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TECHNICAL GUIDELINES FOR 400 kV AND 220 kV OH-LINES SvK TR 5:113 EARTHING 14 September, 2000

13 EARTHING

2 SvK TR 5:113 EARTHING 14 September, 2000

Contents

13.1 13.2 13.3

Page

REFERENCES ................................................................................................................. 4 SCOPE ............................................................................................................................. 5 DEFINITIONS................................................................................................................... 5 Shieldwire ......................................................................................................................... 5 Continuous shieldwire ...................................................................................................... 5 Insulated shieldwire .......................................................................................................... 5 Operational earthing ......................................................................................................... 5 Potential grading earthing................................................................................................. 5 Earthing ............................................................................................................................ 5 Earthing conductor ........................................................................................................... 5 Earth electrode ................................................................................................................. 5 Down earth conductor ...................................................................................................... 5 Downlead earth conductor................................................................................................ 6 Shallow earthing ............................................................................................................... 6 Deep earthing ................................................................................................................... 6 Continuous counterpoise.................................................................................................. 6 Spirally arranged potential grading earth electrode.......................................................... 6 Radial earth electrode ...................................................................................................... 6 DESCRIPTION................................................................................................................. 6 GENERAL ........................................................................................................................ 6 Operational earthing ...................................................................................................... 6 Potential grading earthing............................................................................................. 6 Touch protection ............................................................................................................ 7 REQUIREMENTS ............................................................................................................ 7 Material............................................................................................................................ 7 Shallow earthing installation ............................................................................................. 7 Deep earthing installation ................................................................................................. 7 Spirally arranged potential grading earth electrode.......................................................... 8 Electrolytic action........................................................................................................... 8 Electrical requirements.................................................................................................. 8 Earthing conductor ........................................................................................................... 8 Operational earthing ......................................................................................................... 9 Potential grading earthing................................................................................................. 9 Arrangement ................................................................................................................... 9 Earthing of lines with shieldwires which are not insulated from supports......................... 9 Earthing of lines with shieldwires which are insulated from the supports....................... 11 Earthing of lines with no shieldwires............................................................................... 12 Earthing of concrete poles.............................................................................................. 12 Earthing of wooden poles ............................................................................................... 12 Crossings ....................................................................................................................... 12 TESTING........................................................................................................................ 13 General .......................................................................................................................... 13

13.4 13.4.1 13.4.2 13.4.3 13.4.4 13.5 13.5.1 13.5.1.1 13.5.1.2 13.5.1.3 13.5.2 13.5.3 13.5.3.1 13.5.3.2 13.5.3.3 13.5.4 13.5.4.1 13.5.4.2 13.5.4.3 13.5.4.4 13.5.4.5 13.5.4.6 13.6 13.6.1

3 SvK TR 5:113 EARTHING 14 September, 2000

13.6.2 13.6.3 13.6.4 13.7 13.7.1 13.7.2 13.7.2.1 13.7.2.2 13.7.2.3 13.7.2.4 13.7.2.5 13.7.2.6 FIGURES Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9

Heavy current method ................................................................................................. 14 Light current method ................................................................................................... 14 Step and touch voltage measurements ..................................................................... 14 CERTIFICATE OF DELIVERY....................................................................................... 15 General .......................................................................................................................... 15 Documentation ............................................................................................................. 16 Arrangement drawing ..................................................................................................... 16 List of material ................................................................................................................ 16 Site earthing record ........................................................................................................ 16 Quality system ................................................................................................................ 16 Installation instructions ................................................................................................... 16 Test report ...................................................................................................................... 16 ........................................................................................................................................ 17 ........................................................................................................................................ 17 ........................................................................................................................................ 17 ........................................................................................................................................ 18 ........................................................................................................................................ 18 ........................................................................................................................................ 19 ........................................................................................................................................ 19 ........................................................................................................................................ 20 ........................................................................................................................................ 21 ........................................................................................................................................ 21

