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7/25/2019 Energy Efficiency of Electrical Installations
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Energy Efficiency of Electrical Installations1999 EDITION
PREFACE
This guidebook aims to address the principles and relevant issues of
engineering practices pertinent to sustainable development in building electrical
services design. Achieving sustainabilit emerges to be the universal
commitment of the communities in the ne!t millennium.
The Energ Efficienc Office of Electrical and "echanical #ervice Department
is developing this handbook of guidelines as a supplement to the$ode of
%ractice for Energ Efficienc of Electrical Installations&hereinafter referred to
as the $ode or the Electrical Energ $ode'. The guidelines focus on
recommended practices for energ efficienc and conservation on the design(
operation and maintenance of electrical installations in buildings. The intention
of the guidelines is to provide guidance notes for the Electrical Energ $ode
and recommended practices for the designers of electrical sstems and
operators of electrical plants and installations. The guidelines in this handbookseeks to e!plain the re)uirements of the Electrical Energ $ode in general
terms and should be read in con*unction +ith the Electrical Energ $ode. It is
hoped that designers do not onl design electrical installations that +ould
satisf the minimum re)uirements stated in the $ode( but also adopt e)uipment(
design figures( provision( control methods( etc. above the standards of the
minimum re)uirements. It is also the ob*ective of the handbook to enable a
better efficienc in energ use of the designed installations and provide some
guidelines in other areas not included in the Electrical Energ $ode especiall
regarding maintenance and operational aspects for facilities management and
energ monitoring.
Although ever care has been taken to ensure that design calculations( data
reported and interpretations thereof are as accurate as possible( the Electrical
and "echanical #ervices Department of The ,overnment of the -ong ong
#pecial Administrative /egion +ould not accept an liabilit for loss or
damage occurring as a conse)uence of reliance on an information and0or
analsis contained in this publication.
This hperte!t version of the guideline is prepared from the 2EE/pro*ect at theDepartment of
Architecture(The 3niversit of -ong ong.
%lease send comments to4 [email protected]
CONTENT
Preface
1. Introduction
2. Scope
. !eneral approac"
#. Energy Efficiency Re$uire%ents for Po&er distri'ution in 'uildings
5.1 -igh 6oltage Distribution
5.7 "inimum Transformer Efficienc5.8 ocations of Distribution Transformers and "ain 6 #+itchboard
5.5 "in $ircuits
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5.: ;eeder $ircuits
5.< #ub=main $ircuits
5.> ;inal $ircuits
(. Re$uire%ents for efficient )tilisation of Po&er
:.1 amps and uminaires
:.7 Air $onditioning Installations
:.8 6ertical Transportation
:.5 "otors and Drives
:.5.1 "otor Efficienc
:.5.7 "otor #i?ing
:.5.8 6ariable #peed Drive
:.5.5 %o+er Transfer Device
:.: %o+er ;actor Improvement
:.< Other ,ood %ractice
:..7 #ub=main and ;eeder $ircuits
,. Energy Efficiency in Operation - aintenance of Electrical Installations in /uildings
@.1 Emergenc "aintenance
@.7 %lanned "aintenance
@.8 %urpose of [email protected] Economic and Energ Efficienc of "aintenance
INTRO0)CTION
1. Introduction
Electricit is the most common and popular form of energ used in all tpes of buildings including
residential( commercial and industrial. -o+ever( through inappropriate design of the po+er
distribution sstems and misuse of electrical e)uipment in buildings( it also costs us dearl in terms
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of losses as far as energ efficienc is concerned. The $ode of %ractice for Energ Efficienc of
Electrical Installations&hereinafter referred to as the $ode or the Electrical Energ $ode' sets out
the minimum re)uirements of the energ efficient design on electrical installations for the guidance
of engineers and other parties concerned in the electrical services design and operation of buildings.
This guidebook outlines and e!plains the provision of those clauses in the $ode in simple terms
together +ith design e!amples and calculations. It aims to impress upon both electrical engineers indesign and operation of buildings the importance of taking ade)uate energ conservation measures
for compliance +ith the $ode and to guard against unnecessar energ losses in the distribution and
utilisation of electrical energ.
This guide should be read in con*unction +ith the other 2uilding Energ $odes in ighting( Air
$onditioning( ift Escalator( etc.( the $ode of %ractice for the Electricit &Biring' /egulations
and #uppl /ules published b the po+er companies( in +hich some data and information are
referred and used in this guide.
