Carr - Divergent Evolution of Ds

8/17/2019 Carr - Divergent Evolution of Ds

1/9

I EEE

Translctions on Power Delivery, Vd. 7 No.

3.

J d y 1992

1601

J.

C a r r

Seni or Member L. V. McCal l , Fel l ow

Acres

I nternat i onal , L M. Chtari o Hydro

- -

This

paper di scueses the fact0 .B whi ch

a f f e c k d

the

evol ut i on of worl d' s di st ri but i on systems,

and

thei r

di vemence, w th i mpl i cati ons f or appl i cat i on in l esser

devel oped count r i es. I t dwr i bes t he advantages of the

'North Ameri can' and

' ropean-

styl e systems, whi l e

r e m g n i i n g

that nei ther is i nt rh i cal l y super i or .

Fi nal l y, i t bri ngs

i nto

f c cm t he need f or mi t i o n

of l egi t i mate vari ancea i n di str i buti on systems and

thei r associ ated equi pment, when devel opi ng rel evant

StandardE.

x xax b

El ectr i c Power di str i buti on systemdmigns and practi cea

throughout t he worl d have evol ved

i n

di vergent

di recti ons due to a vari ety of f act om Most can

be

t raced back

to

ei ther the

'European'

or

' North

Ameri can-

approach.

These evol ved separat el y and spread w th

col oni al ambi t i ons

to

many other parts of the worl d

whi ch t oday i ncl ude a l arge number of l esser devel oped

count ri es.

For moet

pupoeee,

the di f f erence i n system desi gn,

conf i gurat i on

and

practi ces have

been

of l i t t l e

concern,

because

each

haa

been emnent l y sui tabl e for

i t s own

envi ronment . However , di vergent practi ces do

become

si gni f i cant when these

are

to be consi dered i n the

devel opnent Of i nternat i onal Standards which mandate

pract i ces and must , t heref ore, accommodate any

di f feren-.

The di f f emcea

i n

approach

are

al so si gni f i cant i n

l esser devel oped count r i es where maj or el ectr i cal

di st r i but i on rehabi l i t at i on and extensi on program are

undernay. The soci al , economc and techni cal context for

di str i buti on 13ystenm in

these countr i es can be qui t e

di f f erent

than

i n ei ther

&rope

or

Nort h

Ameri ca whi ch

raises quest i ons about t he most appropri ate approach.

This Paper describes t ypi cal di st ri but i on systern8 in

Emwe

and

i n

Nort h Ameri ca, i denti f i es si gni f i cant

di f femnces

and

cutl i nes soroe aspects of thei r

di vergent evol uti on. Agai nst thi s bckground, i t t hen

di acueees ~ o m e of t he i mpl i cati ons of di f f erent

di stri buti on systemconf i gurat i omi n l esser devel oped

count ri es.

This

papex was presented at

the Transmission

and Distribution Conference in Dallas, Texas

from September 22-27, 1991

at

the Dallas Con-

vention Center. Sponsored by the

IEEE

Power

Engineering Society.

f f erent nomencl ature i s

used

to descri be

some

di st r i but i on systemel emeats

i n

the

European

and North

Ameri can envi ronments. The fol l ow ng tabl e di spl ays the

term

i n

quest i on. I n thi s paper , North Ameri can

tern

are

wed to

avoid conf usi on.

lpuape

gh Vol tage Subtr ansmssi on Vol tage

Medi umVol tage

Primary

Vol tage

Low Vol tage

seconctary

Voltage

Earth, Ear thi ng, Ground, Groundi ng,

Earthed

G md e d

Generai

Al l di st r i but i on system13 have a number

of

CORmon

f eatures. For exampl e, al l system

are

compri sed of a

number of pr i mary ci r cui t s, as

shown

i n Fi gure

1

whi ch

suppl y a rather l arger number of eecondary ci rcui te,

thmugh

many di st r i buti on

transformers.

The rel ati ve

extent of each of the

foregoi ng

el ements i s a funct i on

of the di st r i but i on vol t age, and t he magni tude and

densi ty of the l oa& suppl i ed.

Further camon f eatures

i ncl ude

-

Pri mary ci rcui te are nonnal l y suppl i ed f rom

subt r anemssi on/ pr i r y t ransf onnati on at

a di str i but i on suppl y stat i on. Suppl y from

generati ng stati ons i s unusual .

-

Pri mary

ci rcui ts, emnati ng from the

di str i kut i on suppl y stati on, are general l y

three phase. I n

sorne

European

syst ems,

notabl y

i n

the Uni ted Ki ngdom some si ngl e

phaee (phase-phase) ci rcui ts branch off the

main

cir cui t to suppl y l i ght l y l oaded rural

ares. I n North Ameri ca, si ngl e phase,

(phase-neut ral )

extensi ons

f romthree phase

mai n ci rcui ts are used extensi vel y.

-

Pri mary vol tage l evel s art? comparabl e f or

al l systems, w th a range of

8-34. 5

kV.

Two

part i cul arl y popul ar vol tage ranges are

amul d 12 kV and 25 kV.