4 SvK TR 5:113 EARTHING 14 September, 2000

13.1

REFERENCES

Note that standards, regulations etc. which are referred to in these guidelines are subject to continuous change and can be withdrawn, revised or replaced. The contractor shall immediately inform the client of such changes. Ritningsregler - Skalor Kvalitetssystem - Krav vid produktion och installation. Isolation för elektriska friledningar för starkström Luftledningskorsningar - Högspänningsledning (friledning), högst 52 kV, över järnväg - Trädsäkert korsningsspann Fasta installationer för jordning i ställverk med systemspänning högre än 1 kV

SS ISO 5455 SS ISO 9002 SS 421 07 10 SS 436 02 63

SS 436 21 10

STEV-FS 1957:601 Starkströmsförordningen - Kapitel 3 § 4, Kapitel 13 § 1 ELSÄK -FS 1994:7 Statens Energiverks föreskrifter om utförande och skötsel av elektriska starkströmsanläggningar (Starkströmsföreskrifterna) § 74 o.75 ELLAGEN Ref. 1 Ref. 2 §5 Underhåll ledningar 0,4 ­ 420 kV EBR Jordning av 11- 400 kV luftledningar - Huvudprinciper - VAST - Vattenfall - Elverksföreningen Jordning av stationer och ställverk - VAST - Vattenfall Elverksföreningen Elsäkerhetsanvisningar

Ref. 3

Ref. 4

5 SvK TR 5:113 EARTHING 14 September, 2000

13.2

SCOPE

These guidelines are applicable to earthing of overhead lines and contain general instructions on how to arrange operational and protective earthing in earthed neutral systems for 220 and 400 kV overhead lines with supports made of conductive or non-conductive material.

13.3

DEFINITIONS

Shieldwire Transverse orientated horizontal earth conductor on overhead lines, normally located above the phase conductors. Continuous shieldwire Shieldwire arranged as a continuous horizontal earth conductor longitudinally along the line. Insulated shieldwire Shieldwire electrically separated from the supports using an insulator. Operational earthing Earthing designed to disperse lightning and 50-periodic fault currents so safe tripping is obtained. Potential grading earthing Earthing designed to disperse 50-periodic current in order that unallowable step and touch voltages do not occur. Earthing Electrically conductive connection between the construction and ground Earthing conductor A conductor forming part of the permanent construction for earthing purposes. Earth electrode Conductor located in the ground designed to provide a conductive connection with the ground. The conductor can consist of rod, wire, sheet-metal or similar types of material. Down earth conductor Conductor between the earth electrode and earthing connector or, in case of there being no earthing connector, the conductor between the earth electrode and the part designed to be earthed.

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Downlead earth conductor Conductor for connecting the insulator string attachments, crossarms, crossing cradle guard wires, associated support steelwork and shieldwire to a fixed support mounted earthing connector. Shallow earthing An earth electrode which is generally buried at a shallow depth. This can consist of a continuous counterpoise, radial earth electrodes or other earth conductors arranged horizontally. Deep earthing An electrode which is generally buried or driven vertically to a greater depth. Continuous counterpoise Conductor buried underground continuously along the line. Spirally arranged potential grading earth electrode Potential grading earth electrodes of stranded conductors arranged in a spiral in the ground around poles and/or stay anchors. Radial earth electrode An earth electrode buried horizontally and radially at an appropriate depth depending on location.

13.4

13.4.1

DESCRIPTION

GENERAL An installation being part of an earthed neutral system shall automatically and immediately be disconnected resulting from an earth fault. The rise in earth potential from an earth fault shall be levelled out to guarantee safety. This is achieved by operational and potential grading earthing. See ELSÄK-FS.

13.4.2

OPERATIONAL EARTHING Operational earthing shall be effected with a shallow or deep earthing installation taking into consideration such circumstances as terrain and obstructions. In arable land the earthing shall be of the deep earthing or alternatively radial earth electrode type.

13.4.3

POTENTIAL GRADING EARTHING Potential grading earthing shall be installed at supports and stay anchors in residential and well frequented areas in an attempt to reduce unallowable step and touch voltages.

7 SvK TR 5:113 EARTHING 14 September, 2000

The earthing shall consist of a potential grading earth electrode arranged in a spiral and connected to the support or stay anchors. In locations such as beaches, playgrounds and sports grounds and the like it may be necessary to take additional precautions. 13.4.4 TOUCH PROTECTION Insulation applied on parts of the construction which are easily assessable from the ground and installed at locations described in section 13.4.3. As an example touch protection can consist of plastic covering of supports.

