transformer name plate data , coil , insulation class presentation

DISCUSSION ON TRANSFORMER NAME PLATE STUDY

DISCUSSION ON DISSCUSSION OF DIFFERENT TYPES OF COIL

DISCUSSION ON INSULATING MATERIAL OF TRANSFORMER

TRANSFORMER NAME PLATE

STUDY

Provides vital information on How the transformer is to be connected and operated.

Transformer birth certificate

MINIMUM NAMEPLATE REQUIREMNTS

The minimum information to be shown on a transformer nameplate depends on the KVA rating. The standards require the follow information for transformers rated > 500 KVA

• Name of manufacturer

• Serial number

• Month/year of manufacture

Cooling class where the class of transformer involves more than one rating. all ratings are shown. windings having different ratings have their individual KVA ratings described. If the transformer has more than one temperature rating, These ratings are shown on the nameplate. Provisions for future cooling equipment are indicated.

•

•Frequency

• KVA or MVA rating

• voltage ratings

• Tap voltages

• Rated temperature rise. °C

Percent impedance The percent impedance is specified between each pair of windings with the voltage connection and the KVA base stated. The percent impedance shall he tested.

• Basic lightning impulse insulation levels (8W) The BlL of each winding and each bushing are specified. .

• Approximate mass of the core and coils, tank and fittings, insulating oil, total weight, and heaviest piece

•Maximum negative pressure of the tank for vacuum filling

• Oil volume of each transformer compartment

• Type of insulating liquid.

• Number of phases

• Phasor or vector diagram (poly-phase transformers)

• The word “transformer” or “autotransformer”

• Maximum positive and negative operating pressures of the oil preservation system, kPa or psi

Cooling class : The kinds of cooling medium and their symbols adopted by I E C :

Name of the Cooling Medium

Symbol

Mineral oil or equivalent flammable insulating liquid

o

Non flammable synthetic insulating liquid

L

Air A Gas G water W

The kinds of circulation for the cooling medium and their symbols are:

Name of the Circulation Cooling Medium

Symbol

Natural N Forced (Oil not directed) F Forced (Oil directed) D

Name of the Cooling Class DescriptionONAN ( Oil Natural Air Natural )

Oil Immersed Natural cooled

Name of the Cooling Class DescriptionONAF (Oil Natural Air Forced Oil Immersed Air Blast -

Type In this case circulation of air is obtained by fans. It becomes possible to reduce the size of the Transformer for the same rating and consequently save in cost.

Name of the Cooling Class DescriptionOFAF (Oil Forced Air Forced ) Forced Oil Air Blast Cooled

In this system of cooling also circulation of oil is forced by a pump. In addition fans are added to radiators for forced blast of air. .

Name of the Cooling Class Description

OFAN (Oil Forced Air Natural ) Forced Oil Natural Air Cooled

In this method of cooling, pump is employed in the oil circuit for better circulation of oil.

Name of the Cooling Class DescriptionOFWF (Oil Forced Water Forced ) Forced Oil Forced Water

Cooled Oil is forced through cooler. Cooling water is also circulated in closed loop.

Symbol Title DescriptionO.N.A.N. Oil Natural

Water Force30 MVA. ≤

O.N.A.F. Oil Natural Air Force

Between30 MVA and 60 MVA.

O.F.A.F. oil Forced Air Forced

60 MVA.

O.F.W.F. Air Natural Water Forced

do

A.N. Air Natural 1.5 MV ≤

Nominal Rating of Various Cooling Classes

Percentage Impedance (Z%) ? DefinitionThe percentage impedance of a transformer is the volt drop on full load due to the winding resistance and leakage reactance expressed as a percentage of the rated voltage.

It is also the percentage of the normal terminal voltage required to circulate full-load current under short circuit conditions

The percentage impedance can then be calculated as follows:Z% = Impedance Voltage x 100 Rated Voltage

Example : It is easy to calculate the maximum current that a transformer can deliver under symmetrical fault conditions.

