Warrington West 132kV...

New 132kV electricity substation - Marsh Lane, Cuerdley, Warrington: Strategic Optioneering Report 1

Warrington West 132kV ReinforcementNew 132kV electricity switching substation Marsh Lane, Penketh, Warrington

Strategic Optioneering ReportOctober 2011

Warrington West 132kV ReinforcementNew 132kV electricity switching substation - Marsh Lane, Cuerdley, Warrington

Strategic Optioneering Report

October 2011


Contents

1.0 Introduction

2.0 Background

3.0 Design Process

4.0 Need

5.0 Options Evaluation

6.0 Conclusions

FIGURES

Figure 1: Geographic Representation of Existing SP Manweb Mid Cheshire 132kV network

Figure 2: Single Line Diagram of Existing SP Manweb Mid Cheshire 132kV Network

Warrington West 132kV Reinforcement4

1.0 Introduction1.1. This report describes the process of developing and assessing options which led to a

proposal to create new 132 kV infrastructure within the West Warrington area being identified as the preferred option which addresses the identified issues and achieves compliance with the company’s statutory and licence obligations. The proposal is promoted by SP Energy Networks on behalf of SP Manweb plc (referred to in this report as “SPEN”).

1.2. The report first considers the background to the development of new electricity distribution infrastructure, and then addresses the need case for the proposed reinforcement. The process of option development and assessment is described and finally a range of options is described and evaluated.

2.0 Background2.1. SP Manweb is a public distribution network operator (DNO) and owns the electricity

distribution licence for Merseyside, Cheshire and North Wales. The distribution network is operated by SPEN. SPEN is part of the ScottishPower group, which is in turn owned by Iberdrola, Spain’s number one energy group and is one of the largest utility companies in the world. SPEN is responsible for distributing power between the National Grid Supply Entry/Exit Points and load/generation customers connected within the distribution network.

2.2. The SP Manweb distribution system operates at 132,000 volts (132 kV), 33,000 volts (33 kV), 11,000 volts (11 kV), 6,600 volts (6.6 kV) and 400 volts (230 volts single phase). The SP Manweb 132 kV network comprises some 1,316 kilometres (km) of overhead lines, 233 km of underground cable and about one hundred 132/33 kV Grid substations. Within the Mid Cheshire area there are some 480 km of 132 kV overhead line circuits and about 54 km of 132 kV cable

2.3. SP Manweb has a statutory duty to offer terms to connect new load or generation to its distribution system. The form which these connections might take will depend on a number of factors including the location, capacity and timing of new load and generation. In order to connect this additional load or generation, reinforcement of the distribution system, including uprating and reconductoring existing lines, new overhead lines, new underground cables and new or extended substations may be required. Because of the interconnected nature and topology of the existing SP Manweb distribution system, system reinforcement or enhancement works may be required before the new load or generation can be connected.


2.4. At privatisation, and as required by its distribution licence, SP Manweb and the other UK DNOs implemented the Distribution Code, which is designed to permit the development, maintenance and operation of an efficient, co¬ordinated and economical system for the distribution of electricity, to facilitate competition in the generation and supply of electricity and to promote the security and efficiency of the power system as a whole. This reflects SP Manweb’s statutory duties under the Electricity Act 1989. It does this by providing a clear technical basis for its requirements for suitable performance from electrical equipment connected to the distribution system, and by specifying clear levels of expected performance from the distribution system on which the design of other parties’ equipment may be based or reviewed. By application of these standards, material damage to other parties’ equipment, resulting from credible events in the development, maintenance and operation of the distribution system, may be avoided. Additionally, the technical interface between SP Manweb and National Grid is governed by the Grid Code, whilst the commercial interface is dictated by the Connection and Use of System Code (CUSC).

2.5. Under the terms of its distribution license, SPEN is required to plan, develop and operate its distribution system in accordance with a standard not less than that set out in Energy Networks Association (ENA) document Engineering Recommendation P2/6 – Security of Supply. It is required to offer and honour terms for connection of new load or generation which do not conflict with this obligation. Accordingly such offers are assessed on the basis of the minimum scheme to provide the connection which meets the requirements of the Distribution Code and Grid Code. In addition, Ofgem recognises the need for significant generation related reinforcement projects to take into account future additional requirements and therefore provides the Distributed Generation Incentive Mechanism (DGIM) which encourages the DNO to provide some additional capacity beyond that which is immediately required for the contracted connections.

2.6. Section 9(2) of the Electricity Act 1989 requires SPEN:

a) “to develop and maintain an efficient, co-ordinated and economical system of electricity distribution; and

b) to facilitate competition in the supply and generation of electricity.”c) Section 38 and Schedule 9 of the Electricity Act requires SPEN, when

formulating proposals for new lines and other works, to:

“have regard to the desirability of preserving natural beauty, of conserving flora, fauna, and geological or physiographical features of special interest and of protecting sites, buildings and objects of architectural, historic or archaeological interest; and shall do

what he reasonably can to mitigate any effect which the proposals would have on the natural beauty of the countryside or on any such flora, fauna, features, sites, buildings or objects”

2.7. SP Manweb’s Schedule 9 Statement sets out how the company will meet the duty placed upon it by the aforementioned legislation. The Statement also refers to the application of best practice methods to assess the environmental impacts of proposals and identify appropriate mitigation measures. Effective consultation is promoted by the Statement.

2.8. The Fiddlers Ferry/Carrington 132 kV group, in the north east of SP Manweb’s service area was required to have the capacity to provide a 2010/2011 winter maximum demand of 372MW. It has experienced increasing load requirements in recent years, and there is a continuing flow of applications for new connections from large commercial and industrial users.

2.9. As a result of recent studies it has been identified that the overall Fiddlers Ferry/Carrington 132kV Group does not meet ER P2/6 requirements. Work has also been carried out to identify measures that will be necessary to restore compliance with the requirement of ER P2/6 for the overall group. A proposed solution has been identified, but this will take around two years to carry out once all consents have been received. In addition a number of interim measures have been put in place to mitigate the impact of potential circuit thermal overloads.

3.0 Design Process3.1. There are five key issues affecting the existing distribution system which drive the need for

reinforcement:

n thermal conditionsn fault levelsn voltage levelsn security of supplyn losses

3.2. Thermal conditions - Overhead line conductors are designed for a certain operating temperature and safe clearances between the conductors and the ground/structures are based on this assumption. The thermal rating translates into standard seasonal current ratings. Overloading causes conductors to overheat which will increase the sag of the conductors and reduce safety clearances. Operating at a temperature greater than their design temperature could also lead to a reduction in conductor strength.


3.3. Most existing 132 kV overhead line conductors within the SP Manweb network are ACSR 175 sq mm “LYNX”, which has a summer rating of 389 Amps (89 MVA). New or replacement conductors are 200 sq mm AAAC “POPLAR”, which has a higher summer rating of 542 Amps (124 MVA). POPLAR conductors can be accommodated on either heavy duty wood pole (HDWP) or steel lattice tower construction. In certain circumstances, It is possible to place 300 sq mm AAAC “UPAS” conductors (761 Amps, 174 MVA) on new HDWP, although this has a tendency to reduce the span lengths between poles, introducing more poles per km. “L4” construction steel towers can accommodate two 132 kV circuits with 300 sq mm conductors (i.e. rating of 174 MVA per circuit), whilst L7 construction steel towers can accommodate double circuits with 500 sq mm AAAC “RUBUS” conductors, with a summer rating of 245 MVA (1071 Amps per circuit).

3.4. Fault Levels – The SP Manweb 132 kV design fault level limit is 20 kA (4500 MVA). A high fault level improves the quality of supply by reducing the magnitude of short-term voltage fluctuations, but the fault level must also be kept within the capability of the plant and switchgear, otherwise catastrophic equipment failure can result during a network fault. Therefore, the design approach is generally to keep the fault levels as high as possible, whilst also maintaining sufficient design margins relative to the plant rating.

3.5. Voltage levels – The statutory voltage level limits at 132 kV are +/-10%. This allows for a voltage gradient along the length of a 132 kV circuit. The voltage gradient is directly related to the current flowing in the conductor and it is primarily this voltage gradient that limits the practical length of a 132 kV circuit. As a general rule of thumb, a circuit rated at 124 MVA is useable up to a distance of about 100 km, whereas a circuit rated at 245 MVA is useable up to a distance of about 50 km. Beyond these distances, it is generally not possible to utilise the full thermal rating of the circuits.

3.6. If there is an instantaneous change in power flow (for example as a result of a large generator or load disconnecting itself from the network or a circuit or transformer being switched out) this will cause an instantaneous step change in voltage. Plant and equipment can be sensitive to sudden changes in voltage, therefore events that cause instantaneous changes in power flow are avoided as much as possible (for example, the generator ramps up and down its export in a “slow” and controlled manner). Therefore, voltage step change is considered as part of the design process.

3.7. Security of Supply – Distribution networks in the UK are generally designed according to the security standard defined within the ENA Engineering Recommendation P2/6 “Security of Supply”. The basic principle of P2/6 is based on the need to provide greater levels of supply security as the size of the group load increases. Network security is created by a combination of plant redundancy and load transfer capability. In other words, for large load groups, it should be possible to maintain supplies to customers following an outage of any single item of plant or to restore supplies by transferring the load into another load group by network switching.