13.5

13.5.1 13.5.1.1

REQUIREMENTS

MATERIAL Shallow earthing installation Earthing conductors to be buried in the ground shall be made of copper, copper clad steel or hot-dip galvanised steel. Stranded copper clad conductors are to be annealed and have 40% IACS conductivity. Earthing conductors to be installed above ground shall be made of copper, copper clad steel, hot-dip galvanised steel, aluminium, aluminium alloy or aluminium clad steel. Stranded copper clad conductors are to be annealed and have 40% IACS conductivity The dimensions shall not be less than: Material Copper wire Copperclad steelwire 1) Steel wire Aluminium Aluminium alloy wire Aluminium clad steel wire Copper plate Dimension 25 mm2 25 mm2 50 mm2 30 mm2 30 mm2 30 mm2 1mm * 0,5 m2

1) The copper coating of copper clad steel shall be 0.12 mm minimum and be bonded to the steel in such a way that it will resist stresses likely to occur in service without becoming separated from the steel. 13.5.1.2 Deep earthing installation Tubes, rods or angle sections made of copper, copper clad steel or alternatively hot-dip galvanised steel shall be used for deep earth installations.

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The dimensions shall not be less than: Material Steel tube Steel angle section Copper clad steel rod 2) Dimension 49 mm dia. 60*60*6 mm 16 mm dia.

2) The copper coating of copper clad steel shall be 0.12 mm minimum and be bonded to the steel in such a way that it will resist stresses likely to occur in service without becoming separated from the steel. 13.5.1.3 Spirally arranged potential grading earth electrode Hot-dip galvanised 50 mm2 soft steel wire with three strands shall be used as the conductor for potential grading earthing. ELECTROLYTIC ACTION Measures shall be taken to prevent corrosion of steel which is buried in the ground and is in galvanic contact with earth conductors made of copper or copper clad steel. Contact between copper and other dissimilar metals beneath the ground surface is not allowed. All such connections shall be made above the ground surface. In corrosive soils, when continuous earthing conductor or down earth conductors made of copper are used, supports shall be installed with spark gaps. With such soil conditions all stays shall in addition either be installed with stay insulators or spark gaps. Potential grading earthing is never to be connected through spark gaps. 13.5.3 13.5.3.1 ELECTRICAL REQUIREMENTS Earthing conductor Earthing conductors shall be of such a cross-sectional area that the current density caused by any earth fault current is limited to the values given below. See Swedish Standard SS 436 21 10 Material Allowed current density for 1 second. A/mm2 65 200 130 130 85

13.5.2

Steel Copper Copper clad steel Aluminium Aluminium clad steel

9 SvK TR 5:113 EARTHING 14 September, 2000

13.5.3.2

Operational earthing Shallow earthing shall be so arranged such that a maximum earthing resistance of 50 ohms is achieved and the touch voltage does not exceed 600 V. Deep earthing shall be so arranged such that a maximum earthing resistance of 100 ohms is achieved and the touch voltage does not exceed 600 V. Deep earthing shall be installed in such a way that variations in the moisture content of the surrounding soils have a minimal effect on the earthing resistance See ELSÄK-FS §74 mom. b and §75 mom. g.

13.5.3.3

Potential grading earthing Potential grading earthing shall be so arranged that step and touch voltages do not exceed 600 V. Where potential equalising according to the above is not adequate, touch protection can be required.

13.5.4 13.5.4.1 13.5.4.1.1

ARRANGEMENT Earthing of lines with shieldwires which are not insulated from supports Continuous counterpoise The earthing conductor shall buried in the ground between the boundaries formed by the outer phase conductors and be continuous along the line. It shall be connected to the supports and stays it passes. See figure 1. If the continuous counterpoise in a section of line is to be terminated before a pole which is individually earthed, the counterpoise shall be extended for a minimum of half the span beyond the last pole connected to the continuous counterpoise. If this cannot be done the counterpoise is to be terminated with a vertical or radial earth electrode. See figure 2. In the case of obstacles such as rock, roads, railways etc. which prevent the counterpoise being buried between the outer phases of the line, the counterpoise is to be arranged as follows: If the extent of the obstacle beyond the outer phases of the line is small, the counterpoise is to be routed around it If the obstacle extends to a significant distance beyond the outer phases, perpendicular to the line, the continuous counterpoise is to be discontinued in the span . See figure 3.

