Methodology of 132kV Underground XLPE Power Cable Installation

Purbachal PGCB (Power Grid Company Bangladesh) 230/132kV substation to Banani DESCO (Dhaka Electric Supply Company) 132/33/11kV substation.

Project Name: 

Design, Supply, Installation and Commissioning of 132 kV Underground Transmission Lines on Turnkey Basis under Power System Expansion and   Efficiency Improvement Investment Program (Trance2).

Cable Route:

Purbachal PGCB (Power Grid Company Bangladesh) 230/132kV substation to Banani DESCO (Dhaka Electric Supply Company) 132/33/11kV substation.

Project Description

Under the terms and condition of contract no. : DESCO/CS/PSEEIIP Tranche-2(Lot-2 of Package-C1)/Tender-4(27)/370/2016/154, dated 24/08/2016, LS Cable & System Ltd. as Contractor, together with our specialist Subcontractor BNF Engineers Ltd., will be responsible for completing all design, engineering, procurement, transportation/delivery to site, installation, related civil, and pre-commissioning, commissioning and performance testing for the whole laying and commissioning of 132kV underground HV cables.

Fig-1: Purbachal to Banani Proposed UG Cable Route

Key Personnel to Implement the Cable Installation Works

Under the management of the Project Manager, the Project Team consists of the following key personnel to implement the 132kV XLPE cable installation works:

1.    Construction Manager;

2.    Civil Engineer (Site Manager);

3.    Electrical Engineer (Site Manager);

4.    Safety Manager;

5.    Certified Chief Cable Jointer;

6.    Administration Manager;

The Project Manager, Construction Manager, Site Manager, and Certified Cable Jointers are well experienced in this kind of full turnkey project and have proven track records of successful projects here in Bangladesh and abroad in the past.

A dedicated Project Team with a well-equipped set-up is ready to carry out the aforementioned cable installation work, under the authority of the client Project Director, to implement the Work Scope for this Cable Route of the Project, in a safe and efficient manner.

Cable Route Description for Purbachal Substation to Banani Substation

Fig-2: Kuril to Banani part of Purbachal to Banani Proposed UG Cable Route

Fig-3: Natun Bazar to Banani part of Purbachal to Banani Proposed UG Cable Route

Fig-4: Single Line Diagram of Purbachal to Banani Proposed UG Cable Route

Sl. No.	Route Description	Route Length (Km)	Section (nos)	Joint/termination Bay (nos)	Estimated Installation Time (days)	Road Authority
01	Purbachal to Banani	13.090	24	25		RAJUK & DNCC
02	Purbachal to Bashundhara Gate (North)	5.40	9	10		RAJUK
03	Bashundhara Gate (North) to J.Future Park Gate	3.5	6	6		Bashundhara
04	J. Future Park Gate to Natun Bazar	1.55	4	3	60	DNCC
05	Natun Bazar to Banani SS	2.635	5	6	100	DNCC

 -Less traffic area     -Moderated traffic     -High traffic & very important area

Work Schedule

Natun Bazar to Banani Substation							Remarks
Section	Length(m)	Required time (day)
		Bridge Construction	Trench Excavation	Cable Pulling	Backfilling	Cable Jointing
24: Banani SS to Road-11(eleven square ANZ)	527	0	8	2	5	0
23: Road-11(eleven square ANZ) to end of  Road-27	527	0	8	2	5	8	JB Road-11
22: End of  Road-27 to End of road-46	527	40	8	2	5	8	JB Road-27
21: End of road-46 to Baridhara lake bridge west end	527	0	8	2	5	8	JB Road-46
20: Baridhara lake bridge west end to Natunbazar More	527	40	8	2	5	8	JB Baridhara Bridge
19: Natun Bazar More to Akthar Furnitur	527		8	2	5	8	JB-19
18: Akthar Furniture to FOODy Restaurant	527		8	2	5	8	JB-18
17: FOODy Restaurant to MTB Bank	527		8	2	5	8	JB-17
16: MTB Bank to J. Future Park	527		8	2	5	8	JB-16