-

The l ocati on and rati ng of di str i kuti on

t ransf ormera

are sel ected

to provi de

an

adequate suppl y of power/ energy at the

uti l i zati on vol tage ef f i ci entl y and at

an

adequate vol tage l evel .

- Protecti ve apparatus and gr omdhg are

appl i ed as needed

to

adequatel y

limit

the

adverse ef f ects of ci rcui t f aul t a.

0885-8977/92/ 3.0001992 I EEE


2/9

1602

I

Figure 1 North American European) Distribution System Elements

Three phaee,

three

conductor pri mary Ci rcui t6 are used

al most excl usi vel y i n Ru-wean practi ce. As

shown in

Fig u re 2,- are suppl i ed f m ubstati on t ransf ormers

where the l oad si de w ndi ng

may

be wye connected, or

del ta

comeckd

Where wye connected, the neut ral poi nt

of the t ransf ormer w ndi ng

i s

grounded di rect l y, or

thraagh a resi stor or r eactor, but the neut ral i s lrrt

extended out of t he stat i on w th the pri mary ci rcui ts.

Most of the

econdary

ci rcui te are suppl i ed f rcmt hree

phase

di str i buti on t ransf ormers, typi cal l y connected i n

a del ta-wye conf i gurati on to suppl y

220/380

vol ts,

230/400 vol ts,

or

240/416 vol ts. I n urban areas, h me r

capaci ty

uni te

are

empl oyed extensi vel y

to

suppl y a

large

number of

customers.

Si ngl e

phase

di stri buti on

t mf o me r s

are

used

rmch

l ess f requentl y f or s u ~~l y

to

naral

areas,

notabl y i n the Uni ted Ki ngdom

mppl i ed w th si ngl e

phase

servi ce, at 220

to

240 Vol ts.

The

two amductom

provi di ng

t h i s

connect i on usual l y

ampr i ee one phase and one neut ral conductor.

compared

to Nort h Ameri ca, t he secondary syst ems suppl i edby each

di str i but i on t ransf ormer

are

t ypi cal l y very extensi ve

i n lhropam practi ce, due to the hi gher uti l i zati on

vol t age, and rel ati vel y l i mted di versi f i ed demand

Per

cust omer.

General l y, domeet i c and

d l

omnerchl

CUStomers

are

Mul ti ground pri mary di st r i buti on systems predomnate

i n Nort h Ameri can practi ce. As shown i n Figure 3 three

phaee

pri mary f eeders compri se three

phase

conductors,

and a neutr al conductor. The neut ral conductor i s

connected to the neut ral of the substat i on suppl y

t ransf ormer, extended out of the stati on w th t he phase

conductors, and connected to ground at f r wuent

i nterval s al ong i t s l ength. Si ngl e p h m extensi ons f rom

three phase pri mary f eeders, compri si ng one phase

conduct or

and

a neutral conductor are

mch

more

extensi vel y used than i n

Europe.

I n most cases the w ndi ng of the me r tr ansformer

suppl yi ng North Ameri can di str i but i on pri mary ci rcui t s,

i s w e conn-, w th the neutral grounded. l ess

cormnon

al ternati ve i s a del ta mec t i on w th a

-d ng

bank

to establ i eh the systemneut ral .

- - ~

-~

Most

or

me loads suppl i ed are si ngl e phase and

therefore di st r i but i on t ransf ormers are predomnant l y

si ngl e phase. For t hese, t hepri mary

i s

des- f or , and

connected fr cm phase to neutr al , and t he

secondar y

arr anged to suppl y a

three

w re,

120/240

vol t connect i on

to customers. The center of the secondary w ndi ng i s

grounded and connected to theBecondary ci rcui t neut ral

conductor. Smal l er

three phaee

l oader

my

be suppl i ed try

banki ng si ngl e

phaee

t ransf ormers.

The l i mt ati ons

imposed by

t he combi nat i on of the l ower

uti l i zati on vol tage,

and

the rel ati vel y hi gher

di versi f i ed demand per custoaer s*i fi cantl y mt r ai r i

t he di mensi ons and l oadabi l i t y of

North

Ameri can

secondary

system.

Cbneeqm l y, rel ati ve to m a n

system, a

much

l arger number of di st r i but i on

t ransf ormers are requi redto suppl y an equi val ent number

of

customers.

IkV

The el ectr i c power i ndust ry was evol vi ng more or l ess

si r m t anemsl y i n both

Euro=

and

North

Ameri ca i n the

cl osi ng years of the

l ast

century

and

i n

the ear l y years

of thi s one. Thi s was a peri od i n hi story

when

many

areas of the worl d, nowref err ed to as l esser devel oped

count r i es, were col oni zedby one of t he major Euro-

powers. I t shoul d be of no surpri se, therefore, that the

di st ri but i on pract i ces throughout mch of the worl d tend

to fo l l owEuropean practi ce.

