rkm d hoi transformer mod

7/30/2019 RKM D HOI Transformer Mod

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Transformers :

Principle, Types andConstructional Details.

R. K. Mishra

Director & Head of Institute

NPTINER, Guwahati.


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Layout of Switchyard showing locations

of different Transformers in a TPS :

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Transformer :

Static Apparatus

Core Type (small size)

Shell Type (large size)

1 Transformer

3 Transformer(either 3 Nos. of 1 Transformer or,single unit 3 Transformer)


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Advantages of single unit 3

Transformer :

Greater efficiency

Smaller size

Less cost compared with a Bank

having equal kVA capacity of three1 Transformer


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Advantages of three 1 units :

Greater availability with a singlestandby.

Ease of maintenance.

Ease of manufacture, transportationand erection.


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Symbols :


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Symbols (contd.) :


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Name Plate Details :

(1). IS standard IS:2026:1962 etc.(2). Manufacturers Name.

(3). Serial No.(4). Rated kVA.

(5). Frequency.

(6). Number of phases.

(7). Rated voltage on noload(HV/LV).


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Name Plate Details (contd.) :

(08). Rated current (HV/LV).

(09). Impedance voltage in %.

(10). Winding connection vector diagram.

(11). Type of cooling.

(12). Weight of core assembly andwinding in Kgs.


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Name Plate Details (contd.) :

(13). Total quantity and weight of

insulating liquid.

(14). Weight of complete transformer.(15). Temperature rise in oil.

(16). Year of manufacture.

(17). Customer reference.


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Core type transformer :


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Core Type Transformer (contd.) :

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http://www.leonardo-energy.org/files/root/Images/2007/UI39.preview.JPG


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Core Type Transformer (contd.) :

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Core Type 3 Transformer :

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Core Type 3 Transformer (contd.) :

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Shell Type Transformer :

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Shell Type Transformer (contd.):

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Shell Type Transformer (contd.):

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Shell Type Transformer (contd.) :

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Shell Type 3 Transformer :

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Core and Shell Type Transformer :

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Types of Transformer :

(1). As per construction :

(a) Core type transformer

(b) Shell type transformer

(2). As per voltage :

(a) Stepup transformer(b) Stepdown transformer

(c) Auto transformer


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Types of Transformer (contd.) :

(3). As per phase :

(a) 1 Transformer(b) 3 Transformer

bank of 3 Nos. of 1Transformer

single unit 3Transformer


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(4). As per application :

(a) Power Transformer

(b) Distribution Transformer

(c) Isolation Transformer


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(5). As per winding :

(a) Single winding transformer

(b) Two winding transformer

(c) Three winding transformer


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Tertiary Winding :

(1). Reduces triple harmonic contents

of output voltage thereby

stabilizes potential of neutral

point.

(2). Suppresses 3rd harmonic current

which causes communicationinterference.


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Tertiary Winding (contd.):

(3). Permits the transformation of

unbalanced 3 load.

(4). Reduces system zero sequence

impedance for effective

grounding.

(5). Supplies additional auxiliary load.


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Differences between Power Transformer

and Distribution Transformer :

Power Transformer Distribution Transformer

01.

Single 3 unitor, three 1units, / and/, 3wire.

01.Single 3 unit,/, 4wire.

02. Capacity : MVA 02. Capacity : kVA


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and Distribution Transformer (contd.) :


03.voltage rating :220 kV/11 kV or,higher as 400 kV

03.

voltage rating :

11 kV/415 V,(HV : 33 kV also),415 V/230 V etc.

04.Flux density :

1.5 to 1.7 Wb m

2

04.Flux density :

1.7 Wb m

2

05. Load : on full load 05.Load : part of dayon noload, partload.


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and Distribution Transformer (contd.):


06.Ratio of iron lossto copper loss =1:1

06.Ratio of iron lossto copper loss =1:3

07.% impedance =6% to 18%

07.% impedance =4% to 5%


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and Distribution Transformer (contd.) :


08.

