Electricity Act 1989 (Sections 36, 37, 62(3) & Schedule 8) Town and
Country Planning Act 1990 (Section 90) and the Electricity Generating
Stations and Overhead Lines (Inquiries Procedure)(England and Wales)
Rules 2007
Application by SP Manweb PLC, dated 2 December 2009 for consent
under Section 37 of the Electricity Act 1989 to install and keep installed a
132kV overhead electric line connection from the proposed Llandinam
Wind Farm to Welshpool Substation (the “Application”)
Proof of Evidence
Of
Eric Paalman
On
Engineering Project Design
SPM/ENGINEERING/POE/PAALMAN/003A
1 QUALIFICATIONS AND EXPERIENCE 1
2 SCOPE OF EVIDENCE 2
3 THE PROPOSED LLANDINAM SCHEME 3
4 UNDERGROUNDING 14
5 SELECTION OF WOOD POLE DESIGN (CONSIDERATION OF TRIDENT AND HDWP TECHNOLOGY) 16
6 TECHNICAL AND COST CHARACTERISTICS OF CONNECTION ALTERNATIVES. 22
7 CONCLUSIONS 32
1
1. QUALIFICATIONS AND EXPERIENCE
1.1 I graduated in 2004 from John Moore‟s University with a BEng in
Electrical Plant Engineering. Since July 2011 I have been employed as
a Lead Design Engineer in the Asset Strategy section for Scottish
Power Energy Networks ("SPEN"). I am part of a team that is
responsible for 132kV design to deliver investment projects to ensure
that the electrical connectivity, equipment layout and technical
specifications are appropriate to meet the needs identified for SP
Manweb plc's ("SP Manweb") electrical networks.
1.2 As a Lead Design Engineer for SPEN I am also responsible for
ensuring that investment projects are designed appropriately to meet
SP Manweb‟s licence obligations and are done so in a cost effective
manner. In my previous role at SPEN, as a System Design Engineer, I
was responsible for the preparation of investment projects to develop
and maintain the network infrastructure and connectivity.
1.3 I have worked in the electricity supply industry since 1992 and in that
time I have held numerous positions from overhead linesman to senior
engineer. The roles have involved design, construction, operation and
maintenance activities on electrical network equipment at all voltages
from 230 Volts up to 132kV.
1.4 I confirm the opinions set out in this proof of evidence which I have
prepared and provide for this inquiry are my own truly held professional
opinions.
2
2. SCOPE OF EVIDENCE
2.1 In December 2009, SP Manweb applied for consent under section 37 of
the Electricity Act 1989 (CD/COM/023) to construct a single circuit
132kV Heavy Duty Wood Pole (“HDWP”) overhead line between the
Llandinam Repowering Wind Farm substation and Welshpool Grid
substation (the "Llandinam Scheme"). My proof of evidence describes
how the engineering design of the Llandinam Scheme takes account of
the technical requirements of the electricity distribution system,
customer requirements and the costs of the connection.
2.2 Section 3 provides a summary of the engineering design and the key
components of the Llandinam Scheme.
2.3 Section 4 discusses part undergrounding of the Llandinam Scheme.
2.4 Section 5 addresses the selection of the overhead line design.
2.5 Section 6 discusses the technical and cost characteristics of alternative
connection options.
2.6 Section 7 sets out my conclusions.
2.7 I have reviewed the objections to the Llandinam Scheme. Some
objectors have commented on engineering design matters (such as
undergrounding and the selection of the overhead line design). My
proof addresses these comments.
3
3. THE PROPOSED LLANDINAM SCHEME
Introduction
3.1 Dr Beddoes (SPM/NETWORK/POE/BEDDOES/001A) describes the
need for a circuit that is capable of carrying 90MVA at 132kV between
the Llandinam Repowering Wind Farm substation and Welshpool Grid
substation.
3.2 Having regard to all SP Manweb‟s statutory duties and licence
obligations, an overhead line solution typically facilitates compliance
with these various requirements.
