LV cables

 PART 1 GENERAL

1.1 The scope of works involve the supply, installation, testing and commissioning of all low voltage cables, sub-mains circuits and final circuits to provide electricity supplies to all electrical and mechanical equipment, equipment of statutory bodies, tenants including lighting points and power points.

1.2 The wirings covered under this contract shall include:-

 

i. PVC insulated and sheathed and PVC insulated cables for all sub-mains and final sub-circuits to electrical fixtures in trunkings, trays or conduits;

ii. Fire resistant cables for all mains to the direct termination, emergency MCCB distribution panels all submains between MCCB Panels & MCB distribution panels, all final sub-circuits from the distribution panels to lightings and equipment on emergency circuits;

iii. Fire resistant cables mains between the low tension switchboards and the generator;

iiv. Control cables

v. Any other as indicated in the drawings; and

vi. All other incidentals interconnections including all necessary transformation sections for busduct connection.

1.2 The contractor shall ensure that all conductors are adequately sized so that voltage drops are within limit set by the Code of Practice, and that the short circuit capacity (I2t) at any point. The Contractor shall be required to submit calculations for verifications when directed by the Employer.

 

PART 2 PRODUCT

2. CABLES  

 

2.1 PVC Insulated and Sheathed Cables

i. Except where otherwise specified, all cables shall be PVC insulated and sheathed or PVC insulated of approved manufacture of 450V/750V grade as applicable and conforming to BS 6231 type BK, BS EN 60228, BS 6004 and subsequent amendments whichever is applicable. Cables shall be delivered to site in the maker's standard packing with seals and labels intact, except that cables larger than 4 mm2 may be delivered in required lengths. Only cables with the maker's identification clearly visible shall be used. The cable size shall be selected to ensure that they have adequate current carrying capacity and that the voltage drop at the apparatus served will not be excessive. Consideration should be given to the possible de-rating of cables in conduits.

Multi-strand conductors with a minimum of three strands shall be used. All cables terminated at equipment, isolators, load switch, switchboard, etc. shall be equipped with cable gland to BS 6121-1.

 

2.2 Armoured Cables

i. The cables shall be single layer wire armoured with galvanised steel wires of a nominal diameter of not less than 1.60 mm complying with BS EN 10257-1 which shall be laid on a PVC bedding extruded over this insulation.

ii. Outer sheathing shall be of extruded PVC having a radial thickness of not less than 1.2mm and shall be coloured black.

iii. Compression type glands shall be provided for the termination of all PVC/SWA/PVC cables.

iv. Compression glands shall comply with BS 6121-1 and shall be designed for the termination and clamping of armour wires and shall be fitted with an earth bond terminal attachment. It shall be possible to erect and dismantle compression glands without the use of special tools.

v. All cables entering or leaving equipment shall be provided with separate termination so that any one cable can be removed without disturbing the remainder.

vi. No straight through joints shall be used without the expressed written authority of the Employer.

 

2.3 Fire Resistant Cable

i. The fire resistant cable shall be of 600/1000 volts grade, suitable for surface wiring and wiring in conduit or duct. The cable shall be fire resisting, oil resistant and flame retardant to IEC 60331, BS 6387 Cat C, W, Z and IEC 60332-3 Cat A. The fire resistant cable shall have low smoke and halogen content complying with IEC 61034 and IEC 60754-2. It shall be approved by the local authority for use as fire resistant cables in emergency circuit applications. Test Certificates to substantiate the compliance to IEC standards shall be submitted with the tender.

ii. The conductor shall be made of stranded, soft annealed copper wires to IEC 60228 Class 2. The outer jacket shall be made of fire retardant halogen free PVC. Core identification of the cable shall be by colour of the insulation according to IEE Wring Regulation 17th Edition or BS7671 or the latest revision. The maximum resistance of the conductors at 20C shall not exceed that specified in BS 60228.

iii. The cable and accessories shall be designed for operation up to a conductor temperature of 90C.

iv. The cable shall be suitable for installation by conventional methods without requiring expensive special tools, seals or terminations. They shall be non-hygroscopic, maintenance free and insensitive to vibrations.

 

2.4 Multipair Control Cables

The multi-pairs control cable shall conform to BS EN 60811 suitable for operation on 110V DC. The control cables shall be PVC insulated with lead alloy sheath, copper tape shielding, and PVC outer sheath.

