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 :.: :.: