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7/31/2019 KEMA Review of International Network Design Standards Practices and Plant and Equipment Specifications - 2009

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REVIEW OF INTERNATIONAL

NETWORK DESIGN STANDARDS,

PRACTICES AND PLANT AND

EQUIPMENT SPECIFICATIONS

KEMA LimitedURN 09/748


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DWGDWGDWGDWG PG2PG2PG2PG2

REVIEW OF INTERNATIOREVIEW OF INTERNATIOREVIEW OF INTERNATIOREVIEW OF INTERNATIONALNALNALNAL

NETWORK DESIGN STANDNETWORK DESIGN STANDNETWORK DESIGN STANDNETWORK DESIGN STANDARDS,ARDS,ARDS,ARDS,

PRACTICES AND PLANTPRACTICES AND PLANTPRACTICES AND PLANTPRACTICES AND PLANT ANDANDANDAND

EQUIPMENT SPECIFICATEQUIPMENT SPECIFICATEQUIPMENT SPECIFICATEQUIPMENT SPECIFICATIIIIONSONSONSONS

CONTRACT NUMBER:DG/CG/00089/00/REP

URN NUMBER: 09/748

ContractorContractorContractorContractor::::

KEMA Limited

The work described in this report was carried out under

contract as part of the DECC Emerging Energy Technologies

Programme, which is managed by AEA. The views and

judgements expressed in this report are those of the

contractor and do not necessarily reflect those of the DECC

or AEA.

First published 2009

Crown Copyright 2009


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(i)

EXECUTIVE SUMMARY

The objective of this study is to identify good international practices and learningopportunities in the construction of efficient and low carbon distribution networks.

The Electricity Network Strategy Group (ENSG) provides advice to the British

Government and electricity regulator on issues associated with the development ofelectricity distribution and transmission networks. It is chaired jointly by theGovernment and the regulator, and has senior representation from networkoperators, generators and other industry participants. Their aim is to identify and co-ordinate the technical, commercial and regulatory issues in electricity distributionnetworks in transition to a low carbon future.

As part of their on-going work the ENSG has commissioned KEMA to undertake areview of International Network Design Standards, Practices and Plant andEquipment Specifications.

KEMA has interviewed Distribution Network Operators (DNO) in the Netherlands,

Germany, Spain, UK and the United States to collect the necessary information onnetwork planning and design standards. These DNOs were selected because of theircomparability with the UK network in relation to network structure, size, density andregulation.

To facilitate and structure the discussions with the DNOs, KEMA developed aquestionnaire, covering topics such as Network Planning Standards, networkarchitecture, network characteristics, network Distributed Generation (DG)penetration and rate of deployment, network innovation, design specifications andoperational considerations.

The questionnaire outlined the type and extent of information required from each

DNO in order to obtain a consistent set of data. The questionnaire was issued toeach DNO in advance of the face to face meeting. This enabled participants toconsider questions beforehand for the information gathering meeting.

The findings from the discussions form the basis of the Review of InternationalNetwork Design Standards, Practices and Plant and Equipment Specifications. Thereview is further supplemented by an extensive documentation research and reviewof international publications and European and American collaborative research anddevelopment projects.

The main findings can be categorised under three main headings of Network Design,Loss Management and Integrating DG & Renewable Energy System (RES) and the

key study findings under each heading are;

Network Planning, Design and Specification:

Of the countries studied, only GB has a national baseline planning standard(Engineering Recommendation P2/6) encompassing the distribution networkand stating the minimum requirements for network security and loadrestoration following an unplanned interruption.


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This British planning standard is the only one to to formally acknowledge thepotential security contribution of DG and RES for consideration duringnetwork planning activity. The other DNO study participants do not currentlyformally consider the potential contribution from DG or RES at the networkplanning phase.

All companies participating in the study recognised and utilised the globalInternational Electrotechnical Commission (IEC) standards but to varyingdegrees. The European companies all cited IEC standards as the principalstandards used with the US company stating a lesser reliance. In the US thepredominant equipment specifications utilise the IEEE and ANSI standards.

There is a general consensus that it is preferential in the long run to selectequipment based on the total cost of ownership (TCO) or life-cycle cost (LCC)than simply initial capital cost. All study participants use the LCC approach toselect network components such as transformers, cable and auto-reclosers.

All the European companies consider they have rationalised equipment

ratings and stores inventory as far as practicable to provide a minimised set ofcomponents to meet current design requirements. They acknowledge thisapproach may introduce a degree of over capacity in network installations butit also allows a degree of flexibility for any future development.

Loss Mitigation:

Approximately 70% of the losses in electricity networks occur in thedistribution network with conductor accounting for 42% of these losses andtransformers circa 30%.

Two studies from British universities examined the carbon benefits from the

use of conductor with a greater cross sectional area than the supplied loaddemanded. Both studies concluded that there are significant carbon benefitsfrom the reduction in losses over the life time of the oversized conductor; thepayback period was found to be 20 years which is well within conductor lifespans. The more recent Bath study also accounted for the embedded carboncost of producing larger cables and concluded that this is not a material factorcompared to the loss savings achieved when assessing life time benefits.

In the United States the Energy Policy and Conservation Act (EPCA) directedthe Department of Energy (DOE) to specify minimum efficiency standardsinitially for LV and subsequently MV distribution transformers.

A new standard, EN 50464, for oil-immersed distribution transformers up to36kV was introduced to improve the efficiency of installed transformers at thespecific request of the European Commission. New high efficiency classes oftransformer have been introduced in respect of both load and no load losses.

Integrating DG & RES:

DG penetrations relative to the total installed capacity of HV/MV transformersis highest in the German and Dutch DNOs. This situation is also reflected in


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the national deployment levels of DG & RES in relation to total generationcapacity.

The high penetration of DG & RES has been readily achievable in Germanyand the Netherlands to date due to the ability of the robust network designs toaccommodate generation capacity through traditional network design

approaches.

The awareness of active network management technologies, particularly inthe fields of voltage control and power flow management, is strongest in theGB industry. Although DG & RES deployment is comparatively low in GBthese issues arise sooner than in other jurisdictions due to the nature oflegacy network designs.

In addition to the more immediate network operational needs, research,development, trial and deployment of ANM technologies is further encouragedwithin the GB DNOs by Regulatory incentive through the Innovation FundingIncentive (IFI) introduced in 2005 and the Registered Power Zone (RPZ)

scheme for innovative DG & RES connection. This has led to the directparticipation of DNOs in the identification, development and ownership ofappropriate new technology projects and is a distinct advantage over theEuropean counterparts that rely to a greater extent on collaborativeapproaches with academia or participation in European programmes.

There is scope to reduce the high levels of time and effort expended on theassessment of proposed DG and RES network connection viability. A webbased assessment tool has been developed and trialled by 3 UK DNOs andlong term development statements are available to reduce DNO anddeveloper engineering effort.

Recommendations

The study has determined that the UK DNOs are at the forefront of developinginnovative technical solutions for the connection of low carbon RES and otherdistributed generation into distribution networks. This direct participation should beencouraged through the continuation of schemes such as the IFI and RPZ incentiveschemes.

Commercial tools are now available that enable a DNO to significantly reduce theeffort required from scarce engineering resources in the assessment of the viabilityof proposed generator connections. One tool offers a stand alone web basedsolution whilst another utilises the GIS environment to integrate other legacy

applications. DNOs should explore the business case for employing such tools intheir own operational environment.

Providing appropriate locational signals to generation developers for the extent andlocation of generation capacity acceptable to particular network locations wouldreduce the effort expended by DNOs on assessing site applications that prove to beunviable. Such tools are at an early stage in development but are considered worthyof moving to trial development by DNOs following successful modelling.


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Consideration should be given to mandating the installation of high efficiencytransformers initially at the lower distribution voltages.