 

The conductors shall be high conductivity copper wire and shall comply to BS EN 60228 and tested for solderability to BS EN 60068. The conductors shall be individually insulated with colour coded PVC to BS 6346, twisted into pairs, right hand laid to form a compact, symmetrical multipair cable.

MV cables

 PART 1 GENERAL

1.1 Introduction

a The intent of this Specification is to define the technical requirements of 17.5KV cross-linked polyethylene insulated armour power cables auxiliary cables and accessories.

b The power cables auxiliary cables and accessories shall be designed and constructed in accordance with the most up-to-date experience for a system of this voltage level and shall incorporate the latest improvements of design and manufacture for the type of power cables required as currently employed in the industry.

 

 

 1.2 Scope of Work

a The works shall comprise the design, manufacture, type testing and routine testing at manufacturer's premises, supply and delivery to site and installation, testing and commissioning at site of 17.5KV power cables, auxiliary cables and accessories for cable network and transformer circuits as specified.

b The Contractor shall survey the cable routes and propose suitable cable system designs and submit prices for the cable routes on the basis of his design.

c The total price shall include for all items which are required for the completion of the cable system design including all cable bridges, road crossing pipes and other items required on site. The Contractor shall survey the proposed cable routes to determine all the items required, taking into special consideration the soil condition at the site.

 

 

 d On notification by the Employer that his tender has been accepted, the Contractor shall immediately survey the routes in detail to determine the actual quantities of materials to be supplied and delivered and all items of work to be done. The final cable route design shall be to the approval of the Employer.

e The Contractor shall also submit unit rates for all individual items of plant and materials to be supplied and delivered and all items of work to be done in the Schedule of Rates.

g All items of accessories, fittings, sundries, apparatus or labour which cannot be specified in detail but which in the opinion of the Employer are usual or necessary for the satisfactory completion of the works shall form part of the scope of the works and shall be deemed to be included in the total contract price.

 

1.3 Standards

All plant items shall be designed, manufactured and tested generally in accordance with the latest revision of the following Standards except where specifically directed otherwise:

Item Standard

Cross-linked polyethylene insulated IEC 60502

power cables

Pilot cable, supervisory control BS-3573

and telephone cables

Annealed copper for cable BS EN 60228

conductor IEC 60228

Insulation polyethylene BS 6234

Lead and lead alloy sheaths for

electric cables BS EN 50307

High voltage test techniques BS 923

IEC 60230, IEC 60060

Determination of current ratings

of power cables IEC 60287, IEC 60059

Guide to the short-circuit temperature limits of

electric cables with a rated voltage

From 1.8/3 (3.6) kV to 18/30 (36) kV IEC 60986

Smoke density of cables IEC 61034

Gas emission of cables during combustion IEC 60754

Earthing IEC 60364-5-54

 

IEC stands for International Electrotechnical Commission, BS stands for British Standard.

If the specifications conflict in any way with any of all of the above standards, the Specifications shall have precedence and shall govern.

Where deviation from the above standards is minor, the approval of the Employer may be given to the use of other national or international standard prevalent in the Country of manufacture. No departure from the standards specified will be considered after the contract has been awarded unless specific authorization in writing has been granted by the Employer.

 

1.4 Cable Network

The 17.5KV power system network for which the cables are required is shown in the drawings. Cables sizes for all feeders and switchgears to transformer connections are indicated.

1.5 Auxiliary Supply Voltages

The auxiliary supply voltages shall be 220/380 volt ac and 24 volt dc.

 

 

PART 2 PRODUCT

2.1 Power Cable and Accessory Ratings

The 17.5KV power cables and straight through joints shall be rated in accordance with the relevant standards in 1.3 of this Technical Specification and as follows:

a Rated frequency : 50Hz

b Rated insulation level :

i Rated voltage : 17.5KV

ii Five-minutes single

phase AC voltage : 30.5KV

iii Impulse withstand voltage : 95KV peak

2.2 Basis for calculation of Rated Current

The cables shall be laid directly in the ground and the calculation of rated current shall be based on the following conditions:

a Ground thermal resistivity : 1.2 0 CM/W

b Maximum ambient

temperature (Aiv) : 36.1 0C

c Average ambient

temperature (Aiv) : 30.1 0C

d Ground temperature : 30 0C

e Depth of burial (measure

to the top of the cable) : 1000mm

 

2.3 CROSS-LINKED POLYETHYLENE INSULATED POWER

CABLES AND ACCESSORIES

2.3.1 Type of power cables

The power cables shall be the cross-linked polyethylene insulated, shielded, copper tape screened, high density polyethylene oversheathed type with stranded copper conductors, of 3 core construction and shall be in accordance with the relevant standards in Clause 1.3 of this Technical Specification.

