R01 HMR Connection to 220kV Main Grid Undergrounding Study Attachment1 Appendix5and6

7/29/2019 R01 HMR Connection to 220kV Main Grid Undergrounding Study Attachment1 Appendix5and6

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Appendix 5

Comparisons between installing 220kV undergroundtransmission cables and installing other longitudinal

infrastructure for example, high pressure gas or waterpipe lines; underground distribution cables and

communication cables

Installation requirements and provision for maintenance & repairs differ

significantly between those for extra high voltage (220kV) undergroundtransmission cables and lower voltage underground distribution cables;

underground communication cables and high pressure gas or water pipe lines.

There are also variations in easement requirements and easement conditions

In simple terms:

Metallic or polymeric (plastic) gas or water pipes are transported to site and laid

in manageable sections (and manageable weights) and welded, or otherwise

connected together, as trench excavation progresses.

Trenches are narrow and, other than a bedding comprised of sand (to protect the

outer surface of pipes) there are no special trench excavation or back-filling

requirements.

Similar installation conditions to those for gas & water pipes may apply for lower

voltage underground distribution cables and communications cables (whether

electric or fibre optic). These are often laid in ducts.

Trenches are narrow (the width of a small back-hoe bucket) and other than for

sand bedding there are no special trench excavation or back-filling requirements.


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In the case of extra high voltage underground power cables (including 220kV)

there are factors that impose significant differences in installation & maintenance

requirements to those for water or gas pipes or lower voltage circuits namely:

1. Dissipation of heat generated by underground cables.As underground cables transmit energy (in this case from the wind farm to the

main grid) the cables generate heat which, if not efficiently dissipated, will cause

the cables to over-heat and eventually fail. (This was precisely one of the

contributing factors that led to the cable failures and eventual black-outs in

Auckland in 1998)

Soil samples taken from site in the Limestone Downs Orton area are estimated

to have a high thermal resistivity meaning the soil will impose a barrier to heatwanting to escape from the cables to the surface. This shall be confirmed by

thermal resistivity test on site & in laboratory prior to proceeding with the project.

Well accepted practice, world wide, is to improve this situation by bedding and

covering the cables with a controlled medium comprised of a weak mix of sand

and cement. (Refer diagram below)

Vast quantities of this mix (equivalent to excavated spoil) would be required

adding substantial costs and transport difficulties in acquiring, delivering, placing& compacting it over the entire cable route.

Typical cable installation in trench with cables in flat formation


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2. Installing and jointing cables

Cables of this size and voltage are not manufactured in New Zealand. Each

cable drum, containing around 700metres of cable and weighing up to 20 Tones,

would require to be transported from Auckland on multi-wheeled vehicle to sites

at 700 m intervals, there to be craned off, winched/pulled into position (in the

cable trench), then to be bedded & covered with protective concrete cable covers

and special backfill and then to be jointed in a controlled environment in what is

known as a joint bay comprising a tented enclosure of the size, and with

features, as shown below. The duration of works associated with Joint bays

(construction and cable jointing) could be as long as 3 to 4 weeks.

Joint bay (4m x 12m) in roadway Interior of joint bay prior to jointing(Would exceed width of Baker Rd.

in places)

3. Managing cable sheath losses

At transmission voltages, including 220kV, special bonding techniques termed

cross bonding provide the only practical means to mitigate losses in outer

metallic sheaths of underground power cables. (For technical explanation refer to

Appendix 6)

Cross bonding systems include surge arrestors and other equipment mounted in

underground link boxes that require testing at regular intervals (usually annually).

For that purpose that equipment is located within pits as shown below which, for


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ready access and safety to testing staff, are located away from trafficable roads

in footpaths see below.

Link box U/G concrete pit

Baker, Wairamarama and Matakitaki Rds. would present considerable challenges

in that they are very narrow and in many cases bounded by steep drops on one

side and steep inclines on the other where they are carved into mountain sides

see Photos No 4 & 5 in Attachment No.1 to Consolidated report.

In these situations there would be no alternative but to install link pits together

with joint bays and pits for optic fibre cables (if fibres were to be part of the cable

installation) in road ways.


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Appendix 6

Current rating and electrical losses of highvoltage power cable systems

1. Cable Rating Influencing Factors

The current rating of high voltage (HV) underground (U/G) power cable circuits is,

primarily, influenced by the environmental factors and cable losses.

