EDS 08-1105 Guidance for the Application of ENA EREC P2 …library.ukpowernetworks.co.uk/library/asset/662a9ce5-39... · 2018. 9. 13. · Document Number: EDS 08-1105 Version: 4.0

Document Number: EDS 08-1105

Version: 4.0

Date: 10/07/2018

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ENGINEERING DESIGN STANDARD

EDS 08-1105

GUIDANCE FOR THE APPLICATION OF ENA EREC P2 SECURITY OF SUPPLY

Network(s): EPN, LPN, SPN

Summary:

This standard provides guidance on the application of Engineering Recommendation P2/6 published by the Electricity Networks Association (ENA); EREC P2 is a guidance document on system planning and network capacity requirements and details the minimum standards for the security of supply. The concepts and requirements relating to the security contribution of distributed energy sources resources (DER) are also included.

Author: Panos Xenos Date: 10/07/2018

Approver: Barry Hatton Date: 07/09/2023

This document forms part of the Company's Integrated Business System and its requirements are mandatory throughout UK Power Networks. Departure from these requirements may only be taken with the written approval of the Director of Asset Management. If you have any queries about this document please contact the author or owner of the current version.

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Guidance for the Application of ENA EREC P2 Security of Supply


Version: 4.0

Date: 10/07/2018

© UK Power Networks 2018 All rights reserved 2 of 22

Revision Record

Version 4.0 Review Date 10/07/2023

Date 10/07/2018 Author Panos Xenos

Reason for update: Document updated to reflect changes to CHLDZ, the Central London Strategy and the latest version of ENA EREC P2

What has changed:

Definitions updated (Section 3).

Clarification about Second Circuit Outage security of supply criteria (Section 4.2.6).

Enhanced level of security of supply area and criteria amended (Section 4.3).

EREC P2 Assessment Process amended and simplified (Section 5).

References to DG security of supply contribution methodology removed.

References amended to capture latest standards (Section 7).

Document re-numbered from EDS 08-0119.

Version 3.0 Review Date 10/09/2019

Date 10/09/2014 Author Stephen Tucker

Reason for update: Document reviewed.

What has changed: Structure revised and EDP 08-0107/EDP 08-0108 integrated into document. Document updated to include the use of demand side response from ENA EREP 130-1.

Version 2.1 Review Date

Date 01/03/2011 Author Pete Lawson

Updated Section 7.1 and 7.2 CHLDZ boundary map and main substations list.


Date 24/1/2011 Author Pete Lawson

Document revised – notes added to tables and reference documents updated. London documents E2/1/1 and E2/1/1/1 integrated into this document.


Date 20/01/2007 Author Matt Freeman

New document.



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Contents

1 Introduction ............................................................................................................. 5

2 Scope ....................................................................................................................... 5

3 Glossary and Abbreviations ................................................................................... 6

4 Security of Supply ................................................................................................... 9

4.1 Class of Supply ......................................................................................................... 9

4.2 Normal Level (for all Regions except the ILSZ) .......................................................... 9

4.2.1 Normal Level Overview ............................................................................................. 9

4.2.2 Class A – Up to 1MW .............................................................................................. 10

4.2.3 Class B – Over 1MW up to 12MW ........................................................................... 10

4.2.4 Class C – Over 12MW up to 60MW ......................................................................... 10

4.2.5 Class D – Over 60MW up to 300MW ....................................................................... 10

4.2.6 Class E – Over 300MW up to 1500MW ................................................................... 10

4.2.7 Class F – Over 1500MW ......................................................................................... 11

4.3 Enhanced Level (Inner London Strategic Zone) ....................................................... 11

4.3.1 Enhanced Level Overview ....................................................................................... 11

4.3.2 Class A – Up to 1MW .............................................................................................. 13

4.3.3 Classes B and C1 – Over 1MW up to 20MW ........................................................... 13

4.3.4 Classes C2 and D – Over 20MW up to 300MW ....................................................... 13

4.3.5 Class E – Over 300MW up to 1500MW ................................................................... 14

4.3.6 Class F – Over 1500MW ......................................................................................... 14

5 EREC P2 Assessment Process ............................................................................ 15

5.1 General ................................................................................................................... 15

5.1.1 Defining a ‘Group’ .................................................................................................... 15

5.1.2 Time at Risk ............................................................................................................ 15

5.1.3 Demand at Risk ....................................................................................................... 15

5.2 Assessing Network Capacity ................................................................................... 16

5.3 Assessing DG Contributions .................................................................................... 16

5.4 Examples ................................................................................................................ 16

6 Other Considerations ............................................................................................ 17

6.1 Distributed Energy Resources (including Flexibility) ................................................ 17

6.2 Innovation ................................................................................................................ 17

6.3 Load Transfers ........................................................................................................ 17

6.4 London Networks .................................................................................................... 18

6.5 Load Shedding ........................................................................................................ 18

6.6 Derogation ............................................................................................................... 18



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7 References ............................................................................................................. 19

7.1 Internal Standards ................................................................................................... 19

7.2 External Standards and Reports .............................................................................. 19

8 Dependent Documents.......................................................................................... 20

Appendix A – Inner London Strategic Zone (ILSZ) ......................................................... 21

Tables

Table 4-1 – Normal Level of Security of Supply (all regions except the London ILSZ) ........... 9

Table 4-2 – Enhanced Level of Security of Supply (Inner London Strategic Zone) .............. 12

Table A-1 – Substations within CHLDZ and Isle of Dogs Feeding Areas ............................. 22

Figures

Figure 4-1 – Inner London Strategic Zone (©Google Maps 2017) ....................................... 11

Figure A-1 – Inner London Strategic Zone (©Google Maps 2017) ....................................... 21



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1 Introduction

This standard provides guidance on the application of Engineering Recommendation P2 published by the Electricity Networks Association (ENA); ENA EREC P2 is a guidance document on system planning and network capacity requirements and details the minimum standards for the security of supply. The concepts and requirements relating to the security contribution of Distributed Energy Resources (DER) are also included.

All Distribution Network Operators have obligations under their distribution licence to 'plan and develop the [licensee’s] distribution system in accordance with a standard not less than that set out in Engineering Recommendation P2 of the Energy Networks Association'.

A further obligation under Licence Condition 9 is to comply with the Distribution Code which is designed so as to ‘permit the development, maintenance and operation of an efficient, coordinated and economical system for the distribution of electricity'.

DPC 4.2.1 of the Distribution Code states that 'DNOs shall plan and develop their Distribution Systems to a standard not less than that set out in DGD Annex 1 Item 5, Engineering Recommendation P2 – ‘Security of Supply’ or such other standard of planning as DNOs may, with the approval of the Authority, adopt from time to time'.

Estimating future demand allows system reinforcement needs to be identified. With an increasing number of network in-feeds coming from distributed generation, demand assessment has and will continue to become more involved. DER contributions can mitigate or delay the need for reinforcement in certain circumstances.

The objective is to ensure that UK Power Networks is maximising asset utilisation and minimising load-related expenditure, whilst at the same time managing network design security risk on its public networks as necessary to meet its Licence and Distribution Code obligations and ensuring that security risk does not adversely affect Customer Interruptions (CIs) and Customer Minutes Lost (CMLs) targets.

EHV networks designed in accordance with EDS 08-4000, HV networks designed in accordance with EDS 08-3000 and LV networks designed in accordance with EDS 08-2000 will generally be EREC P2 compliant.

The appraisal methodology detailed in this standard will provide a robust assessment of risk on a site-specific basis and thus permit the effective prioritisation of reinforcement schemes to address out-of-firm and possible EREC P2 non-compliance situations. The standard incorporates additional security of supply requirements when considering reinforcement of the substations within the Inner London Strategic Zone (ILSZ).

2 Scope

This standard applies to the security of supply as defined in ENA EREC P2 and its application to UK Power Networks distribution networks.

This standard details how UK Power Networks will meet the obligations outlined above, how its processes will be applied to assess compliance and how the effects of load growth will be analysed to develop reinforcement strategies to address out-of-firm and possible EREC P2 non-compliance situations.



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3 Glossary and Abbreviations

Term Definition

Building Network Operator (BNO)

An organisation that owns or operates the electricity distribution network within a multiple occupancy building, between the intake position and customers installations. The BNO may be the DNO, another licensed distributor or a third party exempt from an electricity distribution license

CCCMS Common Connections Charging Methodology Statement

Central High Load Density Zone (CHLDZ)

A defined geographical area within the London network where an enhanced level of security of supply is specified

Circuit

Part of an electricity system between two or more circuit-breakers, switches and/or fuses inclusive. It may include transformers, reactors, cables and overhead lines. Busbars are not considered as circuits and are to be considered on their merits

Circuit Capacity

The appropriate continuous rating or cyclic rating or, where it can be satisfactorily determined, the appropriate emergency rating, taking into account the relevant environmental conditions and the expected demand profile, should be used for all circuit equipment and associated protection systems. Circuit capacity should be assessed in MVA

Customer Interruptions (CIs)

Number of customers whose supplies have been interrupted for 3 minutes or longer per 100 customers per year

Customer Minutes Lost (CMLs)

The average customer minutes lost per customer per year, where an interruption of supply to customers lasts for three minutes or longer

Cold Load Pickup

The difference between the Measured Demand on a circuit following re-energisation of a circuit after being de-energised and the demand that the DNO would have reasonably expected on the circuit had no such de-energisation occurred

Demand Side Response (DSR)

Demand that is controlled in response to an instruction issued as part of an agreed demand side management arrangement with the DNO or other party

Distributed Energy Resources (DER)

All parties who are connected to the Distribution Network and typically includes distributed generation, distributed demand, electric vehicles, electricity storage, industrial and commercial customers but could also encompass domestic consumers

Distributed Generation (DG)

A generating facility connected to the Distribution Network, where a generating facility is an installation comprising one or more generating units

