DISTRIBUTION TRANS JRMER TECHNOLOGY

BEN MCCONNELL

ENERGY DIVISION

OAK RIDGE NATION : LABORATORY

JUNE 13. 1994

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AMENTAL TRANSFORMER OPERATION

DEFINITION: TWO OR MORE COILS COUPLED BY A

MUTUAL MAGNETIC FIELD.

VARYING ALTERNATING VOLTAGE SOURCE IMPLIES

VARYING FLUX ----- Vl*N1=V,*N ITI =IfI^T2_

VOLTAGE TRANSFORMATION DEPENDS ONLY ON THE

EXISTENCE OF ALTERNATING FLUX.

AIR CORE POSSIBLE BUT " ONE' CORE PREFERRED FOR

EFFICIENCY.

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ORNL-DWG 94-1755

SOURCE

LOAD [ I ] v2 i m..

11

0/2

0/2;

P IMARY WINDING

(RolptAnnp = r, )

0/2

N 1 TURNS

N1TlIRN.

SECONDARY WINDING

(Resistance = r2)

4

LAMINATED

IRON

CORE

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CONNECTIONS IN T RZE DISTRIBUTION SYSTEMS

Fig 5

Single- ---:. w;-a-*`3rmer

Fig 7

3-Phase S-Legged Core

ANSI/IEEE

067.105.1978

1 6

2L -Type Tvandormer

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EE-DET-97-550 COMMENT 0D
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Construction O ,r y fOr Cas+ I?eskV

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WER EQUATION

VA = 4.443*f*N*J*AArw-*B..... *Aclw (MIKS UNTfS

where,

VA = RATED 1-PHASE POWER IN VOLT-i E S

f = RATED FREQUENCY IN Hz

N = NUMBER OF TURNS IN WINDING COBS FRED

J = rms CURRENT DENSITY IN A SINGLE TTU`RN (Amps/MZ)

Acrw = CROSS-SECTIONAL AREA / TURN (M=

Brow, = MAXIMUM FLUX DENSITY IN TESAclw = ACTIVE CORE CROSS-SECTIONAL AR.=A M2)

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VOLTAGE (MACHI' EQUATION

E (Volts) = 4.443*f*N*Bmax*Aclw, or

VOLTSEJRN

Volts/T = E/N = 4.443*f*B*Aclw or

MAXIMUM FLUX DENSITY

(4.443*f*Aclw)

EE-DET-97-550 COMMENT 0D
NO LO SSES (NLL)

NO LOAD LOSSES OR CORIE LOSSES ARE BASICALLY THE

RESULT OF HYSTERESIS AND EDDY CURRENT LOSSES IN

THE CORE MATERIALS AND ARE INDEPENDENT OF LOAD.

NLL = Ph + Pe = VOLCO (f*Kh*BXmax + Ke*f *t2*B2

where,

Kh, Ke, x ARE CONSTANTS AND t = LAMINATION T.H C KNESS

TYPICALLY 3-9 MIL FOR COLD ROLLED GRAIN OFIENTTED

HIGH SILICON (3.5%) STEEIS (SiFe) AND B IS 1.6-.8 TESLA.

FOR AMORPHOUS T_ Ph =0 AND t = 1 MIL AND NLL

ARE VERY LOW; BUT Bm= IS 1.4 TESLA.

CORE PACKING FRACTION: = 0.95 FOR SiFe AND 0. FOR

AMORPHOUS METAL NET COST OF AMORPHOUS CORE

TRANSFORMER ABOUT 257o HIGHER.

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ORNL-DWG 94-1757

UtLMAUUNL I VA I ION

CURVE

INITIAL

MAGNETIZATION

CURVE

Hm

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OI NL=L)WO 94,1766

2.0

1.8

1.6

p

ap 1.4

1.2

z

w

0

>G 1.0

0 0.6

0.4

0.2

0 2,500 5,000 7,500 10,000

MAGNETIC FIELD INTENSITY [H(A/m)]

12,500

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2.0

97 +---

a Ell;

R oriented sheers'

:

w.M9't

5

IF J-1. -LI 1. 1

Irk Iiii -T

4 #

Exunple A-6

0.5 i

Example A-5

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45

I I I I I i I I I I

8 10 11- 14 16

Magnetic Faux Densi-, n A,,,auss

q Grain Oriented SiFe - amorphous Metal

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500

450

400

350

w 300

cf)

0250

J

200 0

H

150

100

50

0

ORNL-DWG 94-1765

0.16 0.32 0.48 0.64 0.8 0.96 1.12

PER UNIT LOAD (Nameplate Rating = 1.0)

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TRANSFORMER =` CIENCY

MAXIMUM EFFICIENCY OCCL AT THE LOAD, S, FOR

CH NLL = (S/Sb)2*LL AND E GIVEN BY

EFFICIENCY(Eta) = POWERnut POWEROut + TL)

or at uni: power factor,

Et-z = S / (S + NLL + (S/Sb)2*LL? where

S = LOAD IN kVA, and

NAMEPLATE RATING IN WV

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ORNL-DWG 94-1764

99.5

99.4

PP11

99.2

99.1

99.0

98.9

98.8

98.7

98.6

98.5

98.4

98.3

98,2

98.1

003.0

97.9

97.8

97.7

97.6

97.5

MOD NLL, LOW LL

.t,

0.08 0.24 0.4 0.56 0.72 0.88 1.04 1.2

PER UNIT LOAD (Nameplate Rating = 1.0)

