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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
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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.
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Figure 2 European Style Distribution
System
I
Figure 3 North American
Style
Distribution
System
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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
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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
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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 .
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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.
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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
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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.
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