Thi s practi ce has been modi f i ed i n recent decades

coi nci dent w th t he i ndependence movements that have

swept Af r i ca and Asi a and resul ted i n the el i mnati on

of vi rtual l y al l col oni al rul e. Today, a si rpl i fi cant

port i on of

the

money requi red by l eseer devel oped

count r i es to f i nance thei r power ut i l i t y system comes

f romsuch i nternati onal f undi ng agenci es as t he Worl d

Bank. Thi s resul ts i n the worl dw de avai l abi l i ty of

engi neer i ng expert i se, materi al s and e q u i mt rommany

donor nat i ons.

Whi l e thi s

has

resul ted i n the i ncreasi ng use of North

Ameri can styl e di st r i but i on concepts

i n som

l esser

devel oped countr i es, t he requi rement of mt i bi l i t y

w th t he exi sti ng f aci l i ti es and

standards

cont i nues to

provi de a st rong i ncent i ve to retai n E u m m styl e

system. Thi s i s part i cul arl y t rue i n urban ares that

have been el ect ri f i ed f or many years. However, rural

el ect r i f i cat i on proj ect s someti mes use f our - w re pri mary

mai n f eeders that typi f y the North Ameri can app mch.


3/9

1603

Figure 2 European Style Distribution

System

I

Figure 3 North American

Style

Distribution

System


4/9

1604

Hi&

load densities

d u c e

the need for extensive

secondary networks since the load appropriate for a

single distr ibuti on transformer w i l l he aggregated over

a relatively small area. Voltage regulation and

losees

also improve with shorter secondary cir cui ts, especially

with high load levels. While the differences i r i average

load densities between Europe and North America m o t

alone account for the differences in approach to

e lec t r i c i ty d i s t r ibu t ion , i t is

clear

that they are

rmtually consistent.

-

eneral

I)esjgn of dis tri but ion systems is influenced by several

factors including:

th e need to supply customers adequately and

e f f i c i e n t l y

-

-

the need

to

create a system which can be

operated safely, w i t h provisions to mitigate

adverse effects to the environment, or t r ~

the system itself

th e need

to select

the most economic choice

of design alte rnat ives available w i t h i n the

constrai nts of sati sfyin g other needs

-

Both European and North American distribution system

are designed/configured to sa ti sf y the forwoin g needB

but due

to

fundamental di fference s i n the total

environment i n which each i s placed,

design/configuration divergence is inevitable. Consider

the following:

Customer Hlgher Higher in urban

density

areas; lower

pactor

EumPe

elsewhere

Uti l izat ion Higher Lower

voltage

Individual Lower Higher

loads

Regulatory Higher General1

constraints lower

n Eumpean dis tr ibut ion systm8,there is a d i s t inc t

economic advantage

to

uti l izin g t ,hreephase dis tr ibut ion

transformers

to

supply the secondary system because

individual diversified demands are modest, and are

supplied a t a higher ut ili zat ion voltage. The fact. that

there

is

a much

smaller

volume of l arg er distr ibu tio n

tr a ns f om r s supplying extensive secondary systerns means

that

these elements have l i t t l e or no influence on the

primary

systems

to which t.hese ar e connected. The

configu ration of European primary system config urat ions ,

such as three conductor circuits supplied fmi B

g m d e d wye source are influenced chiefly by needs fm

satisfy protection imperatives, and to conform

to

regulatory constraints.

In

North

America, secondary system are si& nificm~tly

limited, in tern of dimensions, and loadability, due

to the higher diver sif ied demands, and lower ut il iz at io n

voltage.

This

re su lt s i n a requirement fo r a much higher

number

of

distr ibuti on transformers fo r an equivalent

number of

customers.

The customer supply facilities in

North American systems,

i n

contrast. to t h e E ~ ~ v p e a n

case,

have a signific'a nt inf luen ce on primary systenl

cmnfiguration (i.e,multi-groundecl). This

is

b x m s e

phase-neutral conne-kd dis tr ih t ion t rLamformem

i n i t i a l l y f a c i l i t a t e d e c on mi ca l v o l W e

increases,

and

because the se continue to

be

more ecrmomical to purchase

and install, pa rt ic ul ar ly with th e high volume involved

LoadG1.owthandJ ik l zmmn

Load growth resul t ing from increased electricity use

by

exis t ing

customers

is probably more readily accoarnodated

on North American st yl e di str ibu tio n systems. The same

is

true for accomnodating load

growth

due to new

inf i l l

customer

that

a r e

w i t h i n

the

e x is t in g e r v i c e

area. However, the European approach

may

have advantages

in

meeting

load growth due to new

customers

outside the

service

area

that therefore require system extensions.

Theses conclusions result

fm

the fact that the total

l ine length in a distribution system is determined

primarily

by

the number of customers and the geographic

area

served and only secondarily

by

the total load.

These concepts can be further described as follows.

In North American systems the size of the area over

which customers are spread plays a

major role

in

determining the layout of the primary feeder system and

the actual loading leve l of these fe eders is a

subordinate consideration.

In

contrast., with the

European approach, the secondary network layout

is

the

main feature dictated by the physical load area. In

Europe, load leve l dict ate s the locations of

transf ormers which,

in

tur n, determine the layout of t.he

primary system. As a result, a European primary system

is

optimized around load level while a North

American

one

is

optimized around customer l w a t i o n .

