What Are Typical Impedance Values for Power Plant Transformers?

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SUMMARY

The typical impedance values for power plant transformers vary significantly, with primary winding impedance generally expressed in Per Unit and as a percentage of nominal nameplate ratings. For internal distribution transformers, impedance ranges from 2% to 5%, while the main transformer connecting the generator to the grid has an impedance of 17%. This impedance is primarily inductive to minimize energy loss as heat, and electrical system designers aim to keep voltage drops within approximately 10% of the operating range.

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  • Understanding of transformer engineering principles
  • Familiarity with Per Unit system calculations
  • Knowledge of electrical impedance and inductance
  • Basic concepts of power plant electrical distribution
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  • Learn about Per Unit system analysis in electrical engineering
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Electrical engineers, power plant operators, and anyone involved in the design and optimization of transformer systems in power generation and distribution.

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When it comes to power plant transformers, What is the typical inductance and impedance on the primary winding?
 
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http://www.scribd.com/doc/27073343/Transformer-Engineering
 
Last edited by a moderator:
that's an excellent reference, j-rfu.

Impedance is indeed given in Per Unit, % of nominal nameplate ratings.
Transformers for our internal distribution were a few percent, 2 to 5 -ish.

Our main transformer (the one connecting generator to grid) was 17% .
The impedance will be mostly inductive so as to not waste kilowatts as heat.
Electrical system designers spend a lot of time optimizing voltage drops so everything stays within ~10% over operating range of plant.

The main transformer connecting generator to grid was 894MVA so you can see what 0.1% loss would be in kw - almost a megawatt . It's worth making the big ones highly efficient.

Sorry i just don't remember the exact numbers but the guidelines in that reference should give you a feel.

old jim
 

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