transformers technologies

8/11/2019 Transformers Technologies

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Development of New Concepts &

Technologies - Design of Transformersfor Reliable Operation

M. Gopal RaoM.E; F.I.E

Former Director (Transmission),

A.P.TRANSCO, Hyderabad


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A transformer is a static device used for transferringpower from one circuit to another without change infrequency.

Operates on the principle of mutual induction betweentwo ckts linked by a common magnetic field.

EMF induced in a winding is proportional to the fluxdensity in the core, cross section of the core, frequencyand no. of turns in the winding.


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H.V WindingL.V Winding

Core

Fundamental equation of transformer


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A transformer basically consists of:

Magnetic Circuit comprising Limbs, yokes, clamping structures

Electrical circuit comprising primary, secondary windings

Insulation comprising of transformer oil and solid insulation viz.paper, pressboard, wood etc. and bracing devices

Main tank housing all the equipment

Radiators, conservator tank

On or Off load tap changer

Vent pipe, Bucholtz relay, Thermometers

Fans, Cooling pumps connected piping

Terminals i.e. connecting leads from windings to bushing withsupporting arrangements


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Design Parameters

Voltage Ratio No. of phases

Flux density Rated capacity

Current density Insulation& cooling medium

Insulation levels Tap changerVector group Cooling arrangement

Percentage Impedance Oil preservation system

Short circuit withstand

capacity Operating conditions


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Features of Power Transformers

Single Phase

Three phase

Star or Delta connected Primary

Star or Delta connected Secondary With or without Tertiary winding

Provided with Off-circuit tap switch or On-load TapChanger for voltage regulation


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Codes and Standards

Codes or Regulations are mandatory requirementsstipulated to ensure the safety of the product during testingand service.

Standards are the basis of agreement and can be used forlimited scope or even restricted. Standards also promoteinterchangeability. Standards exist for material, product,process, testing, calibration etc.

Specifications are based on mandatory requirements of thepurchaser and agreed requirements of the standard.


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OPERATING CONDITIONS

The environment in which a transformer works and the

quality in design and construction play a role on its

performance. A transformer working under normal operating

conditions, in all probability, gives satisfactory performance

throughout its lifeNORMALOPERATING CONDITIONS:

1. Rated voltage and rated current with permissible margins.

2. Temperatures of oil and windings not exceeding the

prescribed values.3. Availability of auxiliary and control supply and proper

functioning of accessories and protective devices.

4. Free from external faults such as line breakdowns and

equipment breakdowns.


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User should specify the conditions under which transformer is expected

to work viz. quality and nature of load temperature limit, voltageconditions, short circuit withstand capacity considering present and

expected fault levels.

Parameters specific to locations are to be evaluated and specified to

assess the operating requirement.

Manufacturers should ensure that factory tests as required under

standards and the user specifications are done to verify the quality and

ability of the transformer to withstand all service stresses during life timeof the transformer.


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Insulation

Major Insulation: Oil and Paper or cellulose material.

Paper and pressboard insulation immersed in oil and subjected to

temperature for longer periods, lose mechanical strength. Dielectric

strength remains until paper is charred, when free carbon becomes

conducting or too brittle to withstand mechanical shocks. De-

polymerization of insulation takes place when deterioration starts.

Ageing of tr. depends on the dielectric performance of the insulation

system.

Higher the temperature the faster is insulation deterioration.


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Transformer operates at below normal temperatureLoss of life of

insulation is less than normal.

Operating temp. is greater than normalloss of life is higher than

normal.

Transformer may be safely operated for a time at above normal

temperature provided the loss of insulation life during this period isadequately compensated by operating for a sufficiently long time at

temperatures below normal.

Between 80 to 140 deg. C, the rate of loss of life due to ageing ofinsulation is doubled for every 6degrees c rise in temperature.


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Proper upkeep of solid and liquid insulation to their specified levels with

marginal and permissible variations ensure longevity. This is possible byproper operation such as maintaining the load current and voltage and oil

and winding temperatures at their rated levels and not exceeding these

levels.

Paper or oil dielectric have varying degree of sensitivity to degradation

upon overloading, ingress of moisture, improper handling and storage

affecting life. It is necessary that moisture ingress into oil is prevented by

suitable oil preservation system.


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Normally flux density is chosen near knee point of magnetization curve

leaving sufficient margin to take care of voltage and frequency variations.