Both factors are fully considered for determination of cable type and installation

particulars by taking into consideration the economic aspects related to the cost of

materials, installation of cable and accessories, running cost (whole life cost),

capitalised cost of losses and ancillary equipment such as bonding, condition

monitoring systems and compensating equipment.

a. Environmental Factors

The most specific factors which have a greater impact on cable current rating or

loading capacity are as follows:

Air and soil maximum ambient temperature

Soil thermal resistivity (TR) under the most severe climatic conditions in

respect to water (humidity) content

b. Installation Particulars

Extra high voltage (EHV) power cable circuits (including 220kV) are

manufactured in form of single-core cables which could be installed in trefoil or

flat formations.


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The installation option is selected to correlate the cable type /conductor size with

the environmental parameters to get the required cable carrying capacity.

Fig1: Typical installation configuration of single-core power cables in trefoil

formation

This type of cable configuration has the advantage of minimising the sheath

circulating currents induced by the magnetic flux linking the cable conductors and

metallic sheath or copper wire screens. This configuration is generally used for

cables of lower voltages (33 to 132kV) and of smaller conductor sizes

However, for EHV cable systems the trefoil formation is not appropriate for heat

dissipation because there is an appreciable mutual heating effect of the three

cables.

The cumulated heat in cables and cable trench has the effect of reducing the cable

rating and accelerating the cable ageing

In order to improve the natural heat dissipation from around the cable circuits the

three single-core cables could be installed in flat formation (Fig2). This

configuration allows for a significant increase of current rating of EHV cable circuits.


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Fig. 2: Typical installation configuration of single-core power cables in flat

formation

In Fig. 2 are shown the CMS (condition monitoring system) and

communication cables installed between the 220kV single-core power

cables.

In addition, to the centre power cable is attached the DTS (distributed

temperature sensing) optical fibre cable. Both the DTS and CMS are

designed to continuously monitor the cable and environment temperatures

and to perform other supervisory functions as well

The installation of cables in flat formation requires special bonding solutions

of cable metallic sheaths to reduce/eliminate the circulating currents.

Nevertheless, in case of unfavourable environmental conditions related to

soil thermal characteristics or of ambient temperature the sole application of

flat configured cables and of special bonding system may not provide the

expect result and as a consequence the following techniques should be

employed to achieve the required current rating:


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Replace a certain amount of soil adjacent to the excavated cable

trench with aggregates or imported soils of suitable thermal resistivity.

Use of specialised bedding and backfilling materials such as:

Sand/cement mix of 14: 1, 20:1 or of other proportions

Fluidised backfill

Blended sands or crushed rock of variable gain sizes

All ducts and micro tunnels be filled with bentonite and respectively

light concrete

Artificial cooling

Particular installation configurations of single-core cables or of cable

circuits within a given cable corridor

Special bonding system of cable metallic sheaths designed to reduce

the electric losses

Install double cable circuits in a single or adjacent trenches or other

applicable site conditions

2. Electrical Losses

Under service conditions, regardless of magnitude of transported the power

cables are subjected to electrical losses manifested as heat in insulation and

metallic components.

Based on the location were they are generated and the generation cause the

electrical losses could be qualified as current and voltage-dependent losses.

The current-depending losses are generated in cable conductors, metallic sheath

or/and metallic wires designed to carry fault currents

For a simplified cable system (land cable circuit) the three main cable

component responsible for electrical losses are the conductor(s), the insulation

and the metallic sheaths or/and the metallic wire screens.


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2.1 Conductor Losses

Conductors losses are ohmic losses, i.e. heat (Watt/meter) generated by the

current flowing in the cable conductor(s) and are calculated with the following

formula:

Wc = I2 Ra.c

I = current flowing in the conductor (A)

Ra.c= A.C. electrical resistance () of conductor at given temperature (C)

The A.C. electrical resistance () is dependent, in addition to the D.C resistance

(Rd.c) on skin (ys) and the proximity (yp) effects which are responsible for the

uneven distribution of load current across the conductor cross sectional area, so

the Ra.c resistance could be defined as:

Ra.c = Rd.c (1 + ys + yp)

Rd.c = Ro [1 + 20 ( 20)]

Ro = D.C electrical resistance at 20C

20 = Constant mass temperature coefficient at 20C per Kelvin

= maximum operating temperature (C)

Skin effect(ys ) is attributed to the variation of conductor self-inductance which

is greater to the centre of the conductor than to its periphery and as a

consequence the current flow is maximum at the conductor surface and minimum

at the conductor core This phenomenon is one cause of increased A.C.

resistance of conductors.

Proximity effect (yp) is generated by the magnetic field produced by the currents

flowing in parallel cable conductors of another cable circuit or other parallel

current carrying conductors. The associated magnetic field embraces that

conductor and at the same time it encircles the parallel conductors in close

proximity.


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The effect is explained by the fact that when two conductors carrying alternating

current are parallel and in close proximity, the current densities on the inner area

(side facing each other) are smaller than the current density flowing in the outer

area (remote side) of the conductors due to the difference in magnetic flux

densities cutting the conductors cross area.

So, the A.C. conductor resistance is defined by the D.C resistance and the skin

and proximity factors as indicated by the following formula:

Ra.c = Rd.c (1 + ys + yp)

The calculation of skin (ys) and proximity (yp) effect factors is based on the

empirical formula given in the IEC 60287 Standard

The proximity effect factor (yp) is determined by the cable D.C. resistance,

system frequency, cable spacing and cable diameter while the ys is influenced

only by conductor d.c resistance and system frequency:

ys = (R , f)

yp = (dc , R, s , f)

The skin and proximity effects could be ignored for small conductors carrying low

currents, however for high rating cables requiring large conductors these effectsare significant and it is essential to include design feature to compensate their

effect.


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The Milliken or Segmental conductors, which consist of several individually or

alternated insulated sector shaped strands, provide the desired solution (Fig. 3).

Fig. 3: Milliken Cable Conductor (Fluidfilled Cable System)

The modern technologies apply a layer of enamel or Cu oxide on individual wires

forming the sector shaped strands.

The economic justification of this type of conductor is validated when using

cables of minimum 800mm2

2.2 Dielectric and Charging Current Losses

A power cable is a large capacitor of certain capacitance characterised by

dielectric constant () and electrical resistance. The two parameters and the

magnitude and frequency of applied voltage determine the magnitude of charging

current and dielectric losses.

Both, the charging current and dielectric losses are voltage-dependent and they

are generated in cable insulation at any time the cable is connected to the grid.

The charging currents are generated by the cable itself and produce a certain

amount of losses which, in combination with the system reactive power generate

losses reducing the flow of active/real power (MW).

Cableconductor

(Milliken)

CableInsulation


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The charging current charges and discharges the cable (capacitor) 50 times per

second. While the charging current is a reactive current the dielectric losses are

determined by real power currents.

The reactive power transported by the cable is independent of cable system; it isa parameter determined by the system configuration and the elements designed

to compensate the reactive power flow

The charging (IC) and resistive (IR) currents flowing through the cable insulation

are calculated with the following equations:

IC= C Uo (charging current)IR = Uo/R (leakage current),

While the dielectric losses are calculate from the equation:Wd = Uo

Ic tan, orWd = CUo

2tan Where:

109

ln18

=

d

D

c

i

c

C = cable capacitance = 2 = system frequencyUo =

phase voltage

tan = dielectric power factorR = insulation resistance = dielectric constantDi = insulation diameterdc = conductor diameter

For high and extra-high voltage cables the dielectric losses (Wd) could be

relatively high and may have significant contribution to in determination of cable

ratings

The cable dimensions and the insulation dielectric constant are the basic factors

responsible for the size of capacitance.

[C = /18ln (Dinsulation /dconductor)] while the tan is dependent on frequency,

temperature and the applied voltage and is being influenced by the following

factors:


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Leakage current flowing across the resistive component of cable

(capacitor) insulation is very much influenced by the quality-cleanliness of

insulating materials. The leakage current is an ionic conduction due to

the presence of free electrons flowing in the direction of electric field.

Dielectric hysteresis losses caused by the interaction of alternating

electrical field with the molecular structure of cable insulation; a sort of

mechanical work aiming to orientate the bipolar microscopic molecules of

insulation, or of contaminants, in the direction of electrical field. As the

field direction changes 50 times/sec, the cumulative impact of hysteresis

effect could be significant and, in fact, it is the major contributor to

dielectric losses.

Ionisation and low energy discharges inside the insulation.

2.3 Sheath Losses

Sheath losses are current-dependent losses and are generated by the induced

currents when load current flows in cable conductors.

The sheath currents in single-core cables are induced by transformer effect; i.e.

by the magnetic field of alternating current flowing in cable conductor which

induces voltages in cable sheath or other parallel conductors.

The sheath induced electromotive forces (emf) generate two types of losses:

circulating current losses (1) and eddy current losses (1), so the total losses in

cable metallic sheath are:

1=

1 +

1

The eddy currents circulating radially and longitudinally of cable sheaths are

generated on similar principles of skin and proximity effects mentioned in relation

to the conductor Rac resistance; i.e. they are induced by the conductor currents,


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sheath circulating currents and by currents circulating in close proximity current

carrying conductors.

Fig. 4: Magnetic field of a three-phase single-core cable circuit

They are generated in cable sheath irrespective of bonding system of single core

cables or of three-core cables

The eddy currents are generally of smaller magnitude when comparing with

circuit (circulating) currents of solidly bonded cable sheaths and may be neglects

except in the case of large segmental conductors and are calculated in

accordance with formulae given in the IEC60287, which for simplification of this

document is not presented.

Circulating currents are generated in cable sheath if the sheaths form a closed

loop when bonded together at the remote ends or intermediate points along the

cable route.

These losses are named sheath circulating current losses and they are

determined by the magnitude of current in cable conductor, frequency, mean

diameter, the resistance of cable sheath and the distance between single-core

cables; i.e. the mutual inductance, calculated with the following equation:

Cablesheath

Eddy currentsin cable sheath


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Is = Es / (Rs2+ Xm

2)1/2

Es = I XmXm = M x10

-3M = 0.2 ln (2S/dm)Where,

I =conductor currentXm = inductive reactance per phase including the self inductance of the conductorand the mutual inductance with other conductors.M = mutual inductance between conductor and sheaths = Cable spacingdm = sheath mean diameter (m)Is = circulating currentRs= Sheath resistance

The actual calculation of circulating currents need to take into consideration the

magnetic influence of the conductor currents in all three single core cables(conductors and sheaths), the mutual impedance between cable and sheath and

between all three cables.

In addition, for multiple cable circuits the aspect is further complicated by the

magnetic interference of circuits in close proximity. As a consequence the

calculation magnitude of induced voltages and circulating currents is done by

using specialised computer routines as indicated in the IEC60287. The cable

system and the interconnecting network represented by distributed parameters

(Impedances) and the hypothetical electrical occurrences (power frequency or

fast transients). The general model is quite complicated and requires some

computer programming and use of specialised software.

The impact of circulating currents is included in the cable rating equations as a

proportional quantity of sheath currents and sheath resistance to the conductor

current and conductor resistance in form of:

RR

II

C

S

C

S

2

2

1= (Eddy currents not included), quantity which is defined as

[Sheath Loss factor = 1] and is expressed as a proportional quantity of

the total conductor losses.

The general equation for calculation of current rating (100% load factor) is:


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By computing this equation it can be defined , the cable conductor maximumpermissible temperature rise above the ambient in the following form:

= (I2R + Wd) T1 + [I2R (1 + 1) + Wd] nT2 + [I

2R (1+ 1 + 2) + Wd) n (T3 +T4)

However in the case of a simplified cable circuit consisting of three single-corecables provided with metallic sheath and no metallic armour (2 = 0 and T3 =0)and ignoring the environmental thermal resistance (T4) the temperature risebetween conductor and cable outer surface is given with the following equation:

= I2R [T1+ T2 (1 + 1)] + Wd (T1/2 +T2)

Where: = temperature rise above ambient temperatureI = conductor currentR = A.C conductor resistanceWd = dielectric losses

T1, T2 = thermal resistances of cable insulation and anticorrosion jacket of cable.

It is seen that the Loss Factor or power loss factor 1 as generated by the

circulating currents in cable metallic sheath is impacting on the heat crossing the

anticorrosion jacket and soil thermal resistance before being dissipated in air.

2.4 Special Bonding Systems

Single core distribution power cables are normally installed with cable metallic

sheaths or metallic copper screens solidly bonded to earth at both ends.

However, in cases of high and extra high voltage single-core cables installed in

flat formation the circulating currents could be as high as the current in cable

conductors, i.e. several hundred Amps especially if the cable sheaths would be

solidly bonded to earth at both ends.

In order to minimise the sheath circulating currents the single-core cables are

very often laid in close touching trefoil formation. However, as the three cables


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have a considerable heating effect upon one another the heat dissipation is very

poor.

In order to increase the rate of heat dissipation the obvious solution would be to

increase the spacing between cables, regardless if installed in trefoil or flatformations, aspect which in return would have a direct effect of an increased

magnitude of circulating currents. A proper balance of cable spacing must be

identified to optimise the two effects; circulating currents and heat dissipation.

The solid bonding system does not have a limitation impact on cable systems of

MV of up to 33kV but with larger conductor sizes and higher voltages the impact

is significant and alternative sheath bondedind systems need to be used.

For particular cases of short HV cable circuits (few hundred metres) thetechnique of sheath special bonding systems involves earthing the single-core

cable sheaths at one point only and insulating all other points of the sheath from

earth, so that the circulating sheath losses are eliminated and the single-core

cables can be spaced apart to reduce their mutual heating effect without

increasing sheath losses.

Some of the most common Single-point Bonding arrangements are as shown in

Fig. 5

Fig. 5: Diagrammatic representation of single-point bonding systems ofcable metallic sheaths or screens and of induced voltages

V V V

0 0 01

11

a) Sheaths earthed atone end only

b) Sheaths earthed at theimmediate point

c) Sheaths earthed at both endsand sectionalised at theimmediate point


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For long cable connections, where the cable circuits consist of a series of

individual cable sections sequentially jointed, the cable sheaths are connected in

different configurations including the so called cross bonding system (Fig.6)

In this system the corresponding route length is divided in multiples of three

length of ca Each major transposition section is formed of three individual

sections of equal length and installed at equal and uniform spacing.

This solution is expected to provide balanced induced voltages at a vectorial

angle of 120of no resultant circulating current when phasorial summation was

applied.

Fig. 6: Cross-bonding system without cable transposition at each joint bay

However, this is not the case, because when single-core cables are installed in

flat formation the voltages induced in the cable sheaths of outer cables are

higher than the induced voltage in the middle cable and the vectorial (phasor)summation is not zero. As a consequence it is not possible to eliminate the

circulating currents in a cable circuit where only the cable sheaths are cross-

bonded. The imbalanced phasorial voltage (Fig.7) is generating a residual

voltage which, in return would generate circulating currents.

A C B

B A C

C B A


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Fig. 7: Imbalanced induced voltages in a major transposition section withun-transposed minor cable sections

When the cable sheaths of transposed cables occupying the same position in

circuit configuration are straight connected the vectorial summation of induced

voltage would be zero if the system would be of balanced parameters: currents,

spacing and length (Fig.8).

So, it is obvious that in order to significantly reduce or to eliminate the circulatingcurrent losses the cable and cable sheaths must be transposed at every joint bay

position and the sheaths cross-connected with phase rotation in opposition to

that of cable transposition (Fig.8). This would facilitate a direct serial connection

of the cable sheaths of the three cable sections occupying the same position in

cable trench along a major transposition section.

Smaller induced voltage

than in the 1st or 3rd

minor section

Imbalanced

difference


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Fig. 8: Typical diagram of cross-bonding system with cable transposition

By connecting in series the cable sheath of the three phases (120 phasor

displacement) the circulating currents could be eliminated; the phasor sum of

induced voltages could be zero if the geometrical data of cable circuit is uniform

along the three cable sections.

However, it is evident that in practice the circulating currents can not be totally

eliminated. There would be all sorts of site limiting conditions to install the cable

sections at equal spacing and equal length and as consequence a loss factor - 1

in range of 3% for direct buried cable circuits and 5% for cable in ducts are

considered realistic figures (IEC 60287). Even larger losses may be tolerated

based on client acceptance of higher losses balanced against capital expenditure.

A B

O = C

UB

UCUA

Fig. 9: Balanced induced voltage along three consecutivecable sheaths occupying the same position in cable trench

O C

A BUAB

UBCUOA

A B C

R

Y

B

R

Y

B


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The sheath currents and the induced voltages vary as a function of bonding

system, as follows:

i. Solid-bonded cable sheaths (earthing at both ends)

The circulating currents consume the induced voltages and as aconsequence the entire cable sheath is at ground potential. The generated

heat reduces the cable rating

ii. Single-point bonding

The cable sheaths are subjected to a standing voltage varying between

earth potential at grounding point and maximum induced magnitude at

isolated (remote or mid-point) end of cable section

iii. Cross-bonding

The maximum induced voltage in respect to earth depends on the position

of each minor transposition section within the major transposition section.