All cables in the basement of the building shall meet the flame test requirements in IEC 60332 Part 1 and IEC 60332 Part 3 Category A. The cable sheath and bedding shall have flame retardant characteristics corresponding to a critical oxygen index of not less than 30 percent at an ambient temperature of 300C, and have a temperature index of not less than 2600C when operating in normal atmosphere. During combustion, the insulation, bedding and sheathing materials shall emit zero halogen gas complying with the requirement of IEC 60754 and produce minimal smoke complying with IEC 61034.

 

2.3.2 Conductors

The copper conductors shall be annealed, compacted and shall comply with the requirements of the relevant standards in 1.3 of this Technical Specification. The copper used shall have an International Standard Conductivity of 100 percent.

Conductors having an improved space ratio will be considered provided the resistance does not exceed that of normal stranded conductor. The d.c. resistance shall not exceed values stated by the Contractor in the Schedule of Guarantees.

2.3.3 Conductor Semi-conducting Layer

Conductors shall have an extruded semi-conducting polyethylene layer to minimise electrical stresses due to the stranded configuration of the conductor. The semi-conducting material used for conductor shielding shall have no deleterious effect on the conductor.

The thickness of the layer shall be stated in the Schedule of Guarantees.

2.3.4 Insulation

The insulation material shall be extruded cross-linked polyethylene of low dielectric loss, high dielectric strength, low thermal resistivity and long term stability. It shall be free from contamination by oil, chemicals and moisture. The extrusion process shall ensure that the insulation is homogenous and free from voids from impurities which can initiate corona deterioration or treeing under service conditions.

Full details of the manufacturing process shall be submitted with the tender.

The thickness of the insulation when determined by the method specified in 3.41 in this Technical Specification shall not be less than the minimum value. The minimum thickness shall be determined taking into consideration not only the power frequency voltage stresses at withstand voltage tests and impulse voltage tests.

2.3.5 Insulation Semi-conducting Layer and Core Screen

An extruded semi-conducting polyethylene layer shall be provided over the insulation of each core to minimise the possibility of ionisation on the outer surface of the dielectric. Over the layer shall be applied a screen of nonferrous metallic tape.

2.3.6 Extrusion

The semi-conducting polyethylene conductor shield, the insulation and the insulation shield shall be extruded in tandem in one process to ensure that the shield and insulation are intimately bonded together and free from all possibilities of voids between components. The extrusion process shall be carried out under strictly controlled atmospheric conditions. Complete description of such processes shall be submitted at the time of tendering.

2.3.7 Laying up

The cores shall be laid up together with suitable fillers and covered with further layers of polyethylene tapes to form a compact circular cable.

2.3.8 Cable Metallic Screen

A metallic screen consisting either of two lapped copper tapes wound in opposite directions or two layers of annealed copper wires with reversed lay shall be provided over the laid up cores.

The cross-sectional area of the copper screen shall be adequate to

cater for the maximum power system earth fault current.

2.3.9 Double Steel Tape Armour / Polymeric Mechanical Shock Absorber (PSA)

The armour shall consist of two layers of steel tape, applied either by the hot dip or the electro galvanizing process. The zinc coating shall remain adherent during normal installation bending of the cable.

The nominal thickness of the steel tape shall be 0.5 mm with a maximum allowable tolerance of + 10%.

The steel tape shall have a tensile strength in the range of 275 N/mm2 to 480 N/mm2.

 

Alternately, acceptable mechanical protection is a layer of extruded polymeric material shall be applied between the fillers and the outersheath. This layer shall provide, to the complete cable, a similar or better mechanical shock protection with respect to the traditional armoured cable.

2.3.11 Over-sheath

The oversheath shall be an extruded layer of PVC over the entire screened cable cores.