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TABLE OF CONTENTS

Executive summary...................................................................................................iTable of contents......................................................................................................v1. Introduction........................................................................................................1

1.1Background...........................................................................................1 1.2Aim & Objectives...................................................................................1

2. Approach to Project...........................................................................................23. International DNO Review & Comparison........................................................3

3.1 Introduction ...........................................................................................33.2Network Characteristics ........................................................................3

3.2.1 Overview ................................................................................33.2.2 HV Network ............................................................................ 53.2.3 MV Network............................................................................63.2.4 LV Network.............................................................................63.2.5 Installed Transformers............................................................73.3Planning Standards & Practices............................................................73.3.1 Standards...............................................................................7 3.3.2 Security ..................................................................................83.3.3 Availability ..............................................................................93.3.4 DG / RES Considerations.....................................................10

3.4Design & Equipment Specification ......................................................103.4.1 Design Optimisation & Loss Management ........................... 103.4.2 Equipment Standards and Specification...............................113.4.3 Equipment Selection & Rationalisation.................................143.4.4 Issues...................................................................................14 3.4.5 Resource requirement..........................................................15

3.5Performance Measurement.................................................................153.5.1 Overview .............................................................................. 153.5.2 Trends.................................................................................. 19

3.6Network Automation............................................................................203.6.1 Overview .............................................................................. 203.6.2 Auto-reclosing Circuit Breakers............................................203.6.3 Remote Control ....................................................................203.6.4 Automation........................................................................... 21

3.7DG & RES Deployment.......................................................................223.7.1 Generation Technologies ..................................................... 223.7.2 DNO Network Penetration....................................................233.7.3 Country Penetration .............................................................233.7.4 Trend....................................................................................24 3.7.5 Connection Guidelines .........................................................25Great Britain.....................................................................................25

3.8 Innovation ...........................................................................................273.8.1 Overview .............................................................................. 27

4. Potential Low Carbon Network Technologies............................................... 314.1 Introduction .........................................................................................314.2Network Loss Reduction .....................................................................31


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4.2.1 Technical Losses..................................................................324.2.2 Loss Mitigation .....................................................................334.2.3 Conductor selection..............................................................354.2.4 High efficiency transformers................................................. 354.2.5 Regulatory incentives ........................................................... 38

4.3 Integrating DG and RES .....................................................................384.3.1 Introduction...........................................................................384.3.2 Active Network Management................................................394.3.3 Voltage support and network security .................................. 394.3.4 Power Flow Management.....................................................404.3.5 Locational Signals ................................................................404.3.6 Fault Level Management......................................................414.3.7 Grid losses ...........................................................................42

4.4Energy storage....................................................................................434.5Towards Smartgrids ............................................................................ 44

5. Key Findings .................................................................................................... 476. Recommendations...........................................................................................51


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1. INTRODUCTION

1.1 Background

The Electricity Network Strategy Group (ENSG) provides advice to the BritishGovernment and electricity regulator on issues associated with the development of

electricity distribution and transmission networks.

The ENSG is chaired jointly by the Government and the regulator, and has seniorrepresentation from network operators, generators and other industry participants.Their aim is to identify and co-ordinate the technical, commercial and regulatoryissues in electricity distribution networks in transition to a low carbon future.

As part of their on-going work the ENSG has commissioned KEMA to undertake areview of International Network Design Standards, Practices and Plant andEquipment Specifications. The aim of this study is to identify good internationalpractices and learning opportunities in the construction of efficient and low carbondistribution networks.

1.2 Aim & Objectives

The objectives set out for this project are:

To study and document distribution network design and operation standards,principles and practices as applied in developed and developing countriescharacterised by increasing penetrations of DG with strong commitments to reducingcarbon emissions. Comparisons should then be drawn with any equivalent UKdesign standards and operating practices.

To include an overview of the high level design principles and any relevant networkcost, efficiency and performance metrics as adopted in the countries of majorinterest.

To review current International / European plant and equipment specifications and tocompare with typical UK DNO specification.

To identify low-cost / high capacity DG connection techniques and low Carbon / lowloss network design principles in order that similar initiatives may be recommendedfor implementation in the UK.

To identify potential changes to DNO design standards, practices andplant/equipment specifications that could facilitate a transition to lower carbon/lowercost distribution networks in the UK, thus contributing to the delivery of a low carboneconomy in the short, medium and long term.


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2. APPROACH TO PROJECT

To perform the review as set out in section 1.2, the project has been executed with atwo stage approach:

a) Discussions with international Distribution Network Operators

b) Documentation Research & Review

KEMA contacted five Distribution Network Operators (DNO) in Europe and theUnited States to collect the necessary information on network planning and designstandards. These DNOs were selected because of their comparability with the UKnetwork in relation to network structure, size, density and regulation. The finalselection was approved by DWG-PG2 steering group.

To facilitate and structure the discussions with the DNOs, KEMA developed aquestionnaire, covering the topics such as Network Planning Standards, networkarchitecture, network characteristics, network DG penetration and rate ofdeployment, network innovation, design specifications and operational

considerations.

The questionnaire outlined the type and extent of information required from eachDNO in order to obtain a consistent set of data. The questionnaire was issued toeach DNO in advance of the face to face meeting. This enabled participants toconsider questions beforehand for the information gathering meeting.

The questionnaire included several questions seeking statistical network informationthat could be completed prior to the meeting. However, for the majority of thequestions, the questionnaire served as a guideline to structure the discussionmeeting between KEMA and each DNO.

Prior to issuing the questionnaire to the international DNOs, a pilot interview wasconducted with an UK DNO to test and finalise the questions.

After the discussions, the findings were captured in narrative and tabular form byKEMA and submitted for review to the interviewed parties.

These findings form the basis of the Review of International Network DesignStandards, Practices and Plant and Equipment Specifications. The review is furthersupplemented by an extensive documentation research and review of internationalpublications and European and American pilot projects.


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3. INTERNATIONAL DNO REVIEW & COMPARISON

3.1 Introduction

Discussions were held with several European (Britain, Germany, Spain,

Netherlands) and one US distribution network operator (DNO) based on a standardset of topics and queries that were issued to each participant in the form of aquestionnaire prior to the meeting. High level characteristics of each DNO area areshown in Table 1.

Representative DNO CharacteristicsCharacteristics

GB Spain Germany NL USA

Customers (million) 2.2 11.5 1.6 4.5 1.7

Peak Demand (GW) 4.3 19.4 2.8 4.5 9.8

Annual Demand (TWh) 20 107 17.6 35 67

Population Density (/km2) 244 88 233 393 -

Table 1 International DNO characteristics

The following sections outline and compare the results by questionnaire topic areafrom these discussions.

3.2 Network Characteristics

3.2.1 Overview

In common with distribution networks globally those investigated in detail for thisstudy exhibited a typical hierarchical model for transformation points and voltagelevels from the transmission infeed to the customer connection. This demonstrates a

universally applied approach to energy supply; from centralised generation, to bulktransportation and a tapered uni-directional distribution system to the point of use.

Within this hierarchy, however, there are notable international differences in thedegree of rationalisation of voltage levels and the network kilometres required toserve the end customer. There are several historical reasons for this situation suchas the planning philosophies that have been in place and the topology of thegeographical area served.

Network voltage categorisation also differs between the UK and Europe as indicatedin Figure 1.


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220kV

380kV

400kV

HV275kV

400kV

Tran

smis

sion

400VLV400VLV

20kV

10kvMV

6.6kV

11kVHV

50kV

38kVMV

66kV

33kVEHV

110kVHV132kV132

EuropeUK

Transmission

Distribution

T1

T2 T3

220kV

380kV

400kV

HV275kV

400kV

Tran

smis

sion

400VLV400VLV

20kV

10kvMV

6.6kV

11kVHV

50kV

38kVMV

66kV

33kVEHV

110kVHV132kV132

EuropeUK

Transmission

Distribution

T1

T2 T3

Figure 1 Voltage categorisation in UK and Europe

The distribution network hierarchy in England and Wales generally commences atthe 132kV transmission boundary which is sometimes stepped down to 66kV butusually 33kV (EHV) levels prior to transformation at Primary substations to the maindistribution HV voltages of 11kV and 6.6kV. Final voltage transformation from HV toLV is performed at Secondary substations.

To aid network comparison the UK 6.6kV, 11kV and 33kV (and US 2.4kV to 46kV)network voltages have been aligned with the European MV voltage category and the66kV and 132kV (US 115kV to 161kV) networks aligned with the European HV

voltage category.

