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Pole/ Column / Post Tender Documents

Technical Specifications for 11kV & LV Distribution Overhead Line Supports


1. SCOPE

 

This Technical Specification has been prepared by MOE. This specification covers the provision of tubular steel supports, crossarms, fittings and accessories suitable for 11kV overhead lines with maximum conductor size 120/20 ACSR and LV lines with maximum conductor size 120mm2 AAC. It supersedes all previous specifications for 11kV & LV distribution overhead line supports that have been issued by MOE.

 

2. GENERAL REQUIREMENT

 

The equipment shall generally, except where varied by this specification, comply with the appropriate requirements of all relevant sections of ISO/CEN, current at the time of bidding. When bidding, all non-compliances with the appropriate Standards shall be stated by the Manufacturer.

 

 

Service Conditions

Altitude:

Up to 1000metres above sea level

Ambient temperatures:

 

Outdoor:

 

Maximum peak:

+55⁰C

Maximum daily average:

+40⁰C

Maximum yearly average:

+30⁰C

Lowest minimum:

-10⁰C

Highest one day variation:

+25⁰C

Ground maximum:

+35⁰C

Indoor:

 

Maximum Daily Average:

+35⁰C

 

 

Humidity:

 

Max relative humidity:

92%

Min relative humidity:

12%

Yearly average:

44%

 

 

Wind:

 

Max wind velocity:

140km/hr (for design purposes)

Rain fall: 

Minimum yearly:

50mm

Maximum yearly:

500mm

Maximum in one day:

65mm

Yearly average:

150mm

 

Atmosphere:

 

General:

Subject to sand storms and windblown dust.

Average number of days of dust storms:

21.5

Average number of day of thunder storms:

15

 

Soil Conditions:

 

Ground Thermal Resistivity:

1.200C m/watt or as determined by local test

 

 

 

NETWORK PARAMETERS

Parameter

Network

11 kV

LV

Nominal Voltage

11kV

0.416kV

Highest System Voltage

12kV

0.454kV

Number of Phases

3

3

Frequency

50Hz

50Hz

Neutral Point

Resistance or reactance earthed

Solidly Earthed

3 Phase Short Circuit Capability

31.5 kA

12kA

Duration of Short Circuit

1 sec

1 sec

Impulse Withstand Voltage (wet)

75kV

3kVp

Power Freq. Withstand Voltage 1 min (wet)

28kV

2kV

Minimum creepage distance (mm/kV)

25

25

 

 


 

3. SCHEDULED EQUIPMENT

 

 Load Cases

 

            Case 1: Working load + self weight + wind on structure (Ps)

            Case 2: (Working load + self weight + wind on structure) x 1.5 (Pp)

            Case 3: (Working load + self weight + wind on structure) x 2.5 – Destruction (Pb)

 

Tubular steel poles shall be supplied to the following dimensions and classifications.

 

Type 1

Type 2

Effective length (M)

11.00

9.00

Top Section

 

 

Length x outside diameter (mm)

3100 x 216.3

2000 x 165.2

Minimum wall thickness (mm)

3.5

3.5

Middle Section

 

 

Length x outside diameter (mm)

3050 x 267.4

2300 x 216.3

Minimum wall thickness (mm)

4.5

4.5

Bottom Section

 

 

Length x outside diameter (mm)

4850 x 318.5

4700 x 267.4

 

 

 

Length x outside diameter (mm)

4850 x 318.5

4700 x 267.4

Minimum wall thickness (mm)

5.0

5.0

Sinking Depth (M)

1.8

1.5

Working Load (kgf)

700

700

Point of load application from top (M)

1.2

0.6

Factor of Safety Case 1(Ps)

1.0

1.0

Factor of Safety Case 2(Pp)

1.5

1.5

Factor of Safety Case 3(Pb)

2.5

2.5

Maximum deflection Case 1 (mm)

0.0

0.0

Maximum deflection Case 2 (mm)

13.0

13.0

Min yield strength ≥

N/mm²

340

 

 

Tubular Steel Supports

Supports shall be manufactured from longitudinally welded tube sections of hot rolled carbon steel of minimum yield strength ≥340 N/mm2). The Contractor is responsible for ensuring that the final design complies with the load cases stated in section of 3.1 of this specification.

