TABLE OF CONTENTS 7.0 CABLE INSTALLATION IN UNDERGROUND STRUCTURES

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2 TABLE OF CONTENTS 1.0 SCOPE 2.0 BURIAL DEPTH 3.0 MINIMUM BENDING RADIUS FOR POWER CABLES 4.0 PULLING TENSIONS AND SIDEWALL PRESSURES 5.0 PARAMETERS OF CABLE PULLING 6.0 DIRECT BURIED CABLE INSTALLATION 7.0 CABLE INSTALLATION IN UNDERGROUND STRUCTURES 8.0 CABLE TRENCH DESIGN PARAMETERS PAGE NO. 2 OF 26

3 TABLES Minimum Cover Requirement in mm from Grade Level to the Top Surface of a Cable or Duct Minimum Bending Radius for Power Cables Coefficient of Friction Minimum Allowable Percent Conductor Cross-Section Within a Conduit or Duct Clearances of SEC Cables and other utilities PAGE NO. 3 OF 26

4 FIGURES Typical Cross-Section of Trench for 110 kv, 115 kv or 132 kv XLPE Power Cable; Single Circuit, Trefoil Formation, Direct Burried Typical Cross-Section of Trench for 110 kv, 115 kv or 132 kv XLPE Power Cable; Single Circuit, Trefoil Formation, Concrete Ductbank Typical Cross-Section of Trench for 110 kv, 115 kv or 132 kv XLPE or LPOF Power Cable; Single Circuit, Flat Formation, Direct Burried Typical Cross-Section of Trench for 230 kv or 380 kv XLPE or LPOF Power Cable; Single Circuit, Flat Formation, Direct Burried Typical Cross-Section of Trench for 110 kv, 115 kv or 132 kv XLPE or LPOF Power Cable; Single Circuit, Flat Formation, Concrete Ductbank Typical Cross-Section of Trench for 230 kv or 380 kv XLPE or LPOF Power Cable; Single Circuit, Flat Formation, Concrete Ductbank Recommended Clearances Between SEC Underground Power Cables 110kV to 132kV and Other Utilities's Lines Recommended Clearances Between SEC Underground Power Cables 110kV to 380kV and Other Utilities's Lines PAGE NO. 4 OF 26

5 1.0 SCOPE The purpose of this section is to provide design considerations of cable installation for direct buried or duct applications in the system of Transmission Business Unit (TBU) of Saudi Electricity Company (SEC), Kingdom of Saudi Arabia. 2.0 BURIAL DEPTH 2.1 Unless otherwise required at greater depths by Agency/Ministry having right-of-way jurisdiction, or due to adjacent utilities limitations or ampacity requirements, the burial depths for conduit and cable shall be as shown in Table Table 05-01: Minimum Cover Requirements in mm From Grade Level To the Top Surface of a Cable or Duct Voltage Direct Buried Cables Direct Buried Conduit Direct Buried Rigid Steel Conduit (kv) Type A Type B 110 to Type A: Type B: Light Traffic Areas Heavy Traffic Areas 2.2 For paved roads, the grade level is the surface immediately below the concrete or asphalt pavement. Subgrade is another term for this surface. For unpaved roads or areas, the grade level is the road shoulder surface or natural ground level. 3.0 MINIMUM BENDING RADIUS FOR POWER CABLES 3.1 Bending of Power Cable at a short radius may damage the insulation, shielding or jacket of the cable, therefore, during cable installations, care must be taken that no sharp bends or sharp twists are made. Whenever angles and/or bends in the route are encountered, care shall be taken to ensure that the rollers are properly positioned so that the allowable bending radius of the cable is not exceeded. 3.2 The rollers shall be adequately braced against tensions and side pressure that will be encountered during the cable pull. The transition through the angle and/or bend shall be uniformed to conform to the arc of a circle. Radii at the angles shall be as large as practical to minimize pulling tensions and sidewall pressures. The bending radii shall match those used in tension and sidewall pressure calculations. 3.3 Power Cable's bending radius shall not be less, under any circumstances, than the recommended values given by the power cable's manufacturer. 3.4 The cable shall not be bent to less radius than the drum's radius of the cable reel on which it was shipped. PAGE NO. 5 OF 26

