HV & MV CABLE SIZINGJ08423A-E-AC-15051, REV
B1.__________________________________________________________________________________________
ALRAR INLET SEPERATION AND BOOSTING FACILITIES,ALGERIAPETROFAC
PROJECT NO. : JI-2020
HV & MV CABLE SIZING
B1Issued For Client ApprovalMVGMJKJ / VSBKRM/MTS
RevDateReason for IssuePrepared ByChecked ByApproved byProject
Approval
Project CodeDiscipline CodeDocument TypeSequence
NoBilingualIdentifierRev.
J08423AEAC15051B1
Bir Seba Field DevelopmentDoc. No.:PVEP-ALG-BRS-PR-G-401
STANDARD DOCUMENT FORMATDate:28 July 2008
Rev.:Q1
REVISION HISTORYRev.SectionDescription of Revision
B1
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B1
B1
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HOLDS
HoldSectionDescription of Hold
TABLE OF CONTENTSGLOSSARY41CODES AND
STANDARDS61.1General61.2Order of Precedence61.3Algerian Government
Requirements61.4Project Documents61.5International Codes and
Standards62SCOPE83NOTES94GENERAL CRITERIA104.1Site
Conditions104.2Cable Parameters104.2.166kV Power Cables104.2.25.5kV
Power Cables116 ALLOWABLE VOLTAGE DROPS127CABLE derating
factors137.1HV cable Derating Factors137.2MV cable Derating
Factors147.2.1Laying Conditions: Laid in Air147.2.2Laying
Conditions: Buried in trench168CABLE SIZING CALCULATIONS198.1Basis
for Calculations198.266kV Cable Sizing208.35.5kV Cable Sizing20
GLOSSARYA.C.Alternating CurrentCDegrees CentigradeAWA Aluminium
Wire ArmourCAContracting AuthorityEIEnergy InstituteEPCEngineering,
Procurement and ConstructionEMCElectromagnetic CompatibilityGISGas
Insulated Switchgearhhour (60 minutes)H.V.High Voltage M.V.Medium
Voltage HzHertz (frequency)IECInternational Electrotechnical
CommissionIPIngress ProtectionISOInternational Standards
OrganisationkgkilogrammekmkilometrekWkilowattmmetrep.f.Power
FactorS.I.Le Systeme International dUnites (metric system)SPLSound
Pressure LevelVVoltsWWattsXLPE Cross-Linked Polyethylene
CODES AND STANDARDSProject DocumentsProject Documents consist of
the following:Document NumberDescription
J08423A-E-PH-15001Electrical Design Philosophy
J08423A-E-SP-15110Electrical Power & Control Cable
Specification
International Codes and StandardsThe Codes & Standards
referred in order to perform the cable sizing calculations are as
listed below:Document NumberDescription
IEC 60183Guide to the Selection of High-Voltage Cables
IEC 60228Conductors of Insulated Cables
IEC 60287Electrical cables - calculation of the current
rating
IEC 60331Test on Electric Cables under Fire Conditions - Circuit
Integrity
IEC 60332Test on Electric Cables under Fire Conditions
IEC 60502 All partsPower Cables with Extruded Insulation
IEC 60364Electrical Installations of Buildings
SCOPE The document covers the sizing of all HV (66kV) & MV
(5.5kV) cables used in electrical power distribution.The purpose of
this document is to determine the Electrical HV & MV Cable
sizes Vis-a-Vis the installation methods used in Alrar Inlet
Separation and Boosting facilities Project in Algeria.