Distribution Network Operator (DNO)

The person or legal entity named in Part 1 of the Distribution Licence and any permitted legal assigns or successors in title of the named party – an organisation that owns and/or operates a Distribution Network

EDS Engineering Design Standard

ENA EREC Energy Networks Association Engineering Recommendation

ENA EREP Energy Networks Association Engineering Report

Extra High Voltage (EHV)

Term used to describe parts of distribution networks typically at a voltage level of 22,000V or more but less than 132,000V

First Circuit Outage (FCO)

Signifies a fault or a pre-arranged circuit outage



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Term Definition

Flexibility Modifying generation and/or consumption patterns in reaction to an external signal to provide a service within the Distribution Network

Group Demand

The sum of the Latent Demand and Measured Demand – the DNO’s estimate of the maximum demand of the group being assessed for EREC P2 compliance with appropriate allowance for diversity

Note: When estimating the maximum demand of the group the DNO should, where necessary, take into consideration (but not be limited to) the following: the Latent Demand due to DG, the Latent Demand due to DSR, the Latent Demand due to electricity storage, the effect of Suppliers’ time of use tariffs, the effect of Network Operator price signals, the effects of Cold Load Pickup and data granularity implications (instantaneous peak vs time averaged flow)

High Impact Low Probability (HILP)

A HILP event would have severe network implications but is not defined as a credible fault by traditional Grid Code Planning Standards. Such an event would lead to prolonged outages, introduce concerns over the health and safety of UK Power Networks’ employees and members of the public, and have a significant impact on customers along with reputational consequences for UK Power Networks

High Voltage (HV) Term used to describe parts of distribution networks typically at a voltage level of over 1,000V but less than 22,000V

HV Feeder Group

A group of interconnected HV feeders that are arranged with open points between them to provide n-1 support for feeders within the group. Note the LV network supplied from a HV feeder group may also have interconnection or normally open points

Independent Distribution Network Operator (IDNO)

An accredited company which develops, operates and maintains local electricity distribution networks. IDNO networks are directly connected to the DNO networks or indirectly to the DNO via another IDNO

Inner London Strategic Zone (ILSZ)

A defined geographical area within the London network where an enhanced level of security of supply is specified. It incorporates the CHLDZ and the Isle of Dogs

Intermittent Generation

Generation plant where the energy source of the prime mover cannot be made available on demand (e.g. wind)

Latent Demand

Demand that would appear as an increase in measured demand if the DG was not operating, the DSR was not implemented or other means (e.g. time of use tariff, export from electricity storage devices) of suppressing the measured demand within the network (for which the Group Demand is being assessed) were not operating

Note: DSR may be considered as either a reduction in network demand or an increase in network capacity in line with ENA EREP 130-2; UK Power Networks considers DSR an increase in network capacity

Low Voltage (LV) Term used to describe parts of distribution networks typically at a voltage level of up to 1,000V

Measured Demand Summated demand measured at the normal (network) infeed points to the network for which Group Demand is being assessed

Non-Intermittent Generation

Generation where the energy source of the prime mover can be made available on demand



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Term Definition

Second Circuit Outage (SCO)

Signifies a fault following a pre-arranged circuit outage

Note: The recommended levels of security are not intended at all times to cater for a first fault outage followed by a second fault outage or for a simultaneous double fault outage. Nevertheless, in many instances, depending upon switching and/or loading/generating arrangements, they will do so

Supplier

(a) A person supplying electricity under an Electricity Supply Licence or; (b) A person supplying electricity under exemption under the Electricity Act 1989 (as amended by the Utilities Act 2000 and the Energy Act 2004)

In each case acting in its capacity as a supplier of electricity to customers in Great Britain

Transfer Capacity The capacity of an adjacent network which can be made available within the times stated in EREC P2 Table 1. Transfer capacity will be limited by circuit capacity or other practical limitations on power flow

Value of Lost Load (VoLL)

Represents the value that electricity users attribute to security of electricity supply (£/MWh)



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4 Security of Supply

4.1 Class of Supply

Table 1 in EREC P2 details the normal levels of security of supply requirements for different classes of supply. This is reproduced in Table 4-1 and has been modified in Table 4-2 to include the enhanced level of security of supply within the Inner London Strategic Zone (ILSZ).

Each class of supply refers to ranges of Group Demand. The Group Demand may now include Latent Demand that was not previously assessed hence re-assessment under EREC P2 could result in the Group Demand being higher than the Measured Demand. The effects of this are described in Section 4.2.5.

The classes of supply are defined in MW but due regard should be paid to power factor when assessing plant capabilities.

4.2 Normal Level (for all Regions except the ILSZ)

4.2.1 Normal Level Overview

Table 4-1 provides an overview of the normal level of security of supply and should be read in conjunction with the notes in the sections that follow.