3.3 To minimise the environmental effects of overhead lines, consideration
is given to the type of support to be used, the overhead line route,
balancing technical requirements with SP Manweb's licence obligations
and other aspects of the design of an overhead line
3.4 While 132kV circuits were previously supported by steel lattice towers
(pylons) or steel portal design structures (similar to goal posts), the
lighter conductors and availability of „post‟-type freestanding insulators
has made it possible to utilise a single circuit wood pole design. The
shorter span lengths of the pole supports, compared to lattice pylons,
result in lower profiles and this, combined with careful routeing, can
lessen the visual impact of a line. A height comparison of typical wood
pole structures, pylons, and a wind turbine is shown in Appendix 1
Comparison of relative electrical infrastructures.
3.5 The proposed wood pole overhead line design supports the
requirements as set out by Dr Beddoes
(SPM/NETWORK/POE/BEDDOES/001A). In section 5 I carefully
consider the use of two woodpole overhead line designs: Trident and
HDWP.
3.6 The Trident design specification is described in ENA technical
specification 43-50 issue 1 & 2 132kV Single Circuit Overhead Lines on
Wood Poles (Appendix 2). The HDWP design specification is set out in
4
OHL-03-132 issue 2 Technical Guidance for the Design and Analysis of
SP 132kV Single Cct, 4-Wire Heavy Duty Wood Pole OHL (c/w
underslung OPGW Earthwire) (Appendix 3). This guidance is in
accordance with BS EN 50341 Parts 1-3:2001 Overhead electrical lines
exceeding AC 45 kV; ENA-TS 43-8 Issue 3, 2004 (with respect to safety
clearances) and as required under the Electrical Safety, Quality and
Continuity Regulations 2002 (CD/SPM/LEG/01).
Engineering specification of the overhead line
3.7 The Llandinam Scheme primarily comprises the installation of a 132kV
single circuit overhead line between Welshpool Grid substation and the
proposed Llandinam Repowering Wind Farm substation. The
connection comprises (for the majority of its length) of an overhead line
on wood pole supports with a short cable section at the termination at
Welshpool Grid substation.
3.8 The wood pole overheadline support structures have to carry a single
circuit containing three phase conductors (these are what are
commonly known as the "wires" on an overhead line). Depending upon
the ground conditions at the Llandinam Repowering Wind Farm
substation an additional aerial earth wire may have to be incorporated
within the overhead line construction. The justification for this earth wire
is described in section 5.
3.9 The three phase conductors are made of an aluminium alloy whilst the
earth conductor is made of aluminium alloy with steel reinforcement in
the centre. The primary circuit conductors have an overall diameter of
20mm whilst the earth conductor has a diameter of 14mm.
3.10 The woodpole structures are designed to support bare overhead
metallic conductors. The current HDWP design can support a conductor
with a cross sectional area of either 300mm2 (referred to as “Upas”) or
200mm2 (referred to as “Poplar”). The Trident design, as described in
ENA technical specification 43-50 issue 1 & 2 132kV Single Circuit
Overhead Lines on Wood Poles (Appendix 2), can support 200mm2
5
Poplar. In this instance a 200mm2 conductor is proposed, providing a
summer rating of 124MVA which is sufficient to meet the design
connection requirement of 90MVA. Both wood pole designs, Trident
and HDWP, can support this Poplar conductor.
3.11 There is need for a fibre optic communication circuit between
Welshpool Grid substation and the proposed Llandinam Repowering
Wind Farm substation. To protect the overhead line and high voltage
equipment at the wind farm substation, a reliable communication circuit
is required between Welshpool Grid and Llandinam Repowering Wind
Farm substation. This communication circuit transfers essential system
information such as measurements and operational conditions of the
switchgear to the distribution network operator. The most economic
method to provide a communication circuit is to integrate a fibre optic
circuit with the proposed overhead line. This can either be achieved by
installing a fibre optic circuit within the earthed conductor or live phase
conductor.