CRGO steel with silicon content of approx. 3% is used for magneticcircuit. Characteristics of good core are :

1. Max. magnetic induction to obtain a high induction amplitude in an

alternating field.

2. Minimum specific core loss and low excitation current

3. Low magnetostriction for low noise level

4. Good mechanical processing properties.


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Magnetostriction is change in configuration ofa magnetizable body in a magnetic field whichleads to periodical changes in the length of thebody in an alternating magnetic field.

Due to magnetostriction of laminations in analternating field core vibrates generating noisein the core.


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Current density is an important parameter to design the section of the

conductor for a specified temperature rise, rated capacity and short

circuit withstand capacity of the transformer.

Different types of windings :

Distributed crossover winding

Spiral windingHelical winding

Continuous disc winding

Interleaved disc winding

Shielded layer winding


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CHARACTERISTICS OF TRANSFORMER OIL:

A. PHYSICAL

Appearance

The oil shall be clear, transparent and free from suspended

matter

If color of oil is

a) Light - indicates degree of refining

b) Cloudy or foggy - Presence of moisture

c) Greenish tinge - Presence of copper salts

d) Acid smell - Presence of volatile acid. Can causecorrosion


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Density: At 27deg. c is 0.89gm/cu.cm. This ensures that

water in the form of ice present in oil remains at the bottom

and does not float up to a temp. of about

10 deg. c.

Viscosity: Is a measure of oil resistance to continuous flow

without the effect of external forces. Oil must be mobile in

transformers to take away heat. Viscosity shall be as low as

possible at low temperatures. Maximum value at 27deg.cshall be 27 cst

Flashpoint: is the temperature at which oil gives so much

vapor, which when mixed with air forms an ignitable mixtureand gives a momentary flash on application of a flame.

Minimum flash point of a good oil shall be 140 deg. C.


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Pour point

is the temperature at which oil will just flow under prescribed

conditions. If oil becomes too viscous or solidifies it will hinderthe formation of convection currents, thus cooling ofequipment will be affected.

Maximum pour point shall be -9 deg. C

Interfacial Tension

Is the measure of resultant molecular attractive force betweenunlike molecules like water and oil at the interface. Presence ofsoluble impurities decrease molecular attractive force between

oil and water. This gives an indication of degree of sludging ofoil.

Minimum value 40 dynes/M or 0.04 N/M

.


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CHEMICAL

Neutralization Number

Is a measure of organic and inorganic acids present in the oil.Expressed as mg. of KOH required to neutralize the totalacids in one gm. Of oil.

Limits for fresh oil - 0.03 mg KOH/gm - maximum

Limits for used oil - 0.05 mg KOH/gm - maximum

It leads to formation of sludge, metal surface corrosion andlowering of dielectric strength.

Corrosive SulphurIt indicates the presence sulphur, sulphur compounds, whichare corrosive in nature and corrode the copper surface.


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Oxidation Stability

This is measured by ageing the oil by simulating actualservice condition of a transformer. Covers the evaluation

of acid and sludge forming tendency of new mineral oils.For used oil, should be minimum to minimize electricalconduction and corrosion

Water Content: Due tomoisture entry into oil.

a) By accidental leakage

b) Breathing actionc) During oil filling or topping up

d) By chemical reaction

In unused oil - Maximum 30 ppm

Oil in transformer 145 KV & above - Maximum 15 ppmOil in transformer below 145 KV - Maximum 25 ppm

It reduces electrical strength and promotes degradation of

oil as well as paper.

ELECTRICAL


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ELECTRICAL

Electric Strength

Is the voltage at which arc discharge occurs between two

electrodes when oil is subjected to an electric field under

prescribed conditions.

New oil unfiltered - 30 KV minimum (rms)

New oil filtered - 60 KV minimum (rms)

Resistivity

It is numerically equal to the resistance between opposite facesof a centimeter cube of oil. Insulation resistance of thewindings of transformer is dependant on the resistivity of oil.A low value indicates the presence of moisture andconducting contaminants.

Values for a new transformer are(12)

At 27 deg. c 500x 10 ohm.cm

(12)

At 90 deg. c 30x 10 ohm.cm


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Dielectric Dissipation Factor (Tan Delta & Loss Tangent)

Is measure of dielectric losses in oil & hence the amount of heat

energy dissipated.

It gives an indication as to the quality of insulation. A high value

indicates presence of contaminants or deterioration products

such as water, oxidation products, soluble varnishes, and resins.

