Dry type & Energy Efficient Transformers

For BSNL internal circulation only

E1-E2Electrical

Dry type & Energy Efficient

Transformers


WELCOME

• This is a presentation for the E1-E2 Electrical

Module for the Topic: Dry type & Energy Efficient

Transformers

• Eligibility: Those who have got the Upgradation

from E1 to E2.

• This presentation is last updated on 01-04-2011.

• You can also visit the Digital library of BSNL to

see this topic.


AGENDA

Introduction

Types of Dry type Transformers

Efficiency & overload capacity

Higher Efficiency Transformers

Energy Efficient Transformers


Introduction

The oil filled transformers are substituted by dry

type transformers from point of view of fire safety

and environmental aspects.

These transformers are used when they are to

be located near load center and in a fire

hazardous place.

As there is no oil used in the transformer and

special type of fire resistant insulation are used for

the windings the fire risk is considerably reduced in

dry type transformers.


Construction

The cast-resin transformers consist of HV &LV

windings made of copper conductors, which are

completely impregnated & cast under vacuum in

epoxy resin.

Glass fiber reinforced epoxy insulation of very

good electrical and mechanical quality is used.

Both the HV and LV windings are separately

cast under high vacuum.

5


Construction ( contd..)

The iron core is made from laminations of cold-

rolled grain-oriented (CRGO) sheet of steel.

The complete core is coated with special resin

as a protection against corrosion.

These transformers are designed to work without

any space heater even at 100 per cent humidity.

To control the temperature of transformer

thermistors are used.

6


Applications

1. Fire resistant Cast resin transformers are

suitable for installation in

High-rise buildings,

Hospitals,

Underground tunnels,

Schools,

Steel factories,

Chemical plants

And places where fire safety is a great concern.

7


Classification

According to type of insulation of windings,

transformers are classified as

Open wound

Vacuum pressure Impregnation (VPI)

Vacuum Pressure Encapsulated (VPE)

Encapsulated ( sealed)

Cast coil (moulded epoxy sealing)

8


Selection of Transformers

According to environment the selection of particular

transformer is done.

For improved resistance to corona-VPI type

For harsh environments like chemical process

plants-Cast coil type

For critical & harsh environment- VPI/VPE/Cast coil

can be used. But cast coil is the best choice.

9


Selection of Transformers( contd..)

The cast coil has disadvantage that

Cast resin used decreases the life of transformer.

The cyclic expansion & contraction due to heating

& cooling of the coils can crack the resin which

reduces the life of transformer.

The epoxy encapsulation in VPI transformer can

withstand these expansion & contraction.

The design Engineer has to choose appropriate

transformer.


Selection of Transformers( contd..)

The fans are also used to cool the transformer

which ultimately increase the rating of

transformer. The increase in KVA rating in

various transformer is as below

Cast coil type - 50% increase

VPE / VPI type – 33% increase

Fan assist rating means depending on moving

parts. So fan assist rating is used for unusual

overloads for critical installations.


Efficiency of Dry type transformer

Energy efficiency is determined by dividing its

nameplate rating by the sum of its nameplate rating

plus its total losses.

A small difference in energy efficiency can be

significant when valued over the life of the

transformer. A differential of just one-half percent

efficiency can easily add energy costs that exceed

the original purchase price.


Efficiency of Dry type transformer

Liquid filled transformer have lowest losses &

higher efficiencies as compared to dry type.

The typical losses in dry type are 1.5 - 2 times

greater than liquid type.

These losses are converted into heat in the core &

coils, causing the transformer to heat up which

ultimately reduces energy efficiency.


Overload capacity of dry type

transformer

Liquid filled transformers can withstand more

overloads as compared to dry type.

This is possible due to cooling system available in

liquid filled transformer.


Higher efficiency Transformers

Low loss transformer are called Higher efficiency

Transformers. There are two types of losses.

Operating losses & No load losses.

