Vestas Wind Farm Earthing System for Anchor Cage Foundation

Vestas Wind Systems A/S · Alsvej 21 · 8940 Randers SV · Denmark · www.vestas.com

Class 1

Document no.: 0014-6511 V01

2011-06-30

Vestas Earthing System

Description of Earthing System for an Anchor Cage Foundation

VESTAS PROPRIETARY NOTICE: This document contains valuable confidential information of Vestas Wind Systems A/S. It is protected by copyright law as an unpublished work. Vestas reserves all patent, copyright, trade secret, and other proprietary rights to it. The information in this document may not be used, reproduced, or disclosed except if and to the extent rights are expressly granted by Vestas in writing and subject to applicable conditions. Vestas disclaims all warranties except as expressly granted by written agreement and is not responsible for unauthorized uses, for which it may pursue legal remedies against responsible parties.



Table of Contents

Date: 2011-03-21

Issued by: Technology R&D Class: 1

Type: T05 - Manual Page 2 of 15


Table of Contents

1 Foreword .............................................................................................................................. 3 1.1 Related Documents ............................................................................................................... 3 1.2 List of IEC Standards ............................................................................................................. 4 1.3 Basic Design Criteria and Assumptions ................................................................................. 4 1.3.1 Lightning Protection Issues .................................................................................................... 4 1.3.2 High Voltage Issues ............................................................................................................... 5 2 Main Earth Bonding Bar ...................................................................................................... 5 3 Lightning Protection Earthing System ............................................................................... 9 3.1 References to IEC Standards ................................................................................................ 9 3.2 System Description ................................................................................................................ 9 3.3 Construction and Design ...................................................................................................... 10 4 Low Voltage Earthing System ........................................................................................... 12 4.1 References to IEC Standards .............................................................................................. 12 4.2 System Description .............................................................................................................. 12 4.3 Construction and Design ...................................................................................................... 12 4.4 Responsibility ....................................................................................................................... 12 5 High Voltage Earthing System .......................................................................................... 12 5.1 References to IEC Standards .............................................................................................. 12 5.2 System Description .............................................................................................................. 12 5.3 Construction and Design ...................................................................................................... 14 6 Earthing During Turbine Installation ................................................................................ 15



Foreword

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1 Foreword

The Vestas Earthing System consists of individual earthing electrodes

interconnected as one common earthing system.

This document describes the earthing system and the background related to an

anchor cage foundation.

The Vestas Earthing System is designated for both safety earthing and functional

earthing.

The Vestas Earthing System consists of the following sub systems:

High voltage system.

Low voltage system.

Lightning protection system.

Foundation earthing.

Earthing between wind turbines.

In terms of lightning protection of the wind turbine, Vestas has no requirements

for a certain minimum resistance to remote earth for this system. The earthing for

the lightning protection system is built into the construction of the Vestas Earthing

System.

One part of the Vestas Earthing System is the main earth bonding bar placed

where all cables enter the wind turbine. The earthing electrodes are connected to

the main earth bonding bar. In addition, equipotential connections are made to all

cables entering or leaving the wind turbine.

The Vestas Earthing System specifications and work descriptions are the

minimum requirements from Vestas and IEC. Local and national requirements

may require additional measures.

If, for any reason, distances between wind turbines and substation prohibit the

use of doubled interconnections as outlined in section 1.3.2 High Voltage Issues,

p. 5, the requirements for the Vestas Earthing System are not fulfilled. The design

and design principles outlined in this document are void. Vestas does not assume

any responsibility for the earthing functionality.

If any changes are to be made to the Vestas Earthing System, case studies must

be undertaken to ensure that the alternate design provides sufficient safety

earthing as well as functional earthing protection for the wind turbines. The

design must be in compliance with applicable local, national and project

requirements.

1.1 Related Documents

Document no. Title

0019-2575 Vestas Earthing System - Foundation Earthing - Work

Description of Foundation Earthing on Anchor Cage

Foundation



Foreword

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Document no. Title

0019-2576 Quality Control of Foundation Earthing, Anchor Cage

Foundation

961635 Earthing Between Wind Turbines. Work Description of

Earthing between Wind Turbines

960451 Quality Control of Earthing Between Wind Turbines

961636 Equipotential Connections On Cables. Work Description of

Equipotential Connections of Cables Entering a Wind Turbine

Table 1-1: Required documentation.