The outersheath shall be embossed with the manufacturer's name and the legend "17.5KV XLPE ELECTRIC CABLE.........." along each of two or more lines approximately equally spaced around the circumference of cable.

The embossed letters/figures shall be raised and consist of upright block letters/figures not less than 15% of the nominal or specified external diameter of the cable expect that in no case shall they be greater than 13mm.

The outersheath shall be graphited for ease of laying.

 

2.3.12 Cable Drum

Cables shall preferably be wound on steel drums. Wooden drums and drum battens shall be suitably impregnated with an approved wood preservative, preferably under pressure against dampness dry rot and termites.

Each cable drum shall have an identifying number distinctly displayed and shall either by branded or displayed on the outside of the flange. Full particulars of the cable ie voltage, length, conductor size, number, gross and nett weight together with an arrow showing the direction for rolling shall be clearly shown on the drum.

Pulling eyes shall be fitted at the manufacturer's premises to every length of cable before despatch.

The power cable shall be of 500 metre drum length.

 

2.3.13 Power Cable Accessories

Power cable straight through joints shall be a type that will ensure that electrically the joints are equal to the cable.

The conductors shall be connected by the compression type of connectors. The semi-conducting conductor layer, cross-linked polyethylene insulation and the semi-conducting layer over the core insulation may be built up by applying void free tapes over the conductor or by the moulding process.

The metallic screen tapes or wires of the cables shall be connected together by welding or by compression to ensure good conductivity of the screen.

The outersheath of PVC shall then be applied over the finished joint.

The jointing of XLPE power cables shall not require complicated techniques or tools.

Each joint shall be complete with all its jointing material, compression type conductor connectors, stress core material, etc. A list of all items supplied with a joint shall be submitted by the Contractor.

All jointing materials necessary for the termination of the type of power cables to the switchgear and transformers shall also be supplied.

 

2.4 AUXILIARY CABLES AND ACCESSORIES

2.4.1 Types of Auxiliary Cables

The auxiliary cables to be supplied and installed with the power cables shall be as follows:

a Protective equipment pilot cables

b Control cables

2.4.2 Protective Equipment Pilot Cables

Pilot cables for use with protective equipment (pilot wire protection, intertripping etc) shall be of 10 pairs, twisted paired type, local graded, polyethylene insulated, polyethylene oversheath and bitumen coated steel tape armoured. Conductors shall be of high conductivity copper and shall be of 1.5mm². Except where otherwise specified the cables shall comply with BS 3573 tab3 for core identification.

After the cores have been laid up a core binder shall be applied and over the complete assembly shall be a polyethylene sheath. A copper shielding tape shall then be applied over the polyethylene sheath and a further polyethylene oversheath shall be applied over the copper tapes. The armouring tapes and an outer serving of PVC shall be provided over the polyethylene oversheath.

 

2.4.3 Pilot Joints

Straight through joints suitable for the type of pilot cables to be supplied shall be provided. The design of the joints shall be to the approval of the Employer.

2.4.4 Control Cables

Control cables shall be of multi-pairs, twisted pair type, local graded, polyethylene insulated, bitumen coated steel wire armoured and PVC oversheathed. Conductors shall be of high conductivity copper and shall be of 1.5mm² or 2.5 mm² as indicated in the relevant drawings. Except where otherwise specified the cables shall comply with BS 3573. Insulation polyethylene shall comply with BS 6234.

The cores of the cables shall be colour-coded in accordance with B.P.O. CW-128L.

2.4.5 Control Cable Joints

Straight through joints for the type of control cables to be supplied shall be provided. The design of the joints shall be to the approval of the Employer.

 

2.4.6 Cable Drum

Cables shall preferably be wound on steel drums. Wooden drums and drum battens shall be suitably impregnated with an approved wood preservative, preferably under pressure against dampness, dry rot and termites.

Each cable drum shall have an identifying number distinctly displayed and shall either be branded or displayed on the outside of the flange. Full particulars of the cable ie voltage, length, conductor size, number of cores, drum number, gross and nett weights together with an arrow showing the direction for rolling shall be clearly shown on the drum.

Pulling eyes shall be fitted at the manufacturer's premises to every length of cable before despatch.

The auxiliary cables shall be of 1000 metres drum lengths.