Transformers in the UK have been classified as follows:

HV / MV (T1 and T3 in Fig 1) 132kv/33kV, 132kV/11kV, 66kV/11kV

MV / MV (T2 in Fig 1) 33kV/11kV

MV / LV 11kV/0.4kV

Comparisons of network and transformer parameters for representative DNOs fromeach of the countries studied are shown in Table 2 and Table 3 respectively.

In general, it appears that GB has a comparatively efficient network in terms of thenumber of customers serviced per network kilometre and other countries are lessreliant on intermediate voltage levels with HV/MV (typically 110kV/10kV)transformation more prevalent.


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Representative DNO ComparisonNETWORK


Voltages (kV)HV 132, 66 132, 110, 66 110 none 161, 138, 115

MV

33, 11, 6.6 36,25,11 30, 20, 15, 10 30, 20, 10, 3 46, 34.5, 24.9,22, 20.8, 13.2,12.47, 12,11.76, 11.7,9.1, 7.2, 5.25,4.16, 2.4

SC Rating

HV5,700 MVA(132kV)

5,800 MVA(110kV)

4,000 MVA(110kV)

n/a 40kA (115kV)

MV250 MVA(11kV)

176 MVA(11kV)

260 MVA(20kV)

250 MVA(10kV)

270 MVA(12.47kV)

Configuration

HV 132kV radial,66kV closedring

Mesh Mesh n/a Closed ring

MV Open ring,radial

Closed ring,some crossconnection

30kV closed,20/10kV openring + crossconnection

Open ring,radial. 10kVcleaninterconnectors.

Radial, openring.

LV radial radial radial radial radial% Network overhead

HV 86 96 99 n/a 99

MV 46 70 38 0 71

LV 6 7 42 0 Not available

Network Km / 1000 customersHV 1 2 4 n/a 10

MV 10 10 16 18 64

LV 12 15 30 24 Not available

Table 2 Comparison of DNO network parameters

Representative DNO ComparisonTRANSFORMERS


Installed transformer capacity (MVA)HV/MV 12,156 79,020 10,003 n/a 16,330

MV/LV 6,743 48,869 5,715 n/a unavailable

Customers / transformerHV/MV 8,200 5,825 5,000 8,300 1,592

MV/LV 70 90 95 50 3

Installed MVA / 1000 customers

HV/MV 6 7 6 4 9.6

MV/MV 6 0.2 0.2 n/a n/a

MV/LV 3 4 4 6 14

Table 3 Comparison of DNO transformer parameters

3.2.2 HV Network

In the Netherlands the DNOs no longer operate network assets at or greater than110kV. This network is now operated by the national Transmission System Operator,TenneT.

The HV network across Europe and the United States is generally designed andoperated with redundancy providing a security level of n-1.


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A high percentage of the HV network, circa 90%, is overhead in all countries studied.

3.2.3 MV Network

The higher level medium voltage networks operating at 30kV and above in all DNOsstudied tend to be configured as a closed ring or mesh, providing n-1 levels of

security.

Distribution feeders in the 10kV and 20kV range are commonly operated as openrings in more densely populated areas and radially in more rural areas in allcountries. In Germany these rings are often reinforced with cross-connectionsbetween rings and in the Netherlands greater flexibility and security is achievedthrough the use of clean interconnectors between MV distribution stations. Boththese configurations provide operational advantages and provide greaterredundancy to the GB DNO network.

As illustrated in Table 2, compared to the GB DNO the installed MV networkkilometres per 1000 customers is 60% higher in the German DNO, with a similar

country population density, and 80% higher in the Dutch DNO with a higherpopulation density. This demonstrates the higher levels of redundancy built into theDutch and German DNO MV networks as a consequence of historic planningphilosophies.

There is a greater variation in the proportion of overhead MV networks in each DNOranging from 0% in the Netherlands to 64% in the United States. All DNOs reportedthat the preference today is to design and install MV networks underground.

Rationalisation of MV voltage levels has been greater in Europe than the US with10kV (NL), 11kV (GB, Spain) and 20kV (Germany) being the most commondistribution feeder voltages. Although a large variation exists in the US the prevailing

voltage level is 12.47kV (90%) and the opportunity to convert legacy networks to thisstandard is taken whenever possible.

3.2.4 LV Network

Low voltage network configurations employed today are universally radial in naturealthough legacy networks in GB and Germany do have a degree of interconnectionand redundancy. Interconnected LV networks are considered expensive to maintainin the German DNO which has approximately 20,000 link boxes, and in all the DNOsstudied new LV networks are radial as the economic case for additional expenditurein providing interconnection is poor.

European LV network installations are predominantly underground except inGermany where 42% is overhead. Figures for the US DNO were not available,however, overhead distribution remains commonplace.

The LV network kilometres per 1000 customers in the Netherlands and Germany ishigh at 24km and 30km respectively and is double that installed in GB and Spain.


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3.2.5 Installed Transformers

In GB there is a greater reliance on the intermediate MV(EHV)/MV(HV) (33kV/11kV)transformation level than in other countries where HV/MV transformation is morecommon. This is clearly illustrated when the installed MV/MV capacity per 1000customers in GB, 30 times that of Spain & Germany, is compared in Table 3.

Similarities are apparent between the number of customers connected pertransformer in GB / Netherlands and Spain / Germany.

3.3 Planning Standards & Practices

3.3.1 Standards

Of the countries studied, only GB has a national baseline planning standard(Engineering Recommendation P2/6) encompassing the distribution network andstating the minimum requirements for network security and load restoration followingan unplanned interruption. This standard is based on load recovery criteria of ademand group by capacity and time, rather than network characteristics andpurpose.

In the Netherlands there are national planning requirements for the 110kV, andhigher, network but operational and development responsibility for this network hasrecently transferred from the DNOs to TenneT, the Transmission System Operator.

All the review participants have formalised and documented Company planningstandards in place that have recently been reviewed. The review cycle is eitherdriven by periodical review, expiry date and by regional changes in networkrequirements. These standards may vary by region within companies where DNOoperations cover a large area where different legacy technical requirements haveevolved, but there is a desire to harmonise future network development.

Historically, in GB company planning policies often exceeded national planningstandard requirements and the extent of current planning enhancements isinfluenced by regulatory capital expenditure allowances and performance incentives.

The Spanish DNO has adopted a unique approach to the advancement of networkplanning standards through the development of optimised Best Grid models. Twomodels have been developed, one for the HV network and one for the MV, and arebased on known load and generation locations from which an economically andreliability optimised, best model, network is planned. Actual network practicalitiesand requirements are then referenced against the best model to achieve as close amatch as possible.

In recent times the introduction of regulatory incentives in GB and minimum legalrequirements in Spain for customer service criteria has had a major influence onnetwork planning activity. The GB DNOs are financially rewarded for performancebeyond declared regulatory annual performance targets and have responded byimplementing network automation and remote control investments within the currentplanning standards. If they fail to meet performance targets there is a symmetricalfinancial penalty.


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In Spain national customer service targets have been established which all DNOsmust achieve or face a financial penalty. There is no financial reward for achieving alevel of performance beyond the minimum requirement, resulting in networkinvestment geared to this end.

All companies regard their design philosophy as fluid and require constant reviewing

and updating to reflect changes in technology, regulation, embedded generation anddemand.

3.3.2 Security

The security of supply to customers is dependent on the level of equipmentredundancy in the network. For instance, a group of customers supplied by a singlecircuit will experience a loss of supply for a fault on that circuit; but if a second circuitwere to be operated in parallel with the first no supplies would be lost due to a singlefault on either circuit. These network configurations are commonly referred to,respectively, as n-0 and n-1 security criteria.

Information sourced from interviews suggests that the High Voltage category ofdistribution network is normally planned to a security level of n-1 in German, Dutchand the Spanish DNO. In GB, although not strictly required by the security planningstandard Engineering Recommendation P2/6, the majority of HV networks also meetn-1 criteria in reality.

The security criteria of the Dutch 110kV and 150kV network complies with n-1criteria with the caveat that up to a maximum of 100 MW of load may be interruptedfor a period not exceeding 10 minutes. In the event of a network fault occurringduring a maintenance outage a load interruption not exceeding 100 MW or 6 hours ispermissible.