In Higher Efficiency transformer operating losses

are low. No load losses are reduced by replacing

conventional electrical steel by amorphous metal.

Amorphous metal is obtained when molten metal is

cooled to solid state at a very high speed rate.

Sheet thickness of 0.025 mm can be obtained.

15



( contd)

The amorphous metal strips of thickness 0.25

mm are available & core is called Power core.

These strips are four times harder than CRGO

steel. The hardness & reduced thickness restrict

their use for transformer manufacturing.



( contd)

The advantages of amorphous metal core are that

hysteresis loss & eddy current losses are low. In

totality core losses are reduced by 42 % &

magnetizing current by 53%.

By using amorphous metal core, size of core,

conductors, tank & insulating oil is increased. So

overall cost of transformer is increased by

20–30 %.

Load losses can be reduced by using thicker

conductors.But after all it is uneconomical.


Energy Efficient amorphous

Transformers

The iron loss of any transformer depends upon the

type of core used in the transformers. The

conventional transformer is made up a silicon

alloyed iron (Grain oriented) core.

The latest technology is to use amorphous material

for the core. 70 % reduction in energy loss is

expected, which is quite significant.

Distribution transformers made with amorphous

metal cores provide an excellent opportunity to

conserve energy right from the installation .


Energy Efficient amorphous

Transformers

Though these transformers are costlier than

conventional iron core transformers, the overall

benefit towards energy savings will compensate for

the higher initial investment.

At present, amorphous metal core transformers

are available up to 1000 KVA.


No load losses & Load losses

The table shows the no load and full load loss of

conventional (CRGO) and amorphous metal core

transformers.

_____________________________________


Distribution Transformer Efficiency

Winding of Transformer: The choice of winding

material-copper or aluminium-affects efficiency.

Use of copper windings minimizes transformer

full-load losses and may permit smaller cores,

minimizing core (no-load) losses.

Core of Transformer: The choice of Core Material -

CRGO or Amorphous.

Loss occurs whenever the transformer is

energized & it does not vary with load.


Distribution Transformer Efficiency

(contd.)

Amorphous core is expensive but reduces core loss

to less than 30% those of conventional steel cores.

Loading of Transformer: Efficiency of distribution

transformer varies as per loading conditions.

Closer operation to the rating of the transformer,

increases the efficiency.


Purchasing High Efficiency

Transformers

The selection & purchase of a high – efficiency

transformer is a complicated process.

Some purchasing tips are given below which

should be considered while selection.

1) Know your facility’s load profile – know your type

of load correctly.

2)Consider what type of equipment the transformer

will be powering.- The load may be linear or non-

linear. Non-linear load produces harmonic

distortion & increases transformer losses..


Purchasing High Efficiency

Transformers (contd)3) Do not be misled by transformers that are rated

at full load efficiency – The transformers are rarely

run at their full load.

The efficiency of transformer is different at low load

& full load.

4) Do not select your transformer solely on the

lowest temperature rise.

The low temperature rise transformers decrease

the load losses but increase the no-load losses.


Conclusion

From above discussion conclusion is that -

Dry type transformers can be located near load

center.

Dry type transformers have replaced oil filled

transformers as far as fire safety is concerned.

Cast coil transformers are suitable for harsh

environments but are very costly which increase

overall cost of the project.


Conclusion

Fan used for cooling of transformers increase

the KVA rating of transformers.

Overload capacity of dry type transformers is

less than liquid filled transformers.

Higher efficiency transformers are low loss

transformers. Power core made up of

amorphous metal strips is used in it.


Conclusion

By using amorphous material core, Energy loss

is reduced by 70%.

They are helpful for energy conservation.

These transformers are available up to

1000 KVA.


Conclusion

While selecting transformer for particular

application, design Engineer should observe all

points like

Economy

Higher efficiency

Energy conservation

Dry type & Energy Efficient Transformers

Documents

Transcript of Dry type & Energy Efficient Transformers