2. Scope
2.1 The Electrical Energ $ode shall appl to all electrical sstems other than those used as
emergenc sstems( for all ne+ buildings e!cept those specified in Item 7.7( 7.8 and 7.5 belo+.
2.2 The follo+ing tpes of buildings are not covered in the $ode4
&a' buildings +ith a total installed capacit of 1CCA or less( single or three=phase at nominal lo+
voltage( and
&b' buildings used solel for public utilit services such as po+er stations( electrical sub=stations(
and +ater suppl pump houses etc.
2. 2uildings designed for special industrial process ma be e!empted partl or +holl from the
$ode sub*ect to approval of the Authorit.
2 # E)uipment supplied b the public utilit companies &e.g. -606 s+itchgear( transformers(
cables( e!tract fans etc.' and installed in consumers substations +ill not be covered b the $ode.
2.( In case +here the re)uirements of the $ode are in conflict +ith the re)uirements of the relevant
2uilding Ordinance( #uppl /ules( or /egulations( the re)uirements of this $ode shall be
superseded. This $ode shall not be used to circumvent an safet( health or environmental
re)uirements.
. !eneral Approac"
.1 The $ode sets out the minimum re)uirements for achieving energ efficient design of electrical
installations in buildings +ithout sacrificing the po+er )ualit( safet( health( comfort or
productivit of occupants or the building function.
.2 As the $ode sets out onl the minimum standards( designers are encouraged to design energ
efficient electrical installations and select high efficienc e)uipment +ith energ efficienc
standards above those stipulated in the $ode.
. The re)uirements for energ efficient design of electrical installations in buildings are classified
into the follo+ing four categories4
&a' "inimising losses in the po+er distribution sstem.
&b' /eduction of losses and energ +astage in the utilisation of electrical po+er.
&c' /eduction of losses due to po+er )ualit problems.
&d' Appropriate metering and monitoring facilities.
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#. Energy Efficiency Re$uire%ents for po&er distri'ution in 'uildings
#.1 ig" oltage 0istri'ution
The $ode re)uires that high voltage &-6' distribution sstems should be emploed for high=rise
buildings to suit the load centers at various locations. A high=rise building is defined as a building
having more than :C stores or over 1>:m in height above ground level.
The number of modern air=conditioned high=rise office buildings in -ong ong is increasing rapidl
during the past decade. ;ollo+ing the release of height restriction in certain areas after the opening
of the ne+ -ong ong International Airport at $hek ap ok in 199@( it is e!pected that the gro+th
of high=rise buildings +ill continue to boom.
The electrical demand of a modern high=rise office building could reach +ell over 7CC 6A0m7
depending on the nature of the business tpe and services provided. #ome of these electrical loads
+ill be concentrated in basement( intermediate mechanical floor( or rooftop plant rooms for the
accommodation of chiller plant( pump sets( air handling units( lift machiner( etc. Other loads( such
as landlord0tenants lighting and small po+er( +ill be evenl distributed throughout the building
floors.
These high=rise buildings( +ith their large demand re)uirements( +ill normall have at least one -6
intake( usuall at 11k6( provided b the po+er compan. The distribution &copper' losses +ithin the
building can be kept to a minimum if large block of po+er can be distributed at -6 to load centres
at various locations of the building. As the substation is sited at the centre of its load( the loss and
voltage drop in the 6 distribution sstem +ill be minimised. The cost ma also be significantl
cheaper than an all 6 sstem due to less copper mass re)uired.
It should be noted that the -6 distribution cables are defined as $ategor 5 circuits under TheElectricit &Biring' /egulations. #eparate cable ducts and riser ducts( segregated from cables of all
other circuits categories( must be provided for -6 cable distribution +ithin the buildings.
A tpical #;< gas sealed tpe 1:CC k6A 8=phase 11 k608@C6 distribution transformers used in -ong
ong have a total +eight of about :(CCCkg. The transportation of these distribution transformers
from ground floor level to their high level substations in a high=rise building might therefore pose a
ma*or problem.
#.2 ini%u% Transfor%er Efficiency
The $ode re)uires that the privatel o+ned distribution transformers should be selected to optimise
the combination of no=load( part=load and full=load losses +ithout compromising operational and
reliabilit re)uirements of the electrical sstem. The transformer should be tested in accordance +ithrelevant IE$ standards and should have a minimum efficienc sho+n in Table 5.1 at the test
conditions of full load( free of harmonics and at unit po+er factor.