This subtl e differ ence

in

approaches to system planning

resu l t s in an inherent margin of additional load

carrying capacity in the

North

American approach. For

example,

in

a North American town mo re

streets

w i l l have

primary feeders than would be the c se i f t he town w e r e

transplanted to Eumpz. In

E ur ope ,

som

of the primary

mileage would be replaced with secondary runs w i t h a

resulting reduction in load carrying capacity.

The difference between the

t w o

approaches is shown XI

simplified form in Figure 5. Comparative figures fo r the

two systerns are as follows.

Customers

(number) 17 17

Service

Area (size)

40

4n

Primary circuits (length) 18

Secondary

circuits

(length) 10 zn

Transformers (numkr) 6 2

Put another way,

for a given load area, a Nort3hAmerican

s ty le d i s t r i h t io n system

w i l l

inherently have a greater

kW/cimit-krn capability than a European system. To

serve a growing load within th e ex isti ng ser vice area ,

it is necessary only to ch,mge c u t individual

transformers

or

perhaps add an add it ion al transformer

and

reconnect

a few customer service dropB. a

European system increasing load is more likely to

requ ire adding transf ormer capac ity and rearr,mging the

secondary lines to cr ea te new secondary subsyetenis.

On th e other hand, load growth thmugh t.he addition

of

new

customers

and th e extension of t he se rvic e area

is

typical ly easier with the

European

approach. The

secondaw line s ar e simpler to extend than the primary

lin es and siza ble extensions a re o ften possible without

the need for addit iona l transformer capa city. In

contrast, on North American systems

an

extension of any

consequence req uire s no t only ad dit io nal primary

constnict ion, but al so the ins tallat. ion of one or mre

transformers.

North American E u r o p e


5/9

The evol uti on of the North Ameri can f cur conductor,

mul t i - grounded system i s l i nked to

the

l i mtati ons

i mposed on physi cal di mensi ons of

econdary

system

by

the

lower

uti l i zati on vol tage

(120/240) and

the

general l y hi gher cust omer l oads, w th a consequent

requi rement f or a substant i al l y hi gher number of

di str i buti on tr ansformers.

I n the ear l y decades of thi s century, three conductor

pri mary systers, operati ng at 2400vol ts

phase

to phase,

predomnated i n North Ameri can pract i ce. Si ngl e phase

di str i buti on t ransf ormers, w th

2400

vol t pr i mary

w ndi ngs, were connected

phase

to phase.

Begi nni ng i n the l ate 1930.8, di st ri but i on systeml oads

i ncreased beyond t he capabi l i t y of the

2400

vol t

standard part i cul arl y i n tennsof mai ntai ni ng acceptabl e

vol tage regulati on. I ncr eashw the pr i mary vol tage

w thai t changi ng the

three

conductor conf i gurati on was

a logi cal pr cg~ei on, ut woul d have entai l ed the very

substant i al expense of repl aci ng the m y i stri buti on

t ransf ormers.

I t was at thi s stage that the f our w re conf i gurat i on

became

most at t racti ve. s own i n Fi gure 4 by

repl aci ng the aubstat i on t ransf ormer to suppl y 2400/4160

vol ts

to

the reconf i gured pri mary ci rcui t s,

i ncl udi ng

a neut ral conduetor , al l exi st- di str i buti on

t ransf ormers coul d be retai ned in

service,

by

i mpl ement i ng a sl mpl e reconnecti on. Fur ther econmy was

real i zed

?JY

el i mnati ng one protect i ve f use, and one

surge ar restor f or each di st ri but i on t ransf ormer . Thi s

conversi on provided t he i ncreased l oadabi l i t y requi red

at the l owest possi bl e cost , and was

i mpl emented

auccessf i l l y on a w de scal e a c ms the conti nent.

Mul t i - grounded neutr al , f our conductor pr i mary systeme

became

the norm i n North Ameri can pract i ce, and have

been cont i nued into other

voltage

cl asses up

to

and

i ncl udi ng

34.5

kV appl i cat i ons. The

~IUF US

cont i nue8

to be

t he economies

real i zed due to t he reduct i on

achi evabl e

i n

di st r i but i on t ransf ormer

primary

w ndi ng

i nsul ati on,

and

the reduced r equi rement f or

fuse

and

surge

protecti on

at

e ch

t ransf ormer. These economes

magni f i ed by

t he

very l arge number of di st r i buti on

t r ansf omr s i nvol ved.

1605

ort h Ameri ca i s

vastl y l arger t han

E u r o p e which

hae

resul ted

i n

a general l y l ower wpul at i on densi t y.

Carr yi ng a neutral conductor on mai n

three

phase f eeders

al l ows branch si ngl e phase feeders to have onl y

a

s wl e

phase conductor pl us a neutr al conduct or. Not only

does

the neut ral conduct or not need an i nsul ator , but i t

can

saf el y be mwu?ted wth

less

g m d cl earance than m

energi d phase conductor.

