Power Transformer Models

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# Power Transformer Models - PowerPoint PPT Presentation

Power Transformer Models. by Kinlay Dorjee & James Wang. Presentation Outline. Introduction Ideal transformer Practical transformer Conclusion Questions/Discussion. Introduction. Typical power system scheme. Generator. Step up Transformer. Transmission Line. Step down

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Presentation Transcript

### Power Transformer Models

by Kinlay Dorjee

& James Wang

Presentation Outline
• Introduction
• Ideal transformer
• Practical transformer
• Conclusion
• Questions/Discussion
Introduction

Typical power system scheme

Generator

Step up

Transformer

Transmission

Line

Step down

Transformer

Introduction

Importance of Power Transformers:

• Generation voltage restriction of about 25 kV.
• Isolates the Generator from the over voltage transients in the Overhead lines.
Ideal Transformer
• Assumption
• 1. Zero Winding Resistance
• 2. Permeability of the core is infinite -- Zero Magnetic Reluctance
• The transformer flux is totally confined to the magnetic core – No Flux Leakages
• 4. Zero hysteresis and eddy-current losses in the core
Ideal Transformer

Ampere’s Law

Practical transformer and its model

Mutual flux due to currents i1 and i2

Leakage flux and mutual flux due to i1 alone

Leakage flux and mutual flux due to i2 alone

Define

Rearrange the V1 equation, we get

Defining:

Leakage inductances

Leakage reactances

Shunt magnetizing susceptance

Defining:

Transformer equivalent circuit with magnetizing current neglected

Conclusion

• Depending on the requirements, the Power Transformer can be modeled in many different ways:
• In the practical model, Bm is neglected because magnetizing current is very small compared with the load current. But for some other studies, the branch may be necessary to account for the exciting current in the transformers.
• Similarly, the resistance is neglected in most models because the reactance is much larger.
• When dealing with the power system stability studies, resistance component should be included in the transformer model to provide necessary damping.

References

• Power System Analysis by John J. Grainger and William