GENERAL CRITERIASite ConditionsThe following outdoor site
conditions have been used as the basis for cable sizing:Maximum
Ambient Air Temperature + 55 C
Minimum Ambient Air Temperature - 5 C
Normal Design Temperature + 55 C
Soil Temperature + 35 C
Soil Thermal Resistivity 2.5 K-m/W (Hold- 1)
Depth of laying for HV & MV cables 1000 mm
Cable Parameters66kV Power CablesCable Type:XLPE/PVC/AWA/PVC
66kV rating flame retardant for single coreRated Voltage:38 / 66kV
System Voltage:66kV: 3 phase, 3 wires A.C.Service:Power
distribution Construction:Conductors;Annealed stranded plain copper
(Class 2), compacted circular or milliken (segmented compacted
circular)Core Screen:Extruded, non-metallic, semi-conducting
compoundInsulation:XLPEInsulation Screen:Semi-conducting
compoundMetallic Screen:Corrugated aluminium or lead alloy Core
Identification:1 core = BlackRadial Water Barrier:Semi conducting
non-woven water swellable tapeLaying Up:Cores to be laid up
together with non-hygroscopic fillersArmouring:Single layer
aluminium wire armour.Over sheath:Extruded PVC or XLPE Colour =
redFire Performance:Cable shall meet the requirements of IEC
60332-1 and IEC 60332-3-22 (category C)
5.5kV Power CablesCable Type:XLPE/PVC/SWA/PVC 6.6kV rating flame
retardant for multi core cables & XLPE/PVC/AWA/PVC 6.6kV rating
flame retardant for single core cables.Rated Voltage:3.8 / 6.6kV
System Voltage:5.5kV: 3 phase, 3 wires A.C., high resistance
earthedService:Power distribution Construction:Conductors;Annealed
stranded plain copper (Class 2), circular or shaped sectionCore
Screen:Extruded, non-metallic, semi-conducting tape in combination
with a copper tape of 3mm thicknessInsulation:XLPEInsulation
Screen:Semi-conducting layer: Extruded, cold strippableMetal layer:
Copper tape or wireCore Identification:1 core = black3 core =
brown, black, grey. Coloured strips will be used under copper tape
screen. Natural colour of outer semi conductor material is
BlackLaying Up:Cores to be laid up together with non-hygroscopic
fillersBedding:Extruded PVC Armouring:Multi core cables - single
layer of galvanised steel wire armour. Single core cables - single
layer of non-magnetic aluminium wiresOver sheath:Extruded PVC
Colour = redFire Performance:Cable shall meet the requirements of
IEC 60332 part1 and IEC 60332 part 3 category C (and have an acid
gas emission of not greater than 17% and oxygen index of 30%
(minimum)Comment:Cable shall be suitable for use on a system which,
under fault conditions, is operated for a short time with one phase
earthed, provided it does not exceed 8 hours on any single occasion
and a total duration of 125 hours during any 12 month period.
Limiting / Permissible (Max.) conductor temperature under rated
current carrying conditions: 90CLimiting / Permissible (Max.)
conductor temperature under short circuit conditions: 250C
6 ALLOWABLE VOLTAGE DROPSPermissible Cable Voltage
DropsFeedersFrom GIS (HV SWGR) to Transformer : 1% of supply
voltageFrom MV SWGR to Transformer : 1% of supply voltageMotor
Feeders (under motor rated conditions)Under Running Conditions
(from MV SWGR to Motor) : 5% of motor rated voltageUnder Starting
Conditions (from MV SWGR to Motor) : 15% of motor rated voltage
1. CABLE SIZING PHILOSOPHYSizing CriteriaCable sizing shall take
into account the following parameters:a)Current carrying capacity
of cable. b)De-rating factors for current carrying capacities
depending on cable type and method of installation.c)Voltage drop
in the cable/circuit run.d)Short circuit withstand capacity of
cable.Current Carrying CapacityCurrent ratings for cables installed
In Air, Direct Buried and In single Way Ducts, are detailed in the
HV & MV Cable Data Sheets J08423A-E-DS-15210 &. The maximum
continuous current ratings detailed in the Electrical Cable Data
Sheets take into consideration the following cable derating
factors:a. Cables installed In Air Ambient Temperature Grouping of
cablesb. Cables Direct Buried Ground Temperature Depth of Laying
Thermal Resistivity of Soil Grouping of cablesc. Cables In single
Way Ducts Ground Temperature Depth of Laying Thermal Resistivity of
Soil. Grouping of cablesThe cable derating factors applied to the
Electrical Cable Data Sheets are based on the Prysmian cable
catalogues. Details on the cable derating factors are given below
in section 6.3.
HV cable Derating Factors Ground Temperature (C1)The rating
factors due to the ground temperature for XLPE cables laid direct
in the ground taken from Polycab catalogue is shown below:
Thermal resistivity of soil (C2)The rating factors due to the
thermal resistivity of soil taken from Polycab catalogue is shown
below:
Depth of Laying (C3)The rating factors due to the depth of
laying taken from Polycab catalogue is shown below:
Spacing of cables (C4)The rating factors due to the grouping
taken from Polycab catalogue is shown below:
0. MV cable Derating Factors Ambient Air Temperature (C1)
The rating factors due to the ground temperature for XLPE cables
laid direct in the ground taken from Polycab catalogue is shown
below:
Ground Temperature (C1)The rating factors due to the ground
temperature for cables laid direct in the ground taken from IEC
60502-2 are shown below:
Depth of Laying (C2)The rating factors due to the depth of
laying taken from IEC 60502-2 is shown below:
Thermal resistivity of soil (C3)The rating factors due to the
thermal resistivity of soil taken from IEC 60502-2 are:Spacing of
cables (C4)The rating factors due to the grouping taken from IEC
60502-2 are shown below:
Spacing of cables (C4)
C4 for a grouping of 4 cables in a group at spacing of 150 mm is
taken from the table B.22 of IEC 60502-2.
Overall Derating factors
Overall Derating FactorThe overall derating factor for MV
Multi-core cables areas shown below:Voltage/ Cable TypeIn AirDirect
Buried
CABLE SIZING CALCULATIONSBasis for CalculationsCables are sized
in accordance with whichever of the following criteria gives the
largest cable cross sectional area requirement: Continuous current
carrying capacity Short circuit current carrying capacity Volt drop
at full loadIn addition, some degree of standardisation in cable
size may be applied to avoid having to purchase short lengths of
particular cables.The continuous current carrying capacity for the
different cross sectional areas and different installation
conditions are as per the manufacturers data. The continuous
current ratings will generally consider two basic installation
methods i.e. in air (on ladder racks or trays) and direct buried.