13.5.4.1.2

Radial earth electrode The earthing conductor shall be laid horizontally and radially from the object to be earthed and the number of radial earth conductors limited to 8 lengths. The length of each radial conductor is to be adjusted depending on the conductivity of the soil. See figure 4.

10 SvK TR 5:113 EARTHING 14 September, 2000

Where necessary radial and deep earthing can be combined to achieve the required earthing resistance. 13.5.4.1.3 Excavation depth Earthing conductor, both for continuous counterpoise and radial earth electrodes, shall be buried to a minimum depth of 60 cm. However, in arable lands and meadows it shall be buried 80 cm minimum. When rock is encountered at a depth less than that stipulated above the earthing conductor may be laid directly onto the rock. However, only in exceptional cases may the earthing conductor be laid on surface rock. If the earthing wire is to be laid onto surface rock it shall be bolted to the rock and hidden by stones and peat or by protective channels made of impregnated wood boards. Earthing conductor for potential grading earth electrodes arranged in a spiral are to be buried at a depth of 20 ­ 30 cm. 13.5.4.1.4 Deep earthing Earthing conductor in accordance with 13.5.1.2 is to be driven vertically into the ground. If so required several rods shall be installed, separated by a distance not less than the length of the rod, adjacent to each other to obtain the required earth resistance. The vertical earthing conductors shall be installed within a distance of 25 metres from the closest part of the earthed object. See figure 5. 13.5.4.1.5 Spirally arranged potential grading earth electrode Potential grading earth electrodes shall be arranged in a horizontal spiral around stays and associated support legs. See figure 6. At supports on rock, where potential grading earthing cannot be installed, exposed parts of the construction which are accessible shall be touch protected. Potential grading earthing is to be directly connected to supports or stays. 13.5.4.1.6 Touch protection Insulation shall be installed on those parts of the construction which are accessible within 3 metres from the ground . See figure 8. Connection to support and stays The down earth conductor shall be installed with a loop under the ground surface to prevent conductor breakage occurring and also to prevent it from coming loose from clamps attaching it to support members or stays. See figure 7. Down earth conductors made of copper or copper clad steel shall, when installed in contact with steel members under the ground surface, be insulated with plastic hose made of a material which is neither attacked by animals nor is destroyed by

13.5.4.1.7

11 SvK TR 5:113 EARTHING 14 September, 2000

frost or low temperatures. The plastic hose shall insulate the down earth conductor from the support leg and the stay anchor continuously to a point approximately 0.5 m from the support leg, the foundation or the adjustable anchor bolt. In the event of there being a crossing beneath the ground surface between the down earth conductor and another conductor made of steel, i.e. potential grading earth electrode as arranged in a spiral, the insulation shall be extended to protrude a minimum of 0.5 metres beyond such a conductor. 13.5.4.1.8 Connection to downlead earth conductor Connections to downlead earth conductors for wood and concrete poles are to be arranged in accordance with figure 9. Connection and jointing under the ground surface The connection of down earth conductors to earth electrodes and the jointing of earth electrodes is to be performed in such a way that a durable contact is achieved and corrosion of the connection is prevented. This can be achieved with screw joints, compression joints, welding or twist joint tubes. 13.5.4.1.10 Spark gap Down earth conductors shall, if the soil is corrosive and the conductor is made of copper or copper clad steel, be connected to the support and the stays by means of a spark gap. The spark gap shall be placed a minimum of 0.5 metres above ground level. See figure 7. 13.5.4.2 Earthing of lines with shieldwires which are insulated from the supports The following rules shall be applied at the connection of conductors made of copper or copper clad steel to supports and stays for lines with shieldwires which are insulated from the supports: Support in corrosive soil For supports with steel foundations and/or stays in soil with backfill consisting of corrosive material the connection is to be made by means of a sparkgap. Support with concrete foundation For supports where all legs and stays are attached to concrete foundations the connection is to be made directly. Support in non-corrosive soil For supports where all legs and stays are attached to concrete, rock or steel foundations the backfill consists of non-corrosive soil the connection is made directly.