Cooling : forcedair, forced oil,forced water,self oil cooled.

08.Cooling :self oil cooled.

09.Regulation :6% to 10 %

09.Regulation : 4%to 9%


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Distribution Transformer Ratings :

kVA ratings : 63 kVA, 100 kVA,

25 kVA, 40 kVA etc.

Voltage ratings : 6.6 kV/415 V,

11 kV/415 V

Tappings : 2.5%, 5.0%


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Transformer Specifications :

(1). kVA rating

(2). Rated Voltage

(3). No. of phases(4). Rated Frequency

(5). Connections

(6). Tappings


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Transformer Connections :

3 connections

(a) connection : schematic diagram


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Transformer Connections (contd.) :

3 connections

(a) connection : features :

0 phase shift.

Economic for small HV Transformer,because No. of turns per phase andamount of insulation is minimum asVph = VL/(3). So, conductors are of

large cross section. Less expensive and mechanically

strong winding.


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3 connections

(b) connection : schematic diagram


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3 connections

(b) connection : features :

0 phase shift. Economic for large, LV Transformer

in which insulation problem is noturgent.

Vph = VL


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3 connections

(c) connection : features :

+30 phase shift.

Main use at sub-station end wherevoltage is to be stepped down.

Ratio between primary line voltage

and secondary line voltage is= 3:1


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3 connections

(d) connection : features :

30 phase shift.

Main use at the beginning oftransmission system where voltageis to be stepped up.

Ratio between primary line voltageand secondary line voltage is= 1:3


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3 connections

(e) Open or, Vconnection :

(schematic diagram)


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3 connections

(e) Open or, Vconnection : features

one of the Transformers of a bank is out and 3 supply isconnected.

Voltage output = 58% of

Power output = 86.6% of


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3 connections

(f) Scottconnection or, TT connection :

One of the Transformers has centretaps both on primary and secondarywindings and known as MainTransformer, other one has tapping

at 0.866 and known as TeaserTransformer.


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3 connections

(f) Scottconnection or, TT connection :

(schematic diagram)


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Impedance Voltage :

It is the voltage required to be applied at ratedfrequency between line terminals of a 3 winding or,between terminals of a 1 winding to cause the ratedcurrent to flow into these terminals when the terminals ofthe other windings are shorted. It is measured as % ofrated voltage of former winding.


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Vector Group :

1st symbol HV winding connection

2nd symbol LV winding connection

3rd symbol phase displacement

1 1 Oclock 302 11 Oclock +303 6 Oclock 1804 12 Oclock 0


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Vector Table :

(a) 0 phase shift :

yo

Ddo

Dzo

Zdo


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Vector Table :

(b) 30 phase shift (Lag) :

Dy1 yd1

yz1

zy1


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Vector Table :

(c) +30 phase shift (Lead) :

Dy11 Yd11

Yz11

Zy11


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Vector Table :

(d) 180 phase shift :

Yy6

Dd6 Dz6

Zd6


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Construction :

(01). Core(02). Windings(03). Tap Changers(04). Tanks

(05). Bushings(06). Auxiliary Equipment(07). Cooling System(08). Insulating Oil(09). Conservator Tank

(10). Breather(11). Radiators(12). Buchholz Relay


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Construction (contd.) :

(1). Core :

laminated, thickness : 0.28 mm to 0.30 mm,

CRGO,

3% silicon iron.


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(2). Winding :

type : spiral, helical, or, disc type. selection depends on

current rating

short circuit strength

temperature rise

overload condition impedance

voltage surge strength


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(3). Tap Changers :

OFFLoad type and ONLoad type. In generating stations mainly OFFLoad

types are used as voltage regulation isdone by AVR. Power Transformers in receiving stations

are having ONLoad type. In Power Stations, station service

transformers have ONLoad type. Tappings are provided on HV side.


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(4). Tank :

Body is made up of rolled steel

plate. Conservator tank is cylindrical and

permits free expansion of oil w.r.t.temperature.