The North Ameri can approach

to di st r i hti on therefore al l ows the use of shorter

pol es wt hout c w ~ mms nd hal f the number of

i nsul ators on si ngl e phase f eeders. The resul t i ng cost

savi ngs over theEuropean approach

are

magni f i ed by the

greater di stances i nvol ved, part i cul arl y i n rural areas.

I n the Western parts of North Ameri ca,

where

the grcund

resi st ance i s p a r t i m l a r l y

low,

i t ha8 been FoeBi bl e to

go one st ep f urt her by el i mnat i ng even the neutral

conductor and rel yi ng on

ground

return to cnmpl ete t he

ci rcui t for

phase

to ground l oads. These ground return

syst ems

are reduced f urt her i n cost by usi ng ti ght l y

tensi oned

steel

conductors whi ch al l ows f or

fewer

and

even shorter

poles

f or accepbbl e md- span mound

cl earance. Ground return systeme are used al so i n

Aust ral i a and on a

l i mted

scal e in West

Afr i ca.

Compared

to Europe, North Ameri ca

harr

a cl i mate of

ext remes. Col der w nters and hott er

sumers

t ogether

wth

high

humdi ty i n areas such

as

the southeastern USA

and around the Great

Lakes

oombi ne to create l arger

l oads f or

both

heati ng and cool i ng. Load densi t i ee and

energy use per

cust omer

are t herefore general l y hi gher

i n

Nort h Ameri ca than i n Europe.

Even

in the

earl y years of t he ut i l i ty i ndustr y when

elect ri c heat i ng and mechani cal ai r condi t i oni ng were

r are, North Ameri can l oad densi t i es tended

to

be

hi gher

than

i n Europe.

These were t he days of mass mgrat i on

from

Europe to Nort h Ameri ca.

The

' New Worl d' waa

desperatel y short of peopl e to

w or k

i n i ts grow

manufactur i ng i ndustr i es, and mechani zat i on was t he

answer. Such i nnovati ons

as

the assembl y l i ne

i ntensi f i ed producti vi t y and f orced the use

of

l arger

and f aster

tool s

and

proceeees

w th corresponding

i ncreased use of el ectr i c power.

I

Figure

4 Conversion from

3

o CWire PrimaryCircuits

on North American Distribution Systems


6/9

1606

I /

m

vy \ I

t

I

Figure 5 Comparative Feeder Plans

and

Because,

as

mentimed above, in the European approach,

e l e c t r i c i t y d i s t r i bu t i o n r e s u l t s i n a higher proportion

of the li ne mileage being second- ins te ad of primary,

there

are

advantages to the overall appearance of

the

system.

The most eff ec ti ve methcd of improving dis tr ib ut io n

aesthetics is to utilize underground construction

and

t h i s is

simpler

and cheaper a t secondary voltage than

a t primary voltage. Cable and equipmsnt are emaller and

safety and ineulat ion coneiderations are lees onerow.

Coats

are

also

reduced

by t h e fact that fa i lu res a f fec t

a re la t ive ly

smaller

number of cuetomereso that circuit

loopins and switching

points.

to provide alternative

supply are not as necessary.

Ilndergmding

is

a l so much simpler with European style

distribution systems because there

are

far. fewer

transformers required resulting in fewer expensive

vaults or problem in finding space fo r padmount

equipmsnt. This a l l resu l t s in

fewer fuses

and switches

located out and m d he underground which

simplifies

operating requirements both for routine switching and

fuse replacement during service restoration.

Even when all-overhead systems ar e compclred, the

&ropean approach has aesthetic advantages. Reflection

w i l l

confirm

that

t h e

most unsightly aspects

of

dis tr ibut ion

systems

are associated w i t h transformer

installations and their associated surge arres tore, fuse

cutouts,

and connecting w i r i n g The str ai ght of

line

between poles, and

simple

tangent

poles

without any

equigment do not assault the eye to the same ex tea t .

While the extensive three-phase secondary lines on

European sy~ tem e ave more conductors th at ar e li kel y

heavier

gauge

than the corresponding single-

primary that

m i g h t

serve the - ustomers on

North

American systems, this visual disadvantage is often

o f f s e t

by

the re la ti ve absence of transformers and othe r

equipment.

e v e r s u S r e n m

Distribut ion engineers i n

k s e r

Develod coun t r i es

have to comider the economic aspects of their projects

not only in terns of i n i t i al cost and ongoing

costs

but

a l s o i n

t e rms

of the re lat ive amounts of foreign

exchange and local currency.

Foreign exchange is typ ica l ly d i f f i c u l t to acquire

because it is generated by the country 's or i t s

income

from

tourism, Meanwhile,

foreign exchange is

needed

to

buy not only essential

i t i e s

such

as

o i l, medical supplies and industrial machinery but also

the vast array of

modern

manufactured consumer goods

that symbolize

success

and wellbeing to

people

a l l over

the world.