In Germany the 30kV, in GB the 33kV and in the US the 34.5kV MV networks arealso generally planned to observe n-1 security criteria.

Medium Voltage networks operating at 20kV and below in all countries tend to beoperated as open rings, are more radial in nature and are planned with no immediateredundancy, ie n-0. However, alternative supplies to restore the majority ofcustomers are quickly available from the other side of the open ring. In Spain butparticularly in Germany networks are sometimes further reinforced through additionalcross-connection lines between rings.

The Dutch 10kV distribution network operates at two levels; 1) a strong backbonewith parallel circuits connecting 10kV busbar stations and 2) an open ring or radial

distribution feeder network radiating from the busbar stations. The 10kV backbone isplanned to n-1 criteria (as a minimum) and the feeder network to n-0. Very fewcustomers are connected to the backbone circuits and it is now policy to connect allcustomers to the distribution feeder network.

At the Low Voltage level, historical networks, particularly in GB and Germany, adegree of redundancy that enables feeder reconfiguration and supply restoration inthe event of a fault may be available. Today, however, all DNOs install radial LV


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networks with little or no interconnection but capable of support from mobilegenerator connections when required.

Output measures for annual network reliability are recorded as CI (CustomerInterruptions per 100 connected customers) in Germany, GB and the Netherlandsand NIEPI (interruptions per installed transformer MVA) in Spain. The US uses

System Average Interruption Frequency Index (SAIFI) as a measure of reliability.

The regulator in the UK, legislature in Spain and Public Utility Commissions (PUC) inthe US have set annual targets for CI, NIEPI and SAIFI performance respectively.

3.3.3 Availability

All companies measure network non-availability parameters as a measure ofnetwork and customer service performance. These measures vary betweencountries and can be based on customers (Customer Minutes Lost, CML), lostenergy (Energy Not Supplied, ENS), installed transformer capacity (time interruptedper equivalent power installed, TIEPI) or simply the number of interruptions. CML is

also expressed as the System Average Interruption Duration Index or SAIDI.Performance measurement is discussed in more detail in Section 3.5.

CML (SAIDI) per connected customer is the availability measure used in Germany,GB, the Netherlands and US whereas in Spain the minutes lost per installedtransformer MVA (TIEPI) is recorded.

In Germany the focus on minimising the duration of outages is left to the integrity andmotivation of the operational staff. There are no company criteria or specifiedstandards for customer or load restoration.

The US Company also relies on the skills and motivation of the operational staff buthas a standard requiring supply restoration to all affected customers within 12 hours.

Although there is no formal restoration criteria in the Netherlands the planningphilosophy of the studied DNO has changed so that MV networks are now beingsimplified to enable the restoration of all but the faulted section of network withinthree switching operations. This represents a marked improvement over previousnetwork configurations that could require up to six actions to restore supplies to thehealthy network. The DNO is currently assessing criteria to measure its ownrestoration performance.

In Spain there is an annual target set by statute for the maximum TIEPI minutes thatcan be incurred by a DNO. The TIEPI target recognises the topological differencesacross the country and is delineated into four zones; urban, semi-urban,concentrated rural and dispersed rural. Zone targets vary from two hours for urban to12 hours for dispersed rural. This TIEPI target implicitly defines the averagerestoration criteria each Spanish DNO must achieve.

A more clearly defined approach to supply restoration criteria is taken in GB where aset of Guaranteed Standards stipulates the maximum time period for supplyrestoration during both normal and severe weather conditions. Failure to meet these


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standards will result in potentially uncapped fixed penalty payments being made bythe DNO to the affected customers.

The definition of outage duration that constitutes a recordable event is uniformacross the countries and DNOs reviewed and is based on the EN 50160 definition ofa long interruption lasting three minutes or longer. However, the Spanish DNO

reported that discussions and debate had commenced to reduce the recordableevent duration to 1 minute.

3.3.4 DG / RES Considerations

All distribution companies in the study acknowledge their obligation to connectDistributed Generation or Renewable Energy Systems to the appropriate networkpoint.

However, the only planning standard to formally acknowledge the potentialcontribution of DG and RES for consideration during network planning activity is theER P2/6 standard utilised by all DNOs in Britain.

The other DNO study participants do not currently formally consider the potentialcontribution (such as voltage support, loss management or deferment of networkreinforcement expenditure) from DG or RES at the network planning phase.

Although the Dutch DNOs have long had a collaborative approach to cogenerationresulting in an agreed Technical Terms of Connection, the DG connected has notbeen considered as supporting DNO network development. The network has beenplanned and designed to accommodate the high levels of DG. Consideration ofnetwork support benefits from larger DG units during network planning and designactivities is now under review by the Dutch distribution network operator.

In Germany, nationally and with the DNO studied, the level of wind generationcapacity connected at HV (>60kV) and EHV is sufficiently high that it could not becovered by reserve generation in the event of a sudden collapse of wind generationoutput. To mitigate this situation all renewables generating plants connecting to theHV or EHV network from September 2004 must provide ancillary services and are nolonger automatically disconnected in the event of a network fault. A guidelinedocument REA generating plants connected to the high- and extra-high voltagenetwork for these connection requirements is published by the Association ofGerman Network Operators, VDN.

3.4 Design & Equipment Specification

3.4.1 Design Optimisation & Loss Management

The Dutch DNO has adopted a risk based, integrated design approach thatconsiders all aspects from technical specification, component reliability, lossminimisation, life cycle costs and environmental considerations.

Losses in the network can be minimised by reducing inefficient power flows in thenetwork through optimising the position of open points in the common open ringdistribution feeder. Only the German DNO selected the location of open points onthis basis, the others cited operational convenience and speed of fault restoration as


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the prime criteria for open point location. Estimated losses for each studied DNO areprovided in Table 4.

Representative DNO Network LossesEstimated Losses


Network Losses

% of input energy 5.5% 8% 5% 4% 12%

Table 4 Percentage network losses

The German and Dutch DNOs experience the lowest losses and also contain thehighest network densities and distributed generation deployment. It was not possiblein the scope of this study to determine if network redundancy or the contribution fromDG had the greatest influence on loss management.

Fault level management and loss management were quoted as secondary criteria foropen point selection by the GB and Spanish DNOs respectively.

A common approach to loss minimisation is the use of larger cross-section conductoror cable than technically required. Of the European DNOs the German and Spanishcompanies are also specifying and installing low loss transformers as an aid to lossreduction, where economically justifiable.

The German DNO also has a policy of optimising the utilisation of HV/MVtransformers at 40%

In the US the Energy Policy and Conservation Act (EPCA) has directed theDepartment of Energy (DOE) to specify minimum efficiency standards for distributiontransformers. The DOE has accepted the efficiency level of LV transformersspecified in the National Electrical Manufacturers Association standard, NEMA TP-1-

2002 and this has been in force for all LV transformers greater than 15kVA capacitymanufactured since January 1, 2007.

From January 1, 2010 there will be a DOE mandatory requirement1 to install higherefficiency MV transformers in the range 10kVA to 2500kVA. It should be noted thatthe economics of high efficiency transformers are impacted by a range of variablesincluding; efficiency improvement, transformer loading, forecast energy cost, timehorizon and cost of capital. In addition the benefits of high efficiency transformers arelinked to transformer utilisation and therefore decline with increasing networkredundancy.

3.4.2 Equipment Standards and Specification

To ensure interoperability and compatibility the power industry, like many industries,have developed many technical standards over the years. These standards aredefined, discussed and formalised in a standards organisation. This can take placeat a national, European or global level.

1DOE 10 CFR Part 431; Energy Conservation Program for Commercial Equipment: Distribution

Transformer Energy Conservation Standards; Final Rule.


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This section presents the best known standard bodies in use by the power industry.At the end of the section a summary list is provided of the most common standardsin use by the network operators.

ISO standards

ISO (International Organisation for Standardization) is a global network that identifieswhat International Standards are required by business, government and society.Standards are developed in partnership with the sector concerned. The derivedcodes, rules and guidelines are the result of consensus from input by numerousnational working groups. ISO is responsible for worldwide implementation ofstandards.