1) Tan delta at 90 for unused oil - maximum 0.2

2) Tan delta at 90 oil before charging transformer -

maximum 0.005 (1/2%)

Low value of tan delta indicates low losses


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Vector Group and Polarity

When induced voltages of pri . and sec. windings are in same direction, polarity

of the two windings is same. This is called subtractive polarity. When theinduced EMFs are in opposite direction , the polarity is called additive.

Pri. and sec. windings on any one limb have induced emfs that are in time phase.

Different combinations of internal connections and connections to terminals

produce different phase divergence of sec. voltage.

Vector group or connection symbol of a transformer denotes the method of

connection of pri. and sec. windings and the phase angle divergence of sec. with

respect to primary.


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Vector Groups

1

3

4

U

VW

u

w

v

u

w

v

1 & 3 YNd1

2 & 4

YNd11

U

VW

2


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U

VW

u

v

w

u

v

w

1

2

3

4

Vector Groups

U

VW

1 & 3 Dyn11

2 & 4 Dyn5


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Vector Group Test

A

BC

a

b

c

A

BC

a

bc

DY 11

VAb = VAc

VBb = VBc

VCb > VCc

Aa = 0

Ab = bc = ca

Bb = Cc


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Tap changer

Device for regulating the voltage of transformer.

Off circuit tap changer : Tap changing is effected when tr. is off. These

are cheaper. They are used where frequency of tap changing is very less.

On load tap changer : Here tap changing is effected without interruptingload. On load tap changer normally consists of transition resistors which

bridge the circuit during tap changing operation.

Two types of OLTCs :

Single compartment typeIn this type selection of taps and switchingare carried out on the same contacts.

Double compartment typeIn this tap selection is done separately and

switching is done in a separate diverter switch.


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Externally mounted OLTC/1

Requirements for a tap changer


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Requirements for a tap changer

Percentage variation required for each tap

No. of taps and step voltage

Maximum through currentInsulation level to ground and between various contacts.

No of steps and basic connections

Temporary overloads and short circuit strength

Automatic voltage regulating relays are used for automatic control of bus

bar voltage.

Output of voltage transformer connected to controlled voltage side of the

tr. is used to energize AVR relay. When voltage deviation exceeds a

preset limit, a control signal to raise or lower tap operation is given. A

time delay unit is connected in the circuit to prevent unnecessary

operation or hunting of tap changer during transient voltage change.


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Types of Tap Changers

Based on function

Constant Flux Voltage Variation (CFVV)

Variable Flux Voltage Variation (VFVV)

Combination of above both Based on method of tap change

Linear

Reversing

CoarseFine Bridging


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Tap Changer Location

Neutral End Middle of winding Line End


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Linear Reversing Coarse

Fine


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Basic conditions of operation

Load current must not be interrupted during tap

change operation.

Tap change must occur without short-circuiting the tap

winding directly. Positive change of tap position.

It means make-before-break mechanism to beused. This calls for a transition impedance.

Also the mechanism should be fast acting typespring loaded.


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General Design considerations

Capable to normal load/overloads on transformer.

Maximum system voltage

Step voltage & no. of steps

Test voltage to earth and across tapping range

Maximum surge voltage to earth and across range.

Maximum test voltages between phases (whereapplicable)

Current ratingnormal and overload


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Parts of Tap Changer

Selector switch

Tap selection takes place in this switch

Diverter Switch

Makebefore-break mechanism with transitionimpedance. Arcing takes place and hence housed ina separate compartment.

Surge relay

Conservator with oil level gauge.


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Transition Impedance

Reactor type

Resistor type


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P i i l f T h ti


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R2R1

75

3

1

8

6

4

2

N

Principle of Tap changer operation

M2 T2 T1 M1


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M2 T2 T1 M1 M2 T2 T1 M1 M2 T2 T1 M1

M2 T2 T1 M1 M2 T2 T1 M1 M2 T2 T1 M1

1 2 3

4 5 6


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Parts of Tap Changer

Motor drive mechanism

Should rotate in both the directions

Step-by-step operation

Tap change in progress indication

Tap change complete indication

Sequence contact

Remote Tap position control & indication


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Cooling Arrangement

Controlling the temperature inside the tr. is necessary to reduce thermal

degradation of insulation to ensure longer life. Heat generated in the tr. istransmitted to atmosphere through oil.

Different types of cooling:

ONAN typeOil natural and air natural. Hot oil is circulated by natural

means dissipating heat to atmosphere by natural means.ONAF typeOil natural, air forced. Here air is blown on to the cooling

surfaces. Forced air takes away heat at a faster rate.