3.8. However, the standard does not apply to individual (large) customers if:

a) the customer requests a security different from that defined in P2/6 (either better or worse) and

b) it is possible to provide the level of security that the customer requests

3.9. Losses – Losses occur in the circuits and transformers used within the distribution network as a result of the power flowing through them. One of the dominant loss mechanisms is Ohmic losses, which is proportional to the circuit resistance, R, and the square of the current (I2). This is generally referred to as the “I squared R” losses. The ‘R’ in a 132 kV circuit is proportional to its length, therefore, the longer the circuit, the greater the losses. One way to reduce the losses for a given circuit length is to operate at a higher voltage. For example, for a given power transfer, if the voltage is increased by a factor of three (say, from 132 kV to 400 kV), the current is reduced by a factor of three and the I2R losses are reduced by a factor of nine.

4.0 Need4.1 The Fiddlers Ferry/Carrington 132 kV ‘demand Group’, in the North East of SP Manweb’s

franchise area, had a required winter maximum demand in 2010/11 of 372MW and increased load requirement and there is a continuing flow of applications for new connections from large commercial and industrial users. As a result of studies in 2008 it has been identified that the overall Fiddlers Ferry/Carrington group does not meet ER P2/6requirements, a standard set by the industry Regulator Ofgem.

4.2 The reason for this is that under the current system configuration when there is an outage on the group, there is a risk of exceeding the power flow limitations on overhead lines between Fiddlers Ferry and Warrington, Fiddlers Ferry and Sankey Bridges and Sankey Bridges and Warrington. Therefore, the existing System is non-compliant with P2/6 presenting a risk to electricity supplies to 190,000 customers and 78,000 households fed from this group. Consequently, Licence derogation was subsequently applied for and granted by Ofgem on condition that the network reinforcement progresses in a timely manner.


4.3 Engineering recommendation P2/6 specifies the requirements for supply security. Table 1 contained within the document highlights the minimum levels of security for distribution networks classified in groups of demand ranges. The Fiddlers Ferry/Carrington group falls within Class of Supply E (over 300MW and up to 1500MW) of Table 1 and the subsequent level of system security required is detailed below.

First circuit Outage(Restore) Immediately: Group demand

Second circuit outage(Restore) Immediately: All consumers at 2/3 group demand.

Within time to restore arranged outage: Group demand

Table 1 - Requirements of ER P2/6 For a Demand Group of Class ‘E’

4.4 The intention of the statement ‘All consumers at 2/3 group demand’ within P2/6 is that maintenance outages are carried out during periods when the group load is below 2/3 of its annual maximum and that should a fault then occur all customers will continue to be supplied. Therefore if the maintenance period load is above 2/3 then this is the load to be met during a second circuit outage. The Fiddlers Ferry/ Carrington group had a demand requirement in the winter of 2010/11 of 372MW and therefore falls into category E of Engineering Recommendation P2/6. This peak demand figure takes into account the group infeeds from NGET, and generation from Hays Chemicals CHP and Winnington CHP.

4.5 Using P2/6 assessment criteria, under the maintenance period demand where there is an outage on any of the 132kV circuits or NGET transformers within the group, loss of a second circuit or NGET transformer in the group results in overloads of one or more of the following circuits or transformers:

n Warrington – Sankey Bridges 132kV circuitn Fiddlers Ferry – Sankey Bridges 132kV circuitn Fiddlers Ferry – Warrington 132kV circuitn Carrington SGT1A transformern Carrington SGT2A transformer

4.6 The overloads are caused by an imbalance of load sharing between the supergrid transformers at Fiddlers Ferry and Carrington. This imbalance is caused by a difference in system impedance between the supergrid infeed points and the demand centres, which are at Warrington and Sankey Bridges. In simple terms, because the load at Warrington

and Sankey Bridges are closer to Fiddlers Ferry than Carrington, the Fiddlers Ferry supergrid transformers and associated circuits provide most of the groups demand requirements.

4.7 This imbalance will affectively increase the existing 132kV circuit overloads further compounding the P2/6 issue. The solution is to ‘balance’ the demand between Fiddlers Ferry and Carrington which will reduce the demand on Fiddlers Ferry and alleviate the overloads on the affected circuits and achieving compliance with P2/6. The existing 132kV circuit configuration at Fiddlers Ferry also imposes operational flexibility issues on the network which further compounds the P2/6 issues and increases the risk to supplies during outage on the supergrid transformers or their associated 132kV circuits.

5.0 Options Evaluation5.1 In evaluating the options due regard was given to the key criteria of economy, efficiency

(including system compliance and deliverability) and environmental factors as follows:-

OPTION “DN”: DO NOTHING5.2 The Do Nothing option is discounted because it would be a clear breach of SP Manweb’s

distribution licence obligation to maintain supply security with the requirement of ER P2/6 and its ability to provide and honour terms for connection to our distribution network.

