DR. JIVRAJ MEHTA INSTITUTE OF TECHNOLOGY

Department Of

Electrical Engineering

DATE: 23-08-2018

REPORT ON INDUSTRIAL VISIT AT ATLANTA

VENUE -: “Atlanta Transformer”

DATE OF VISIT -: 23 August 2018

SEMESTER -: 5th and 7th

OUTCOME OF THE VISIT -: The Students Learnt About the transformer.

INTRODUCTION

Atlanta electrical is the leading manufacturer of electrical

transformer that also include power and distribution transformer.

Incorporated in the year 1983, Atlanta electrical pvt. Ltd. , has

consolidated its position in the power generation and transformer

industry as a manufacturer of wide range of special application

transformers which conforms to the quality expectation of both domestic

and international market.

TYPES OF TRANSFORMER

Atlanta electrical built different types of transformers.

1) POWER TRANSFORMER

2) DISTRIBUTION TRANSFORMER

3) STEP UP TRANSFORMER 4) STEP DOWN TRANSFORMER

BASED ON CONSTRUCTION Core type transformer

Shell type transformer

BASED ON USE IN POWER SYST Power transformer

Distribution transformer

BASED ON POWER SUPPLY 1- ᴓ transformer

3- ᴓ transformer

TYPES OF WINDING

1) Cylindrical winding

2) Helical winding

3) Double layer helical winding

4) Continuous disc winding

5) Interleaved disc winding

6) Cross over winding

1) Helical winding

The helical winding has its turns wound in axial direction along screw line with

an inclination corresponding to the height of a conductor and an oil duct between

turns. The winding consist of single section conductor or no of strands in parallel

wound in the form of a continuous helix.

Helical winding is generally used for low voltage, medium capacity and high

current rating. In low voltage winding current is very high compared to high

voltage winding so no of small conductor strips used instead of single large

conductor. A distinguishing feature of the helical winding is the use of transposed

conductor by changing the relative position of individual conductor and group of

conductors. The transposition is essential to equalizing resistance and leakage

reactance of each parallel conductor. In absence of transposition these conductors

having different length and being situated in the leakage field having un equal flux

densities, will have different resistance and leakage reactance.

This would lead to non-uniform distribution of current in parallel conductors

thereby overloading of portions of conductors and causing additional eddy current

losses in conductors. The standard maximum size of conductor limited to 17mm x

4mm.

( Atlanta electrical pvt. Ltd.)

2) DISC WINDING

a) Conventional disc winding

b) Interleaved disc winding

The winding consist of no of flat coils or discs connected in series or parallel. The

coils are formed with rectangular strips wound spirally from centre outwards in the

radial direction. The conductor used is in such lengths as are sufficient for

complete winding or section of winding between tapping. The conductor can be

single strip or a no of strips in parallel, wound on the flat side.

Disk winding is generally used for high voltage, large capacity, and low current

rating. In high voltage winding current is low as compared to low voltage winding.

So single copper conductor or sometimes multi conductor (large capacity

transformer) used in disc winding. Interleaved disc winding is as shown in fig.(c).

Interleaving improves voltage distribution for transient voltages with steep like

lightning surges, switching surge.

CORE

Cold Rolled Grain Oriented (CRGO) silicon steels are used for laminations of

the Power Transformers. Cold Rolled Grain Oriented (CRGO) sheets will have

superior magnetic properties in the direction of rolling.

Thickness of the CRGO sheets will be of the order of 0.33mm to 0.25mm.These

CRGO Steel Laminations are stacked together to form a magnetic core for the

Transformer. The Commercially available CRGO steel sheets will have 3% of

Silicon. Higher the Silicon content increases the resistivity and reduces the eddy

current losses. But Silicon Content above 3.5% makes the CRGO silicon steel

sheets brittle. Silicon content of3% to 3.25% is used in commercial grades of

CRGO steel.

The following features or properties influence for selecting the CRGO steel

sheet as magnetic core circuits for transformers.

• Core loss will be independent of the load of the transformer. By

using CRGO steel sheets core loss is low result in reduction of the

constant losses.

• Low apparent power input (Low hysteresis loss) results in low no

load current

• Good mechanical processing properties

• Low magnetostriction results in low noise level.

( 3 LIMB CORE ) ( 3 LIMB 2 AUXILIARY CORE )

CORE CUTTINGS

The use of mitered joints assures that the flux flows along the direction of grain

orientation thereby minimizing both the core loss and the magnetizing current.

TYPE OF CORE CONSTRUCTION

In core due to magnetic flux small emf induced in itself and current starts

flowing in core & this current known as eddy current. So due to presence of eddy

current losses take place in core and increase core temperature. To avoid eddy

current losses core made up of number of stampings. so current reduced and

divided in multiple path.

THERE ARE TWO TYPES OF CORE CONSTRUCTION

1) conventional core

2) step lap core

Magnetic flux produce in core and this flux flow in core. At corner flux passes

from joint. In conventional core flux direction are as shown in fig. and in step lap

core flux passes as shown in fig. Core losses depend on corner joints. Core losses

reduced in step lap core compared to conventional core construction. Noise also

reduced in step lap core.

(Flux passes through conventional core joints)

(Flux passes through step lap core joints)

CONSTRUCTION OF CORE

1) Before starting to arrange lamination sheets on frame channel, check its

alignment of both frames, leveling of channel and limb plates. Also check proper

insulation arrangement.

2) Measure leg centre after completion of each stack and also check centre of the

channel during process.

3) Check diagonal dimensions at least 2 to 3 times during process.

4) Provide adequate bottom support and frame supports as stacking increase.

5) Lamination stack should be padded using permawood block.

6) Now after completing stacking process put remaining frame plates and fitted

using nut-bolt. also provide belts to support core stampings during lifting core for

placed in vertical position.

7) Now check stack dimensions on each side and compare both reading. it should

be nearly same.

8) Check for limb diameter, leg centre and window height. And note down all

readings during checking.

9) Also check alignment of both channel bottom to bottom and top to top.

10) Now wound fiberglass tape around each limb to provide sufficient mechanical

strength to core stampings. and apply araldite on tape.

11) If oil circulation duct is present in core then connect both core sides using

copper strip. Proper press board or paper isolation should be provided to avoid

short circuit between stampings due to copper strip.

12) Copper strip should be inserted minimum 5inches deep in to core.

13) Then yoke clamps will be fitted using MS NUT-BOLT.

14) Provide adequate isolation between all frame parts and core part. Also

isolation provided between H.V and L.V frame plates. It will provide ease in fault

detection whether it will be on LV or HV side.

15) Ensure there are no sharp edges on studs. to avoid high density hot spots.

PARTS OF TRANSFORMER

1. Frame plate (upper yoke)

2. Press board cylinder for circular shape and isolation between core and coil.

3. Bottom yoke plates

4. Warn

5. Fitting and insulation between job and tank

6. Tank

7. Radiators for cooling

8. Transformer winding or coil

9. Tapping leads

10. Tank cover

11. OLTC box

PHOTOS

***THE END***