Steel shall have a low silicon and phosphorus content (Si <0.04%. P<0.02%).

The poles shall be manufactured using the following methods:-

Type 1 and type 2 – Welded sections

The Contractor shall submit, with the bid, drawings showing overlap lengths in the case of welded sections and detail dimensions of all filling pieces used in the manufacture of welded section poles.

All supports shall be galvanized using the hot dip method according to ISO 1461.

 

 Drillings

Poles shall be drilled according to the dimensions given in Figs 1 & 2. All holes shall be drilled prior to the galvanizing process and have smooth uniform finish after galvanizing.

 

Pole Cap

Each pole shall be supplied with a pole cap, to seal the aperture at the top of the pole.  The cap shall be manufactured according to the dimensions given in Figs 1 – 2.  ‘A’ Clamps

Type 1 poles shall have welded to the top, an ‘A’ clamp for the purpose of supporting the pin stalk of a top phase insulator. The additional height due to the attachment of the clamp shall not be considered as part of the effective length of the pole and, where measurements are quoted “from the pole top”, they refer to the top of the main pole structure.

The A shaped clamps shall be manufactured according to the dimensions in Figs 1 from steel plate of the same grade and properties as the material of the main pole and the completed clamp shall be welded to the pole before galvanizing. All welding and drilling involved in the manufacture of the ‘A’ Clamp will be carried out prior to the galvanizing process.

 

 Crossarm (Strain)

Each Type 1 pole shall be supplied with a cross arm and its associated clamp according to the dimensions in Fig 1. The cross-arm is intended to be fixed to the pole by means of the clamp at a distance of 600mm below the pole top.  Every set shall include the following:

·       One galvanised steel channel cross arm according to the dimensions given in Fig 1 manufactured from steel of grade S235JR:

·       One galvanised steel clamp according to the dimensions given in Fig 1 manufactured from steel of grade S235JR:

·       Two galvanised, high-tensile steel M16 x 60 bolts with a minimum threaded length of 50mm.  Each bolt shall be supplied complete with a galvanised nut, plain washer and spring washer.

 

 Galvanising

Galvanizing shall be in accordance with ISO 1459 and ISO 1461. The zinc coating shall not be less than 650g/m2 and minimum thickness in any one place shall be 85 microns.

Poles and other hollow items shall be galvanized both inside and out.

The zinc coating shall be smooth, continuous and uniform. It shall be free from acid spots and shall not scale, blister or be removable by handling or packing. There shall be no impurities in the zinc or additives to the smelter bath that could have a detrimental effect on the durability of the zinc coating

Before pickling, all welding, drilling, cutting and grinding shall be completed and all grease, paint, varnish, oil and welding slag shall be completely removed. All protuberances which could affect the life of galvanizing shall also be removed.

To avoid the formation of white rust all galvanized material shall be packaged in such a way to ensure adequate ventilation between parts during shipping and storage.

                                                                                                                           

5. QUALITY CONTROL

The Contractor shall submit evidence of ISO 9001 accreditation with his bid. The Contractor shall also submit detailed quality control procedures with his bid. Any potential Contractor that does not submit these documents shall be disqualified from the evaluation process.

Random samples from each batch shall be inspected by the Employer’s engineers or the Employer’s nominated inspector. The minimum quantities for sampling from each batch are listed in the table below:

 




 

 

 

Batch size

Number of poles

up to 500

5

501 - 1000

8

1001 - 2000

13

2001 - 3000

18

3001 and above

20

 

The Contractor shall aid the work of the Employer’s inspector by providing copies of all relevant standards, and allowing the inspector full use of the necessary tools, instruments and laboratory equipment, together with ample space and assistance in the handling of poles for inspection.  Any costs incurred in assisting with the inspections shall be borne by the Contractor.