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Ta'le #.13 ini%u% Transfor%er Efficiency
Transformer $apacit "inimum Efficienc
1CCCk6A 9@F
G1CCCk6A 99F
Transformers can be manufactured +ith efficiencies as high as 9@F to 99F. "ost transformer
manufacturers offer a variet of loss designs +ith associate differences in cost. Transformer losses
are determined at 1CC load and at a +inding temperature of @:o$ or >:o$ depending on the tpe of
transformer &e g. #;< gas sealed dr tpe and silicone fluid tpe'. The +inding &copper' loss varies
appro!imatel as the s)uare of the load current &and varies slightl +ith the operating temperature'.
The no=load &core' loss is more or less stead &fundamental value' at constant voltage and
fre)uenc.
;or privatel o+ned distribution transformers( an efficienc of not less than 9@F at full load
conditions( free of harmonics and at unit po+er factor( is re)uired b the $ode. The transformers
should be tested in accordance +ith IE$ >< or 2# 1>1. 3tilit o+ned transformers are e!empted
from the re)uirement of the $ode.
IEEE paper $:>.11C=19@
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Transformers and main 6 s+itch rooms could be provided on these floors to minimise 6
distribution losses. %roblems need to be considered include separate cable ducts provision for -6
&11 k6' cables( vertical transportation for transformers &normall single=phase tpe to reduced si?e
and +eight' and s+itchgear( fire protection and E"I problems to ad*acent floors etc. #ubstations
sited other than at ground floor locations must be e)uipped +ith non=flammable e)uipment to satisf
;#D re)uirements( e g #;< or vacuum circuit breaker( #;< or silicone=fluid filled transformers and#;0%E cables etc.
#.# ain Circuits
The $ode re)uires that the copper loss of ever main circuit connecting the distribution transformer
and the main incoming circuit breaker of a 6 s+itchboard should be minimised b means of either4
5a6locating the transformer room and the main s+itchroom immediatel ad*acent to( above or belo+
each other( or
5'6restricting its copper loss to not e!ceeding C.:F of the total active po+er transmitted along the
circuit conductors at rated circuit current.
The cross=sectional area of neutral conductors should not less than that of the corresponding phase
conductors.
In an electrical circuit some electrical energ is lost as heat +hich( if not kept +ithin safe limits(
ma impair the performance and safet of the sstem. This energ &copper' loss( +hich also
represents a financial loss over a period of time( is proportional to the effective resistance of the
conductor( the s)uare of the current flo+ing through it and the duration of operational time. A lo+
conductor resistance therefore means a lo+ energ lossJ a factor of increasing importance as the
energ efficienc and conservation design is concerned.
The length of the main distribution circuit conductors connecting the distribution transformer and
the main incoming circuit breaker &"I$2' of the 6 s+itchboard should be as short as possible b
means of locating the substation and the main 6 s+itchroom ad*acent to each other. A ma!imum
conductor length of 7Cm is recommended +hich is based on -E$s ,uide to $onnection of #uppl.
Due to the possibilit of large triplen harmonic currents e!isting in the neutral conductor for
building loads +ith a large proportion of non=linear e)uipment( it is not recommended to use neutral
conductors +ith a cross=sectional area less than that of phase conductors in the main circuit.
Tpical sample calculations for various +iring sstems used for a main circuit feeding from a
1:CCk6A 11k608@C6 8=phase distribution transformer to a main 6 s+itchboard having a circuit
length of 7Cm are provided as follo+s4
1. 7:CCA 5=+ire copper insulated busduct sstem
7. 8!>m0m at @Co$ &2ased on data provided b a reputable busduct
manufacturer'
Total po+er losses K 8 ! 77@C7A7! C.CCCC1>>0m ! 7CmK:.:7kB &C.588F'
Case 5263 8!
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/esistance per conductor &2ased on 2#>141997( Table 5E12' K KC.C58m0m &at
9Co$'
Effective resistance per phase +ith 8 conductors in parallel K C.C5808 m0m K C.C158 m0m
Total po+er losses K 8!77@C7A7! C.CCCC1580m ! 7Cm K 5.58m0m &at
9Co$'
Effective resistance per phase +ith 8 conductors in parallel K C.C5>808 m0m K C.C1:@ m0m
Total po+er losses K 8!77@C7A7! C.CCCC1:@0m ! 7Cm K 5.98kB &C.8@>F'
;or design purpose( the e!amples above provide a )uick guideline for main circuit design using
different tpes of conductors up to 7Cm in length. All three cases above can fulfill the re)uirement of
ma!imum po+er loss of C.:F under full load( balanced and undistorted conditions. Designers
should ensure ade)uate precautions have been taken in balancing the loads and harmonic reduction
in the design of main circuits.