3.12 The line is approximately 34.3km in length and has to be supported on
wood pole support structures containing galvanised steelwork bracings
onto which the insulators and conductors are fitted.
3.13 At the Welshpool Grid substation, the overhead line terminates onto a
cable supporting structure (cable sealing ends) from where a 50m
section of cable provides the connection to the existing 132kV network.
The woodpole cable sealing end structure consists of 4 wood poles with
steel galvanised bracings on the top that support the conductors and
surge arresters. Typically, 4 stays are needed to support each
structure. At Llandinam Repowering Wind Farm substation the
overhead line terminates via overhead conductors into the customer's
substation compound.
3.14 The minimum ground safety clearance distance for a 132kV overhead
line is 6.7m (including the lower earth wire). The overhead line is
designed to ensure that this distance is maintained at all times and in all
6
conditions. For example, in winter the conductors may be subject to
severe ice and wind loadings and in summer hotter weather may cause
the conductors to expand and sag lower. The line is also designed to
take account of varying ground levels, height and topography (slopes
and gradients).
3.15 Span lengths are optimised to achieve sympathetic pole placements
and pole heights have been minimised whilst maintaining statutory
ground clearance. The detail of the different wood pole structure
configurations are provided in Mr Livingston‟s evidence
(SPM/CONSTRUCTION/POE/LIVINGSTON/004A).
3.16 The line supports comprise of timber poles varying in length from 11.5m
to 16m with galvanised steelwork bracings onto which the insulators
and conductors are fitted. The pole heights referred to in Appendix 04b
pole schedule (Volume 3a of the Updated ES (CD/SPM/ES/01)) are the
actual pole lengths. Taking into account that the nominal depth of the
poles is 2.5m and the steel bracings and insulators add typically 2.3m to
the length, the net result is that the actual conductor height above
ground (at pole positions) is about 0.2m less than the pole length
referred to.
3.17 The span length or distance between supports depends on similar
criteria to the line height and varies from 31m to 137m, with an average
span of approximately 90m between supports.
Engineering specification of the underground section
3.18 Miss Berry describes the National Policy Statement (NPS) for Electricity
Networks Infrastructure (EN-5) (CD/COM/003) in her evidence
(SPM/PLANNING/POE/BERRY/011A) and how it applies to Llandinam
Scheme. NPS EN-5 contains guidance on the approach which should
be taken in assessing the merits of an underground cable option as a
full or partial alternative to an overhead line solution
7
3.19 There exists a physical constraint associated with achieving entry to the
substation site at the Welshpool end of the route. The construction of
overhead lines requires a relatively wide hazard free zone. For this
reason, where there are multiple lines needing to access a limited area
and to allow safe segregation of electrical assets in and around
substations, it is often necessary to provide cable sections to connect
the switchgear to the overhead lines.
3.20 The short section of cable (50m) terminating at Welshpool will be
achieved by installing 3 single 800mm2 Aluminium Cross-Linked
Polyethylene (XLPE) insulation cables. The dimension of the cable
trench is typically 1 meter wide and 1 meter deep and may vary
depending on whether the installation is either laid direct or ducted and
if the cables are installed in road, verge or field. In the case of the
Llandinam Scheme, the trench would be excavated between Welshpool
Grid substation and the overhead line termination in the field opposite
the substation. The trench would be backfilled and reinstated after the
cable has been installed.
3.21 The engineering specification of the underground cable section is in
accordance with CAB-03-031 Issue 2 Single core power cables with
extruded insulation and associated accessories for 132kV (Um = 145
kV) networks (Appendix 4).
Engineering specification of the Substation
3.22 At Welshpool Grid substation the 132kV compound has to be extended
to accommodate 132kV electrical equipment such as disconnectors,
circuit breaker, cable termination structures and surge arresters.