The following parameters shall be examined:

·       General appearance

·       Finish

·       Dimensions

·       Sweep

·       Thickness and appearance of galvanising

 

As a minimum requirement, the following dimensional checks shall be witnessed by the inspector:

 

Dimension

Tolerance

Length

+0.25%

Butt diameter and circumference

+2.5%

Top diameter and circumference

+2.5%

Wall thickness

+10%

Concentricity

±1%

Accuracy of drillings

±0.5%

Sweep, where appropriate

±1%

 

 

 

Crossarms, clamps and fittings shall have the following parameters examined:

·       General appearance

·       Finish

·       Dimensions

·       Straightness

·       Appropriate markings

·       Accuracy of drillings

·       Thickness and appearance of galvanising

 

As a minimum requirement the following dimensional checks shall be witnessed by the inspector:

 

Dimension

Tolerance

Length

+0.25%

Cross section of cross arm

+10%

Dimensions of clamp

+2.5%

Position and size of suspension holes

±0.5%

Verticality of all through holes

±0.5%

 

The group of poles or fittings offered at any one time shall constitute a batch. Within a batch, poles and fittings presented for inspection shall be segregated on a size basis. If the inspected items have damage or deviations on a quantity greater than 5% of the batch, then the entire batch shall be unconditionally rejected without further sorting.

Poles delivered to stores or sites shall be free of all damage to protective zinc coating, and shall not be out of straight by more than one thousandth of the length of the pole.

 

 

 

 

. DRAWINGS

 

Fig 1: Type 1 Tubular Steel Pole c/w Accessorie

(please e-mail to request the drawing)

 

Fig 2: Type 2 Tubular Steel Pole

 

(please e-mail to request the drawing)

 

 TECHNICAL SCHEDULES

 

To be completed by all Contractors:

Schedule A: Type 1 Tubular Steel Pole

Item
Number

Description

Unit

Offer

1

Weight

kg

 

2

Wall thickness

 

 

a

Bottom section

mm

 

b

Middle section

mm

 

c

Top section

mm

 

3

Length of sections

 

 

a

Bottom section

mm

 

b

Middle section

mm

 

c

Top section

mm

 

4

Outside diameter of sections

 

 

a

Bottom section

mm

 

b

Middle section

mm

 

c

Top section

mm

 

5

Effective length of pole

M

 

6

Manufacturing method (swaged/welded)

 

 

7

Working load (Ps)

kg

 

8

Deflection at Pp

mm

 

9

Breaking load (Pb)

kg

 

10

Factor of Safety (FOS)

 

 

11

Type of corrosion prevention system used

(Details and specification utilised to be enclosed)

 

 

12

Grade and specification of steel

 

 

 

 

 

 

 

 

Schedule B: Type 2 Tubular Steel Pole

Item
Number

Description

Unit

Offer

1

Weight

kg

 

2

Wall thickness

 

 

a

Bottom section

mm

 

b

Middle section

mm

 

c

Top section

mm

 

3

Length of sections

 

 

a

Bottom section

mm

 

b

Middle section

mm

 

c

Top section

mm

 

4

Outside diameter of sections

 

 

a

Bottom section

mm

 

b

Middle section

mm

 

c

Top section

mm

 

5

Effective length of pole

M

 

6

Manufacturing method (swaged/welded)

 

 

7

Working load (Ps)

kg

 

8

Deflection at Pp

mm

 

9

Breaking load (Pb)

kg

 

10

Factor of Safety (FOS)

 

 

11

Type of corrosion prevention system used

(Details and specification utilised to be enclosed)

 

 

12

Grade and specification of steel