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TO DECREASE NO LOAID LOSSES

or

or

CHANGE CORE MATERIALS

REDUCE FLUX DENSITY (B) BY

INCREASING CORE X -SECTION (Aclw) or

DECREASING VOLTSITURN (EIN)

REDUCE CORE FLUX PATH LE ` GT}I BY

DECREASING CONDUCTORS X-SECTION (Acrw)

FREE PARAMETERS: MATERIAL A lw, E/N, Acrw, HEIGHTS

OF CORE AND COIL WINDOWS.

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or,

DECREASE LOAD LOSSES

CHANGE CONDUCTOR MATERIALS

REDUCE CONDUCTOR CURRENT DENSITY ( by

INCREASE' : G CONDUCTOR X-SECTION (. is

or

REDUCE CONDUCTOR LENGTH by

REDUCING CORE X-SECTION (Acrw) or

INCREASE VOLTS PER TURN (E/N)

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, o 1: ^ -/Cd, tf:J

e^ v N cv A A r&

° V

4.17 o o ° o° o° 0 0 o

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TRANSFORMER LIFE

A DESIGN LIFETRlE OF 20 YEARS IS TYPICAL ASSUMING

FULL TIME OPERATION AT THE NAMEPLATE. TIllS

DESIGN LIFETIME IS RELATED TO INSULATION LIFE

WHICH DEPENDS ON THE HISTORY OF THE OPERATING

HOT SPOT TEMPERATURE.

PRESENT PRACTICE IS TO DESIGN FOR A HOT SOT

TEMPERATURE RISE OF 65 DEGREES CELSIUS ABOVE

AMBIENT IN OIL PAPER INSULATIONS AND 150 DEGREES

CELSIUS IN DRY TYPE INSULATIONS. EXCEEDING THIS

LIMIT FOR ANY SIGNIFICANT TIME QUICKLY REDUCES

EXPECTED TRANSFORMER LIFE WHILE BEING BELOW IT

GREATLY EXTENDS THE LIFETIME. NOMINALLY 50%

REDUCTION IN LIFE FOR EACH 8 DEGREE RISE

OTHER FACTORS INFLUENCE USEABLE LIFETTh E, SUCH

AS LIGHTNING, ACCIDENT, AND EARLY RETIREMENT

DECISIONS.

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UJ

360 2'S 0 220 180 40 120 100 80

HOTTEST SPOT TEMPEUTURE $ IIEGREES C

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_oss of life after one day's

operation v7 fW load as a function of

ambient te--^peature

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f

Operating time against hot spot temperature for on: y loss of life

4

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OVERLOAD ABILITY

OVERLOAD IS RELATED T ALLOWED TEMPERATURE

RISE AND HEAT REMOVAL RATE. TYPICALLY OIL PAPER

SYSTEMS CAN OPERATE AT UP TO 200% LOAD FOR

PERIODS OF HOURS WITH JUT SIGNIFICANT LOSS OF

PERFORMANCE BUT WITH LOSS OF TRANSFORMER LIFE.

WHILE DRY TYPE INSULATION MATERIALS ARE CAPABLE

OF OPERATING AT HIGHS TEMPERATURE, THESE

LNSULATION SYSTEMS AR SS TOLERANT OF

OVERLOAD BECAUSE OF D HEAT REMOVAL

CAPABILITY.

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SUMMARY

CLEARLY TRAIN N FORMER DESIGN IS AN I-- ERATIVE

PROCESS AND T- HE CHOICE OF OPTDIIZA-ION VARIABLE

CAN BE KEY. TI- 'ERFORMANCE OF THE INSULATING

SYSTEM, THE V4 EIGHT AND EXTERNAL D I SIGNS MUST

BE INCLUDED r,-- THE ANALYSIS.

AT PRESENT TIT: TRANSFORMERS ARE I ESIGNED FOR

THERMAL LIMITS AND PERHAPS TOTAL C -ING COSTS

AND NOT FOR .f IMUM EFFICIENCY, M UM

EFFICIENCY OVER SOME RELATIVE LOAD= RANGE OR

MINIMUM LOSSES. THE DIFFERENCE IN TTTLITY AND

INDUSTRLAL LOADING AND ECONOMIC PRACTICES WILL

PLAY KEY ROLES IN ANY ANALYSIS.

SINCE COST IS N RY STRONGLY RELATED TO MATERIALS

QUANTITIES AND PERFORMANCE AND REDUCED LOSSES

REQUIRE MORE AND/OR BETTER (MORE EXPENSIVE)

MATERIALS, RE)U CED LOSSES AND INCREASED

EFFICIENCY Mt ST BE CLOSELY EXAMINED RELATIVE TO

INCREASED COTS..

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