6 3.5 Minimum bending radius (r) to which cables may be bent refers to the inner surface of the cable and not to the axis of the cable at the bend as shown in the below figure: The minimum bending radius for permanent training during cable installation shall be as shown in Table During cable installation, large diameter wheels, pulling sheaves, and cable guides shall be used to maintain the specified bending radius. Larger radii are recommended wherever the cable is being pulled under tension, preferably not less than twice the values for permanent training. Table 05-2: Minimum Bending Radius for power cables Type of Cable Minimum Bending Radius (r) as a multiple of Cable Diameter (d)* Permanent Training Radius(mm) Pulling Under Tension Radius(mm) Single Core Cable - Shielded r = 8 d r =16 d Single Core Cable- Non shielded r =10 d r =20 d Multi Core Cable - Shielded r = 6 d r =12 d Multi Core Cable- Non shielded r = 8 d r =16 d Single Core Cable with segmental r =12 d r =24 d Conductor Armored Cable r =12 d r =24 d Corrugated Al. Sheathed r =15 d r =30 d * Note : In case the cable manufacturer recommends larger bending radius, his recommendation shall be complied with. PAGE NO. 6 OF 26

7 4.0 PULLING TENSIONS AND SIDEWALL PRESSURES 4.1 General The axial and tangential forces applied during the pulling process shall not damage any component of the cable assembly during the installation of XLPE, UGNMFOC and LPOF Cables When installing cable in vertical runs, pulling the cable from the top of the run rather than the bottom will greatly reduce the pulling tension, and reduce mechanical forces on the cable accordingly Detailed maximum pulling tension and sidewall pressure calculations with the route drawings showing bending radii, roller placement and dimensions shall be developed and submitted to SEC (TBU) for each specific cable pull section within the cable route. The maximum values shall not exceed the values specified and recommended by the cable manufacturer Detailed cable pulling calculations shall be submitted to SEC (TBU) for approval and review prior to all cable pulling operations Pulling calculations and drawings which indicate the maximum allowable pulling tensions and sidewall pressure, shall be provided to pulling crews prior to all cable pulls The placement of all rollers that conforms to the radii bends and degree angle curves shall be verified prior to commencing the cable pull The tensile capability of every cable formation is dependent upon the tensile limitations of the conductor plus the overall integrity of the cable design. Each factor has finite limitations which shall not be exceeded. 4.2 The maximum pulling tension placed on a cable shall not exceed the following For cable equipped with a pulling eye or bolt attached to the conductor. a. For copper of any temper and hard-drawn aluminum, maximum tension in newtons (N) is equal to times the cross-sectional area of the conductor in square millimeters (mm 2 ). b. For 75% hard-drawn aluminum, maximum tension in newtons (N) is equal to times the cross-sectional area of the conductor in square millimeters(mm 2 ). PAGE NO. 7 OF 26

8 4.2.2 For cable to be pulled with a cable grip over the sheath: a. For a cable with a lead sheath, maximum tension in newtons (N) is equal to times the lead cross-sectional area in square millimeters(mm 2 ). b. For cable with copper or aluminum sheath, the maximum pulling tension shall not exceed 4.45kN newtons and, shall not exceed the maximum tension calculated in accordance with paragraph above. c. If manufacturer recommends less maximum tension to be placed than the specified above, his recommendation shall be followed The pulling tension (T) for a given installation shall be calculated from the following formulas or shall be as per manufacturer s requirements: For a straight section: T = 9.8 x L x W x f x OF x N (Eq.05-1) Where: T = Pulling tension in newtons L = Length of duct run in m W = Weight of cable plus 1% allowance per single core cable in Kg/m f = Coefficient of friction (generally assumed as 0.5) OF = Occupancy factor N = Number of cables per duct Coefficient of friction shall be usually taken as 0.5. For new installations where ducts are well aligned and clean and the cable well lubricated, a value lower than 0.5 shall be used. Table 05-03: Co-efficient of Friction Jacket Pulling on Roller Pulling into duct Material Without Lubricant With Lubricant Polyethylene 0.1~ ~ ~ 0.25 PVC 0.1 ~ ~ ~ 0.35 a. For single-core cable per duct, equation becomes: T = 9.8 x L x W x f (Eq.05-2) Where: OF = 1 N = 1 PAGE NO. 8 OF 26