ISO 9001:2000 Quality management systems

ISO 14001:2004 Environmental management systems

IEC standards

The International Electrotechnical Commission (IEC) is a worldwide organisation forstandardization comprising all national electrotechnical committees (IEC NationalCommittees). The object of IEC is to promote international co-operation on allquestions concerning standardisation in the electrical and electronic fields. To thisend and in addition to other activities, IEC publishes International Standards,Technical Specifications, Technical Reports, Publicly Available Specifications (PAS)and Guides. Their preparation is entrusted to technical committees; any IEC NationalCommittee interested in the subject dealt with may participate in this preparatorywork (website IEC). International, governmental and nongovernmental organisationsliaising with the IEC also participate in this preparation. IEC collaborates closely withthe International Organisation for Standardization (ISO). Equipment specifications

applicable to network operators include;

IEC 62271-100 Circuit Breaker,

IEC 62271-102 Disconnector & Earth Switch,

IEC 60076 Power Transformers and

IEC 60502 MV Power Cables.

European standards

The most important European Governmental organisation involved in standards is

CEN, the European Committee for Standardization (Comit Europen deNormalisation). This Committee is an organisation providing an infrastructure tointerested parties for the development, maintenance and distribution of coherent setsof standards and specifications. CEN works closely with the European Committee forElectrotechnical Standardization (CENELEC), the European TelecommunicationsStandards Institute (ETSI), and the International Organisation for Standardization(ISO). CENELEC (European Committee for Electro-technical Standardisation) dealswith the creation of standards in the electro-technical field.


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National implementation of standards is performed by national standard bodies. Inthe case of European Standards (designated 'EN'), the Members must transpose thefinal text ratified by vote into national standards, translating them if desired, butwithout deviation or alteration, and retain the prefix EN in the national designation:e.g. BS EN 1234, NF EN 1234, DIN EN 1234. Thus the number and reference of thestandard are exactly the same throughout Europe. In most countries the technical

content is completed with requirements of explicit national validity and is often basedon long-term practice. Widely used standards include;

EN50160 Voltage characteristics of distribution networks.

EN 60265-2:1994 Specification for high-voltage switches.

EN 50464-2-3:2007 Three-phase oil-immersed distribution transformers 50Hz, from 50 kVA to 2500 kVA with highest voltage for equipment notexceeding 36 kV.

The standardization bodies of the twenty-nine national members represent the

twenty-five member states of the European Union, three countries of the EuropeanFree Trade Association (EFTA) and Turkey, which is likely to join the EU or EFTA inthe future.

Engineering Recommendation (UK)

Engineering recommendations are standards developed by the Energy NetworkAssociation (ENA), the Trade association of the network operators in Great Britain.The ENA is responsible for maintaining the industry-originated TechnicalSpecifications and Engineering Recommendations schedule. Over 400 publicationsare available in the ENA document catalogue. Examples of recommendationsinclude;

Engineering Recommendation G59/1: Recommendation for the connectionof private generating plant to the Public Electricity Suppliers distributionsystems.

Engineering Recommendation G75/1: Recommendations for theconnection of embedded generating plant to public distribution systemsabove 20kV or with outputs over 5MW.

Engineering Recommendation P2/6: Security of Supply.

Engineering Recommendation P14: Preferred switchgear ratings.

Engineering Recommendation P26/1: The estimation of the maximumprospective short circuit current for three phase 415V supplies.

Engineering Recommendation P28: Planning limits for voltage fluctuationscaused by industrial, commercial and domestic equipment in the GreatBritain.

Engineering Recommendation P29: Planning limits for voltage unbalance inthe Great Britain for 132kV and below.


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Engineering Recommendation G83/1: Recommendations For TheConnection Of Small-Scale Embedded Generators (Up To 16 A Per Phase)In Parallel With Public Low-Voltage Distribution Networks.

Trends

All companies participating in the study recognised and utilised the globalInternational Electrotechnical Commission (IEC) standards but to varying degrees.The European companies all cited IEC standards as the principal standards usedwith the US company stating a lesser reliance.

The European companies also subscribe to Comit Europen de Normalisation (EN)standards adapted appropriately for national requirements.

In the US the predominant equipment specifications utilise the IEEE and ANSIstandards.

Where changes to the specifications due to regional technical variations are requiredthese were always cited as operational, safety related or mechanical modificationsby all participants. The electrical specification is not modified.

The GB DNO was the only one to indicate that it was now specifying equipment witha higher short circuit rating as an approach to future-proof the network against ananticipated increase in fault levels above the current 250MVA design level.

All DNOs have changed their MV circuit breaker specification away from SF6interruption medium to vacuum interrupters. However, due to technical limitations ofvacuum interrupters, circuit breakers operating in excess of 36kV are specified withSF6.

3.4.3 Equipment Selection & Rationalisation

There is a general consensus that it is preferential in the long run to selectequipment based on the total cost of ownership (TCO) or life-cycle cost (LCC) thansimply initial capital cost. All study participants use the LCC approach to selectnetwork components such as transformers, cable and auto-reclosers.

All the European companies consider they have rationalised equipment ratings andstores inventory as far as practicable to provide a minimised set of components tomeet current design requirements. They acknowledge this approach may introduce adegree of over capacity in network installations but it also allows a degree offlexibility for any future development.

Due to the many voltages in the inherited legacy networks the extent ofrationalisation in the US has not been so great. However, the company studied iswell aware of the advantages of standardisation and rationalisation and is workingtoward this at every opportunity.

3.4.4 Issues

One common theme regarding design issues emerged with all DNOs; the integrationof current and legacy network designs. These were not regarded as technical issues


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but mainly centred on sourcing equipment which is non-standard with the resultingimpact of lead times and cost.

Optimisation and recovery of DG/RES connection costs is an issue in Germany andthe US, with connection ownership also raised as a concern in the US.

The accuracy of demand forecasting and weather correction techniques hinder thedesign process of the GB DNO whilst the German DNO is receiving requests fromthe transmission network operator to limit fault current levels.

Interestingly, the US network company reported cultural resistance to themodernisation of network design and the Dutch DNO met similar conflict whenproposing design changes.

3.4.5 Resource requirement

As the volumes of DG and RES connections, and therefore the design workload,increases there has been a mixed impact on design resources amongst thecompanies studied. Two countries, GB and the Netherlands, reported a generalshortage in staff with the necessary design knowledge and skills regardless of anyimpact from increasing DG and RES workload. The US DNO has recentlyestablished a new connections group with one person dedicated almost full time toaddressing generator requests for distribution connection.

Only the German, despite having the highest penetration of DG, and Spanish DNOsreported no issues with the availability of design expertise.

3.5 Performance Measurement

3.5.1 Overview

The parameters utilised by each DNO in the study for network performancemeasurement are determined at a national rather than DNO specific level. Thisapproach allows accumulation of individual DNO performances to provide nationalperformance statistics and enables a degree of national and internationalbenchmarking.

Distribution network performance measurement parameters and methodologies varyconsiderably between countries from some recording only the number ofinterruptions, to those measuring reliability and availability indices for each of thehigh, medium and low voltage networks.

The most common reliability indicator utilised is the System Average Interruption

Frequency Index (SAIFI), also expressed in some countries as CustomerInterruptions (CI) per 100 customers. The corresponding network availability index isthe System Average Duration Index (SAIDI), expressed in some countries asCustomer Minutes Lost (CML) per connected customer.

Alternative indices to the customer centric ones above are also employed and maybe based on the installed transformer capacity or annual energy consumption.Indices based on installed transformer capacity are favoured by Spain and Portugal


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and express network availability as TIEPI (minutes per installed MVA) and reliabilityas NIEPI (interruptions per installed MVA).

A table of the performance indicators employed by 20 EU countries2 by voltage levelis shown in Table 5.

