What does percentage impedance of a transformer mean?

The percent impedance (\%Z) is the percent of the rated load impedance possessed by a transformer. The percent impedance is important in that it allows us to: Calculate available fault currents (both individual and bank).

What is the formula for percent impedance of a transformer?

Actual Load current = 300 amps. Voltage drop at actual load = 300 x 1.732 x 0.027648 = 14.36 volts (14.36 / 480 = 0.0299, or 3\% of 480 volts) Effective percent impedance = 6\% x (300 / 601.4) = 2.99\%

Why we consider the percentage reactance of all the elements on a common kVA rating?

(ii) above that percentage reactance of an equipment depends upon its kVA rating. Generally, the various equipments used in the power system have different kVA ratings. Therefore, it is necessary to find the Percentage Reactance in Power System of all the elements on a common kVA rating.

How can the impedance of a transformer be increased?

As impedance is predominated by inductive reactance, the most effective way to change the impedance is often to change the number of turns. This will generally have an effect on the core dimensions and the winding resistance.

What is the impedance voltage in transformer?

The \% impedance is formally referred to as impedance voltage. It is the supply voltage, expressed as a \% of rated voltage, that is required to circulate rated current through the transformer. It is measured in the factory by a short circuit test at rated frequency.

What is the effect of impedance?

In addition to resistance as seen in DC circuits, impedance in AC circuits includes the effects of the induction of voltages in conductors by the magnetic fields (inductance), and the electrostatic storage of charge induced by voltages between conductors (capacitance).

What is transformer percentage reactance?

Transformer reactance is often specified as a percentage, say 10\%. This is a per unit value expressed as a percentage on the power base of the transformer. Example: A 350 MVA, 230/20 kV transformer has leakage reactance of 10\%.

What do you understand by percentage reactance?

Percentage reactance can be defined in the same way as percentage resistance. It is the voltage drop across the given reactance expressed as percentage of normal voltage when carrying full-load current pertaining to normal rating, i.e., \%X = (IX/V) × 100 … (1.2)

How do you find the impedance voltage of a transformer?

The supply voltage magnitude that results in rated current is then referred to as the impedance voltage. When it is divided by the rated voltage of the transformer, it becomes the \%- impedance voltage, or more commonly, the \%-impedance.

What is \% impedance of a transformer?

The \% of primary voltage that is required to produce the rated secondary current is what is known as \%impedance or per-unit impedance. There is another way of defining the \%Z or \% Impedance or leakage reactance. A transformer is a nothing but two (or more) coils coupled by magnetic field.

What is the difference between impedance and equivalent impedance?

When referring to the impedance of a transformer, it is the equivalent impedance that is meant. Definition. The percentage impedance of a transformer is the volt drop on full load due to the winding resistance and leakage reactance expressed as a percentage of the rated voltage.

Is the value of impedance same for primary and secondary windings?

The value of percentage impedance is the same for both windings as it is the percentage of rated voltage. However, the value of the rated current will be different for primary and secondary windings. Accordingly, value of short circuit current will also be different for primary and secondary windings.

Why rated voltage is applied at the primary winding of transformer?

If we apply rated voltage at the primary winding of a transformer keeping its secondary winding short-circuited, then the amount of current at both windings will be extremely high as compared to the rated current.