1.2 List of IEC Standards

The Vestas Earthing System design is based on and complies with the following

international standards and guidelines:

IEC 61400-24. Wind turbines - Part 24: Lightning protection.

IEC 60364-5-54. Second edition 2002-06. Electrical installations of buildings -

Part 5-54: Selection and erection of electrical equipment – Earthing

arrangements, protective conductors and protective bonding conductors.

IEC 61936-1. First edition. 2002-10. Power installations exceeding 1kV a.c.-

Part 1: Common rules.

1.3 Basic Design Criteria and Assumptions

The following subchapters are the basic design criteria and assumptions with

which Vestas Wind Systems A/S fulfils the requirements in the specified

standards.

The standards permit different options where choices have to be made in order to

define how the standard is fulfilled.

1.3.1 Lightning Protection Issues

The earth termination system (earthing system) for the lightning protection

system and the wind turbines is based on a ‘Type B arrangement’, according to

IEC 61400-24 Wind turbine - Part 24: Lightning protection, clause 9.4.

Based on these standards, the Vestas Earthing System consists of a foundation

earth electrode including a minimum of two horizontal earth electrodes

(interconnection wires).

The standards do not require a minimum resistance to remote earth on the

earthing system from a lightning protection point of view. Based on the fulfilment

of the above mentioned requirements, the soil conditions around the wind turbine

and its foundation do not matter, only the extension of the foundation and the

added horizontal earthing electrodes.

Protective measures against injury to living beings due to touch and step voltage,

according to IEC 61400-24, clause B.3 are dealt with by the following:

The down conductor of the wind turbine is designed to reduce touch voltage

to an acceptable level in order to protect living beings from injury. The down

conductor of the lightning protection system is defined as the entire tower



Main Earth Bonding Bar

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construction (a natural down conductor) which is practically one large

extensive metal framework.

Equipotentialisation of constructions and surrounding soil by means of a

meshed earthing system reduces step voltage to a tolerable level in order to

protect living beings from injury. The design is done by connecting the entire

interconnected foundation earthing (all steel bars in the foundation) to the

earth interconnection wires between the wind turbines.

1.3.2 High Voltage Issues

The high voltage earthing system for the wind turbines is a multi-earthed system

(global earthing system) according to IEC 61936-1. First edition 2002-10. Power

installations exceeding 1kV a.c.- Part 1: Common rules.

The high voltage earthing system is called a multi-earthed system because all

wind turbines and substations are connected by interconnection wires and a

concentric cable screen or earth wire. This forms a part of the high voltage cables

that are also connected to the wind turbines and the substation.

Because of the double interconnection of all wind turbines and the substation in

connection to the grid, the earthing system is not dependent on the earth/soil as

a return path for the fault currents in the grid.

Based on this assumption, the soil conditions around the wind turbines and the

resistance to remote earth of the earthing system are not a concern because all

fault currents are handled by direct connections of known dimensions and

lengths.

2 Main Earth Bonding Bar

A main earth bonding bar is installed at the bottom of the tower. All earthing

connections are connected directly to this bar. In addition, equipotential

connections to all cables or cable screens are made immediately after the cables

enter the wind turbine.

The equipotential connections on all cables are made to secure a strict line in the

lightning protection zone concept, which is the basis of the entire IEC based

lightning protection system for Vestas wind turbines. The connections are also

made to avoid any large current loops inside the tower, which can cause

hazardous induced voltage in the control systems of the turbines.

The main earth bonding bar is bolted directly to the base frame of the switch

gear’s backside, which is installed directly on the foundation section of the tower.

The main earth bar is connected directly to the tower and all other metal parts of

the wind turbine through two 50 mm2 earth copper wires.

The placement of the main earth bonding bar can be seen in Figure 2-1, p. 6. The physical dimensions of the main earth bonding bar can be seen on Figure 2-5, p. 8.

The switch gear is available in three versions: a two panel, a three panel and a

four panel. The installations of the main earth bonding bar for the three different

versions are shown in Figure 2-2, p. 6, Figure 2-3, p. 7 and Figure 2-4, p. 7.