Consider a 2 MVA transformer with an impedance of 5%

The maximum fault level available on the secondary side is:

2 MVA x 100/5 = 40 MVA

From this figure the equivalent primary and secondary fault currents can be calculated.

A transformer with a lower impedance will lead to a higher fault level (and vice versa)

The figure calculated above is a maximum.

In practice, the actual fault level will be reduced by the source impedance, the impedance of cables and overhead lines between the transformer and the fault, and the fault impedance itself.

Basic Impulse Insulation Levels (BIL)

Lightning surges or Even if the lightning strikes the line some distance from the transformer voltage surges can travel down the line and into the transformer

Opening or Closing of High voltage switches and circuit breakersBoth types of surges have steep wave fronts and can be very damaging to electrical equipment . To minimize the effects of these surges, the electrical system is protected by lighting arresters

but

they do not completely eliminate the surge from reaching the transformer.

The basic impulse level (BIL) of the transformer measures its ability to withstand these surges.

OPERATING PRESSURE RANGE

Most modern power transformers are designed to be “vacuum oil filled.

Before attempting to ‘‘pull vacuum’. on a transformer, it is important to consult the nameplate first to verify that the tank is designed to withstand the negative pressures.

The positive range of operating pressures is also specified on the nameplate. The nominal atmospheric pressure is 14.7 psi a sea level.

Thus, when the transformer contains a perfect vacuum. the negative pressure on the tank will be approximately 15 psi at sea level. and slightly less at higher elevations.

Vector Group :

Three phase transformer winding connected in several ways

based on the connection-->

The vector group of the transformer is determined . indicated in the name plate .

The vector group indicates the phase difference

betweenthe primary and secondary sides.

Why the phase difference happen ?

Phase difference due to the particular configuration of the transformer winding connection.

Determination of vector group is very important , why?

If different vector group transformers are parallel connected Then

the phase difference exist between secondaries of the transformers and large circulating current flows between two transformer

which is very harmful !!The three phase transformer primary and secondary windings are connected are the following ways, •Wye - Wye ( also called star-star)•Wye-Delta ( also called star –Delta)•Delta – Wye ( also called Delta-star)•Delta-Delta

VECTOR GROUP LIST

DESCRIPTION OF NAME PLATE AT SITE :

KVA - 500

VOLTS AT HV

NO LOAD L V

AMPERES HV

PHASE LV

HV

LV


KVA - 500

VOLTS AT HV

NO LOAD L V

11000

433

AMPERES HV

PHASE LV

HV

LV


KVA - 500

VOLTS AT HV

NO LOAD L V

11000

433

AMPERES HV

26.27

666.7

PHASE LV

HV

LV


KVA - 500

VOLTS AT HV

NO LOAD L V

11000

433

AMPERES HV

26.27

666.7

PHASE LV

HV

LV

3

3

TYPE OF COOLING

FREQUENCY HZ

CORE & WINDING Kg

OIL Kg TOTAL WEIGHT Kg OIL IN LITRE

ONAN

TYPE OF COOLING

FREQUENCY HZ

CORE & WINDING Kg


ONAN

50

TYPE OF COOLING

FREQUENCY HZ

CORE & WINDING Kg


ONAN

50

942

TYPE OF COOLING

FREQUENCY HZ

CORE & WINDING Kg


ONAN

50

942

510

TYPE OF COOLING

FREQUENCY HZ

CORE & WINDING Kg


ONAN

50

942

510

1750

TYPE OF COOLING

FREQUENCY HZ

CORE & WINDING Kg


ONAN

50

942

510

1750

600

GURANTEED MAXIMUN TIMPRAISE IN OIL / WININD DEG.C

Vector Group

45/55◦

Dy1

Tap Position :

