The relationship between percent and per unit impedance

In summary, the conversation discusses the relationship between percent impedance and per unit impedance in transformers. The homework equations involve determining x% by short circuiting the secondary windings and converting it into number form as x p.u for easier calculations. The speaker is unsure if there is anything else to add and asks for guidance on choosing a per unit base for studying the national power grid.
  • #1
Callum Plunkett
27
8

Homework Statement


For one of my assignments I’ve been ask about the relationship between percent impedance and per unit impedance.

Homework Equations

The Attempt at a Solution


I know that the x% is determined in transformers by short circuiting the secondary windings and slowly increasing the voltage until the secondary gives the desired full load current. And that x p.u is the x % converted into number form which has the advantage of simplifying calculations on more complex circuits. But other than that I’m unsure if there is anything else I can add to my answer. Can anyone point me in the right direction?
 
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  • #2
If you were doing a study of the national power grid, how would you choose a per unit base for the study?
 

1. What is the formula for calculating percent impedance?

The formula for calculating percent impedance is (Z% = Zpu * 100), where Z% is the percent impedance, and Zpu is the per unit impedance.

2. How is percent impedance related to per unit impedance?

Percent impedance is the value of per unit impedance expressed as a percentage. It is used to compare the impedance of different transformers on a standardized scale.

3. What is the significance of percent impedance in power systems?

Percent impedance is an important factor in power system design as it affects the efficiency and voltage regulation of the system. A higher percent impedance can result in higher losses and lower voltage regulation.

4. How does percent impedance impact transformer sizing?

The percent impedance of a transformer is used to determine the size and rating of the transformer. A higher percent impedance requires a larger transformer to handle the same load, resulting in higher costs.

5. Can percent impedance be changed after a transformer is built?

No, the percent impedance of a transformer is fixed and cannot be changed after it is built. It is determined by the physical characteristics of the transformer, such as the size and number of windings.

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