OFAF typeOil forced, air forced. If the oil is force circulated within the

tr. and radiator by means of an oil pump, in addition to forced air, still

better rate of heat dissipation is achieved over ONAF


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OFWF typeOil forced, water forced. Here water is employed for

cooling oil instead of air. Ambient temp. of water is less than atmosphericair. Hence better rate of cooling is obtained. In this type oil to water heat

exchangers are employed. Differential pressure between oil and water is

maintained. Oil is circulated at a higher pressure.

ODAF/ODWF typeOil directed, air/water forced. If the oil is directed

to flow past the windings, large quantities of heat can be taken away by

oil. Cool oil is directed to flow through the windings in predetermined

paths. Oil is circulated by a forced oil system like oil pumps. This ensures

faster rate of heat transfer.


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Oil Preservation System: Oil readily absorbs moisture. Presenceof moisture reduces dielectric strength of oil. Different methods are

available to reduce contamination of oil with moisture.

1. Silica gel Breather: It is connected to the conservator tank. It consists

of a cartridge packed with silica gel dessicant and a small cup containing

oil. Air is drawn into the conservator thro. oil cup and breather where

most of the moisture is absorbed.

2. Bellows and Diaphragm sealed conservators: A bellow type barrier or

a diaphragm type barrier is fitted in the conservator. Air entering the

conservator tank pushes the diaphragm downwards. As oil expands the

diaphragm is pushed upwards. Position of diaphragm is indicated by oillevel indicator. Diaphragm acts as a barrier.


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3. Gas sealed Conservators: In this method a cushion of an inert gas like

Nitrogen is provided over oil surface in the conservator. Gas pressure is

always maintained higher than atmospheric pressure. Nitrogen gas

pressure inside the conservator is regulated by nitrogen cylinder andpressure reducing valve which admit Nitrogen to the conservator when

the pressure falls. Excessive pressure developed inside the conservator is

relieved through a relief valve.

4. Refrigeration Breathers: An air dryer is fitted to the conservator. Air

breathed thro. the unit is dried in passing down a duct cooled by a series

of thermoelectric modules based on Peltier effect. Top and bottom ends

of the duct are terminated in the expansion space above oil level in the

conservator and air is continuously circulated thro. the duct bythermosyphon forces.


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Short circuit withstand Capacity:

Effects of short circuit: Energy in the system gets released in

the form of heavy flow of current when fault occurs.

Every fault fed by the transformer stresses the windings. The

stress developed in the winding is related to the intensity of

fault.

Each fault causes sharp rise in temperature and producesmechanical forces in the winding.

These forces act in the axial and radial directions of the

winding, and cause compressive or tensile stresses on the

winding and tend to deform it.


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RADIAL FORCES: ARE DUE TO FLUX IN THE SPACE

BETWEEN COILS. TEND TO BURST COILS AND

CRUSH ON THE CORE.

STRENGTHENING OF WINDING

AXIAL FORCES: ARE DUE TO RADIAL COMPONENT

OF FLUX WHICH CROSSES THE WINDING AT THE

ENDS AND GIVES RISE TO AXIAL COMPRESSIVE

FORCE TENDING TO SQUEEZE THE WINDING IN

MIDDLE.

PROPER DRYING, COMPRESSION AND CLAMPING


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THERMAL EFFECT: RAPID RISE OF TEMPERATURE

CAUSES

i) MECHANICAL WEAKENING OF INSULATION DUE

TO THERMAL AGEINGLONG TERM EFFECT.

ii) DECOMPOSITION OF INSULATION TO PRODUCE

GASESSHORT TERM EFFECT.

iii) CONDUCTOR ANNEALINGBECOMES BRITTLE

& CRACKS WILL BE FORMED.

LIMIT OF MAX. AVERAGE TEMPERATURE AFTER

SHORT CIRCUIT IS 2500C FOR OIL IMMERSED

TRANSFORMER USING COPPER WINDING.


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Design Basis

Life-time cost of transformer

= Initial cost of transformer

+

Operational cost for its life period

This is called the

Capitalized cost of transformer.


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Design Basis -Capitalization

Rationalized CBIP Capitalization Formula:Capitalized Cost = Initial Cost (IC) + Capitalized { No-

load Loss (Wn) + Load Loss (Wl) + Auxiliary Losses (Wa) }

Capitalized cost = IC + Xn.Wn +Xl.Wl +

Xa.Wa

Factors affecting Xn; Xl and & Xa

Rate of Interest

Rate of Electrical Energy

Life of Transformer

Design Basis


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Design Basis

The design of a transformer aims at achievinglowest capitalized cost.