There is therefore a strong incentive in

many

Lesser

Developed countriee to maximize the local content of

dis tr ibut ion projects in order to minimize foreign

exchange requirements. Most countries can use

local

materials for

line

construction to som extent but few,

i f any, are self sufficient . A listing

of

l i n e

m t e r i a l s , in order of decreasing likelihood of local

ava i lab i l i t y might be as followe:

untreated poles

milled lumber

(crossam)

cxwmon hardware (nuts, bolts, angle i ron)

hu l a t o r e for secondary vol tages

treated poles

bare aluminum conductor

Less likely, but s t i l l possible for local supply in

some

countries are:

special hardware (insu lator s, pins, clamps)

g a l v a n i d steel w i r e

tranef

ormers

covered conductors

insulated conductors

Other i t e w are almost. invariably imported including

things such as

fuses

compression connectors and tools

which North American and European u t i l i t i e s t a k e fo r

granted.

Sig nifi cant new construction therefore requires a

substantial amount of foreign exchange which l ike ly

requires a loan

f r o m

an internat,ional

funding

agency

such a s t he World

Bank.

Obtaining such a l a m requires

a significant planning and administrative effort. which

oft en involves t he governrent, and

is

therefore not

undertaken l i g h t l y by the u t i l i t y .


7/9

1607

D f f i cul t as i t may

be to

j usti f y an i nternati onal l oan

f or new di et ri bt i on constructi on, i t is

even wr e

di f f i cul t to demonetrate t he need for

forei gn

exdyrnee

f or mai ntenance

puposes.

Whi l e govemment a msfi t see

meri t i n extending t he el ectr i ci ty suppl y

new

areas

they

are

l ees l i kel y to appreci ate

t he

w subt l e

advantages of i mprovi ng t he qual i ty of servi ce to

exi st i ng cust omers.

The resul t i s t hat new constr ucti on and maj or

rehabi l i t ati on oft en recei ves more at tent i on than

rout i ne mai ntenance. Thi s si tuat i on f avors a

di str i buti on systemthat r equi res l i tt l e

maintenance

even i f such a

system

requi res a hi gher i ni ti al coet.

I n general , t he European styl e di stri buti on

system

f i t s

thi s patt ern beet . Bal anci ng between phases

OCCUI'B

at

the l owest vol tage l evel and therefore does not mui r e

speci al at tent i on. Groundi ng i s probabl y l ese cri t i cal

and cert ai nl y requi re6 nowhere near t he amount of care

and at tent i on that i s essenti al f or

North

Ameri can

ground

return

systems.

TheEuropean styl eof system al so

has l ess equi pment by vi rt ue of using f ewer but l arger

di etr i bti on tr ansformers. Thi s tr ansl ates i nto f ewer

f uses, sw tches and surge arrestors, al l of whi ch

are

probabl y imported and subj ect t o mai ntenance.

The European

system

al so requi ree l ess f orei gn exchange

expendi t- when a f ewnewcustceaers

are

added or mnor

l i ne extensions undertaken. I n the si mpl eet and most

mmo n

cases,

a l l

extensions

nvol ve onl y t he

secondary

ci rcui ts.

New cust omers

si mpl y i ncreaee the ci rcui t

l oadi ng, vol tage drop and l osses

as

wel l

as

add to t he

l oad on the di etr i bti on tr ansformer. I f pol es, l ow

vol tage i nsul ators and bare conductor are al l avai l abl e

l ocal l y, these types of system extensi ons requi re no

f orei gn exchange.

The abi l i ty to extend t he system

so

si mpl y i s one of the

maj or pi t f al l s that r esul t6 i n subetandard el ectr i ci t y

servi ce i n many l esaer devel oped countr i es w th Raropean

styl e di str i buti on system. I t i s of ten i mpracti cal to

resi st the pressure

to

connect j ust one

mor e

cust omer

to an al ready overl oaded di st r i but i on t ransf ormer

thereby reduci ng the suppl y vol tage for al l cust omers

and J eopardi zi ng thei r securi t y of suppl y by i ncreasing

the l i kel i hood of premature t ransf ormer fai l ure. I n one

extreme h h c e , cuet omera were f ound to be

successful l y

win

120vol t appl i anws on a nomnal

240

vol t suppl y.

S can

be appreci ated, t he techni cal or I ZR l ossee on

di st r i but i on SYStem i n l esser devel oped count r i es can

be very hi gh. I t seem l i kel y that the European

syi3tem

i s more prone to excessi ve l osses because i t

i s

more

subj ect to overl oad ak ue due to the si mpl i ci ty of

extendi ng i t and addi ng customers.

I n contr ast,

t he North Ameri can styl e of di etr i bt i on

system impOsee

Bcwe

di sci pl i ne when connect i ng new

cust omers

because

addi ti onal t ransf ormer i nstal l ati ons

are

often eesent i al . Si nce each t ransf ormer

i s

amal l er

and serves f ewer cust omers i t hae l ees l oad di versi ty

and therefore crosses the over l oadi ng boundary more

deci si vel y. he ef f ect of addi ng one more customer

w l l probabl y be i mmedi ate and dramati c and

corr esporadhgl y l ess acceptabl e.

Non- techni cal l osses i s t he pol i t e euphemism f or power

that

cust omers

use but do not pay f or. I n many

si tuati ons, non-techni cal 106- are si mpl y di rect t hef t

by customers w th i l l egal systemconnecti ons.