"ain circuits designed( supplied and installed b the utilit companies are e!empt from the
re)uirement of the $ode.
#.( Feeder Circuits
A feeder circuit is defined as a circuit connected directl from the main 6 s+itchboard to the ma*or
current=using e)uipment such as chiller plant( pump sets and lift sstem. The code re)uires that the
ma!imum copper loss in ever feeder circuit should not e!ceed 7.:F of the total active po+er
transmitted along the circuit conductors at rated circuit current. This re)uirement does not appl to
circuits used for compensation of reactive and distortion po+er.
;or a 8=phase circuit +ith balanced and linear load( the apparent po+er transmitted along the circuit
conductors in 6A is4
Active po+er transmitted along the circuit conductors in B is4
Total copper losses in conductors in B is4
Pcopper= 3 x Ib2x r x L
+here 3 K ine to line voltage( 8@C6
Ih K Design current of the circuit in ampere
cos K Displacement po+er factor of the circuit
r K a c resistance per metre per conductor at the conductor operating temperature
K ength of the cable in metre
%ercentage copper loss +ith respect to the total active po+er transmitted(
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This ma!imum copper loss re)uirement is deemed to compl +ith for an 8=phase balanced circuit
+ith linear characteristic( if feeder circuits are designed to the conventional safet re)uirement of the
Electricit &Biring' /egulations.
The conventional method of cable si?ing can briefl be described as follo+s4The relationship among circuit design current &Ib'( nominal rating of protective device &In' and
effective current=carring capacit of conductor &I?' for an electrical circuit can be e!pressed as4
$o=ordination among Ib( In( I?4 Ib In I?
$alculated minimum tabulated value of current4
Effective current=carring capacit4Iz=Itx Cax Cgx Ci
BhereItK the value of current tabulated in Appendi! 5 of 2#>141997( The /e)uirements forElectrical Installations
CaK $orrection factor for ambient temperature
CgK $orrection factor for grouping
Ci=K $orrection factor for thermal insulation
A +ork e!ample on feeder cable si?ing is given as belo+4
A 8@C 6 8=phase feeder circuit to a 5CkB sea +ater pump set is +ired in a 5=core %6$0#BA0%6$
copper cable. The cable is mounted on a perforated cable tra +ith 7 other similar cables touching.
The steel +ire armour of the cable is to be used as circuit protective conductor. -/$ fuses to 2#@@
are lo be used for circuit protection. Assuming the ambient=air temperature is 8:o$ and star0delta
starter is used for motor starting. The efficienc and po+er factor of the motor at full load are givenas C.@ and C.@: respectivel. The length of the cable is @Cm from the main s+itchboard. The
minimum cable si?e for compliance +ith the Electricit &Biring' /egulations is determined as
follo+s4
Design current of 5CkB motor circuit( IbK @9.8> A
-/$ fuse rating selected( InK 1CCA as protective devices
$orrection factors $gK C.95 $aK C.@1
"inimum current=carring capacit( It&min ' K 181 A
;rom table 5D5A&2#>1'( ItK 18:A for 8:mm750c %6$0#BA0%6$ cable
6oltage drop K 1.1 m60A0m ! @9.8> A ! @C m K >.@< 6 &7F'
Effective current=carring capacit( I?K 18: ! C.95 ! C.@1 K 1C7.@ A
/esistance of conductor &Table 5.7A'( r K C. 7 ! C.CCC
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;or a 8=phase non=linear circuit having kno+n design currentIbor fundamental currentI1and total
harmonic distortion THD( the apparent po+er transmitted along the circuit conductors in 6A is4
+here
;rom definition4
Therefore(
And( fundamental current
Assuming voltage distortion is small( UL = U( and active po+er transmitted along the circuit
conductors in B is given b4
+here
UL K #uppl line voltage at 8@C6I K ;undamental phase current of the circuit in ampere
cosK Displacement po+er factor of the circuit
And( Total %o+er ;actor K
Assuming the skin and pro!imit effects are small( total copper losses in conductors including
neutral in B is given b
PcopperK!3 x Ib2" I#2$ x r x L+here
I#K Neutral current of the circuit in ampere
Ib K Design rms phase current of the circuit in ampere
r K a.c. resistance per metre at the conductor operating temperature
K ength of the cable in metre
%ercentage copper loss +ith respect to the total active po+er transmitted(
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3sing the same +ork e!ample above( if the feeder circuit is designed for 6#D drive instead of the
conventional star0delta starter( the ne+ feeder circuit have to be re=designed as follo+s. ,iven that
T-D at full=load and full=speed condition is @CF &a figure for illustrating the harmonic effect and
does not compl +ith Table 1'( ItK 7:1 A for 9:mm750c %6$0#BA0%6$ cable
6oltage drop K C.58 m60A0m ! 17
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Therefore( ma!.