In assessing the continuous current carrying capability, the
calculations in this report assume no additional bunching factor
need to be applied. However, additional de-rating may be needed in
certain cases after the exact laying conditions are finalised.The 1
second short circuit withstands are indicated on the attached
typical cable manufacturers data tables and is based on the below
equation:k2 S2 = I2 t (1)For XLPE insulated copper cables with a
short circuit temperature rise from 90C to 250C, k factor is 143
(XLPE copper multi core cables). Conversion of the 1 second values
to different times is given as:I12 t1 = I22 t2 (2)The volt drop at
full load is assessed from the following calculation:V.D. (ph-N
basis) = I Rph cos + I Xph sin (3)Where, k -143 (for copper)S
-cross sectional areaI1 -Cable short circuit current (Refer
Attachment 4)I2-Higher than the bus Short Circuit currentt1-Time in
Sect2-Fault Clearing time in SecRph -Cable Resistance
(Ohms/km)Xph-Cable Reactance (Ohms/km)cos-Power FactorThe values
for Rph and Xph for a given cable are calculated from the per km
values respectively given in Attachment 4 typical cable
manufacturers data tables. The Rph value is for operation at 90C.
Typically 66kV & 5.5kV cables are sized on continuous current
and short circuit withstand capability. A minimum cable size is
needed for short circuit withstand for cables protected by circuit
breakers. The minimum size depends on the maximum short circuit
current and the anticipated fault clearance time. For this report
the 66kV & 5.5kV short circuit current is taken as the
switchboard rated value of 25kA & 40kA rms respectively. Fault
clearance times are taken as:For 5.5kV system:Breaker Operating
Time
60 ms
Relay operating time50 ms
5PCT error margin50 ms
Safety Margin60 ms
Total Fault Clearing Time220 ms
It is assumed that the switchboard rated fault current is
sustained at the switchboard rating but in practice there will be a
rapid decrement in fault current due to decaying generator and
motor contributions to the fault current. Consequently the design
will incorporate a safety margin.66kV Cable Sizing Cable sizing is
based upon typical manufacturers data. After finalisation of cable
vendor the selection of high voltage cable shall be in accordance
with IEC 60183 and the actual cable manufacturers data.After
identifying the minimum cables size to satisfy the cable short
circuit withstand capacity, the cable size is selected in
accordance with continuous current based on equipment rating or
maximum volt drop, whichever is higher.5.5kV Cable Sizing Cable
sizing is based upon IEC 60502-2 and typical manufacturers data.
After finalisation of cable vendor the selection of high voltage
cable shall be in accordance with IEC 60183 and the actual cable
manufacturers data.After identifying the minimum cables size to
satisfy the cable short circuit withstand capacity, the cable size
is selected in accordance with continuous current based on
equipment rating or maximum volt drop, whichever is higher.
Gas Turbine Generator Incomer H-EW-081101& H-EW-081201(5.5
kV)Generator Rating 3.15MVA, 5.5kVa) Minimum Conductor Sizing for
short CircuitMinimum cross section area of cable S = I t / k (ref
Equation 1)The maximum short circuit current in the generator
cable, I, can be taken as the switchgear fault level less the
generator short circuit contribution (based on 12% impedance) i.e.
I = (31.5 - 2.75)kA = 28.75 kAt = 0.75 s (generator breaker
protection operating time)k = 143 Hence min. cross section of cable
S = 28.75k x 0.75 / 143 = 174 mm2 Next nearest conductor size
available is= 185 mm2 (Cu, XLPE)b) Sizing based on continuous
currentFull load current = 330 A De-rated current = 330 A/0.63
(Direct Buried, 2 circuits, as per 7.3.6) = 523.8 AProposed cable
size = 3 C x 185mm2, Cu conductorCable Ampacity (Laid in Ground) =
436 A ( Ref. Table -9)Min number of cables required = 2 Runs x 3C x
185mm2 c) % Voltage drop calculation%Voltage drop = (1.732 x I x L
x (R Cos + X Sin) / (NxVx1000)) x100Where,I - Load current (330 A)L
- Cable Route length (150m)R - Resistance of cable (0.128) for 185
mm2, refer to attachment 4X - Reactance of cable (0.0881) for 185
mm2, refer to attachment 4Cos - Power factor, 0.8 N - No. of Runs
(2)V - Voltage (5.5kV)% V.D. =
(1.732x330x150x(0.128x0.8+0.0881x0.6)/(2x5500x1000))x100 = 0.00121
x 100= 0.121 % which is acceptable ( as per the clause 7.4)Hence
selected cable size = 2 Runs x 3C x 185mm2
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