13.5.4.1.9

13.5.4.2.1

13.5.4.2.2

13.5.4.2.3

12 SvK TR 5:113 EARTHING 14 September, 2000

13.5.4.2.4

Stay in corrosive soil For supports the connections for any associated stay in corrosive or unknown material is to be made according to one of the following alternatives: Stay insulator to be installed for the stay concerned which shall not be connected to any earthing system. Connection to be made with spark gaps and augmented by installing earthing with galvanised steel wire at the location where the least earthing resistance can be achieved. The steel wire is to be directly connected to the support or the stays with no stay insulator.

13.5.4.3

Earthing of lines with no shieldwires The operational earthing is to be arranged as shallow or deep earthing. For the connection of the earth electrode to support legs and stays the same rules apply as for lines with shield wires which are insulated from the supports.

13.5.4.4

Earthing of concrete poles The crossarm, insulator attachments and reinforcing shall be connected to the earth electrode of the pole through the downlead earth conductor within the pole. Earthing of wooden poles Earthing of wooden poles is necessary when the wooden insulation does not comply with the requirements of Swedish Standard SS 421 07 10. Crossings General The minimum distance between the earth electrode and installations as listed below is to be considered as indicative only. Step and touch voltages shall be measured to verify the adequacy of the earthing. Water pipes and sewers Main pipe made of metal The required distance from the metallic parts of the power line which have been buried in the ground is a minimum of 10 metres. To comply with the above requirement in the case of continuous counterpoise, the counterpoise is to be insulated thereby achieving the 10 metres minimum distance. The counterpoise is to be buried a minimum of 0.5 metres under the pipe which is crossed. Alternatively the counterpoise may be discontinuous. Other types of pipe made of metal The required distance from the metallic parts of the power line which have been buried in the ground is a minimum of 50 metres.

13.5.4.5

13.5.4.6 13.5.4.6.1

13.5.4.6.2

13 SvK TR 5:113 EARTHING 14 September, 2000

To comply with the above requirement in the case of continuous counterpoise, the counterpoise is to be insulated thereby achieving the 50 metres minimum distance. The counterpoise is to be buried a minimum of 0.5 metres under the pipe which is crossed. Alternatively the counterpoise may be discontinuous. 13.5.4.6.3 Power cable System voltage 10 kV and higher The required distance from the metallic parts of the power line which have been buried in the ground is a minimum of 10 metres. To comply with the above requirement in the case of continuous counterpoise, the counterpoise is to be insulated thereby achieving the 10 metres minimum distance. The counterpoise is to be buried a minimum of 0.5 metres under the power cable which is crossed. Alternatively the counterpoise may be discontinuous. System voltage less than 10 kV The required distance from the metallic parts of the power line which have been buried in the ground is a minimum of 50 metres. To comply with the above requirement in the case of continuous counterpoise, the counterpoise is to be insulated thereby achieving the 50 metres minimum distance. The counterpoise is to be buried a minimum of 0.5 metres under the power cable which is crossed. Alternatively the counterpoise may be discontinuous. 13.5.4.6.4 Telecommunication line The required distance from the metallic parts of the power line which have been buried in the ground is a minimum of 50 metres. To comply with the above requirement in the case of continuous counterpoise, the counterpoise is to be insulated thereby achieving the 50 metres minimum distance. The counterpoise is to be buried a minimum of 0.5 metres under the telecommunication line which is crossed. Alternatively the counterpoise may be discontinuous. 13.5.4.6.5 Railway Line The required distance between the centre of the track which is closest to the power line and the metallic parts of the power line is a minimum of 20 metres.

