What is Transformer Impedance?
Impedance is the total resistance and reactance of a transformer’s primary & secondary windings.
When connected to an alternating current (AC) power supply, the transformer’s impedance resists the flow of current, resulting in a voltage drop between the windings.
When an alternating current voltage is given to the primary winding, it produces a magnetic flux.
However, not all of the flux is entirely connected to both windings; some flux leaks. This leakage flux is expressed by the leakage reactance of the transformer.
As a result, the transformer windings are both resistant and reactive, contributing to the whole impedance.
During operation, the transformer’s resistance resists the current flow, causing a voltage drop in windings.
The magnitude of that voltage drop is proportional to the transformer’s impedance, or percentage impedance.
The percentage impedance represents the percentage of rated voltage needed for passing the rated current via one winding when the other is short-circuited.
What is Transformer Percent Impedance?
Transformer Percent Impedance is a measurable figure stamped on the nameplate that represents a voltage measurement.
It is a tested value that manufacturers use for power & distribution transformers & is utilized in fault current calculations.
This is essential for
- Coordinating Over-Current Protection Devices (OCPD),
- Short Circuit Analysis,
- Harmonic Analysis, and
- Arc Flash Analysis.
The percent impedance is the amount of rated voltage necessary for the rated current to flow when the secondary windings are short-circuited at the specified voltage tap and frequency.
Importance of Percentage Impedance
• Increasing percentage impedance reduces short circuit current.
• High percentage impedance results in voltage drop and poor regulation. Finally, transformers perform less efficiently.
• The%Z is utilized to design a protective switchgear. In general, it is utilized to compute the maximum fault current. So that we may design a switch gear that can tolerate the highest degree of fault current.