3.23 At the Llandinam Repowering Wind Farm substation a new 132kV
compound is to be constructed to accommodate SP Manweb‟s 132kV
equipment such as disconnectors, circuit breaker, metering equipment,
overhead line termination structures and surge arresters.
8
3.24 The engineering specification for the substation works is in accordance
with Part 2 Balance of Plant – Generic Document (Appendix 5). This
guidance is in accordance with BS 7354:1990 Design of High Voltage
open terminal stations (Appendix 6) and NGTS 2.1 issue 5 Substations
(Appendix 7).
Routeing the overhead line
3.25 While SP Manweb‟s internal environmental planning team and external
consultants have a good understanding of the engineering aspects of
the required electrical connection, regular dialogue is maintained with
the engineering design team throughout the route selection and
environmental planning process. This enables any engineering
constraints which may not have been fully appreciated to be brought to
light as may be required and factored in to the routeing process. The
environmental planning and routeing details are further described in
Miss Berry‟s evidence (SPM/PLANNING/POE/BERRY/011A) and is
also described in the Review of Needs Case and Alternatives section
4.1 (Volume 5 of the Updated ES (CD/SPM/ES/01)) (the “Alternatives
Paper”).
3.26 Guidance on routeing an overhead line is provided by the „Holford
Rules‟ (CD/SPM/GUID/01). Rule 3 assists in minimising the number
and angle of line deviations (in other words, minimising the number of
times that the line has to change direction), which also serves to reduce
costs. In addition, it is necessary to be careful not to propose the
construction of assets in a location where other parties‟ infrastructure
operations would compromise operational or safety requirements for SP
Manweb's assets or vice versa. It is also necessary to seek to avoid
areas where lines might introduce significant hazards to the leisure and
commercial activities being carried out there.
3.27 Clearly there are limits to the physical dimensions of the obstacles that
can be overcome by overhead lines due to the strength of the materials
and the technically viable solutions which are available within a design
9
specification. Wood pole line supports become relatively expensive and
difficult to source when extra long or unusually stout wood poles are
required. This in effect provides a height constraint and in turn has a
bearing on the span lengths. The average span length for the proposed
design of the Llandinam Scheme is 90m. The maximum span for the
Llandinam Scheme is 137m utilising the HDWP design. Whilst an
occasional high pole or a long span necessitating extensions to the
existing pole top steelwork can sometimes be accommodated, as part
of an economical design solutions these exceptions must generally be
minimised.
3.28 It is also economically and technically desirable to minimise the number
of transitions from overhead to underground assets. Apart from the
cost, these transitions can be problematic when investigating faults in
an electrical circuit with multiple cable sections. For practical purposes,
overhead lines can be quickly re-energised after a fault clearance as
typically no permanent damage would be sustained. By contrast, an
underground cable will need to be repaired before it is possible to
successfully re-energising it.
3.29 To facilitate the above, in 2008, SP Manweb engaged an external
overhead line design consultancy LS Transmission Consultancy Ltd
("LSTC") to consider initial high level designs based on the route option.
LSTC developed an optimised design in August 2009 as part of the
Application in December 2009. In response to comments received
following statutory consultee feedback, further revisions were
undertaken and Revision F was produced as an Addendum to the ES in
December 2010. The resulting overhead line design has been
developed as an iterative approach and is aligned within the 100m
corridor identified by the environmental routeing study.
3.30 Further revisions were undertaken in response to landowner and local
people comments and the line was further revised (Revision G) in June
2011 to reduce likely environmental impacts. A further revision, Line
Revision G(1), is referred to in the Updated ES (CD/SPM/ES/01). This
10
revision is noted as showing the indicative line route that has been
assessed in that document. This revision takes into account alterations
made in response to statutory consultee comments and landowner
feedback. Revision G(1) sits within the Revision F corridor applied for
by SP Manweb pursuant to the Application.
3.31 In Revision G(1) of the overhead line design there are no significant
engineering constraints identified along the route as defined.