3 3 34 4 45 5 5

6 6 67 7 78 8 8

2 3

1U 1V 1w

2U 2V 2w

2N

SWITCHPOSITION

H.V VOLTS

L.V VOLTS

JOINTAPS

1

2

3

4

5

113300

11000

10670

10340

10010

433

433

433

433

433

5-6

6-4

4-7

7-3

3-8

1

2

34

5

TAP POSITIONINDICATOR

NAME PLATE OF THE TONGI GRID S/S STATION TRANSFORMERSECTION - 1

NA

ME

PLATE

OF

TH

E T

ON

GI G

RID

S

/S

STA

TIO

N T

RA

NS

FOR

ME

RS

EC

TIO

N -

2

NAME PLATE OF THE TONGI GRID S/S STATION TRANSFORMER

SECTION - 3

DISSCUSSION ON

DIFFERENT TYPES

OF COIL WINDING

Conductor

Aluminum Copper

Less Expensive More expensive

Lower Mechanical Strength

Higher Mechanical strength

Used In Bigger Size Used in Smaller size

TRANSFORMER WINDINGS (Coils)

2 types of Winding Primary winding Receives Energy .Secondary Winding delivering electrical energy

What is it (Winding /Coil) made of ?High grade of copper for high current capacity and made it higher by using standard conductors are used for carrying higher current.

Why insulation is used is used in winding ?To avoid the each turn to come in contact with each other

The following are the most important requirements of transformer windings:

• The windings must be economical.

•The heating conditions of the windings should satisfy standard requirements.

• The windings must have good mechanical strength to combat the force that originates due to short-circuit.

•The windings must have the necessary electrical strength during over-voltage.

Two Types of winding :

1)Concentric Winding : Usually used in Core-type Transformer .

2) Sandwich Winding : Usually used in Shell –type Transformer

Concentric windings are classified into four following groups:• Spiral windings.

•Helical windings.

•Cross-over windings.

•Continuous disc windings.

This type or winding is normally used up to 33 kV and low current ratings.

Strip conductors are wound closely in the axial direction without any radial ducts between turns.

Spiral coils are normally wound on a Bakelite or pressboard cylinder

Spiral windings.

Double Layer

Helical winding •This type of winding is used in low voltage and high-current ratings. •A number of conductors are used in parallel to form one turn. •The turns are wound in a helix along the axial direction and each turn is separated from the next by a duct. •Helical coils may be single layer or double layer or multi-layer, if the number of turns are more.

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Distributed Cross-Over Windings•These windings are suitable for currents not exceeding about 20 A and are used for HV windings in small transformers in the distribution range. •These coils are generally wound on formers. •Each coil consists of several layers •Each layer consists of several turns. •The conductors may be of round wire with paper or cotton insulation •A number of such coils are joined in series, spaced with blocks which provide insulation as well as duct for cooling

Continuous disc windings :This type of winding is used for voltage between 33 and 132 KV and medium current ratings.

These coils consist of a number of sections placed in the radial direction with ducts between them.

Each section is a flat coil, having more than one turn, while each turn itself may comprise one or more conductors (usually not more than four or five), in parallel.

The sections are connected in series, but without any joints between them. This is achieved by a special method of winding.

.

COREDUCT

Individual strands differences in the flux field

Why ?Due to their respective positions within the

winding

What will happen regarding this phenomenon ?

Create differences in voltages between the strands and drive circulating currents through the conductor loops.

What will we do to overcome this problem ?

Proper transposition of the strands cancels out these voltage differences and eliminates or greatly reduces the circulating currents.

A variation of this technique ,involving many rectangular conductor strands combined into a cable, is called continuously transposed cable (CTC), as shown in Figure

DISCUSSION ON INSULATING MATERIAL OF

TRANSFORMER

What are the various types of insulations used in power transformers ?

•In dry type transformers Silicon treated materials are advantageous because of their water repellent property.

• For oil immersed transformers the coil insulation is generally of class A type, paper (craft, paper, manila paper etc.) or paper derivatives such as press boards, crapt boards are used.specially treated tape is applied to the winding conductors , Parts made from sheet insulation such as phenolic resin bonded paper bars, tubes, cylinders are used to support the winding and to provide insulation barriers .