9 b. For three single-core cables in trefoil formation: For a duct with a bend: 1 OF = (Eq.05-03) 2 d 1 D d Where: d = Outside diameter of each cable in mm D = Inside diameter of duct in mm T Te fa 2 = 1 (Eq.05-4) Where: T 2 = Tension for the straight section following the bend in newtons T 1 = Tension for the straight section proceeding the bend in newtons e = Naperian log base (2.718) f = Coefficient of friction a = Angle of bend in radians 4.4 The maximum sidewall pressure shall not exceed kn/m, i.e. the tension in the cable in kilonewtons as it leaves the bend shall not exceed times the radius of the bend in meters. 4.5 The following example outlines the applicable tensile considerations for duct installation. Similar factors are applicable for direct buried cables. For a sample calculations, assume the following: Example: A duct with the following layout: Cable: Three single-core, 240 mm², copper, shielded, triplexed Conduit inside diameter = 154 mm Dimension: Weight = 3.15 kg/m per core Outside diameter = 41.3 mm per core Insulation thickness = 4. mm Assume f = 0.5 PAGE NO. 9 OF 26

10 4.5.1 Pull from point (A) to point (F) in Newtons (N) and meters (m): Normally the tension calculation is a progressive one as follows: 1 OF = = T B = 9.8 x 60 x (3.15 x 1.01) x 0.5 x 1.07 x 3 = 3002 N T C = 3002 x 1.48 = 4442 N T D = [9.8 x 20 x (3.15 x 1.01) x 0.5 x 1.07 x 3] = 5442 N T E = 5442 x 2.19 = N T F = [9.8 x 30 x (3.15 x 1.01) x 0.5 x 1.07 x 3] = 13418N Maximum permissible pulling tension on this cable equipped with pulling eye bolt is ( x 240) x 3 = 50,555 N. Sidewall Pressure (at C) = -3 T C in Newton = Bend Radius, m 3 = 1.48 kn/m 4.371kN/m Sidewall Pressure (at E) = -3 T E in newton = Bend Radius, m 3 = 3.97 kn/m 4.371kN/m Because the sidewall pressure at point (E) is rather high (though not outside design limits) it would be desirable to investigate the results if the cable is pulled from at point (F) to at point (A). 3 3 T E = 9.8 x 30 x (3.15 x 1.01) x 0.5 x 1.07 x 3 T D = 1501 x 2.19 T C = [9.8 x 20 x (3.15 x 1.01) x 0.5 x 1.07 x 3) T B = 4287 x 1.48 T A = [9.8 x 60 x (3.15 x 1.01) x 0.5 x 1.07 x 3] = 1501N = 3287 N = 4287 N = 6244 N = 9246 N Pulling from at point (F) to at point (A) results in considerably less tension both at the bends and overall. While, in this case, it would be acceptable to pull from either direction, it is prudent design to select the direction which results in the least stress on the cable and equipment provided there are no extenuating circumstances such as limited set up or working space at one end or the other. 4.6 During pulling operations, it is frequently necessary to re-reel the cable or pass it over pulleys or sheaves, to avoid damage to the cable. It is imperative that the cable shall not be bent over the minimum radius of the cable which may cause damage. PAGE NO. 10 OF 26