Capital and operational costs
Capital costs
3.32 Until a construction contract has been awarded, the exact cost of a
project is unknown. Decisions on which options are to be promoted and
constructed are, therefore, based upon robust estimates informed by
recent purchasing and project experience.
3.33 For an HDWP overhead line, the base estimate used by SP Manweb in
September 2013 prices is £340,000 per km erected. This value takes
into account the installation of several overhead angle support
structures and assumes an almost straight overhead line route. This
value excludes additional costs such as scaffolding over roads, legal
costs, wayleaving etc.
3.34 SP Manweb estimates overall cable (ie underground line) cost at
approximately £1,100,000 per km installed in arable or unmade ground
with an uplift to £1,300,000 per km in the case of made ground, for
example, within a roadway. These are typical costs, not taking into
account underlying rock formations and terrain difficulties.
3.35 It must be kept in mind that these costs are in respect of normal
engineering installations. When considering additional transitions
between overhead lines and underground cables the length of cable at
shorter distances becomes less significant with the cost being
dominated by the relatively expensive terminal structures. These
terminal structures support the overhead line and underground cable
11
termination. When terminating overhead lines onto underground
cables, surge protection to protect the underground cable has to be
installed and adds to the cost. Typical cost for a cable termination
structure is £220,000 and for a section of overhead line to be
undergrounded two termination structures are needed.
3.36 The costs of the Llandinam Scheme connection to Welshpool Grid is
referred to as the „Llandinam Scheme Cost‟ (“LSC”), this is an
estimated cost between £21m - £24m and is based on a new
approximately 35km 132kV overhead line plus associated substation
works.
Operational costs
3.37 Overhead lines are subject to weather and other environmental
interference. Typically, following an instance such as wind borne
material causing a short circuit, the circuit will automatically trip to clear
the fault and the material will fall away clear of the line. This is referred
to as a transient fault. In such circumstances, it would be possible to
successfully put the line into service almost immediately following the
fault.
3.38 The national fault incident rate for overhead line is 0.4 permanent faults
per 100km per year which would give rise to a theoretical fault rate of
one every 7 years for a 35km overhead line. Typical fault repair cost to
restore a grounded conductor is approximately £20,000 per incident.
The repair time for an overhead line is generally measured within hours
or a few days as access is easier and spares are generally more
available. The estimated lifetime maintenance cost for the overhead line
is estimated at (very roughly) £70,000. In the UK, it is unusual for
natural causes to bring down a 132kV overhead line and they have
given reliable service over many years.
3.39 In relation to underground cables, service performance is reliable
provided that third party interference can be prevented. This is achieved
through providing additional mechanical protection at installation.
12
Nevertheless, ensuring that a cable is not compromised while in service
is not economically viable for extensive networks. From time to time,
activities along the route take place which result in damage that can
take several years to come to light. Underground cable faults invariably
lead to permanent damage. A 132kV underground cable fault can take
several days to locate using specialist equipment and several weeks
will then be required to arrange sufficient excavation and to install a
repair section. During all of this time the network is depleted and in this
case customer supply interrupted. It may be that the excavations and
repair activities result in significant disruption to other parties where, for
example, excavations are required in the highway or agricultural land.
3.40 From information contained within the National Fault and Interruption
Reporting Scheme (NAFIRS) 2011/2012 (Appendix 8) the national
incidence rate for 132kV cables is 3.2 faults per year per 100km of
cable installed. For the proposed design, 50m of cable at Welshpool
Grid, this could theoretically result in a frequency of one fault in 600
years. It is not economical to repair this short section of cable and in
case of a fault the 50m of cable will be replaced in its entirety at an
estimated cost of £125,000. The estimated lifetime maintenance cost
for this short section of cable is estimated at (very roughly) £5,000. This
is in contrast to a lifetime maintenance cost estimated in excess of (very
roughly) £20,000,000 if the whole section of the proposed route
between Welshpool and Llandinam is to be undergrounded (based
upon an estimated fault repair cost of £800,000).
