transmission engineering standard tes-p...

PAGE NO. 2 OF 26 TESP10405R0/AAG

TRANSMISSION ENGINEERING STANDARD TES-P-104.05, Rev. 0

Date of Approval: February 18, 2007

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




TABLES 05-01 Minimum Cover Requirement in mm from Grade Level to the Top Surface of a Cable or

Duct 05-02 Minimum Bending Radius for Power Cables 05-03 Coefficient of Friction 05-04 Minimum Allowable Percent Conductor Cross-Section Within a Conduit or Duct 05-05 Clearances of SEC Cables and other utilities




FIGURES

05-01 Typical Cross-Section of Trench for 110 kV, 115 kV or 132 kV XLPE Power Cable;

Single Circuit, Trefoil Formation, Direct Burried. 05-02 Typical Cross-Section of Trench for 110 kV, 115 kV or 132 kV XLPE Power Cable;

Single Circuit, Trefoil Formation, Concrete Ductbank. 05-03 Typical Cross-Section of Trench for 110 kV, 115 kV or 132 kV XLPE or LPOF Power

Cable; Single Circuit, Flat Formation, Direct Burried. 05-04 Typical Cross-Section of Trench for 230 kV or 380 kV XLPE or LPOF Power Cable;

Single Circuit, Flat Formation, Direct Burried. 05-05 Typical Cross-Section of Trench for 110 kV, 115 kV or 132 kV XLPE or LPOF Power

Cable; Single Circuit, Flat Formation, Concrete Ductbank. 05-06 Typical Cross-Section of Trench for 230 kV or 380 kV XLPE or LPOF Power Cable;

Single Circuit, Flat Formation, Concrete Ductbank. 05-07 Recommended Clearances Between SEC Underground Power Cables 110kV to 132kV

and Other Utilities's Lines 05-08 Recommended Clearances Between SEC Underground Power Cables 110kV to 380kV

and Other Utilities's Lines




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 05-1.

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 380 920 610 310 460

Type A: Light Traffic Areas Type B: 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.




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 05-2.

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 Conductor

r =12× d r =24× d

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.




4.0 PULLING TENSIONS AND SIDEWALL PRESSURES 4.1 General 4.1.1 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.

4.1.2 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.

4.1.3 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. 4.1.4 Detailed cable pulling calculations shall be submitted to SEC (TBU) for

approval and review prior to all cable pulling operations. 4.1.5 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.

4.1.6 The placement of all rollers that conforms to the radii bends and degree angle

curves shall be verified prior to commencing the cable pull. 4.1.7 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 4.2.1 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 70.216 times the cross-sectional area of the conductor in square millimeters (mm2).

b. For 75% hard-drawn aluminum, maximum tension in newtons (N) is

equal to 52.662 times the cross-sectional area of the conductor in square millimeters(mm2).




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 10.342 times the lead cross-sectional area in square millimeters(mm2).

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 4.2.1 above.

c. If manufacturer recommends less maximum tension to be placed than

the specified above, his recommendation shall be followed.. 4.3 The pulling tension (T) for a given installation shall be calculated from the following

formulas or shall be as per manufacturer’s requirements: 4.3.1 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~ 0.2 0.3 ~ 0.4 0.15 ~ 0.25

PVC 0.1 ~ 0.2 0.5 ~ 0.6 0.25 ~ 0.35 a. For single-core cable per duct, equation 05-01 becomes: T = 9.8 x L x W x f (Eq.05-2) Where: OF = 1 N = 1




b. For three single-core cables in trefoil formation:

OFd

D d

=

−−

⎛⎝⎜

⎞⎠⎟

1

12

(Eq.05-03)

Where: d = Outside diameter of each cable in mm D = Inside diameter of duct in mm 4.3.2 For a duct with a bend: T T efa

2 1= (Eq.05-4) Where: T2 = Tension for the straight section following the bend in newtons T1 = 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 4.371 kN/m, i.e. the tension in the

cable in kilonewtons as it leaves the bend shall not exceed 4.371 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




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:

OF =

−−

⎛⎝⎜

⎞⎠⎟

=1

1 413154 413

1072.

.

.

TB = 9.8 x 60 x (3.15 x 1.01) x 0.5 x 1.07 x 3 = 3002 N TC = 3002 x 1.48 = 4442 N TD = 4442 + [9.8 x 20 x (3.15 x 1.01) x 0.5 x 1.07 x 3] = 5442 N TE = 5442 x 2.19 = 11917 N TF = 11917 + [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 (70.216 x 240) x 3 = 50,555 N.