Low No-load Loss means higher magneticmaterial cost and vice-versa

Low Load Loss means higher copper (material)

cost and vice-versa.

Several iterations are made to optimize the totalcost before freezing the design and drawings aremade.

Extensive use of CAD programs is needed forfinalizing design.


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Design Principles - Core

Higher the number of steps in cross section, better is spaceutilization and smaller is the core diameter.

90 to 95 % utilization factor is optimal.

Core area (A) is determined by the Flux Density (B) whichin turn depends on many factors - like loss capitalization

and overall design economics.

As the no load losses attract very high capitalization,

attempts are continuously made to reduce them.

D i P i i l C


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Design Principles - Core

Improved manufacturing techniques likecore building with 2-lamination packets, step-lapjoints, v-notched laminations,bolt-less cores are used.

Hi-core steels like M0H, ZDKH, etc are availablein which the specific core losses are lower thannormal grades.


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A A

View A-A

Conventional Step lap

D i P i i l


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Design Principles

Windings- L.V winding

L.V Windings in Transformers are either Spiral OR layer wound for low current ratings

Helical Wound with radial cooling ductsfor higher ratings.

Disc type wound

Distributed Cross-over (Run-over) coils

The conductor used is paper insulated rectangularcopper (PICC)

For higher currents, transposed conductors are used,to uniformly distribute the current across the cross

section of the wire of coil.


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Spiral/Layer type Winding

Mandrel/Press-board cylinder

Cooling Duct

Conductor Layer 1

Conductor

Layer 2

Conductor Layer 3

Design Principles- L.V winding


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Design Principles L.V winding

Helical Coil (Single layer) Helical coil (Double Layer)

Start Finish


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Transposed Conductors

Transposed conductors (CTC) are used to improve current distribution in the

cross section of the winding wire.

Individual cable can be coated with epoxy so that the cured and finished

conductor is mechanically stronger and withstand short circuit forces better.

Design Principles H V Winding


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Design Principles H.V Winding

HV winding invariably uses PICC orCTC.

Type of winding used is

- Layer winding or

- Disc winding up to 132 kV and/or- Interleaved winding or

- Rib shielded winding


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Temporary Over-voltages Switching Over-voltages Over-voltages due to lightning.

Power Systems Over voltages

POWER SYSTEM OVER VOLTAGES


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Temporary Over-Voltages

Typically due to faults < 1.2 pu

ms to tens of second or even minutes

Not dangerous to insulation

S it hi O V lt


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Switching Over-Voltages

Due to system switching operations

1.5 pu 5 pu depends on system voltage

mostly damped asymmetric sinusoids

front time of first peak tens of s to a few ms.

decides external insulation in EHV/UHV systems


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Over Voltages due to Lightning

Due to direct or indirect lightning strokes.

known to contribute to 50% of system outages in EHV& UHV systems

few hundred kV to several tens of MV.

Few kA to 200 kA

very short duration : time to front : 1 to few tens of s

time to tail : few tens to hundreds of s.

Decides line insulation (BIL)

Severely influences Transformer insulation.


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Cg

Cs= K Cg/Cs

Design Principles

Impulse Voltage Distribution


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Design Principles

Impulse Voltage Distribution

= 0

= 1 0

=5

X

V


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Disc Type Winding

Paper Insulated Conductor

Press-board Cylinder


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V


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Impulse Voltage

Distribution

1. Plain Disc Winding

2. Rib Shield Winding

3. I nter-leaved Disc Winding

Number of discs from line end

O

L

T

AG

E

G

R

A

D

I

E

N

T

P

u

D i P i i l T ti Wi di


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Design Principles Tertiary Winding

In Star-Star Connected Transformers and Auto-

transformers, Tertiary Winding is used-

- to stabilize phase to phase voltages in case of

unbalanced load

- Suppressing third harmonic currents in earthed neutral

- reducing zero sequence reactance

- for supplying auxiliary load or for connecting

capacitors.

D i P i i l T ti Wi di


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Design Principles Tertiary Winding

Tertiary is required to be designed for a power rating equal toone-third the rated power, it increases the cost of thetransformer by 10- 12 percent.