Table 4-1 – Normal Level of Security of Supply (all regions except the London ILSZ)

Class of

Supply

Group Demand Range

Minimum Demand to be Met After

First Circuit Outage (n-1) Second Circuit Outage (n-2)

A Up to 1MW

In repair time: Group Demand Nil

B

Over 1MW

and up to 12MW

(a) Within 3 hours: Group Demand minus 1MW

(b) In repair time: Group Demand

Nil

C

Over 12MW

and up to 60MW

(a) Within 15 minutes: Smaller of Group Demand minus 12MW and 2/3 Group Demand

(b) Within 3 hours: Group Demand

Nil

D

Over 60MW

and up to 300MW

(a) Within 60 seconds: Group Demand minus 20MW (automatically disconnected)

(b) Within 3 hours: Group Demand

(c) Within 3 hours (for Group Demand greater than 100MW): Smaller of Group Demand minus 100MW and 1/3 Group Demand

(d) Within time to restore arranged outage: Group Demand

E

Over 300MW

and up to 1500MW

(a) Within 60 seconds: Group Demand

(b) Within 60 seconds: All customers at 2/3 Group Demand

(c) Within time to restore arranged outage: Group Demand

F Over

1500MW In accordance with the relevant transmission company licence security standard



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4.2.2 Class A – Up to 1MW

The group range may be extended in circumstances where the demand is satisfied from a single 1000kVA transformer to allow for its emergency cyclic rating. For distribution transformer ratings refer to EDS 08-0115.

4.2.3 Class B – Over 1MW up to 12MW

Load groups in Class B are likely to be associated with small primary substations or groups of HV feeders. For the loss of a single circuit an alternative supply shall be available.

4.2.4 Class C – Over 12MW up to 60MW

Class C supplies will normally be supplied by:

At least two normally closed circuits or

One circuit, with automation in place to switch to an alternative circuit if required.

4.2.5 Class D – Over 60MW up to 300MW

Class D supplies could be grid sites, main substation sites, or areas of interconnected network. At the 100MW threshold, the requirements become more onerous.

This presents a potential problem when considering network configuration because of the way Group Demand is defined. If there are significant DERs in the group, Latent Demand may increase the Group Demand figure from a previous year’s assessment, pushing it above the 100MW threshold thus introducing the Second Circuit Outage criterion. The assessment of Latent Demand could also create transitions between Class B and C and Class C and D, but in these cases the Second Circuit Outage considerations would not need to be taken into account.

If the Group Demand is more than 100MW, for a Second Circuit Outage the smaller of Group Demand minus 100MW and 1/3 of Group Demand should be reconnected within three hours and the remainder within the time to restore the arranged outage.

4.2.6 Class E – Over 300MW up to 1500MW

The provisions of Class E apply to infeeds to the distribution system but not to systems regarded as part of the interconnected Supergrid to which the provisions of Class F apply.

EREC P2 states that all customers at 2/3 Group Demand should be restored immediately after a planned outage has been followed by an unplanned outage. The provision for a Second Circuit Outage assumes that normal maintenance can be generally undertaken during the period between calendar week 13 and week 43 when demand is below 67% or 2/3 of the Group Demand.

Hence, the Second Circuit Outage criterion in EREC P2 specifies that the network shall be capable of maintaining supplies to all customers, i.e. fully covering the maximum demand at the time of the planned outage.



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Moreover, due to varying load profiles, maintenance outages are sometimes more difficult to plan and work may need to be undertaken when the demand is greater than 2/3 of the Group Demand (e.g. at Central London summer peaking substations). In these circumstances the Class E Second Circuit Outage requirements should be increased to match the maintenance period demand which will introduce greater resilience than indicated by applying the 2/3 Group Demand criterion. The latter could lead to introducing reinforcement investment to increase network capacity or implementing risk mitigation measures.

4.2.7 Class F – Over 1500MW

Class F is generally only applicable to National Grid.

4.3 Enhanced Level (Inner London Strategic Zone)

4.3.1 Enhanced Level Overview

Figure 4-1 – Inner London Strategic Zone (©Google Maps 2017)

The geographical area covered by the Inner London Strategic Zone shown in Figure 4-1includes the Central High Load Density Zone (CHLDZ) and the Isle of Dogs. These two areas have been selected following strategic review of the impact of unanticipated loss of electrical supplies to UK Power Networks’ customers and the likely severe impact on national infrastructure (refer to EDS 08-1104). Appendix A provides further details of the extent of the ILSZ.



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The distribution system within the ILSZ shall continue to be planned on the principle that a First Circuit Outage at HV or above should not result in a loss of supply, unless it is more economical to accept a loss not exceeding 60 seconds duration. Existing interconnected networks in the enhanced level area should not have their level of interconnection reduced solely to conform to the security of supply standard; for further details refer to EDS 08-0111.

In the area of enhanced level of security of supply, alternative designs will be progressively applied to the existing network, as and when it is economic to do so. Any new UK Power Networks or Connections driven schemes shall adhere to these criteria as far as reasonably practicable. The minimum scheme rule shall still be applied when offering new connections to customers (i.e. cost apportionment is to be based on the minimum scheme); the additional scope required to achieve the enhanced level of resilience specified in this standard shall be funded by the UK Power Networks Asset Portfolio Plan (CON 00 024 & CCCMS refer).