Table 5.7A and 5.72in the $ode provide a )uick initial assessment of cable si?e re)uired for the
common cable tpes and installation methods used in -ong ong.
The tabulated current rating of the selected cable could then be corrected b appling the correction
factors accordingl. The effective=current carring capacit of the selected cable must be checked so
that its value is larger than or e)ual to the nominal rating of the circuit protective device.
A +ork e!ample on sub=main cable si?ing under different loading characteristics is given belo+4
A 8=phase sub=main circuit having a design fundamental current of 1CCA is to be +ired +ith 50$
%6$0#BA0%6$ cable on a dedicated cable tra. Assuming an ambient temperature of 8Co$ and a
circuit length of 5Cm( calculate an appropriate cable si?e at the follo+ing conditions4
&a' 3ndistorted balanced condition using conventional method &cos K C.@:'J&b' 3ndistorted balanced condition +ith a ma!imum copper loss of 1.:F &cos K C.@:'J
&c' Distorted balanced condition +ith I8K88A I:K7CA &T-D 8@.
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ma!. r &m0m'
;rom Table 5.7A 8: mm750$ %6$0#BA0%6$ cable having a conductor resistance of C.141997( The /e)uirements for Electrical Installations(
Table 5D5A 8:mm750$ %6$0#BA0%6$ cable ItK18:A
$onductor operating temperature tlK 8C L 1CC70 18:7! &>C=8C' K :7o$
/atio of conductor resistance at :7o$ to >Co$ K &78CL:7' 0 &78CL>C' K C.95
6oltage dropK 1.1m60A0m ! C.95 ! 1CCA ! 5Cm K 5.156&1.C9F'
Total copper losses in conductors K 8 !1CC7 ! C.18o$
&Note4 conductor operating temperature +ould be >8o$ at this condition +hich is over the ma!imum
of >Co$ for %6$ insulated cable'
/atio of conductor resistance at >8o$ to >Co$ K&78CL>8'0&78CL>C' K1.C1 &over temperature'
Total copper losses in conductors &assuming skin pro!imit effects are negligible for harmonic
currents'
K &8 ! 1C>.77L 997' ! C.CCC
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/efer to 2#>141997( The /e)uirements for Electrical Installations(
Table 5D5A :Cmm750$ %6$0#BA0%6$ cable ItK1.7L99'7 0 &8!1CA( I>K:CA I11K1:A
&T-D @>F' and a ma!imum copper loss of 1.:F &cosK 1'
&ig. '.2( Curre%t )a*e+orm, +or ca,e !-$
;undamental current( I1K 1CCA
-armonic current( I:K>CA( I>K:CA I11K1:A
Ne+ design current( IbKIrmsK188A
Ne+ rating of protective device( InK 1C' K C.9:
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6oltage drop
Active po+er dra+n
Total copper losses in conductors &assuming skin pro!imit effects are negligible'
K 8 ! 1887A7! C.CCC5
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6oltage drop
Active po+er dra+n K
Total copper losses in conductors &assuming skin pro!imit effects are negligible'K 8 ! 89@7A7! C.CCCC9:m60A0m ! C.9>8 ! :7m
K 77@5B &1.1
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:C C.5C C.81: C.88:
9: C.78: C.7:
17C C.19 C.7
1:C C.1: C.1>: C.C@
5CC C.C:>: C.CCo$
%E cable at ma!. conductor
operating temperature of 9Co$
Enclosed in
conduit0trunking
$lipped direct
or on tra(
touching
Enclosed in
conduit0trunking
$lipped direct
or on tra(
touching
1.: 15.: 15.: 1:.: 1:.:7.: 9 9 9.: 9.:
5 :.: :.: