6-36kV Medium Voltage Underground Power Cables

1 6-36kV Medium Voltage Underground Power CablesXLPE insulated cablesMedium Voltage Underground Cables2 cable solutions to ensure the reliability of your energy networkWith energy as the basis of its development e ans the worldwide leader in the able industry offers an e tensive range of ables and abling systems he roup is a global player in the infrastru ture industry building and o al Medium Voltage Underground Cables3 rea etwork markets e ans addresses a series of market segments from energy transport and tele om networks to shipbuilding oil and gas nu lear Power automotive ele troni s aeronauti s handling and automation Medium Voltage Underground Cables4 CABLEl cable Power circuit design 7n Conductor 7-8n Conductor screen 8n insulation 8n insulation screen 8-9n Metallic screen 9-10n Outer protective sheath 10-11l Table of cable ele ents 1 l cable constructions 1 l cable dru s 1 l cable tests following production 1 ACCESSORIESl Introduction 1 l Connectors and lugs 1 l lectrical fields 17l Ter inations 17n ea age path and creepage distance 17-18n lip-on ter ination 18n eat-shrin able ter ination 18n Cold-shrin able ter ination 18l creened separable connectors 18-19l urge arresters 19l oints 19n Transition oints 19 IIIC ontentspageMedium Voltage Underground Cables5 INSTALLATIONl cable ru andling 0l Installation nviron ent 0l T pe of installation 1l Installation Te perature l ulling orces l ending adii l cable upport pacing l pecial Civil ngineering or s l Tests after installation l Current ratings TECHNICAL SPECIFICATIONSl Introduction l 8 7 Three Core ar oured copper conductors 7 l 11 1 Triple ingle Core unar oured copper conductors 8l 11 1 Triple ingle Core unar oured alu iniu conductors 9l 11 1 Three Core unar oured copper conductors 0l 11 1 Three Core unar oured alu iniu

2 Conductors 1l 11 1 ingle Core ar oured copper conductors l 11 1 ingle Core ar oured alu iniu conductors l 11 1 Three Core ar oured copper conductors l 11 1 Three Core ar oured alu iniu conductors l 8 7 1 17 ingle Core ar oured copper conductors l 8 7 1 17 Three Core ar oured copper conductors 7l 1 0 ingle Core copper unar oured conductors 8l 1 0 ingle Core ar oured copper conductors 9l 1 0 Three Core ar oured copper conductors 0l 19 ingle Core unar oured copper conductors 1l 19 ingle Core unar oured alu iniu conductors l 19 ingle Core ar oured copper conductors l 19 Three Core ar oured copper conductors pageIIIIVAll the data given in this brochure is com-municated for information only and is not legally binding to NexansMedium Voltage Underground Cables6 General Power circuit design his bro hure deals with Underground Power ir uits featuring three-phase C Voltage insulated able with a rated Voltage between 6 6kV and 36kV hese lines are mainly used in a distribution network for ele tri al Power onne ting lo al substations or small generating units su h as wind turbines to the main grid supply point or for onne ting plant in industrial pro esses whi h re uire large amounts of Power Medium Voltage insulated ables may also be used in on un tion with bare overhead lines in networks The Voltage of a circuit is designated in accordance with the following principles a ple U U U Phase-to-ground Voltage designated o is the effective value of the Voltage between the conductor and the ground or etallic screenRated Voltage designated is the effective phase to phase Voltage Maximum Voltage designated is the per issible highest Voltage for which the e uip ent is specified In addition the basic impulse level I deter ines the a i u capacit an e uip ent will withstand if

3 Sub ected to a lightning stri e The rated Voltage of a ediu Voltage cable is deter ined b the thic ness of the insulation nli e high Voltage Cables which do not have set values for the insulation thic ness the thic ness of the insulation around a conductor in a ediu Voltage cable is set at specified levels according to international standards The general Voltage levels covered b this publication are Medium Voltage insulated cable circuit consists of three single core Cables or one three core cable with terminations at each end to connect it to the transfor er or switchgear in the networ The ter inations a be outdoor ounted on a pole or indoor t pe in a screened enclosure hen the length of the circuit e ceeds the capacit of a cable dru joints are used to connect the lengths together To ensure the cable is fi ed fir l in place under an echanical or electrical stress cable cleats will be used to fi it to surfaces U V p ase t g und ltageU V ated p ase t p ase ltage U V ig est pe issible ltage t e g idUo kV U kV Um kV kV nsulation hi kness minimum average 8 7 0 111 9 8 71 17 1 0 1 7 0 1 19 19 8 0 Medium Voltage Underground Cables7 The cableThe structure of ediu Voltage Cables with e truded insulation will alwa s involve the following ite s C UC C or ediu Voltage Cables conductors are rated b their effective cross sectional area in this indicates how uch current can flow through the conductor i e the larger the conductor the greater the a ount of current Conductors for ediu Voltage are nor all used in the range fro up to 1000 and are usuall either co pacted stranded or solid construction In so e three core designs sector shaped conductors can be used to reduce the overall dia eter of the cable s copper has a lower electrical resistance than alu iniu it is a ore efficient conductor of electrical current and re uires s aller cross sections to carr the

4 Sa e a ount of Power as an alu iniu conductor or e a ple a copper conductor of 00 cross section can carr appro 70 ps in a buried installation et an alu iniu conductor will carr onl appro ps under the sa e conditions It would re uire a larger cross section of 00 to achieve the sa e rating owever alu iniu is substantiall lighter than copper and therefore has the advantage of enabling longer lengths to be safel handled eaning less ointing lso alu iniu is generall lower in price than copper on the etals co odit ar ets a ing it ore econo ical per a p than copper Therefore alu iniu conductors are usuall used for ediu Voltage distribution networ s re uiring long distances and e tensive cabling whereas copper Cables are used for short lin s in substations and industrial installations where s aller Cables or higher Power trans itting properties are re uired tranded conductors consist of several la ers of spiral wound wires which are co pacted together The are nor all constructed as Class according to I C 0 8 0 8 although it is possible to use Class fle ible stranded conductors in con unction with th lene rop lene ubber insulation for short leads s stranded conductors will have spaces in the interces there a be a re uire ent to longitudinall water-bloc the conductor b using water swellable powders or tapes in the conductor construction These aterials will bloc the travel of an oisture through the conductor if it was to enter at a ter ination or oint position lu iniu conductors are usuall water-bloc ed to prevent the corrosive reaction with water but copper Cables are nor all not specified with these aterials unless the cable is to be used in ver wet conditions e g subsea Cables lu iniu solid conductors b their design are water-bloc ed and usuall are of slightl reduced dia eter than the e uivalent stranded versions owever it is usuall too difficult to

5 Handle these conductors for ter inating and ointing for cross sections above 00 Compa t round ondu tors omposed of several layers of on entri spiral-wound wires Medium Voltage Underground Cables8 round the conductor it is necessar to provide insulation to prevent electrical short circuits In ediu Voltage Cables there are two ain t pes of insulation aterial l Cross lin ed ol eth lene the ost co on aterial for M Cables toda l th lene ropene ubber ore fle ible than but not as efficient at reducing losses in circuits as Cables used in arine and offshore applications are nor all constructed with insulation Note:As the most common type of insulation , all data provided in this handbook is based on Cables with XLPE insulation . ccording to the re uire ents of various standards Cables for ediu and high voltages re uire three specific la ers of e truded aterial around the conductor to for the insulation s ste These la ers are nown as the conductor screen insulation and insulation screen and are nor all e truded in one operation nown as triple pass or triple e truded M -C UC C C UC W C UC C This consists of a la er of blac se i-conductive cross lin ed co pound usuall less than 1 0 in thic ness which is the interface between the conductor and the insulation The e ternal surfaces of the conductor a not be s ooth particularl for stranded conductors so this la er provides a s ooth surface at the sa e potential as the conductor to eep the electric field consistent all the wa around the surface ithout this la er an s all pea s or troughs could cause concentrations of electrical energ which could create s all arcs and over ti e could erode the insulation la er