At the ends of major transposition sections the cable sheaths are at earth

potential while at all other points along the cable the voltage is

proportional to cable length in respect to earthing points or, for the median

(2nd) minor section, of measuring point in respect to the other two minor

sections.

The maximum induced voltage amplitude is generally accepted as 150V.

In special circumstances it could be as high as 250V provided that the

bonding system of cable circuit is properly designed to satisfy the

insulation coordination and safety requirements. Nevertheless there are

examples of cable installations where the induced standing voltage could

be as high as 400V.

The special bonding system requires that the metallic sheaths and cable

accessories (joints, terminations and connections to CMS condition monitoringsystem) are electrically insulated with respect to earth (radial direction) and

between two adjacent cable sections (longitudinal direction).


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The cross-bonding of cable sheaths is made in specially designed boxes,

generically denominated Link Boxes where the incoming bonding leads (single-

core or concentric conductor cables) are cross-connected.

Concentric bonding leads between link boxes and power cable joints aredesigned to minimise the surge impedance between cable sheaths and SVL

protecting the bonding system.

The link boxes are equipped with sheath voltage limiters (SVL) designed to

protect the cable outer sheath (anticorrosion jacket), insulating flanges and

barriers in cable accessories and all other insulating components of bonding

system, against transient voltages propagated along the cable system.

The effect of specially bonding systems is visible when comparing the cablerating of cables installed in solid and cross-bonded systems.

The current rating of cable system of 132kV and above could be up to 50%

higher for specially bonded cable circuits. The rating is influenced by the

following three factors:

Reduction of circulation currents

Increased spacing between single-core cables with direct response of

improved heat dissipation

Reduction of eddy current losses with the increase of cable spacing

However it is recognised that the specially bonding system increases the capital

and running (maintenance) costs of the cable system. The cost of the bonding

system for an average 220kV cable system could be in range of 1 to 1.5% of

material cost for cable and accessories.

Nevertheless these costs are compensated by savings in cable size and the

number of accessories dependent of the length of cable sections (bigger cable =

shorter length) installed in the system and the maintenance costs could be

reduced by acquisition of reliable cable bonding system including cable outer

jacket, joints (insulating barriers), bonding leads, link boxes and sheath voltage

limiters (SVL).


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Fig.10: Cross Bonding Link Box (LB)

The periodical maintenance of a reliable bonding system may be performed on a

three-year basis and even longer periods, depending on local environment and

statistical evaluation of accumulated maintenance data.

3 Conclusions and Observations

The basic factors influencing the current rating capacity of underground (U/G)

power cable systems is govern by three major factors:

a) Cable construction: conductor size, physical dimensions and quality of

materials

b) Installation particulars: single-core cable configuration and spacing,bonding of cable metallic sheaths, proximity to other utilities, thermal

influencing factors and burial depth

c) Environmental parameters: air and soil temperature and thermal

characteristics of soil and of bedding and backfilling materials

Sheath

VoltageLimiters

(SVL)

Post

insulators


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Note:The a) and b) factors are responsible for the magnitude of electrical losses

which, in return, are impacting on current rating of cable system

The calculation of losses and current carrying capacity are based on well

established international standards (IEC 60287 and IEC 60853) or nationalstandards.However, as the fine details of cable construction are very specific to each cabletype produced by each manufacturer, an accurate calculation of losses and ofcurrent rating are performed exclusively by cable suppliers using personalisedcomputer programs and softwaresIn order to verify the accuracy of cable rating and magnitude of losses the cablemanufacturers carry out full scale trial experiments simulating hypotheticalinstallation and loading conditions.

4 Bibliograpfyi. Rating of Electric Power Cables Ampacity Computation for Transmission,

Distribution and Industrial Applications. IEEE Press Power Engineering byGEORGE J. ANDERS

ii. Electric Cables Handbook BICC Cables, by G.F. MOOREiii. Underground Transmission Systems Power Technologies Inc. (J.A.

Williams) & EPRI (RW Samm).iv. IEC 60287 Electric cables Calculation Part 1: Continuous rating

equations (100% load factor)and calculation of losses

R01 HMR Connection to 220kV Main Grid Undergrounding Study Attachment1 Appendix5and6

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