OPTION “WWR”: WEST WARRINGTON REINFORCEMENT5.3 The West Warrington Reinforcement has been identified as the preferred reinforcement

solution because it resolves the thermal issues and achieves compliance with P2/6; is the ‘minimum scheme’ that satisfies SPM’s requirements whilst meeting the company’s statutory and licence obligations for developing and maintaining an efficient and coordinated network.

5.4 This proposal has the least impact from a planning and environmental impact perspective whilst still providing the ability to support future long term development proposals in the mid Cheshire area.

OPTION “NGL”: NEW SUPERGRID SUBSTATION AT LOSTOCK5.5 The New Supergrid Substation at Lostock option is discounted because, apart from a

significant increase in cost to the preferred solution, a new NGET infeed would only offset the demand requirements of Carrington and Fiddlers Ferry. It would not resolve the P2/6 issues, which would still require work to be done at West Warrington to resolve them


OPTION “UEN”: UPGRADE EXISTING NETWORK5.6 The Upgrade Existing Network is discounted because it would require the whole of the

Cheshire 132kV overhead line infrastructure between Fiddlers Ferry, Warrington and Sankey Bridges to be rebuilt to a higher specification to provide the thermal capability required to achieve compliance with P2/6. The cost of doing this would be significantly more than that of the preferred solution and would have a significant impact on environment and take many years to secure the necessary planning and consents.

OPTION “IFI”: INNOVATION FUNDING INCENTIVE METHOD5.7 The Innovation Funding Incentive method option is discounted because many of the

elements of this approach are speculative and require the use of new technologies and methods, many of which are unproven. The reliability and resilience of untried methods cannot be established and would require many years of ‘live’ operation in order to prove suitability for use by DNO’s as part of a recognised design solution. In addition this approach does not provide an enduring solution to the current issues and future network requirements for the Fiddlers Ferry/Carrington group.

FIGURE 1 - GEOGRAPHIC REPRESENTATION OF EXISTING SP MANWEB MID CHESHIRE 132KV NETWORK

Initial Strategic Optioneering Report

Reproduced from the Ordnance Survey map with the permission of Ordnance Survey® on behalf of the Controller of Her Majesty’s Stationery Office, © Crown copyright Licence No. EL273112

KEY:

NTS

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FIGURE 2SINGLE LINE DIAGRAM OF EXISTING SP MANWEB MID CHESHIRE 132KV NETWORK

1

Figure 1 ‐ Single Line Diagram of Existing SP Manweb Mid Cheshire 132kV Network

CARRINGTON GSP Warrington

FIDDLERS FERRY GSP

Dallam

275/132kV Transformer

Reactor

Double Circuit Route

Single Circuit Route

Substation WithCircuit Breakers


Risley

Hartford

Winsford

Sankey Bridges

KEY


Circuits Associated with P2/6 Issues Crewe

Elworth

Knutsford

ICI Wade

Knutsford

Lostock

Authorised Reinforcement

1

Figure 1 ‐ Single Line Diagram of Existing SP Manweb Mid Cheshire 132kV Network

CARRINGTON GSP Warrington

FIDDLERS FERRY GSP

Dallam


Reactor

Double Circuit Route

Single Circuit Route



Risley

Hartford

Winsford

Sankey Bridges

KEY


Circuits Associated with P2/6 Issues Crewe

Elworth

Knutsford

ICI Wade

Knutsford

Lostock

Authorised Reinforcement


6.0 Conclusions6.1 The conclusions of SP Manweb’s initial studies:

a) support the SP Manweb proposal for reinforcement to their 132 kV distribution system in the west Warrington area,

b) demonstrate how SP Manweb’s proposed design would resolve the current non compliance with the Engineering Recommendation P2/6 Supply Security requirements with minimal visual and environmental impact on the surrounding area and,

c) demonstrate how the proposed reinforcement facilitates the connection of new demand within the Warrington geographical area and associated conurbations and’

d) facilitate future SPM 132kV reinforcement requirements with all work being required to be carried out within existing operational boundaries of the proposed and existing grid substations and,

e) demonstrate that the proposed design supports plans for development and expansion of the Warrington area by the local planning authority.

6.2 The proposed reinforcement work will require:

n Construction of a new 132kV switching station near to Fiddlers Ferry.n diversion of the existing 132kV overhead line circuits out of Fiddlers Ferry

power station into the new substation.n At Carrington, the removal of two 132kV reactors from the system.

6.3 Whilst the above is the outcome of SPEN’s current system options studies, the west Warrington project is at an early stage of development and SPEN will be keeping all options under review as consultation takes place.

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