11 4.7 For direct buried, or a combination of direct buried and ducts, cable installations where the length of the circuit must be pulled in, SEC (TBU) approved rollers, shall be used. 5.0 PARAMETERS OF CABLE PULLING 5.1 General The following parameters shall be considered during the course of cable pulling: Conduit or Duct Fill (refer to paragraph 5.2) Jam Ratio (refer to paragraph 5.3) Clearance (refer to paragraph 5.4) Maximum Pulling Tension (refer to section 4.0) Maximum Sidewall Bearing Pressure (refer to paragraph 4.4) Minimum Bending Radii (refer to Table 05-02) For Bending Radii related to communication cables, refer to TCS-T Conduit or Duct Fill The size of the inner diameter of the conduit and the outer diameter of the cable will determine the percentage fill of the conduit. Conduit or Duct Fill is based on the percentage-fill of the cross sectional area of the conduit/duct. The number of conductors shall not exceed the percentage fill specified in Table Jam Ratio (JR) Table 05-04: Maximum Allowable Percentage-Fill of the Conductor Cross Section Within a Conduit or Duct Number of Conductors In Conduit/Duct Maximum Percentage- Fill (%) When three or more single or multicore cables are being pulled into a conduit, their relative position in the conduit, when being pulled around bends can change, causing a condition of Jamming. If the cables jam in the conduit during pulling, the likelihood of cable damage is high. The Jam Ratio (JR) is defined as the ratio of the PAGE NO. 11 OF 26

12 conduit Inner diameter (D) to cable overall diameter (d). The following formula is used to evaluate the jamming potential: D If JR = is larger than 3.0, jamming cannot occur. d D If JR = is between 2.8 and 3.0 jamming is likely to occur and should be d avoided, but clearance must be checked (see paragraph 5.4). D If JR = is less than 2.8, jamming is not likely. d Where: D = Conduit Inner Diameter in millimeters (mm) d = Cable Overall Diameter in millimeters (mm) 5.4 Cable Clearances (CL) in Conduit Clearances must be checked to ensure that the top conductor will not press against the top of the conduit. Clearance shall be between 6 mm and 25 mm. The larger value is used for large cables and severe bends and pulls. The formulae for calculating clearance are as follows: Parallel (Triplexed) Cables CL = 0.5D d + 0.5(D-d) (1-[d/(D-d)]²)½ Multi Conductor Cable CL = D-d 6.0 CABLES INSTALLATION IN DIRECT BURIED 6.1 In the event of minor damage to outer jacket during installation, heat shrinkable split sleeve shall be applied to repair the jacket. 6.2 Cables shall be placed in trenches in a single horizontal tier without crossings except at transition to multi-tier duct banks. Multi-tier direct buried cable arrangements in trenches are not allowed. 6.3 The route of cable trenches shall avoid above ground and below ground obstructions so as to maintain a reasonable access to the buried cables. Trenches in unpaved areas are preferred. A minimum clearance shall be maintained between underground runs and parallel runs of underground piping. Cables shall not be located under present or future parallel runs of low level underground piping which could block access to the cables. Recommended clearances are shown on Fig through Fig PAGE NO. 12 OF 26