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Figure 2-1: Placement of the main earth bonding bar on the back of the switch

gear.

Figure 2-2: Main earth bonding bar installed on the backside of the base frame for

four panels.




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three panels.


two panels.




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Figure 2-5: Physical dimensions of the main earth bonding bar.



Lightning Protection Earthing System

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Cable screens or concentric earth wire in all the high voltage cables entering the

tower are connected to the main earth bonding bar. They are connected directly

at the point of entrance unless the switchgear is placed on the basement floor

where the high voltage cables enter.

Fibre optic cables with metallic cable screens and other metallic components are

also connected directly to the main earth bonding bar at the point of entrance.

All conventional copper signal, control or communication cables must enter the

turbine via overvoltage arresters placed in an equipotential box installed directly

on the main earth bonding bar.

All low voltage cables entering the wind turbine (not main power cables but power

for meteorology stations, outdoor lights, antennas etc.) must enter the turbine via

overvoltage arresters placed in an equipotential box. This box contains

overvoltage arresters specific to the power system in the cables entering and

leaving the turbine. The number of equipotential boxes depends on the number

of cables entering the turbine.

A detailed description of how cables and cable screens are connected to the

main earth bonding bar is given in document 961636 ‘Vestas Earthing System -

Equipotential Connections on Cables’.

Fibre optic cables without metallic components approved by Vestas are allowed

to enter the turbine without connection to the main earth bonding bar.

3 Lightning Protection Earthing System

3.1 References to IEC Standards


international standards and guidelines in relation to lightning protection earthing

system:

IEC 61400-24. Wind turbines - Part 24: Lightning protection.

Vestas offers an approved earthing system designed for an anchor cage

foundation of a tubular steel tower.

The design documentation consists of

– a document describing the foundation earthing at each turbine site

– a document describing the earthing between the wind turbines and/or

substation

– a document describing the equipotential connections of all cables entering

a wind turbine and

– a document describing the requirements of a complete Vestas Earthing

System.

3.2 System Description

The lightning protection included in the Vestas Earthing System consists of the

following three individual earthings:

:

– The foundation earthing




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– The earth interconnection wires (horizontal earthing electrode) for a single

turbine

– The interconnected earth interconnection wires in a wind farm or in a grid

The two horizontal earthing electrodes are expected to run in different directions

at a minimum angle of 90 degrees. The distance between the turbines must be at

least 80 metres (88 yds). Only the first 80 metres (88 yds) of earth

interconnection wire running between the wind turbines contributes positively to

the earthing of high-frequency lightning currents.

Figure 3-1: Principle drawing of Vestas Earthing System. (DWG. NO. 934675)

Figure 3-2: Equivalent diagram of Vestas Earthing System.

Rh1 Horizontal earthing 1.

Rh2 Horizontal earthing 2.

Rfe Foundation earthing.

3.3 Construction and Design

The Vestas Earthing System is designed as a ’Type B arrangement’ based on

foundation earthing supplemented by a minimum of two horizontal earthing

electrodes. The electrodes have a minimum length of 80 metres (88 yds).

Because of this, there are no requirements of a certain minimum resistance to

remote earth as far as lightning protection is concerned. Sometimes local

Main earth bonding bar

Rh1

Rh2

Rfe

E




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requirements require a certain minimum resistance to remote for other reasons.

This issue is described later.

Conductors in the system consist of bare 50 mm2 (AWG 1/0) stranded Cu wires

and the reinforcement steel bars in the concrete foundation. All connections in

the system are doubled.

All parts in the earthing system have the same galvanic potential. This way, no

galvanic corrosion will occur in the earthing system assuming that only parts

specified by the Vestas work descriptions are used on the system.

Additional earthing electrodes can be connected to the system outside of the

turbine foundation, but these additional earthing electrodes or conductors must

be copper and/or stainless steel in order to prevent corrosion.

The 50 mm2 (AWG 1/0) stranded Cu wires embedded in the steel reinforced

concrete foundation are connected by connection terminals for secure

connections between the copper earthing wire and the crossing reinforcement

steel bars every 5 metres (16’) along the earthing wire. Also, the copper earthing

wire is connected to all the crossing reinforcement steel bars with steel wire ties.