6 And cause failure of the cable The conductor screen is full bonded to the ad acent insulation la er U s its na e suggests the insulation insulates the conductor at Voltage fro the outer screens which are at ground potential The insulation ust be of sufficient thic ness to withstand the electric field under the rated and transient operating conditions see the table on insulation thic ness in previous section ue to the cross lin ing structure of it enables the Cables to run safel at higher te peratures than ther oplastic aterials such as C and therefore carr ore current The continuous current ratings found in this docu ent are based on conductor te peratures of 90 C which is the accepted a i u nor al wor ing te perature for Cables in service In a short circuit the can acco odate conductor te peratures of up to 0 C In three core ediu Voltage Cables the insulation is left in its natural colour and is not used for core identification this is achieved b either printing on the insulation screen or colour coded tubes between the cores or ar er tapes M -C UC V C U W U C This la er has a si ilar function to the conductor screen it provides a s ooth transition fro the insulating ediu to the grounded etallic screen This is a la er of blac cross lin ed se i conductive co pound of appro 1 thic ness and is either full bonded to the insulation la er or can be cold strippable b hand hen ter inating or ointing the Cables it is necessar to re ove a part of the insulation screen for full bonded insulation screens this cable omponentsSC c nduct sc een SC insulati nsc eenC nduct Insulati n etallics eat Anti c si n s eat The cableMedium Voltage Underground Cables re uires a special rotar stripping tool with blades at pre-set depths to consistentl re ove the blac se i-conductive la er without re oving the insulation Cold trippable screens so eti es referred to as eas strippable do

7 Not re uire such tools and can be peeled off the insulation leaving a clean la er of insulation owever it can be ore difficult to a e a s ooth tapered transition between screen and insulation with the cold strippable screen and special care has to be ta en when using nives or other tools to achieve this The rotar stripping tools for bonded screens can leave a s ooth tapered edge at the end of the screen which reduces an electrical stress at this transition point or all three core Cables are specified with cold strippable screens as it is difficult to get the rotar tools in between the ad acent cores ingle cores particularl at the higher Voltage levels tend to be full bonded M C C The ain function of the etallic screen is to nullif the electric field outside of the cable it acts as a second electrode of the capacitor for ed b the cable The screen needs to connect to earth at least at one point along the route The capacitive charging current and induced circulating currents which are generated under nor al operating conditions will be drained awa through the screen The screen also drains the ero-se uence short circuit currents under fault conditions this function is used to deter ine the re uired si e of the etallic screen The second function of the etallic screen is to for a radial barrier to prevent hu idit fro penetrating the cable insulation s ste The e truded insulation s ste should not be e posed to hu idit hen hu idit and a strong electric field are present together the insulation deteriorates b what is called water-treeing which can eventuall cause the insulation to fail Note.

8 In the case of an overhead line, the insulation is formed by the air between the bare conductor and the cableCopper Wire reen with e uali ing tapeC ppe i e Sc een it a c ppe e uali ing tapeC nduct C e XLPE insulati nSepa at tape ate s ellable tapePE S eat C nduct C e XLPE insulati nC ppe i e Sc eenAlu iniu il la inatePE S eat aminate foil sheath with additional opper wiresC nduct C e Se i c nducti e tapeXLPE insulati nE t uded Lead all s eat PE S eat ead heathMedium Voltage Underground Cables P M C C Concentric Copper Wire screens (with optional equalising tape).Advantages:l ightweight and cost effective design l igh short-circuit capacit l as to ter inate Drawbacks:l ow resistance of screen a necessitate need for special screen connections to li it the circulating current losses l oes not for a co plete oisture barrier unless water swellable tapes are used under and or over the copper wires Aluminium foil laminateAdvantages:l ightweight and cost effective design l Moisture proof radial barrier Drawbacks:l ow short circuit capacit l More difficult to ter inate re uires special screen connections truded lead allo sheathAdvantages:l aterproofing guaranteed b the anufacturing process l cellent resistance to corrosion and h drocarbons suitable for oil and gas plants Drawbacks:l eav and e pensive l ead is a to ic etal whose use is being restricted in so e countries l i ited capacit for short circuits Other etallic screen constructions such as copper tape screens can be used also co binations of th