• Insulating Varnish. Insulating varnish is used for impregnating (infuse) the transformer winding. The impregnation of trans-former windings by insulating varnish increases the mechanical strength of the windings insulation and fills up the pores of the paper and reduces the tendency to absorb to moisture. Vacuum impregnation is preferable

• Enamel. Enamel insulation is used on conductor for dry type transformers. Oil resistant, air drying enamel applied to copper conductors of small size.

•Transformer Oil. The transformer oil (dielectric oil) is used as an insulation and cooling medium in power transformers and instrument transformers. The oil also has impregnating action on the paper insulation.

The main properties of insulating materials used in power transformer are the following :

1. High dielectric strength at working temperature.

2. Good thermal conductivity.

3. Long life at working temperatures. (Ageing property).

4. Good mechanical properties such as ease for working and application, bending.

5. Resistant to vibrations and abrasion.

6. Compatible with oil and surrounding medium.

7. Non-hygroscopic.

8. Low dielectric loss

Material Picture Application Remarks (Property) Porcelain Enclosures for

Bushing•compression strength 6000 kg/cm2

•Tensile strength 4000 kg/cm2

•High temperature withstand

•Suitable for outdoor and indoor applications.

•Processed clay by molding and firing before and after glazing at l250°C to 1400°C

Dielectric Materials used in Power Transformers

Material Picture Application Remarks (Property) Epoxy Resin

•Support insulators

•Bonding of core laminations •Insulation for conductors

•compression strength 6000 kg/cm2

•Tensile strength 4000 kg/cm2

•High temperature withstand

•Suitable for outdoor and indoor applications.

•Processed clay by molding and firing before and after glazing at l250°C to 1400°C


Material Picture Application Remarks (Property) Glass fiber enforced synthetic resin.

•Insulating components

•High tensile strength •high withstand pres·· •sure, high dielectric •strength.

Dielectric oil

•As an insulation and cooling medium in transformers.

•Good dielectric strength properties as Per as Per IEC 60296Specification for unused mineral insulating oils for transformers


Material Picture Application Remarks (Property) Insulation Press Boards

•solid, soft, Calender pressboards used for cylinders, barriers, spacers washers, yoke insulation, partitions. •-Soft laminated press board used for blocks, supports, cleats, spacers etc.

Pre-compressed solid pressboards for studs, blocks, washers, clamping of winding etc.

As per specification IEC 60641


Material Picture Application Remarks (Property) Laminated Wood

•Packing between core wood and winding •Blocks, wedges for coil supports

•Un-impregrated high density laminated wood.

•High strength

•High dielectric strength


Material Picture Application Remarks (Property) insulating tapes

•For tapping on the conductors

•Cotton tape

•Glass woven tape

•Terylene woven tape

•High dielectric strength

•Moisture retardant

•Good ageing properties •Compatible with transformer oil

•High temperature Withstand


Material Picture Application Remarks (Property) Insulated copper conductor cables

• Paper insulated rectangular copper conductors for winding • Paper covered stranded copper cable

•PVC insulated copper cable single or multi-core (Polyvinyl chloride)

• Synthetic resin insulated conductor

•High tensile strength •high withstand pres·· •sure, high dielectric •strength.


Material Picture Application Remarks (Property) InsulatingPapers

•For winding insulation •For paper boards

• high dielectric strength.•Electrical grade insulating craft paper. •Thermal stability •·High temperature with-stand •Moisture retardation •-Free from voids, gaps •-Good heat dissipation •Chemically compatible with oil •-Good mechanical properties.


Insulating Components in Power Transformers

Components FunctionPress board or synthetic resin bonded paper cylinder

Insulation between Core and L.V. Winding.

Press board or synthetic resinbonded paper cylinder

Insulation between L.V. and H.V. winding.

Synthetic resin bonded paper bars.

For supports, for spacers between L.V. winding/H.V. winding.

Type of paper for conductor. Conductor Insulation in oil immersed Transformer

Glass paper Synthetic resin coating casting

Conductor Insulation for dry Transformer

Thank you

transformer name plate data , coil , insulation class presentation

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