Role of transformers in power systems

PresentersDebojyoti Mukherjee 40

Sayantan Mondal 37Sourav Mondal 38Yogesh Verma 62

IntroductionTransformers are static devices that are used

to transmit power with same frequency between two coupled circuits by means of electromagnetic induction.

Transformers are static machines thus they have a very high efficiency 97-98%

Introduction

Introduction

Introduction

HistoryThe history of transformer was commenced

in the year 1880. In the year 1950, 400KV electrical power

transformer was introduced in high voltage electrical power system.

In the early 1970s, unit rating as large as 1100MVA was produced and 800KV and even higher KV class transformers were manufactured in year of 1980.

Outer construction

Working Principle

Classification of transformersTransformers

Output Voltage

Step Up

Step Down

Phase

Single Phase

3 Phase

Construction

Core Type

Shell Type

Service

Distribution Power

Step up/ Step down transformer

Core type/ Shell type

Phase• Generally 3 phase power is supplied to the consumers because:1. It uses less conductor material

hence it is economic.2. Other electrical devices such

as motors, generators have high efficiency in 3 phase system.

3. 3 phase motors are self starting.

• It is preferable to use bank of three single phase transformer as it is easier to transport three single phase unit separately than one single three phase unit.

Power/Distribution transformers

Power transformers are used in transmission network of higher voltages for step-up and step down application (400 kV, 200 kV, 110 kV, 66 kV, 33kV) and are generally rated above 200MVA.

Distribution transformers are used for lower voltage distribution networks as a means to end user connectivity. (11kV, 6.6 kV, 3.3 kV, 440V, 230V) and are generally rated less than 200 MVA.

Role of transformers

Role of transformersIf the voltage level of a power is increased,

the current of the power is reduced which causes reduction in Joule or I2R losses in the system.

This results reduction in cross sectional area of the conductor i.e. reduction in capital cost of the system.

Also it improves the voltage regulation of the system.

Transformer efficiency

Losses

Core loss

Hysteresis loss

Eddy current loss

Copper/ Joule loss

Transformer efficiencyHysteresis loss in transformer: Hysteresis loss is due

to reversal of magnetization in the transformer core. Wh= ηBmax

1.6fV (watts)where,   η = Steinmetz hysteresis constant             V = volume of the core in m3

Eddy current loss in transformer: some part of the flux also gets linked with other conducting parts like steel core or iron body or the transformer, which will result in induced emf in those parts, causing small circulating current in them. This current is called as eddy current. Due to these eddy currents, some energy will be dissipated in the form of heat.

Transformer efficiencyCopper loss in transformer: Copper loss is

due to ohmic resistance of the transformer windings. Cu loss is proportional to square of the current, and current depends on the load. Hence copper loss in transformer varies with the load.

Other applicationIt can increase or decrease the value of capacitor, an

inductor or resistance in an AC circuit. It can thus act as an impedance transferring device.

Signal and audio transformers are used to couple stages of amplifiers and to match devices such as microphones and record players to the input of amplifiers.

Transformers are also used extensively in electronic products to decrease (or step-down) the supply voltage to a level suitable for the low voltage circuits they contain.

say, from 120V ac to 9V ac

Thank you