The European styl e of di str i buti on system wth its

extensi ve secondary vol tage i s more prone to i l l egal

taps than the Nort h Ameri can st yl e system i nvol vi ng a

hi gher proport i on of pri mary vol tage ci rcui t s. Tappi ng

i nto a pri mary ci rcui t not onl y requi res a tr ansf ormer

whi ch would be di f f i cul t to acqui re but woul d al so be

mor e

hazardous

and consequentl y attempted

less

of ten.

Si nce bare open conduct ors are of ten

used

f or these

secondary rather than i nsul ated tr i pl ex, or quadl upl ex,

i l l egal

taps

are part i cul arl y si mpl e to i nstal l .

CaPclusiaoe

The di vergence i n el ectr i c power di stri txl ti on system

desi gn6 and pract i ces i n Nort h Ameri ca and Europe haa

occurred

for good reasons r el ated to t he envi ronment

of

each. Nei ther approach i s i ntr i nsi cal l y superi or

al though each has defi ni t e advantages.

When consi dered

f or appl i cati on

i n

l esser devel oped countr i es,

the

di f f erence

in

approach

take

on added di mensi ons but t he

appropr i ate choi ce

i s

no more obvious. Thi s i ndi cates

t hat , i n devel opi ng i nternat i onal

standards,

t he

di f f eren- beteween t he system shoul d be adequatel y

recogni zed as l egi t i mate var i ati ons to

insure

the wdest

possi bl e acceptance.

an Ca r r

J an Carr hol ds degrees i n El ectr i cal Engi neer i ng f rom

the Uni versi ty of Toronto and the Uni versi ty of

Water l oo. he

has

been i nvol ved w th the el ectr i c uti l i ty

i ndustr y for more than 2 years begiruiing hi s career at

the Saskatchewan Power Corporat i on. He has

served

on the

f acul ty at the Uni versi ty

of

Waterl oo. He has undertaken

work on di st r i but i on syste1m3both i n Canada and oversea6

and has compl eted i nvesti gat i ons on a w de r ange of

top cer i ncl udi ng pl anni ng,

reeearch

and design. He

is

present l y at Acres I nternat. i ona1 L i m i t e d , consul t i ng

engineers, where he i s Manager of t he Power

System

D vi si on and Head of the El ectr i cal Ensheer i ns

Department.

IlmmzKz

LIccall

Recei ved hi s E3c. E. E.

d e g r e e

from the Uni versi ty of

Mani toba i n

1948

and j oi ned

Chtario

Hydro t he same

year. S h c e that t i me

he

has worked

i n a w de vari ety

of capaci ti es, al l rel ated to di etr i bt i on engi neeri ng.

He has been i nvol ved i n desi gn, protecti on and contr ol ,

and di st ri but i on automat i on. I n

1986

and 1988 he

provided consul t i ng servi ces,

on

Ontari o

Hydro' s behal f ,

to t he Kenya M ni st ry of Energy. He

i s

a past chai noan

of t he

PES

Sw tchgear Ccmni t t ee, and a member of t he

I EEE Standards

Board.


8/9

DISCUSSION

by

Rorano

Sironi, Toronto Hydro

Toronto, Ontario

My discussion is intended to

support the “Aesthetics and Under-

grounding” section of this paper, and,

more specifically, that the

most

effective method of improving distri-

bution aesthetics is to utilize

underground construction and this is

simpler and less costly at secondary

voltage than at primary voltagenn.

In support of this statement, I

would like to bring forward a testi-

mony of the living experience of the

limitations of the North American

system that I am daily facing while

striving to achieve customer satis-

faction and installing an underground

distribution system that provides a

safe working environment for utility

employees.

Toronto Hydro embarked in 1990 on

a 25-year program to convert the

existing

4

kV overhead distribution

system to a partially underground

system.

To allay safety concerns and in

keeping with European trends, Toronto

Hydro decided to install a primary

underground system that is fully

operable from above ground. It is

needless to say that padmounted

transformer installations are not

feasible in t he fully developed and

underground utility congested urban

environment of the City of Toronto.

Hence the development of structural

design that fits into narrow sidewalks

or boulevards.

It is very difficult to convince

a reluctant property owner that a

vault planned to be constructed in the

public allowance in front yards or

sidewalks cannot be relocated to a

nearby parkette.

Carrying further on your obser-

vations, with same power consumption

and the same percent voltage drop,

European secondary distribution

systems can be 3.35 tines longer than

comparable Worth American systems.

Under similar conditions voltage drops

are nearly double

(5

of 220 v. is 11

V., while 5 of 120 V. is

6

V.) and

comparable currents have the same

ratio.

This simple fact allows more

flexibility to the European system in

the selection of transformer vault

locations. These can be chosen more

easily to avoid driveways, trees,

prized lawns and have the least impact

on the streetscape.

The paper does not bring solace

to the distraught customer, but can be

used as scientific evidence that the

ohm’s law cannot be bent to o easily.

M a n u s c r i p t r e c e i v e d S e p te m b e r 16 1991.