In the case of a Group Demand which is located partially in the ILSZ and partially in the normal level area, special consideration will be given to the security level required at the primary substation and higher levels of the system. The class of supply will be determined by the total demand; the choice between normal and ILSZ level will usually depend on the proportions of the demand within the two areas. Specific reliability cost/benefit studies may be necessary to determine the optimum choice.

In the ILSZ area particular care shall be taken to ensure that the method of affording a supply to a customer (particularly at HV) is such that the appropriate level of security is maintained on the associated network. This may necessitate higher expenditure than would be the case in the normal level area, e.g. to ensure correct operation of the interconnected LV network.

The design of LV and HV networks in the ILSZ area is based on the provision of sufficient LV interconnection at or between secondary distribution substations for the loss of a single HV feeder not to cause a loss of supply to the general LV network (EDS 08-0140 refers).

Table 4-2 provides an overview of the enhanced level of security of supply applicable to the ILSZ and should be read in conjunction with the notes in the sections that follow.

Table 4-2 – Enhanced Level of Security of Supply (Inner London Strategic Zone)

Class of

Supply

Group Demand Range



A Up to 1MW

In repair time: Group Demand Nil

B

Over 1MW

and up to 12MW

(a) Within 3 hours: Group Demand minus 1MW

(b) In repair time: Group Demand

Nil

C1

Over 12MW

and up to 20MW

C2

Over 20MW

and up to 60MW


(b) Within 3 hours: All customers at 2/3 Group Demand



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Class of

Supply

Group Demand Range



D

Over 60MW

and up to 300MW


E

Over 300MW

and up to 1500MW


(b) Within 60 seconds: All customers at 2/3 Group Demand


F Over

1500MW In accordance with the relevant transmission company licence security standard

4.3.2 Class A – Up to 1MW

The group range may be extended in circumstances where the demand is met from a single 1000kVA transformer to allow for its emergency cyclic rating. For distribution transformer ratings refer to EDS 08-0115 (as per the normal level).

4.3.3 Classes B and C1 – Over 1MW up to 20MW

The range of Group Demand has been extended up to 20MW, compared with 12MW in the normal level, to broadly correspond with the demand supplied by an HV feeder group. The restoration criteria are such that the restoration of a Group Demand between 12 and 20MW will be more rapid than in the normal level area even though it is included in a lower class of supply. At least two, and usually more, circuits will be required to meet the First Circuit Outage criterion. Through the interconnection of the LV network there should normally be no loss of supply for a first HV circuit outage; though a 60 second restoration by automatic switching is permissible. Any isolated areas of LV network that lose supply should be restored within three hours by manual switching. An arranged circuit outage should not result in interruption of supplies.

A low voltage fault on an interconnected network can lead to a loss of supply within this range of Group Demand. Such a loss should be restricted to a maximum of 3MW of Group Demand and supply restored to all but the faulty section (which may be up to 1MW of demand) within three hours by manual switching. The full Group Demand will be restored in the repair time of the LV fault.

There is no requirement to make design provision for a Second Circuit Outage, but, by the nature of the network design, it will often be possible to achieve some restoration before the outage is restored or the fault is repaired.

4.3.4 Classes C2 and D – Over 20MW up to 300MW

These two classes of supply have been combined in the ILSZ with more stringent restoration criteria than Class D in the Normal Level area. The restoration criterion for a First Circuit Outage specifies no loss of supply but a 60 second automatic switching restoration is permissible. An arranged circuit outage shall not result in any interruption of supplies.



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Design provision shall be made for full restoration of supplies following a Second Circuit Outage, thus a minimum of three circuits shall be provided (though they need not all be EHV circuits). The security of supply criterion matches that of Class E as described in Section 4.2.6, however a more relaxed initial restoration time of 3 hours is specified allowing the available post-fault transfer capacity to be taken into consideration when assessing compliance.

In the case of the larger HV feeder groups that fall into class of supply C2, specific provision need not be made to meet the Second Circuit Outage criteria, but the existence of at least 4 feeders will generally mean that the criteria can be satisfied.

It should be noted that where new connections do not comply with the stipulated enhanced security levels, the customer will be expected to fund the defined minimum scheme only and tacit approval should be sought to implement an enhanced scheme funded by the Asset Portfolio Plan. In some instances it will not be cost effective to implement an enhanced scheme without incurring major costs or delays. Each scheme shall be considered on its individual merits as part of the capital approval process and advice should be sought from the respective Distribution and Infrastructure Planning Managers.

4.3.5 Class E – Over 300MW up to 1500MW

The restoration criteria for this class of supply in the CHLDZ is identical to that in the Normal Level area. There should normally be no loss of supply following a First Circuit Outage, but consideration can be given to the automatic disconnection and reconnection to another source within 60 seconds of up to 60MW of demand if this leads to significant economies. Such a design provision should not restrict the period during which maintenance can be scheduled.