Continuity Indicators Country

Interruptions

SAIDI, SAIFI and MAIFI per voltage level(H, M) (HV, MV, LV)

GB, HU, IT, NO (from 2006)

SAIDI and SAIFI per voltage level (H, M, L) CZ, GR, PT, FR, LT, NO (from 2006)

SAIDI and SAIFI per voltage level (H, M) SI (some data only), BE, Wallonia

SAIDI and SAIFI all voltages SE, EE, IE, (SAIFI from 2006)

Average duration (D) and frequency (F) per

contracted power or other

AT (average D and F weighted on MV power affected,

MV/MV, MV/LV),

ES (average D and F weighted on MV power affected:

TIEPI, NIEPI)

FI (average D and F weighted on yearly energyconsumption)

FI (interruptions are weighted by the yearly energyconsumption of the distribution area that onedistribution transformer feeds).

PT (TIEPI, ENS, excluding LV)

NO (ENS, excluding LV:1kV)

Other/ No indicators LV (number of interruptions), PL (no indicators)

Table 5 CEER continuity indicators for distribution

A distinction, based on the EN50160 definition, is also made between longinterruptions (lasting three minutes or longer, recorded as SAIFI) and short ormomentary interruptions (less than three minutes but greater than one second,recorded as MAIFI). Most EU countries and the US adhere to the three minutedefinition for long interruptions when reporting network performance. No country wasfound to be recording transient interruptions of less than one second duration.

From Table 5 it can be seen that nine EU countries, including GB, differentiate therecording of long interruptions by network voltage. However, only four countries,

Great Britain, Hungary, Italy and Norway also record short interruptions.

Regulatory incentive schemes to encourage investment that improves networkperformance are established in Great Britain, Hungary, Ireland, Italy, Norway,Portugal and Sweden.

2CEER Third Benchmarking Report on Quality of Electricity Supply 2005.


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Performance incentive mechanisms are largely based on SAIDI and SAIFI reportingwith the exceptions of Norway and Portugal where they are based on Energy NotSupplied (ENS) and TIEPI respectively. Hungary, Italy and Portugal exclude plannedinterruptions from the incentive mechanism and all countries have a mechanism forexcluding force majeure or exceptional events.

Great Britain

Targets for network performance (CI and CML) were initially set by the regulator foreach DNO in December 1999 as part of the Distribution Price Control. Delivery ofthese performance targets was reinforced with the introduction of the Informationand Incentive Programme (IIP) in April 2002. IIP was superseded by the InterruptionIncentive Scheme (IIS) at the commencement of the current Price Control period inApril 2005.

A feature of IIS is that the CI and CML targets for each DNO become morechallenging in successive years of the price control period and the correspondingincentive rates also increase. The IIS provides symmetrical rewards and penalties to

a proportion of DNO revenue (3%) with the maximum revenue adjustmentattributable to CI and CML set at 1.2% and 1.8% respectively. Ofgem publishesthe performance and penalty / reward statistics for each DNO in an annual ElectricityDistribution Quality of Service Report.

To aid more direct performance comparison between DNOs with disparate networktopologies Ofgem has agreed the disaggregation of the MV network into 22 circuitcategories based on the proportion of circuit overhead, circuit length and number ofcustomers connected. Data from the disaggregated CI and CML performance doesnot contribute to the incentive scheme reporting but is used to provide publiclyavailable benchmark performance figures for each DNO.

In addition to the performance incentive scheme there is a statutory set ofGuaranteed Standards that define maximum restoration times following supplyinterruption (for both normal and severe weather conditions), notification of plannedinterruptions, response times to connection estimates and voltage complaints andthe penalty payments due to customers for failure to meet any Standards. TheseGuaranteed Standards requirements are customer specific and not averaged systemindices.

Netherlands

All DNOs report annual performance statistics to the Regulator who then developsan informal performance benchmark. Customer service from networks is inherently

high due to the MV and LV networks being entirely underground and the high level ofnetwork security between MV stations. There is no incentive scheme in place toimprove on this performance.

If a DNO performance level varies from the regulatory benchmark there is amechanism in the price review to penalise the DNO but is considered to haveminimal impact.


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There does, however, appear to be a desire amongst Dutch DNOs to improve theirnetwork performance and customer service levels.

Spain

Performance is measured by TIEPI which is essentially installed MVA minutes lost

and NIEPI which equates to installed MVA interruptions.

There is a statutory requirement for distribution companies not to exceed nationallyagreed TIEPI and NIEPI (number of interruptions) limits. The limits applicable to thefour categories of area defined are;

TIEPI and NIEPI Limits TIEPI(mins)

NIEPI(number)

Defined areas

Urban 120 4

Semi-urban 240 6

Concentrated rural 480 10

Dispersed rural 720 15

Table 6 TIEPI and NIEPI limits

Whilst there are penalties for exceeding the TIEPI and NIEPI limits there is noincentive scheme to reward performance that betters these limits.

There are no additional standards governing the response times for restoration ofload or customers following an unplanned interruption.

Germany

The DNO interviewed measures CML, CI, energy not supplied and fault rate perkilometre for the HV, MV and LV networks. These figures are submitted annually to

the German regulator (BDEW) who collates all DNO performance statistics.

Performance figures shown to KEMA indicate that the DNO compares well in relationto its European peers. In fact, the MV network fault rate per kilometre isapproximately half that achieved in Great Britain.

German performance metrics were not available in the CEER 2005 benchmarkingstudy but a VDN facts and figures document3 published in 2007 confirms the highperformance level attained by German networks.

3Facts & Figures, Electricity Networks in Germany, April 2007; VDN.


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Figure 2 VDN chart of network CML performance

There are no separate standards or targets for the restoration of load or customersfollowing an unplanned interruption. The speed of supply restoration is determined

by the effectiveness of the operations team. A number of larger customers do havecontractual obligations for restoration of supplies following an interruption.

No incentive scheme for network performance improvement currently exists but theDNO studied is anticipating this will materialise as regulation matures.

United States

Performance targets for SAIDI and SAIFI are set by each State PUC and penaltiespaid if they are not met. Like Spain, there is no reward for improving on target levels.

Both Guaranteed and Performance Standards are in place at the US DNO with onlythe Guaranteed Standards triggering a compensation payment to customers.Targets for supply restoration (80% of customers within three hours) are includedwithin the Performance Standards but do not result in compensation payments ifthey are not achieved.

3.5.2 Trends

There is a general continuing trend and desire, at DNO and national levels, toincrease network performance year on year but at some point an optimumperformance level against the expenditure required to realise it must be reached.

This is a conundrum for both the DNOs and regulatory authorities. The IISprogramme in GB for instance has delivered significant service improvements since

its introduction but DNOs are now in a position where each marginal improvementmade requires more complex solutions and therefore increased costs. And, in theNetherlands or Germany, do customers require further improvements in service andare they willing to pay for it?

Regulators extol a value for money approach and sustain pressure on capitalexpenditure, and with high performance levels already attained in severaljurisdictions it is probably now time to consider performance value optimisationcriteria. With varying legacy network configurations and operating area topology


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these criteria are likely to be different for each country. However, once determined,these criteria could be incorporated into a network performance ethos at all aspectsof network planning, design and equipment specification.

3.6 Network Automation

3.6.1 Overview

This section reviews the utilisation and deployment of auto-reclosing circuit breakers,remotely controlled equipment and automation schemes.

3.6.2 Auto-reclosing Circuit Breakers

Commonly referred to as autoreclosers, these circuit breakers are utilised solely onoverhead circuits that are prone to non-permanent, or transient, faults. Thesedevices will automatically close after a pre-determined time after initially opening ondetection of a line fault, and it is normal practice globally to attempt two reclosecycles prior to detection of a permanent fault that results in the autorecloser lockedout in the open position.

All study participants make extensive use of auto-reclosing applied to the line sourcecircuit breaker in the substation, in both the MV and HV networks. It is widespreadpractice on MV circuits across all studied DNOs, with most declaring 100% ofoverhead circuits protected in this manner. The GB DNO has approximately 50% ofoverhead circuits protected with auto-reclosers. Delayed auto-reclosing is employedat HV voltage levels.

Where overhead circuits are long or have large spurs, additional pole mountedautoreclosers may be installed that prevent the entire circuit from outage in the eventof a fault occurring beyond the additional recloser. Since the introduction, by Ofgem,of the Information and Incentive Programme in 2002 a large number of thesedownline reclosers have been installed and it is now normal practice in Great Britainwhere economically justifiable.