Tertiary winding is known to fail due to transferred surges andShort circuits

Present practice is to do away with tertiary up to 100 MVA for 3

phase 3 limbed core transformers.

CASE STUDY OF FAILED 100 MVA

220/132 KV AUTO TRANSFORMERS


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220/132 KV AUTO TRANSFORMERSTRANSFORMER NO. 1.- DATE OF FAILURE 11.05.1992

OBSERVATIONS: BURNING AND TWISTING OF TURNS INTHE TERTIARY WINDINGS (V&W PHASES) NEAR THE

TOP END.

FAILURE APPEARS TO BE MAINLY MECHANICAL.

TYPE OF TERTIARY WINDING : SPIRAL WITHOUT ANY

INTENTIONAL COOLING. THE AXIAL ASYMMETRY IN

THE ASSEMBLY OF WINDINGS IS OBSERVED, AXIAL

COMPRESSIVE FORCE IN TERTIARY IS WORKED OUT

TO BE 133% i.e. HIGHER BY 33%.


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REASONS FOR FAILURE:

TERTIARY WINDING USED FOR STABILIZING

PURPOSE FAILURE ACOMPANIED BY EXTERNAL

SINGLE LINE TO GROUND FAULT (132 KV LINE

CONDUCTOR SNAPPING).

DUE TO HIGH CIRCULATING CURRENTS WHEN

TRANSFORMER FEEDS UNBALANCED SYSTEM

(TRACTION, REROLLING, MILLS).

TEMPERATURE RISE LEADS TO INSULATIONFAILURE.

INCREASED SHORT CIRCUIT FORCES ON THE

WINDING.

THE RATING OF TERTIARY WINDING AND THE


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THE RATING OF TERTIARY WINDING AND THE

IMPEDANCES BETWEEN HV TO TERTIARY AND IV TO

TERTIARY IN RESPECT OF TRANSFORMERS WITH

LOADED TERTIARY WINDING AND WITH STABILIZINGTERTIARY WINDING (NOT INTENDED FOR LOADING).

TYPE OF %IMPEDANCE BETWEEN

TERTIARYHV TO IV TO TRANSF.

TERTIARY TERTIARY RATING

LOADED 57 TO 70.5 41 TO 65.5 15MVA

TERTIARY

UNLOADED 28 TO 37 17 TO 22 13 TO 15

TERTIARY MVA

It is observed that failure of transformers particularly with tertiary


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p y y

windings, in no. of cases occurred, where system impedance is low and

the fault level is high.

Impedances between pri. To tertiary and sec. to tertiary is observed to be

low causing excessive stresses in the tertiary winding leading to its

failure.

It is therefore felt necessary to strengthen the tertiary winding andincrease the leakage reactance between tertiary to other windings to bear

the stresses developed under faults.


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ADDITIONAL DESIGN CONSIDERATION FOR

TERTIARY WINDING

1. RAISING THE %IMPEDANCE BETWEEN HV TO

TERTIARY & IV TO TERTIARY TO 35% & 25%

RESPECTIVELYWITHONLYPOSITIVETOLERANCE

OF 15%.

2. INCREASING THE RATING OF TERTIARY

WINDING TO 1/3 CAPACITY OF THE

TRANSFORMER.

3. TO PROVIDE INTENTIONAL COOLING FOR THE

TERTIARY WINDING FOR FASTER AND LARGER

DISSIPATION OF HEAT.


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Design Process

Design should meet

Requirements of customer specification

Relevant national or international standards

Statutory and regulatory requirements

Manufacturers Plant Standards

Optimized design

O ti i ti


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Optimization

Objective of Optimization

To arrive at a design that yields minimum capitalized

cost.

It is a function of the following:

Core diameter

Core height

Flux Density

Current Density

COMPUTER AIDED DESIGN-


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PURPOSE OF IT

Improve productivity of design personnel

Reduce delivery cycle

Better analysis and arriving at a most optimum design

To solve electro-static, electro-magnetic problems and toprovide a robust structural and thermal design.


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More precise calculations

Tailor made designs

No standard ratings specified above 1 MVA

Change of specification parameter

Relative change of material cost

Ongoing development of technology

Poor quality results in failures.


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q y

Types of failures

Infant failures: Early life failures are the result oflatent defects.

- Latent defects are abnormalities that cause failure,depending on degree of abnormality and amount ofapplied stress.

- Delivered defects are those that escape test /inspection within the factory

- They are directly proportional to total defects inthe entire processes.


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transformers technologies

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