Oil Gauge is provided to indicate theoil level.


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(5). Breather :

Air is drawn into conservator

through a vent which has moisturetrap (silica gel).

Blue dry &

Pink moisture.


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Construction (contd.):

(6). Bushings :

connected to HV lines.

moulded high quality glazedporcelain insulator with conductorthrough its centre (up to 33 kV).

HV oil filled condenser patterngraded resin bonded paper.


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(7). Cooling Systems :

ON or, OA type oil immersed natural cooling.

FOW or, OFW type oil immersed forced oil cooled withforced water cooled.

AA or, AN type

dry type self cooled (below 15 kV). AFAAB type dry type forced. AA/AFA & AN/AB type.


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Parallel Operation :

(1). Primary windings of Transformers

suitable for supply system

voltage and frequency.

(2). Transformers should be properlyconnected with regard to

polarity.

(3). Voltage ratings of both primaries and

secondaries should be identical (sametransformation ratio).


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Parallel Operation (contd.):

(4). Percentage impedance should be same,

i.e., (I1Zo1/V1)x100 = (I2Zo2/V2)x100.

(5). Voltage ratio must refer to terminal

voltage of primary and secondary

(not ratio of No. of turns per phase).

(6). Phase displacement between primary

and secondary voltages must be same.(7). Phase sequence must be same.


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Parallel Operation (contd.):

(8). Examples :

can be operated in parallel with

(with same transformation ratio possible). can be operated in parallel with (with same transformation ratio possible).

or, can not be paralled with

or, . and can be paralled by certain

shiftings.


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Transformers in 210 MW Thermal

Power Station :

(1). Main Unit stepup Transformer :

also known as

GeneratorTransformer (GT). voltage rating : 15.75 kV / 220 kV.

capacity : 250 MVA

tapchanger : OFFLoad type.


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Power Station (contd.):

(2).Unit Auxiliary Transformer (UAT) :

stepdown type.

voltage rating : 15.75 kV / 6.6 kV.

capacity : 10,000 kVA

tapchanger : ONLoad type,

2 Nos.


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(3). Station Auxiliary Transformer

(SAT) :

stepdown type. voltage rating : 220 kV / 6.6 kV.

capacity : 16,000 kVA.

tapchanger : ONLoad type,2 Nos.

T f i 210 MW Th l


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(4). Transformers for LT supply :

Cooling Tower two transformers each of 1000 kVA.

Electrostatic Precipitator one transformer of 1600 kVA.

Standby one transformer of 1600 kVA.

Lighting one transformer of 1000 kVA.


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Generator Transformer (GT) :

250 MVA, 3, 50 Hz. Cooling OFWF. HV at NoLoad 230 kV. LV at NoLoad 15.75 kV. HV line current 627.55 Amp

LV line current 9164.29 Amp Temperature rise of oil 50 C Temperature rise of winding 60 C Connection Nd11 Impedance voltage 12.77%

Weight of core and winding 140265 kg Weight of oil 43380 kg (49860 Litre) Total weight 216980 kg


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Unit Auxiliary Transformer (UAT) :

15 MVA / 25 MVA, 3, 50 Hz. Cooling ONAN / ONAF HV at NoLoad 15.75 kV LV at NoLoad 7 kV HV line current 917.5 Amp

LV line current 2064.4 Amp Temperature rise of oil 50 C Temperature rise of winding 55 C Connection Dyn1 Percentage impedance 10.08, 10.22 and 10.38 Weight of core and winding 18300 kg

Weight of oil 7440 kg (7800 Litre) Total weight 37500 kg


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Station Transformer (ST) :

25 MVA / 40 MVA, 3, 50 Hz. Cooling ONAN / ONAF HV at NoLoad 220 kV LV at NoLoad 7 kV or, 11 kV Connection Nyn0d1 Percentage impedance 15.21, 17.32 and

20.53 Weight of core and winding 36000 kg

Weight of oil 27500 kg (31600 Litre) Total weight 88000 kg

rkm d hoi transformer mod

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