13.6

13.6.1

TESTING

GENERAL To process an application for permission to energise, the Elsäkerhetsverket (National Electrical Safety Board) requires a report detailing the earthing conditions. This report shall include the measured resistance values of the earth

14 SvK TR 5:113 EARTHING 14 September, 2000

electrodes together with information confirming that appropriate measures have been taken for installations subject to interference. The measurements are to be performed according to one of the following two methods, namely the heavy current method or alternatively the light current method 13.6.2 HEAVY CURRENT METHOD The intention of this test is to verify compliance with the requirements of clause 13.5.3.2 Measurement of the resistance of earth electrodes shall be performed in accordance with ref. 3 "Jordning av stationer och ställverk" (Earthing of substations) chapter 8. 13.6.3 LIGHT CURRENT METHOD The intention of this test is to verify compliance with the requirements of clause 13.5.3.2 Measurement of the resistance of earth electrodes shall be performed in accordance with ref. 1 "Underhåll ledningar 0,4 ­ 420 kV" (Maintenance of lines 0.4 ­ 420 kV) chapter 301:E. On lines with continuous shieldwire, and with the earth electrode connected without a spark gap, the resulting earth electrode resistance needs only to be measured at a few locations. On lines with continuous shieldwires, and the earth electrode made of copper connected via spark gaps, the individual resistance of the earth electrodes is also to be measured. When measuring the resulting value for the whole system the spark gap shall be short-circuited. On lines with continuous shieldwires which are insulated from the supports, or on lines with no shieldwires, the individual earth resistance shall be measured for every earth electrode. Written records shall be made during the measurement process in accordance with ref. 1 13.6.4 STEP AND TOUCH VOLTAGE MEASUREMENTS The intention of this test is to verify that the step and touch voltages for supports with potential grading earthing are in compliance with the requirements of clause 13.5.3.3. The heavy current method in accordance with clause 13.6.2 is to be used.

15 SvK TR 5:113 EARTHING 14 September, 2000

13.7

13.7.1

CERTIFICATE OF DELIVERY

GENERAL The client shall, according to these guidelines, approve the earthing installations before handing over. For approval the contractor shall demonstrate that the earthing installations comply with the guidelines. The contractor shall provide documentation in accordance with clauses 13.7.2.113.7.2.6 for approval. The approval of documentation by the client does not release the contractor from his obligations of ensuring that the installations comply with the guidelines.

16 SvK TR 5:113 EARTHING 14 September, 2000

13.7.2

DOCUMENTATION A summary of documentation requirements is contained in chapter 14.

13.7.2.1

Arrangement drawing Each arrangement drawing shall be at an appropriate scale in accordance with Swedish Standard SS ISO 5455. On each drawing shall be given: Earthing type Principal dimensions Dimensions of conductors Excavation depth List of materials.

13.7.2.2 13.7.2.3 13.7.2.4 13.7.2.5 13.7.2.6

List of material Description of material in included parts. Site earthing record As installed documentation Quality system Quality system in accordance with ISO 9002 Installation instructions Installation instructions in Swedish or English with the required drawings. Test report Test report in accordance with clause 13.6

17 SvK TR 5:113 EARTHING 14 September, 2000

FIGURES

FIGURE 1

R ock atta chm en t C opper conductor 0,5 m C ontinuous cou nterp oise joint C onnectio n to counterpoise C onnectio n w ith spark g a p C onnectio n to counterpoise 0,5 m

C onnectio n w ith spark g a p P lastic P V C hose C onnectio n w ith spark g a p C onnectio n to counterpoise C onnectio n w ith spark g a p

FIGURE 2

Terrain obstacle

l<a/2

18 SvK TR 5:113 EARTHING 14 September, 2000

FIGURE 3

l>a/2

a

Terrain obstacle

l<a/2

FIGURE 4

60º 60º

19 SvK TR 5:113 EARTHING 14 September, 2000

FIGURE 5

Stayed structure Max 25m

Max 25m

FIGURE 6

0,2-0,3 m

2,0 m

1,5-2,0m c/c 0,4m

1,5-2,0m

c/c 0,4m

20 SvK TR 5:113 EARTHING 14 September, 2000

FIGURE 7

Support centre

min 0,5

Plastic hose on Cu conductor

min 0,5 Loop

Non covered conductor

The counterpoise is to be installed inside the main member

21 SvK TR 5:113 EARTHING 14 September, 2000

FIGURE 8

Touch protection

3m

3m

FIGURE 9

min 1,7m

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