At this time, other countries have not adopted the use of downline autoreclosers tothe same extent as GB. However, the US operator is continuing a programme ofinstallation as part of a performance improvement policy and is likely to achievesimilar deployment levels.

3.6.3 Remote Control

Remote control is defined as the ability to operate equipment at remote locations,such as substations and circuit switching points, from a centralised facility. The

decision making and execution of any control signal is performed manually, usuallythrough the SCADA system. It is possible for a wide range of network equipment tohave remote control facilities incorporated.

Remote control of equipment at HV/MV substations is standard practice and MV/MVsubstations also, generally, have remote control capability through SCADA systems.


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In the British DNO approximately 50% of overhead and 10% of underground circuitshave additional downstream remote control devices such as circuit breakers orswitches to assist with effective customer restoration after an unplanned outage.

The Spanish DNO makes extensive use of remotely controlled apparatus throughoutthe underground MV network and at least one remotely controlled switch in most

overhead circuits. The design and planning of these facilities is targeted at effectiveand rapid customer restoration by centralised manual control after an unplannedinterruption.

Whilst the German DNO has remote control capability to 95% of its MV substationsthe deployment of downline remotely controlled apparatus does not feature in theGerman network.

In the Netherlands the MV feeder circuit breakers have status monitoring only via theSCADA system and are not controllable. Incoming HV circuit breakers in the HV/MVsubstation have full remote control facilities.

The provision of SCADA at HV/MV substations in the US Company reviewed is moremixed with full SCADA functionality to 29% of sites, monitoring only to 11% and noSCADA capability to 60% of sites. It should be noted, however, that many of theHV/MV sites are in remote locations with low customer numbers.

Remote control of overhead and underground switches at the US network operatorhas been applied very judiciously.

3.6.4 Automation

The definition of automation is often loosely translated by DNOs and subsequentlyapplied in an inconsistent manner across the industry. For clarification in this reviewautomation is defined as a scheme of equipment that is capable of networkreconfiguration, without human intervention, to restore supply following an unplannedinterruption. It is a prerequisite that this scheme of equipment has communicationchannels to share network and equipment status parameters that can then be usedby the scheme control module to execute a pre-determined set of operations. By thisdefinition the use of a single auto-reclosing circuit breaker does not constitutenetwork automation. However, it may be possible to utilise auto-reclosing circuitbreakers as an element of an automation scheme as described earlier.

In general, the trialling and adoption of MV network automation varies considerablybetween DNOs from no experience to extensive adoption of underground andoverhead automation technologies.

The GB DNO interviewed for this study has trialled automation schemes for loadrecovery following an unplanned outage at the MV (11kV) level but considered thetechnology insufficiently reliable to retain them in service. There are currently nofurther trials or implementations of network automation planned.

Other GB DNOs, however, have had more encouraging experiences with networkautomation and there are a significant number of schemes installed to managesupply interruptions on high customer density underground and overhead circuits.


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These automation schemes tend to be managed through stand alone systems.Automation functionality in a number of schemes is provided within the RTU/SCADAcombination.

In the US DNO three automation schemes for underground, overhead and mixedcircuits have been trialled with limited success. Communications technology utilised

in the schemes did not prove sufficiently reliable but a more serious issue hinderingperseverance with the trials was the lack of acceptance from operational field staff.

There are no further plans to proceed with MV automation at the US distributionoperator.

No network automation schemes have been installed or trialled at any voltage levelat the DNOs in the Netherlands or Germany and there are no immediate plans to doso.

3.7 DG & RES Deployment

3.7.1 Generation Technologies

The installed capacity of DG and RES by technology type varied considerably acrossthe network operators interviewed. Figures for the major generation technologiesreported per DNO are shown in Table 7.

In all countries the dominant generation type at High Voltage levels is wind andwaste-to-energy/biomass. Medium voltage levels have the greatest mix of generationwith wind, hydro, biomass, landfill gas and photovoltaic. Renewable generation in theLow Voltage network is predominantly from photovoltaic sources.

Solar energy production in the form of photovoltaic cells is most prominent inGermany and Spain, with some larger PV schemes connected at MV.

Representative DNO DG&RES Installed CapacityDG/RES mix


DG&RES technology (MVA)

CCGT 40

CHP 493 1300 1014

Wind 32 2,950 2,367 80 237

Hydro 0 2,117 74 0.7 19.3

Biomass 13 155 114 27 10Landfill gas 98 - 17 - 32

Photovoltaic 0.07 18 53 0.6 0.7

Other 528 525

TOTAL 1,164 5,240 2,624 1,933 1,353

Table 7 Installed capacity of DG&RES technologies


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3.7.2 DNO Network Penetration

To obtain a sense of how the level of generation capacity may impact on thedistribution network it has been compared to the installed HV/MV transformercapacity for each network operator as a proxy for DG penetration, see Table 8.

Representative DNO DG&RES Network PenetrationDG/RES InstalledGB Spain Germany NL USA

Installed DG&RES capacity

% of HV/MVtransformer capacity

9% 7% 26% 13% 8%

Table 8 Network penetration of DG&RES as % of HV/MV transformer capacity

When compared to the installed HV/MV transformer capacities the GB, Spanish andUS companies studied have similar relative penetrations of DG and RES.

High levels of DG & RES capacity in the German and Dutch DNOs has not posed

any particular technical challenge to date due to the ability of the highly robust legacyMV network designs to accommodate it.

The German DNO, however, has an extremely high relative penetration of DG andRES into its network. In fact, the scale of wind generator deployment in particular iscausing issues with power flow resulting, at times, in the backfeed of energy from thedistribution network to the transmission system. This is viewed as an issue by thetransmission operator as it impacts on generation balancing conditions. A novelenergy management system has been developed by the DNO in-house and is nowmonitoring power flows and controlling connected DG and RES as necessary toprevent a backfeed scenario occurring. This solution is considered to be a temporarymeasure until appropriate primary network reinforcements have been implemented.

3.7.3 Country Penetration

The national penetration of DG and RES in each of the DNO countries is shown inTable 9 as a percentage of gross generation production.

National Comparison DG&RES ProductionDG/RES Installed

GB Spain Germany NL

Installed DG&RES production (% gross generation)

DG 6.3% 7.2% 12.5% 30%

RES 4.6% 15% 11.8% 8.9%

Total 10.9% 21% 26% 39%

Table 9 DG&RES production by country as % gross generation production4

4Eurostat and Energy.eu 2006 statistics.


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Distributed generation, or cogeneration, has been encouraged in the Netherlandssince the early 1980s with distribution companies allowed to install their owngeneration with the advent of the 1989 Electricity Act. Each DNO generator plantsize was limited to less than 25 MW but this opportunity provided the incentive toformulate appropriate technical connection requirements for all cogeneration parties,including the DNOs.

This situation in the Netherlands lead to the evolution and strengthening of thedistribution networks over the past 25 years that has enabled them to absorb largevolumes of DG and RES through primary network design practices. This is clearlyillustrated by the volume of DG production shown in Table 6.

RES penetration at the national level, see Table 10, reflects that of the networkpenetration of the representative DNOs studied, Table 8; Germany and Spaindominate both tables.

National RES installed capacityDG/RES Installed


Installed RES capacity (GW) (Excludes large scale hydro)

RES capacity 2006 3.55 12.43 27.39 2.15 123.46

% gross generatingcapacity

4.3% 15.3% 19.6% 9.6% 11.5%

Table 10 Installed RES capacity by country5

3.7.4 Trend

In March 2007 EU Member States signed up to a binding target to have 20% of the

EUs overall energy consumption sourced from renewables by 2020. This target isdriving the trend to increase renewable generation capacities in all membercountries.

Wind generation is viewed as the major contributor to annual growth in distributedgeneration capacity by all studied DNOs, except the Netherlands DNO where goodquality CHP is expected to be the greatest contributor.

Wind generator growth in each DNOs country is illustrated in Table 9 over the years2006 and 2007. Whilst Germany has the highest installed capacity (globally) itsgrowth has diminished, with the USA experiencing the highest growth rate of 45%.

5Eurelectric 2006 statistics.