The design provision for a Second Circuit Outage requires at least three circuits to be available and is based on the assumption that the demand will be below 67% of Group Demand for a sufficient period to allow reasonable scheduling of normal maintenance. Where this is not the case, due consideration is required to ensure the network capacity is able to match the maintenance period demand.

4.3.6 Class F – Over 1500MW

Class F is generally only applicable to National Grid (as per the normal level).



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5 EREC P2 Assessment Process

5.1 General

5.1.1 Defining a ‘Group’

A load group can be interpreted in many ways. A group may relate to a feeder, a number of feeders, a substation, or an area of network, and will depend on how the local network infrastructure has been designed and the running arrangements.

It should be noted that a single customer does not constitute a group for the purposes of EREC P2. However, BNOs or IDNOs shall not be treated as single customers; Tables 4-1 and 4-2 shall be adhered to when assessing compliance, providing new connections and designing the network to achieve adequate levels of resilience.

5.1.2 Time at Risk

Where Group Demand data indicates that a substation has exceeded its firm capacity, it is important to know over what period of the year this condition is likely to prevail. Two substations of equal n-1 transformer capacity could exhibit the same maximum demand, indicating a potential risk of EREC P2 non-compliance under n-1 conditions. However, further analysis of the annual demand profile may show that the substations are at risk for significantly different periods because the load profiles differ.

Under n-1, the healthy circuit(s) at a substation may be subject to loading where a risk of thermal trip exists. The calculation of the seasonal emergency cyclic rating and the time-to-trip are necessary to assess the practicability of taking mitigating action.

5.1.3 Demand at Risk

EREC P2 is structured around demand criteria. It follows that, when prioritising reinforcement to ensure continuing EREC P2 compliance, it is necessary to consider the demand at risk, which includes Latent Demand.

In the case of a single, high-demand customer connected to a demand group requiring Second Circuit Outage capability, the treatment of that customer’s demand when carrying out the EREC P2 assessment could be material in determining compliance. Each case will need to be considered in relation to how the customer’s contractual security arrangements impact on the assessment.

For example at a number of Network Rail sites the contracted firm capacity is in excess of the normal maximum demand. Where an arrangement exists, with demand transferable between supply points, or transferable from generators embedded in the customer’s network, it is necessary to apply their contracted firm capacity when calculating security margins for First Circuit Outages.

While EREC P2 does not make direct reference to customer numbers, it is prudent to assess the potential impact on CIs and CMLs. Due consideration should also be given to the associated reputational impact for UK Power Networks as well as the impact to local economy (assessed by calculating the VoLL; refer to EDS 08-1104).



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5.2 Assessing Network Capacity

The capability of a network to meet a Group Demand after First Circuit and Second Circuit Outages should be assessed as:

The appropriate cyclic rating of the remaining transmission or distribution circuits which normally supply the Group Demand, following outage of the most critical circuit(s).

The transfer capacity which can be made available from alternative sources.

Available Flexibility contracts and the time they can be made available (pre/post-fault).

The available network capacity should be assessed by determining the following:

Cyclic rating of each infeed circuit for the time of year when the Group Demand occurs.

Capacity of the network under normal running arrangements using the cyclic ratings.

Capacity of the network under First Circuit Outage conditions.

Capacity of the network under Second Circuit Outage conditions (where applicable).

Transfer capacity and the time it can be made available.

The diversified sum of new connection demand not yet taking load.

5.3 Assessing DG Contributions

There are two categories of generation described in EREC P2; ‘intermittent generation’ and ‘non-intermittent generation’ (refer to Section 3 for definitions). Intermittent generation (e.g. wind farms) is considered statistically less reliable than non-intermittent generation.

DG contained within a Class A group should not be considered. For the loss of a network infeed with no alternative supplies other than DG, the section of network could become islanded. Given that the DNO remains responsible for meeting statutory frequency and voltage characteristics when part of the network is islanded, it is recommended that only DG in Class

B groups and above should be considered1. Before allowing any contribution to network security from DG that is capable of operating in island mode, there are a number of other considerations that need to be taken into account.

For Class B supplies and above the contribution of DG should be considered in cases where network capacity alone cannot meet EREC P2 and where the de-minimis tests are satisfied as per EREP 130-2.

When considering a contribution to security from DG, due regard shall be paid to the commercial, technical and fuel source availability; the sum of these three elements gives the overall average availability. Other factors to be considered include fault current contribution, DG dominance, fault ride-through capability and common mode failures per generation type. When carrying out more complex assessments, it may be necessary to seek guidance from EREC G59/3-3 and EDS 08-3100.

Refer to EREC P2 supporting document EREP 130-2 for further guidance notes.

5.4 Examples

The approach for assessing EREC P2 compliance including the contribution to security from DG is detailed in ENA EREP 130-2 with Section 8 containing several worked examples to illustrate the process.

1 This may change at a future date, as strategies are adopted to cater for higher penetration of micro generation



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6 Other Considerations

6.1 Distributed Energy Resources (including Flexibility)

Except for the aforementioned considerations for DG, other DER can be considered as contributors to the security of supply and therefore used for EREC P2 compliance. These include, but not limited to; electricity storage, electric vehicles and flexibility services.