13 6.4 Power and associated control circuits can be laid adjacent. Three single conductor cables comprising one three phase circuit (trefoil) shall be laid without spacing. In order to achieve a reasonable derating factor, a minimum spacing shall be determined between all 3-phase power circuits. Refer TES-P-104 for derating effects of adjacent circuits. 6.5 Where cables cross under main roads, concrete slabs, paved areas, railroad, or any areas that would require extensive or impractical excavations to replace, then they shall be run in ducts. Where such duct runs exceed 3 meters, overall cable ampacity shall be based on the duct portion of the run. Bell end or protective bushings shall be provided on each duct where it terminates. 6.6 If underground cables are routed through a concrete encased ductbank, PVC conduits shall be of encased-in type and when routed through direct buried PVC conduit, they shall be of direct buried (DB) type. All conduits shall have bell ends or protective bushings where the conduits terminate underground. 6.7 Riser Cables Protection of Riser Cables Riser cables from underground to overhead systems shall be protected by a covering that gives suitable mechanical protection up to a point at least 3.7 m above the ground and at least 0.3 m below ground level. However, it is desirable that the protective covering be extended as high as practicable. The use of a plastic or steel guard is generally recommended for protecting riser cables. The use of a blackplate on all cable riser shield installations will assure that the cable is completely covered on all sides. Metallic guard shall be effectively grounded. Riser shield sizes shall be determined by table Support of Riser Cables Riser cables shall be supported by suitable clamps fixed on the cable support structure. They shall not be supported by cable termination devices such as cutouts, cable terminal connectors, etc. 7.0 CABLE INSTALLATION IN UNDERGROUND STRUCTURES 7.1 Underground structures, as defined in this Standard, shall include manholes, vaults, substation basements, duct banks, cable trays, handholes and pullboxes. 7.2 All cables installed in underground structures shall be adequately supported and secured to withstand forces caused by the maximum short circuit current to which they may be subjected. 7.3 Adequate access space shall be provided to maintain and operate equipment. PAGE NO. 13 OF 26

14 7.4 Power and communication cables shall be racked from separate walls. Crossing of the two circuits shall be avoided. 7.5 All cables which exit from transformer, switchgear, vault, manhole, handhole or switch enclosures and terminal structures shall be tagged for identification. Tags shall be permanent, non-corrodible and clearly readable. The following minimum information shall be put in English and Arabic on the tag: a. Transmission and Sub-transmission: Voltage and Insulation Material Phase Identification (R, Y, B) for Single Core Cables Destination (From To) b. Distribution: i. Primary: Feeder Name Voltage Phase for Single Core Cables Destination ii. Secondary: Voltage Phase for Single Core Cables Destination iii. Service: Destination or Customer Address c. Communication and Control: Circuit Type Destination 7.6 Cables shall not be laid on top of other cables. 7.7 All cables shall be installed under applicable requirements of Standard IEEE/ANSI C Unless, otherwise specified, all cable installations in substation basements, vaults and manholes shall be fire proofed. PAGE NO. 14 OF 26

15 7.8.1 Power cables shall be fire proofed, except where fireproofing is not necessary according to or In manholes and other structures containing no oil filled equipment (i.e. where no oil fire hazard is involved), fireproofing is only necessary where separation between cables is 45 cm or less Fireproofing is not necessary on single conductor primary cable connections between various items of equipment in transformer vaults. However, fire proofing shall be installed on primary supply cables, including a single supply cable, and any other primary or transmission cables in vault or other structures containing oil filled equipment. 8.0 CABLE TRENCH DESIGN PARAMETERS 8.1 Figure through indicate standard design parameters for the cable trench depth, width, backfill and circuit separation. 8.2 Right-of-Way Requirement Underground Cable s Route a. Parameters of Right-of-Way shall be applicable for both existing and new road/streets. b. The route of the underground cable shall be considered as the shortest route and avoid or minimize: Communication facilities such as telephone cables. Thrust boring. Gas pipelines, water or sewerage pipelines New roads where reasphalting is required. c. The location of the underground cables for new road/streets shall be as shown in drawings no.se and SE for 69kV to 380 kv Duct Location a. Unless otherwise specified, the duct for underground cable shall not be located in the main (busy) lane of the street/road and to be far away from the median bay at least 1.5 m. b. Refer to Figures 05-1 through for the required width and depth of cables trench. c. Bending radius (refer to section 3.0). PAGE NO. 15 OF 26