The following documents describe foundation earthing at each wind turbine:

0019-2575 Vestas Earthing System Foundation - Earthing Work Description of

Foundation Earthing on Anchor Cage Foundation.

0019-2576 Quality Control of Foundation Earthing, Anchor Cage Foundation.

The following documents describe earthing between the wind turbines:

961635 Vestas Earthing System - Earthing Between Wind Turbines, Work

Description of Earthing Between Wind Turbines.

960451 Quality Control of Earthing Between Wind Turbines.

For detailed description of the equipotential connections of cables entering a

wind turbine, refer to 961636 ‘Vestas Earthing System - Equipotential

Connections on Cables’.

These descriptions also contain minimum requirements for inspection during and

after the installation work.

All earthing connections and down conductors are connected to the main earth

bonding bar placed at the bottom of the tower. All incoming cables (cable

screens) are also connected to the main earth bonding bar.

All metal parts in and within reach of the wind turbine are interconnected and

connected to the foundation earthing system. Because of this, all parts and

surrounding soil will be lifted to the same potential when currents are running in

the earthing system. When all metal parts and surrounding the soil are levelled at

NOTE

NOTE

NOTE



Low Voltage Earthing System

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the same potential (voltage), no unacceptable touch or step potential (voltage)

will occur.

4 Low Voltage Earthing System



international standards in relation to low voltage earthing systems:

IEC 60364-5-54. Second edition 2002-06. Electrical installations of buildings

- Part 5-54: Selection and erection of electrical equipment – Earthing

arrangements, protective conductors and protective bonding conductors.


The Vestas Earthing System, when relating to the low voltage system in the wind

turbine, is the same as described in section 3.2 System Description, p. 9.


The construction and design of the Vestas Earthing System in relation to the low

voltage system at a wind turbine site is the same as described in section 3.3

Construction and Design, p. 10.

4.4 Responsibility

Vestas does not have an obligation to review and approve earthing system

designs that deviate from the Vestas Earthing System. Vestas thereby disclaim

the responsibility for designs deviating from the Vestas Earthing System.

5 High Voltage Earthing System



international standards in relation to high voltage earthing systems:

IEC 61936-1. First edition. 2002-10. Power installations exceeding 1kV a.c.-

Part 1: Common rules.


For each wind turbine, the Vestas Earthing System for high voltage is the same

as described in section 3.2 System Description, p. 9. Every wind turbine and

substation is also connected by an earth interconnection wire, as shown in Figure

5-1, p. 13 and Figure 5-2, p. 14.

This earth interconnection wire serves as both a part of the earthing system and

also as a part of the lightning protection of the high voltage cables. The cables

are running between each wind turbine and also between wind turbines and

substations.



High Voltage Earthing System

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Figure 5-1: Principle drawing of earthing system on a grid (transformer and

switchgear inside the wind turbine). (DWG. NO. 934668)



High Voltage Earthing System

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Figure 5-2: Principle drawing of earthing system on a grid (transformer and/or

switchgear outside the wind turbine). (DWG. NO. 934671)


The construction and design of the Vestas Earthing System in relation to the high

voltage system at a wind turbine site is the same as described in section 3.3

Construction and Design, p. 10. Additionally, the system is based on bare 50

mm2 (AWG 1/0) stranded earth interconnection wires connecting wind turbines

and, when possible, the substation.

Additional measures to reduce step and touch voltage around the tower and/or

switchgear/transformer house may be required based on earth fault current

calculations. Additional earthing electrodes to reduce step and touch voltage can

be connected to the Vestas Earthing System outside the foundation. Only

additional earthing electrodes made of copper and/or stainless steel can be used

in order to prevent corrosion.



Earthing During Turbine Installation

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6 Earthing During Turbine Installation

As soon as the foundation earthing wires are connected to the main earth

bonding bar, the foundation earthing can be used as a temporary earthing during

turbine installation. Earthing is done by connecting to the main earth bonding bar.

This procedure is applicable for any part of the wind turbine; blade, rotor, nacelle

and tower sections etc. to avoid static discharge while handling the parts of the

wind turbine during installation.

The foundation earthing can also be used when a portable generator set requires

an interim earthing.