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National - Wind installed generation capacityWind GeneratorGrowth GB Spain Germany NL USA

Installed wind generation capacity (MW)

Wind capacity 2006 1,962 11,623 20,622 1,558 11,664

Wind capacity 2007 2,389 15,145 22,247 1,746 16,913

% increase 22% 17% 8% 13% 45%

Table 11 Wind energy growth by country 2006-20076

3.7.5 Connection Guidelines

None of the DNOs studied considered the technical design of DG & RES connectionto be a barrier to increasing connected capacity. The technical requirements arepublished as guidelines on an industry wide basis in all countries and utilised by thestudied DNOs.

Great Britain

In GB the DNOs have produced guidance documents (EngineeringRecommendations) available from the Electricity Networks Association;

G59/1 for generating plant of 5MW or less.

G75/1 for generating plant >5MW or connecting above 20 kV.

G83/1 for small-scale generating plant connecting at LV.

The Department for Energy and Climate Change (DECC) produces a TechnicalGuide to the Connection of Generation to the Distribution System to guidedevelopers through the entire connection process.

Germany

There are separate guidance documents for the connection of generation plant to theMV and LV networks. They are respectively;

"Eigenerzeugungsanlagen am Mittelspannungsnetz" - Richtlinie frAnschluss und Parallelbetrieb von Eigenerzeugungsanlagen am

Mittelspannungsnetz; 2nd edition of 1998. (Connecting EmbeddedGeneration at Medium Voltage - Guidelines for connection and paralleloperation of embedded generation at medium voltage.)

"Erzeugungsanlagen am Niederspannungsnetz"- Richtlinie fr Anschlussund Parallelbetrieb von Eigenerzeugungsanlagen am Nieder-spannungsnetz; 4th edition of 2001. (Connecting Embedded Generation at

6European Wind Energy Association.


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Low Voltage - Guidelines for connection and parallel operation ofembedded generation at low voltage.)

An additional guideline, VDN Richtlinie; EEG Erzeugungsanlagen am Hoch undHochstspannungsnetz, was introduced by the VDN in September 2004 forrenewables based generating plants connecting to the HV (>60kV) and EHV

networks from that date. This new guideline recognised the contribution from thesegenerators to network support, particularly;

the provision of reactive power and voltage support in the event of a fault,

limitation of reactive power absorption after a fault,

reduction of harmonics at HV and EHV and

setting of protection schemes.

Netherlands

The strong cooperation between DG owners and network operators during the 1980sresulted in the production of guidance document by EnergieNed titled TechnicalTerms for Connection. This document was in force and adhered to by all DNOs anddistributed generators from 1994 to 2000. Since 2000 the connection guidelineshave been embodied in the NetCode.

The Dutch Net Code recognises three bands of generation to the public network:below 2 MW, between 2 and 60 MW and over 60 MW. Generators below 5kVA arecategorised as domestic/micro generation.

In regards to Distributed Generation, the Dutch Netcode requires generators over 2MW but below 60 MW to submit, on a yearly basis, to the network operator their best

possible estimate of the following matters for the coming period of seven years:

place, capacity, technical data, operational limits and regulating behaviourof the individual generation units;

place, dates, technical data, operational limits and regulating behaviour ofgeneration units to be started up;

place of generation units to be decommissioned and the date ofdecommissioning;

maintenance planning for each generation unit (stating period and duration

in weeks).

Generators below 2 MW are generally exempt from this reporting.

Spain

The Spanish DNO has internally developed set of norms, comprising a designdocument library for connections. The majority of these norms can be accessedonline for reference. The main document, "Normas Tcnicas particulares de Endesa"


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or "Particular Technical Rules of Endesa", set outs rules which apply to electricalinstallations up to 30 kV. Voltages above 30 kV are regulated nationally.

The Particular Technical Rules of Endesa covers amongst others the technicalconnection requirements for LV and MV installation, LV and MV distribution grid,transformer centres, sectionalizing and power delivery and special requirements for

PV installations connected to LV distribution grid. The technical parameters includeisolation levels, grid models (rural area, semi urban, urban area, industrial areas),underground and overhead grids and short circuit currents.

United States

In the US the IEEE 1547 Standard on Interconnection Issues provides the minimumtechnical requirements for the connection of Distributed Resources, not exceeding10 MVA aggregate capacity, to the distribution network.

IEE 1547 is not considered to be a guideline but provides the minimum functionaltechnical requirements needed to help ensure a technically sound interconnection.

3.8 Innovation

3.8.1 Overview

With the global pressures to adopt renewable energy production and energy efficienttechnologies that reduce the impact on the environment, several crucial challengesface the DNO to enable the penetration of renewable generation to the level targetedby the European Union to meet the 2020 target. The main challenges include voltagemanagement, fault level mitigation and power flow management.

It is increasingly challenging to meet the different needs of politicians, regulators,network operators and renewables generators, and an appropriate approach todeveloping innovative solutions that satisfy all parties is essential.

Four of Europes electricity utilities, ENDESA, EDF, EDP Innovao and RWEEnergy AG have recently signed an Innovation Utilities Alliance (IUA) agreement.Under this agreement the signatories will collaborate in the field of innovation,developing the electricity networks of the future and energy efficiency initiatives.

Great Britain

Spending patterns of the DNOs on research and development activities declinedmarkedly and rapidly after privatisation, as shown by the trend in Figure 4.


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Figure 3 DNO Research & Development spending since privatisation

In broad terms, the introduction of the Initiative Funding Incentive (IFI) by Ofgem inApril 2005 allowed the DNOs to recover expenditure on research and developmentactivities up to a value of 0.5% of their revenue. This incentive provided thenecessary impetus to re-ignite both short-term and long-term R & D activities.

Each DNO is able to build its own portfolio of initiatives and research projects buteach one must pass specific criteria to qualify for inclusion in IFI, and thereforeeligibility for cost recovery. These portfolios consist of a mixture of projects including;developments with vendors tackling immediate issues, collaborative projects withother DNOs, participation in strategic technology projects, partnerships with

academic institutions and membership of large European grid development projects

A broad range of network technologies associated with network efficiencyimprovement and DG/RES connections is encompassed within the IFI programme,for example; active voltage management of DG, fault current limiting devices, smarttransformers, automation, dynamic rating, redox battery and other energy storagedevices and incipient fault detection.

There is a broad range of innovative network technologies at the development, trialor implementation stage at each DNO.

Another scheme launched by the Regulator is the RPZ, Registered Power Zone. Aregistered power zone is an area of the national grid network, geographical orelectrical, specifically designated for the research, development and demonstrationof new technologies concerning the power network. Specifically to develop solutionsto the problems associated with connecting generating capacity at the distributionnetwork level. There are currently 4 registered power zones in the UK, operated bydifferent Distribution Network Operators.


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Netherlands

A dedicated team has been established in the Dutch DNO to stimulate and manageinnovation and R & D activities. There are collaborations in place with academicinstitutions and membership of the large European projects has been established.

The DNO considers that greater collaboration is required between all Dutch DNOs toestablish an effective programme that is capable of delivering solutions for trial to beshared across all participants. Main areas of immediate interest are; converters forLV generation connection (solar, PV), active network management and smart grids.

There are no trials of new technology currently in progress at the DNO studied.

Spain

In Spain, ENDESA created an innovation circles initiative (CIDE) in 2006 as avehicle for conveying to all interested parties the challenges and goals in technologydevelopment for the electricity business. The CIDE model encompasses initiativesspanning ENDESAs main business areas and involves all agents, such asemployees, suppliers, government bodies and R&D centres, with the mission ofsearching for and identifying innovative solutions collaboratively.

The DNO interviewed did have a company R & D division which is active in severalresearch projects with universities and in developing technology trials. Areas ofmajor interest with initiatives in progress include dynamic wind generator modelling,the impact of photovoltaics in LV networks, energy efficiency and operational safety.

Germany

The DNO interviewed had no R & D programme or funding available within thecompany but did have access to the corporate group level programme. However, itwas intimated that the DNO is somewhat remote from this programme and noprojects of particular interest to distribution network operations had been identifie

kema review of international network design standards practices and plant and equipment...

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