N.B:  Total time required around 160 days to complete the works

Cabling Works for Natun Bazar to Banani Substation

Key Points to be considered:

01.Proposed cable route passes through city centre;

02.Diplomatic and very important area;

03.Two lakes (Baridhara & Gulshan) crossing;

04. Five interrupted points (JB) for cable jointing;

05. Gulshan-2 Circle (roundabout) crossing;

06. Excavation and cable laying of five cable section.

Preliminary Route Survey:

Topographical survey report already submitted and approved that included, expected cable routes, implementation of the join bays and typical cross-section of the cable trench and of the road crossings are plotted.

Trial Trench Excavation and Detailed Route Survey:

The final position of the cable route (roadside, footpath, service road, road meridian)   would be confirmed by a joint site visit with road authority (DNCC), DESCO and LS Cable representative as consider the key plants on the route such as major road crossings, conflicts, with existing utilities, change in direction, joint bay locations etc.

 Based on the joint site visit, collected site data from trial trenches and information received from DNCC authorities, a final route profile including cross-sections and typical details will be prepared to submit for approval.

The tranches would be proposed at distances not exceeding 200mm along the route in straight stretches and at all critical locations as described above.

Trial Pits:

Before final excavation of the cable route, trial pits would be open to confirm the position of other utilities and avoid conflict with others.

Application for Road Opening must be forwarded to have the authorization to excavate. The request form will be collected, filled and then submitted to the Client together with cable route drawings showing the trial pits location.

After been commented and approved through specific forms by the various Authorities, permits will be granted by the Client, for a given period of time and trial pit excavation may start.

Trench Excavation:

Excavation will progress as per the approved schedule and will start only after approval from the concerned Authorities.

01. Before excavation formally informed to police, traffic and related all department. Fire and safety, primary equipment would be available at the site and emergency department phone/mobile numbers would be displayed at the site.

02. Trench route is marked, as per the approved route plan;

03. Display traffic and signboards as required;

04. Hydraulic excavator/rack breaker would be used at all safe area like- main road, enough space area to move the excavator freely, no interrupt local traffic etc.  Excavate manually to expose all existing utilities close to the cable route and across. Existing services will be protected and secured as per the requirements of the concerned utility authorities.

05. Cross check withdrawing that all underground services are located; relevant Authorities can be called prior to excavating as instructed in some cases.

06. Excavated materials are either put in trucked to disposal or for further use.

07. The base of the excavated trench shall be levelled and all sides vertical to the dimensions shown on the drawing.

08. Excavation will continue and proceed to completion. An estimated 1(one) week is required to excavate each section (around 500m) of cable trench.

Baridhara & Gulshan Lake (Bridge/Culvert) Crossing

Baridhara Bridge:

There is an existing road Bridge on Baridhara Lake that would be crossed, cable line cross the lake along and beside the bridge. The proposed procedure shown in the drawing, using required piling both starting and ending point of the bridge and using 3nos PVC pipe for each circuit will be inserted in an MS pipe.

Baridhara existing road bridge length- 15.5 meters

Proposed Cable Bridge length- 16 meters.

Gulshan Bridge:

Similarly, in the Gulshan lake area also there a small existing road bridge that would be crossed in some way.

Gulshan existing road bridge length- 7.5 meters

Proposed Cable Bridge length- 8 meters.

Fig-5: Gulshan & Baridhara Lake Crossing Method

MS pipe Cable Bridge:

Crossing small canal or drain our proposed bridge concept is as below:

One bigger MS pipe will be used for each circuit and 3 nos PVC pipe for each cable and MS pipe ends will be sealed.

MS pipe diameter 400mm;

PVC pipe diameter 150mm;

Length of pipes depends on on-site requirement.

