**Transformers**

**Voltage Regulation**

**2.Why Transformers are Important?**

Make electricity generation possible at the most economic generator voltage level

Make electric power transmission take place at the most economic transmission voltage

Supply electric power to users at a safe and suitable voltage

**Autotransformer**

By:

Mohd Fakhizan Romlie, PhD

email: fakhizan.romlie@petronas.com.my

**Learning Outcomes**

**1.What is a Power Transformer?**

A device that changes AC electric power voltage level to AC electric power another voltage level at the same frequency through magnetic field action

Consist of two or more coils of wire wrapped around a common ferromagnetic core

Construction & How it works

**Ideal Transformer**

vs

Real Transformer

vs

Real Transformer

Ideal Transformer

Real Transformer

**Per Unit System**

Three Phase Transformer

How does a Transformer Work ?

Construction

The permeability of the core, approaches infinity

No core losses

No resistance in the windings

No leakage flux

Therefore:

Schematic Diagram

Example

Power

Impedance Transformation

Understand the purpose of a transformer in a power system

Know the voltage, current and impedance relationships across the windings of an ideal transformer

Understand how real transformers approximate the operation of an ideal transformer

Be able to explain how copper losses, leakage flux, hysteresis and eddy current are modeled in a transformer equivalent circuit

Use the transformer equivalent circuit to find the voltage and current transformations across a transformer

Be able to calculate the losses and efficiency

Be able to derive the equivalent circuit of a transformer from measurement

Understand per unit system

Be able to calculate voltage regulation

Understand auto transformer

Understand three phase transformers

Solution

LOSSES

ACCOUNTED

???

1. Copper Losses

2. Eddy Current Losses

4. Leakage Flux

3. Hysteresis Losses

EQUIVALENT CIRCUIT

OPEN CIRCUIT TEST

EXAMPLE

Referred to Primary Side

Referred to Secondary Side

Approximation - current excitation branch 2-3% only

HOW TO DETERMINE PARAMETERS?

SHORT CIRCUIT TEST

Resistive heating losses in the primary and secondary winding of transformer. Proportional to square of current.

Resistive heating losses in the core of transformer. Proportional to square of voltage applied to transformer.

Associated with magnetic domains in the core. It is a function of voltage applied to the transformer.

Flux escape from the core and pass through only one side of the transformer. Its produce leakage inductance in the primary and secondary winding.

How?

1. Select 2 base quantities

- usually selected - voltage and power

2. Use electrical law

Example

Advantages:

Eliminates the need for voltage-level conversions and impedance transformation at every transformer.

Machine and transformer impedances fall within a fairly narrow range according to voltage and power ratings of the device.

Solution

Text book page 93

Efficiency

EXAMPLE

Example

Voltage and Current Relationship

Apparent Power Rating

Advantage

The Internal Impedance

Example