F. D. Gallagher, (Nova Scotia Power, Halifax, Nova Scotia): The

authors have presented an interesting

and

historical approach in the

determination of the myriad of factors which delineate the

so

called

“North American” and “European” distribution networks.

While concluding that one system is not intrinsically superior, compar-

isons of component and system reliability are noticeably absent. Including

data in this regard, along with examples of economic evaluation of costs

for both typical networks, would have been most informative.

With this paper the authors have identified a critical factor requiring

support and resolution by

a l l

segments of the power utility industry in that

system divergencies may impede the development of acceptable interna-

tional standards in the emerging global economy.

Including references and a bibliography within the paper would have

been an asset.

Manuscript

received October 3,

1991.

Alf

Dwyer, (B. C. Hydro, Vancouver, Canada): This is an interesting

paper which highlights significant differences between the two main

streams of distribution design.

In addition

to

the factors discussed in the paper, I see two additional

factors which affected evolution.

1. Economic Geography

In Europe patterns of community settlement and development were

substantially complete prior to the development of electric systems and

the age of automobile transportation. European roads are often narrow

and crooked and primary distribution lines must travel “cross

country”, their secondary overhead distribution wires are often con-

fined

to a separate set of poles along the settled portion of roads. North

American patterns of settlement

and

development have proceeded in

parallel with development of electrical distribution systems and auto-

mobile transportation. Hence the coincidence of distribution feeder

routes and roadways in North America.

The cost of tall poles is relatively higher in Europe, providing an

incentive to carry conductors at the highest possible point on a pole.

There is a noticeable difference in pole heights between Europe, where

many of the primary feeder routes do not also carry secondary, and

Canada.

With regard to technical differences between the systems I have the

Transformer Protection

An interesting difference between Europe and North America is the

question of small transformer protection. In North America there are more

small transformers and each transformer is fused on the primary side since

there is normally no secondary protection, in Europe fuses

or

circuit

breakers are usually provided on the secondary side.

The resulting large

number

of small primary sized primary side fuses in

North America is more prone to “trouble calls” in areas of lightning

activity. In Europe fewer transformer primary fuses are required and large

size fuses are used. The

number

of primary fuses can

be

further reduced

by the use of “group fusing” where a group of transformers can

be

connected to a single primary

fuse.

Transformer overload protection is

provided by the secondary fuse, short circuit protection is provided by the

primary group fuse. (Ref. 1.)

2.

ost of Materials

following comments:

Technical Losses

I do not agree that it is likely that the European system is necessarily

more prone to losses due to the simplicity of extending it. The European

systems have fewer transformers and can thus

be

much more economically

monitored for load management purposes. Their secondary systems are

lengthy and voltage regulation complaints provide an indication of loss or

load problems. The smaller North American transformers will tend to be

protected against winter overload and the resulting high losses by virtue of

being connected to a 120 volt secondary system, so that here too, voltage


9/9

1609

The observations on pole heights are less convincing however. If the

approach to system design provides fewer opportunities for primary

and

secondary circuits sharing the same pole, the popularity, and hence

availability, of tall poles will be reduced. The shorter average pole height

evident in Europe could therefore be a n effect rather than a cause.

With respect to Mr. Dwyer’s comments on technical losses, we agree

that the European system is not necessarily prone to higher losses through

system extension and also that transformer monitoring is facilitated by

virtue of there being fewer units. However, we are aware of many

European style systems in lesser developed countries where careless

system extension and a complete lack of transformer monitoring have

resulted in a degree of system overloading that would likely be impossible

had the systems followed the

North

American approach to design.

Mr. Sironi’s detailed description of actual experience in dealing with a

real world aesthetic problem provides valuable support to our broad

comments based on generalized observations.

Mr. Gallagher quite correctly points out that the paper lacks quantitative

comparisons between the two approaches to distribution system design.

Analysis of supply reliability would indeed be a worthwhile addition as

also indicated by M r. Dwyer’s description of transformer fusing practices.

We feel however, that the present general lack of adequate data on

component reliability would limit such a comparison to being a compara-

tive assessment in which little confidence could be placed.

regulation problems will normally signal any tendency for overload to

occur.

From personal observation it seems likely that the larger number of

small transformers in North America, when comb with

the

natural

tendency of designers to “play safe”, will result in a higher percentage of

unused capacity, thus increasing “no-load” losses.

ElectromagneticField

By virtue

of

the more balanced nature of the European system it will

produce lower levels of electromagnetic field than

North

American

grounded neutral systems. This may prove to be an advantage.

Reference

[ l ] “Lightning Protection of Distribution Networks” Electricity

Council Research, London,

1973.

Manuscript received September

30

991.

J. Csrr and L. V.

McCall:

We appreciate the thoughtful comments that

have been submitted and would like to make a few observations on the

points raised.

Mr. Dwyer’s comments on the impact of the relative timing between

establishing geographic infrastructure and electrification are interesting.

We agree that this is indeed a significant factor in shaping the approach

taken to distribution system design. Similarly his comments on trans-

former protection and electromagnetic fields are interesting insights.

Manuscript received December 26,

1991.

Carr - Divergent Evolution of Ds

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