Fig-6: MS Pipe Bridge Method to cross drain/small canal/Khal/Nala

Gulshan-2 Roundabout/Rotary Crossing Procedure

To carry out road crossing at Gulshan roundabout/rotary area, the whole trench length divided into section1, section-2, section-3 and section-4 to avoid/control the traffic. Each section will excavate, backfill and open for traffic before starting excavation next section.

Also, the total plan to be informed and coordinate with the traffic control department for this important area ( from Banani substation to Natunbazar).

Fig-7: Gulshan-2 Roundabout Crossing Procedure

Cable Pulling and Trench Back-filling

Each section contains six cables, after preparing the cable trench, the cable will be pulled by a cable puller/winch machine or manually if required to avoid the damage of others existing utilities. An estimated 2 (two) days is required to pull all of 6 (six) cables for one section (around 500m).

Back-filling with sand above cables

After the arrangement of cables, the sand is installed up to 500mm measured from the bottom of the trench and the top surface is levelled. During this operation, care must be taken for not scratching or damaging the outer sheath with a sharp tool such as a shovel.

Laying of cable slabs

Pre-fabricated RCC slabs are transported to the site and installed on both sides and top of the cables to protect the cables from man-made stress.

Back-filling

Back-filling in the remainder of the trench is with selected material containing excavation. Any material which could be harmful is to be removed. Comparing single drum rollers to bring fill levels up as specified. At 300 mm above the cable slabs, warning tape is laid. The backfill materials will be compacted.

 Cable Route Markers

Route markers of approved designs to be installed at certain intervals as per requirement (road crossing, abrupt deviation, joint bays, etc.). The above works shall be inspected and recorded.

 Road Crossing (Trench-less or open cut method)

Authorization:

Before commencement of the works would be informed and authorization must be obtained from authorities as conventional way.

Marking:

Mark the outline of the road cutting and arrange diversions by displaying sign and boards. Work start and end time schedule and procedure of work must be informed to traffic control police/authority, they may inspect the works beforehand. Road crossing might be done one half at a time.

Excavation:

The wearing course is cut with a mechanical rotating wheel cutter or another method. The trench is excavated to the required depth (1.7 meters) and ducts are placed with blocking concrete with double circuit trefoil type 150mm outer diameter PVC pipe to pull the cable inside the pipes. Both ends plus the centre of ducts to keep the proper implementation and spacing in between the ducts during the concreting.

Concreting and Back-filling:

Concreting will be done with the required materials as per the approved design. Filling up above the road crossing up to the required level with compacted soil backfill. Finally, road asphalt reinstatement surfacing as per DNCC standard.

Joint Bay Preparation and Cable Jointing

Concrete Work

There are 5 (five) joint bays in Natunbazar to Banani part. Each joint bay preparation and civil work required 1 (one) week that would be carried out simultaneously with the trench excavation time.

 

Location of the join bays and link boxes shall be placed as per approved route survey and drum schedule. Ready-mix concrete will be used throughout as per the approved design.

Reinforcement will be cut and bent in the Contractor's yard and sent to the site via transportation. All the steel reinforcement installation and protection work will be done in accordance with the drawing and specification.

Earthing Cable at Joint Bay

Earthing cables are laid after joint bay completion as per LS Cable standard.  Earthing resistance value is measured after sand bedding and recorded on a specific form.

Pre-commissioning and commissioning

Upon complete laying, jointing and terminating each circuit, pre-commissioning and acceptance tests would be conducted duly witnessed by the Client and other concerned agencies. The Project Manager, with assistance from the Testing Engineer and Technicians, will directly undertake this phase.

Upon completion of all acceptance tests at the site after the installation as per specifications requirements, commissioning of each circuit would be carried out in conjunction with Client departments based on detailed outage planning for existing circuits and load change over.

As-built Documentation

During the installation phase, changes to be approved drawings would be marked up and records kept for the final compilation of as-built records. These site marked up records are used as the basis together with the accurately verified site data and as-built records prepared for use by the client.