In order to determine the effective security contribution from Demand Side Response (DSR), it is necessary to carry out an assessment of the magnitude and longevity of the demand reduction which is likely to be delivered by the DSR contracts in place at the time when the intervention would be needed to meet the security requirements of EREC P2.

Unless specific guidance is provided in the form of updated EREC P2 or EREP 130 documents, available DER and their contribution to security of supply should be assessed based on:

Technical capabilities and limitations

Commercial capabilities and limitations

Regulatory framework

All EREC P2 assessments should be formally recorded as part of the overall compliance process.

6.2 Innovation

A number of innovative technologies are being trialled nationwide which are aiming at maximising the existing network capacity and provide opportunities for deferring traditional network reinforcement. If these technologies are sufficiently demonstrated and standardised, they could be incorporated into the EREC P2 assessment process and contribute towards achieving compliance.

One example of the above is dynamic asset ratings which can be used to provide peak shaving.

6.3 Load Transfers

Load transfers can be used either as a permanent means of moving demand from one substation to another, thus removing an out-of-firm condition, or as a temporary mitigation measure under outage conditions.

Transferring load to another substation is often necessary to meet Second Circuit Outage requirements. In such cases the load is transferred prior to taking the maintenance outage (First Circuit Outage).

Load can also be transferred subsequent to a First Circuit Outage provided the transfer can be effected within the restoration period allowed by EREC P2. Where the transfer is required to reduce transformer loading rather than restore supply it shall be achievable before the transformer(s) reach a winding temperature trip condition.



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6.4 London Networks

In London a form of load transfer termed a ‘swinging’ group is often configured. This comprises a group of HV feeders connected to two separate main substations. This allows the whole group to be transferred as a single entity (using busbar switching) which is necessary where the underlying LV network is interconnected. The disadvantage is that this means an all-or-nothing transfer, which for large groups can impose its own constraints.

For HV in London reference should be made to the System 8 network design parameters (EDS 08-0111) which provides guidelines for the restructuring of the HV/LV network in central London to remove full LV interconnection and establish simple LV interconnection with the option of applying automation to the 11kV system.

For LV in London reference should be made to the System 4 design guidelines EDS 08-0140.

6.5 Load Shedding

EREC P2 allows some load shedding although this often conflicts with the Company’s need to achieve CI and CML targets. It also impacts on UK Power Networks’ reputation. In reality, there will on occasions be a need to design the network to exceed the requirements of EREC P2.

6.6 Derogation

It should be noted that EREC P2 is not applicable to individual end customers (it applies to Group Demand) so specific solutions may be offered to meet an individual customer’s requirements and written into the supply agreement.

The connection of a new or additional load shall not adversely affect the performance of the existing network or the security of supply provided to existing customers to levels below EREC P2 minimum standard. A group of customers that include a single large customer shall however comply with EREC P2. EDS 08-3000 provides guidance on connecting larger loads to the distribution network.

For many customers a single circuit arrangement is unacceptable and various forms of enhanced supply arrangements are negotiable as described in EDS 08-3100.

There will be occasions where technical compliance with EREC P2 is not achieved. A typical example is where an out-of-firm condition will be addressed within a reasonably short time by planned reinforcement elsewhere on the network. In these circumstances investing in reinforcement at the site that has not met EREC P2 would be an inefficient use of investment capital.

Such a decision not to address an EREC P2 non-compliance needs to be regularised by seeking formal derogation from Ofgem. It will, of course, be necessary to present a sound case to Ofgem citing the reasons for seeking derogation and the measures taken to mitigate risks of losing supplies.



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7 References

7.1 Internal Standards

EDS 08-0111 System 8 Network Design Guidelines

EDS 08-0115 Loading of Secondary Distribution Transformers

EDS 08-0140 System 4 Network Design Guidelines

EDS 08-0113 Guidance for the Application of ENA Engineering Recommendation G88 and G81 Inset Networks (IDNOs and Other Licensed DNOs)

EDS 08-1104 HILP Assessment Process

EDS 08-2000 LV Network Design

EDS 08-2100 LV Customer Supplies

EDS 08-3000 HV Network Design

EDS 08-3100 HV Customer Demand and Generation Supplies

EDS 08-4000 EHV Network Design

EDS 08-4100 EHV Customer Demand and Generation Supplies

CON 00 024 Connection Charge Manual

CCCMS Statement of Methodology and Charges for Connection to the Electricity Distribution Systems of Eastern Power Networks PLC, London Power Networks PLC & South Eastern Power Networks PLC

7.2 External Standards and Reports

ENA EREC P2/6 Security of Supply

ENA EREC G59/3-3 Recommendations for the Connection of Generating Plant to the Distribution Systems of Licensed Distribution Network Operators

ENA EREP 130-2 Application guide for Assessing the Capacity of Networks Containing Distributed Generation

ENA EREP 131 Analysis Package for Assessing Generation Security Capability – Users’ Guide

ACE Report No. 51 Report on the Application of Engineering Recommendation P2/5 Security of Supply

Distribution Code - Issue 30 The Distribution Code of Licensed Distribution Network Operators of Great Britain

VoLL Ofgem Report The Value of Lost Load (VoLL) for Electricity in Great Britain

Review of Distribution Network Security Standards

Extended Report (to the Energy Networks Association), Imperial College London



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8 Dependent Documents

This document is referenced in the following documents any of which may be affected by updates.

