal impedance when supplying the rated current.