16 d. Unless otherwise specified, separate communication handholes shall be provided for the underground optical fiber. Communication Handholes shall be provided at every change of direction, crossing, start and end of duct bank system and at every 500 m of continuous cable run. e. Unless otherwise specified, separation distance between fiber optic cables and power cables shall be 300 mm minimum.as per standard drawing no.sb For lower distance, ampacity adequacy shall be verified Thrust Boring/Directional Drilling Requirements a. Thrust boring or directional drilling shall be used only if other alternative means of crossing are not possible. b. Ampacity adequacy shall be verified where thrust boring or directional drilling is required. c. Thrust boring for 69 kv to 380 kv Underground cables: i. The minimum depth of the thrust boring shall be 2.0 m measured from top of the pipe unless otherwise required at greater depth by the Agency/Ministry having Right-of-Way jurisdiction. ii. iii. The pipe shall be made of steel. The nominal size of the pipe shall be minimum of 1067 mm. The number of Thrustbore shall depend on required number of cable circuits and available Right-of-Way. The spacing between the pipes shall be 2.0 m center-to-center. For more details, refer to standard drawing no. SA d. Horizantal Directinal Drilling for 69 kv to 380 kv Underground cables: i. The process of directional drilling shall be as per contractor s procedure and requirements. ii. iii. The number of directional drilling condiuts shall also depend on required number of cable circuits and available Right-of- Way The CONTRACTOR shall submit his proposal for the directional drilling method. The CONTRACTOR or the CONTRACTOR S approved SUBCONTRACTOR, specialized in the art of directional drilling, shall conduct the PAGE NO. 16 OF 26

17 same. Drawing and procedures shall be submitted to the COMPANY for approval prior to start of construction. iv. The details of the directional drilling method along with description of the machinery that will be used shall be submitted for COMPANY review and approval. The CONTRACTOR shall explain in details, how the required clearance between each circuit and other circuit and other utilities will be maintained. v. Prior to commitment of any directional drilling work, the CONTRACTOR shall get approval and permission from the concerned ROW approving agencies. vi. All the above requirements shall be submitted for COMPANY review and approval. e. Backfilling and Reinstatement shall be in accordance of the requirements of appropriate authority Recommended Clearances between SEC Underground Power Cables and Other Utilities' Lines Unless otherwise specified by the Design Engineer in the SOW/PTS after consultation with relevant facility, the following clearances between U/G power cable and other facilities such as water, sewer, gas, telephone shall be used: Table 05-05: Clearances of SEC U/G Cables & Other Utilities lines SEC UNDERGROUND CABLES Utility 110 kv to 380 kv Horizontal Clearance (mm) Vertical Clearance (mm) Water & Sewer Telephone Gas Cable Route Marker Warning posts shall be installed along the center line of the trench at not over 50 m intervals on congested areas and not over 90 m intervals on open areas and at all locations where the trench changes direction On straight route, the warning post shall have a two-arrow sign to indicate cable route direction. PAGE NO. 17 OF 26

18 8.3.3 On right angle turn, the warning post shall have two signs each having an arrow pointing to the cable route direction. The signs will be placed on the applicable side of the post On oblique turn, the cable route direction shall be indicated by two warning posts each having an arrow. 8.4 Concrete Encased Ducts Refer to standard drawing SA for U/G power cables. PAGE NO. 18 OF 26

19 FIGURE kv, 115 kv or 132 kv XLPE STANDARD TRENCH PAGE NO. 19 OF 26

20 FIGURE kv, 115 kv or 132 kv XLPE STANDARD TRENCH PAGE NO. 20 OF 26

21 FIGURE kv, 115 kv or 132 kv XLPE or LPOF STANDARD TRENCH PAGE NO. 21 OF 26

22 FIGURE kv or 380 kv XLPE or LPOF STANDARD TRENCH PAGE NO. 22 OF 26

23 FIGURE kv, 115 kv or 132 kv XLPE or LPOF STANDARD TRENCH PAGE NO. 23 OF 26

24 FIGURE kv or 380 kv XLPE or LPOF STANDARD TRENCH PAGE NO. 24 OF 26

25 Figure Recommended Clearances Between SEC Underground Power Cables 110kV to 132kV and Other Utilities's Lines PAGE NO. 25 OF 26

26 Figure Recommended Clearances Between SEC Underground Power Cables 110kV to 380kV and Other Utilities's Lines PAGE NO. 26 OF 26