AST 00 006 Asset Management System Manual

AST 02 003 Preparation of Infrastructure Development Plans

EDP 08-0206 Production of Annual Planning Load Estimates (PLE)

EDS 08-0113 Guidance for the Application of ENA ER G88 and G81 – Inset Networks (IDNOs and other licenced DNOs)

EDS 08-0148 Appendices to ENA ER G81

EDS 08-1104 HILP Assessment Process

EDS 08-3000 HV Network Design

EDS 08-4000 EHV Network Design

EDS 08-4100 EHV Customer Demand and Generation Supplies

EDS 08-5031 Demand Side Response



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Appendix A – Inner London Strategic Zone (ILSZ)

The extent of the Inner London Strategic Zone (ILSZ) and the substations serving it is shown below. For more detail on boundary interfaces refer to the HV and LV operational diagrams.

Figure A-1 – Inner London Strategic Zone (©Google Maps 2017)



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Table A-1 – Substations within CHLDZ and Isle of Dogs Feeding Areas

Area Grid / Primary Substations

CHLDZ

1. Aberdeen Place A 11kV

2. Aberdeen Place B 11kV

3. Back Hill A 11kV

4. Back Hill B 33kV

5. Bankside B3 11kV

6. Bankside C 11kV

7. Bankside D 20kV

8. Bankside F 132kV

9. Beech Street A 11kV

10. Beech Street B 11kV

11. Bloomfield Place 6.6kV

12. Calshot Street 11kV (Future)

13. Carnaby Street 11kV

14. Charing Cross 6.6kV

15. City Road B 11kV

16. City Road C 11kV

17. Devonshire Square 11kV

18. Duke Street B 11kV

19. Ebury Bridge 11kV

20. Finsbury Market A 11kV

21. Finsbury Market B 33kV

22. Finsbury Market D 11kV

23. Finsbury Market E 11kV

24. Finsbury Market F 33kV

25. Fisher Street B 11kV

26. Fulham Palace Road C 11kV

27. Georgiana Street 11kV (Future)

28. Hearn Street 11kV

29. Hyde Park Estate A 11kV

30. Hyde Park Estate B 11kV

31. Imperial College 6.6kV

32. Kingsway 11kV

33. Leicester Square 11kV

34. Limeburner Lane 11kV (Future)

35. Longford Street B 11kV

36. Moreton Street B 11kV

37. Moreton Street C 11kV

38. Moscow Road 22kV

39. Moscow Road 6.6kV

40. Old Brompton Road B 11kV

41. Osborn Street 11kV

42. Paternoster 11kV

43. Seacoal Lane 11kV

44. Shorts Gardens 11kV

45. Shorts Gardens 22kV

46. St. Pancras A 11kV

47. St. Pancras B 11kV

48. Victoria Gardens 6.6kV

49. Victoria Street 11kV

50. Whiston Road 11kV

Isle of Dogs 1. Deptford Grid 11kV

2. Deptford West 22kV

3. Simpsons Road 11kV

4. Westferry Circus 11kV

1 Introduction2 Scope3 Glossary and Abbreviations4 Security of Supply4.1 Class of Supply4.2 Normal Level (for all Regions except the ILSZ)4.2.1 Normal Level Overview4.2.2 Class A – Up to 1MW4.2.3 Class B – Over 1MW up to 12MW4.2.4 Class C – Over 12MW up to 60MW4.2.5 Class D – Over 60MW up to 300MW4.2.6 Class E – Over 300MW up to 1500MW4.2.7 Class F – Over 1500MW

4.3 Enhanced Level (Inner London Strategic Zone)4.3.1 Enhanced Level Overview4.3.2 Class A – Up to 1MW4.3.3 Classes B and C1 – Over 1MW up to 20MW4.3.4 Classes C2 and D – Over 20MW up to 300MW4.3.5 Class E – Over 300MW up to 1500MW4.3.6 Class F – Over 1500MW

5 EREC P2 Assessment Process5.1 General5.1.1 Defining a ‘Group’5.1.2 Time at Risk5.1.3 Demand at Risk

5.2 Assessing Network Capacity5.3 Assessing DG Contributions5.4 Examples

6 Other Considerations6.1 Distributed Energy Resources (including Flexibility)6.2 Innovation6.3 Load Transfers6.4 London Networks6.5 Load Shedding6.6 Derogation

7 References7.1 Internal Standards7.2 External Standards and Reports

8 Dependent DocumentsAppendix A – Inner London Strategic Zone (ILSZ)