Sidewall Pressure (at C) = TC in Newton 10

Bend Radius, m

-3×=

× −4442 103

3

= kN/m 4.371 kN/m 48.1 ⟨

Sidewall Pressure (at E) = TE in newton 10

Bend Radius, m

-3×=

× −11917 103

3

= kN/m 4.371 kN/m 97.3 ⟨ 4.5.2 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).

TE = 9.8 x 30 x (3.15 x 1.01) x 0.5 x 1.07 x 3 = 1501N TD = 1501 x 2.19 = 3287 N TC = 3287 + [9.8 x 20 x (3.15 x 1.01) x 0.5 x 1.07 x 3) = 4287 N TB = 4287 x 1.48 = 6244 N TA = 6244 + [9.8 x 60 x (3.15 x 1.01) x 0.5 x 1.07 x 3] = 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.




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: 5.1.1 Conduit or Duct Fill (refer to paragraph 5.2) 5.1.2 Jam Ratio (refer to paragraph 5.3) 5.1.3 Clearance (refer to paragraph 5.4) 5.1.4 Maximum Pulling Tension (refer to section 4.0) 5.1.5 Maximum Sidewall Bearing Pressure (refer to paragraph 4.4) 5.1.6 Minimum Bending Radii (refer to Table 05-02) For Bending Radii related to communication cables, refer to TCS-T-557.05. 5.2 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 05-04.

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 (%)

1 53 2 31 3 40 4 40

5.3 Jam Ratio (JR)

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




conduit Inner diameter (D) to cable overall diameter (d). The following formula is used to evaluate the jamming potential:

If dDJR = is larger than 3.0, jamming cannot occur.

If dDJR = is between 2.8 and 3.0 jamming is likely to occur and should be

avoided, but clearance must be checked (see paragraph 5.4).

If dDJR = is less than 2.8, jamming is not likely.

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:

5.4.1 Parallel (Triplexed) Cables CL = 0.5D - 1.366d + 0.5(D-d) (1-[d/(D-d)]²)½ 5.4.2 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. 05-01 through Fig. 05-06.




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 6.7.1 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 05-04. 6.7.2 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.




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

C2. 7.8 Unless, otherwise specified, all cable installations in substation basements, vaults

and manholes shall be fire proofed.




7.8.1 Power cables shall be fire proofed, except where fireproofing is not necessary according to 7.8.2 or 7.8.3.

7.8.2 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.

7.8.3 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 05-01 through 05-06 indicate standard design parameters for the cable trench

depth, width, backfill and circuit separation. 8.2 Right-of-Way Requirement 8.2.1 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.SE1040521 and SE1040522 for 69kV to 380 kV.

8.2.2 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 05-06 for the required width and depth

of cables trench. c. Bending radius (refer to section 3.0).




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-036352.

For lower distance, ampacity adequacy shall be verified. 8.2.3 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. The pipe shall be made of steel. The nominal size of the pipe

shall be minimum of 1067 mm.

iii. 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-036227.

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. The number of directional drilling condiuts shall also depend

on required number of cable circuits and available Right-of-Way

iii. 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




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. 8.2.4 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 1000 500 Telephone 5000 1000 Gas 1000 500

8.3 Cable Route Marker 8.3.1 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.

8.3.2 On straight route, the warning post shall have a two-arrow sign to indicate

cable route direction.




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.

8.3.4 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-036226 for U/G power cables.




FIGURE 05-01

110 kV, 115 kV or 132 kV XLPE STANDARD TRENCH




FIGURE 05-02 110 kV, 115 kV or 132 kV XLPE STANDARD TRENCH




FIGURE 05-03

110 kV, 115 kV or 132 kV XLPE or LPOF STANDARD TRENCH




FIGURE 05-04

230 kV or 380 kV XLPE or LPOF STANDARD TRENCH




FIGURE 05-05 110 kV, 115 kV or 132 kV XLPE or LPOF STANDARD TRENCH




FIGURE 05-06

230 kV or 380 kV XLPE or LPOF STANDARD TRENCH




Figure 05-07 Recommended Clearances Between SEC Underground Power Cables 110kV to

132kV and Other Utilities's Lines




Figure 05-08 Recommended Clearances Between SEC Underground Power Cables 110kV to

380kV and Other Utilities's Lines

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