3.41 In addition, more time would be needed for the repair as this could be
up to several weeks from the fault occurrence to the return to service,
dependent on the fault location and the availability of spare cable and
jointing accessories.
3.42 A further difficulty is introduced when a circuit has several transitions
between overhead and underground. When such a circuit faults, it must
be ascertained whether the fault is overhead or underground and,
should the circuit have permanent damage, then the task of locating the
13
fault becomes extended. An overhead line which has significant
underground sections is not therefore able to be treated in the same
fashion as one which is mainly overhead. It is therefore considered
industry best practice to minimise the number of transitions in
distribution circuits.
3.43 Maintenance of the line is mainly based on routine inspections either by
foot or by helicopter patrol. As the HDWP is a robust design, the
structures are unlikely to require significant maintenance throughout
their lives. The poles, conductors and insulators have an anticipated life
expectancy of 63 years, 54 years and 45 years respectively. Vegetation
management will be undertaken as part of an ongoing inspection
regime.
3.44 The short section of cable connected at Welshpool Grid will be subject
to regular inspection of the above ground terminations but otherwise
should require nominal maintenance. The short length of cable section
(50m) should ensure the likelihood for a cable fault is significantly
reduced.
14
4. UNDERGROUNDING
4.1 Miss Berry describes in her evidence
(SPM/PLANNING/POE/BERRY/011A) NPS EN-5 (CD/COM/003) and
how it applies to SP Manweb‟s approach on undergrounding. SP
Manweb has a licence obligation to develop an efficient, coordinated
and economical system. An overhead line solution typically facilitates
compliance with this obligation. Overhead line solutions are more
economical than cable alternatives to develop, as well as providing
shorter return to service times under fault conditions.
4.2 SP Manweb accepts however that the justification for undergrounding
should be considered on a case by case basis. These considerations
would take into account cost and system design requirements, and the
specific factors involved in each particular proposal, such as areas of
high technical environmental constraint and areas of the highest
recognised amenity value, in accordance with the requirements of NPS
EN-5 and SP Manweb's statutory environmental duties under the
Electricity Act 1989 (CD/COM/023).
4.3 One section, the A483 near Old Neuadd Bank to Cae-betin Wood, has
been considered for undergrounding due to the "serious concerns" that
arise in relation to this section (as described in the Alternatives Paper
(Volume 5 of the Updated ES (CD/SPM/ES/01)).
4.4 In the event of placing a section underground, SP Manweb would utilise
local roads which generally follow the same direction as the overhead
line route. The potential underground solution for the Old Neuadd Bank
to Cae-betin Wood section of the Llandinam Scheme is illustrated in
Figure 4.1: Location of Potential Underground cabling of Appendix 05a
to the Updated ES (Volume 3a) (CD/SPM/ES/01).
4.5 This route would be likely to follow a route along the track/byway to the
west of the B4335 (Sheep Pen) and then along the B4335 before
turning into a track which runs along the northern foot slopes of Kerry
Hill to join the proposed route near to Cae-betin Wood.
15
4.6 Installing a cable along this route is technically feasible and it is
assumed that a trench can be excavated without encountering
significant rock formations. This assumption has been used for costing
this underground cable section. Excavating a trench in rock is likely to
double or treble the installation costs.
4.7 The net additional capital cost of this route which extends to over 8.5km
would be approximately £8.2m.
4.8 As explained in the Appraisal of the Llandinam Scheme against
National Policy Statement for Electricity Networks Infrastructure (NPS
EN-5) (the "NPS EN-5 Paper") (Appendix 05a to the Updated ES
(Volume 3a) (CD/SPM/ES/01)), SP Manweb considers that there would
be limited benefits to undergrounding in this location as the landscape
is not a nationally designated landscape and not close to residential
areas. In addition, the "serious concerns" identified would remain even
if the Llandinam Scheme were undergrounded in the Old Neuadd Bank
to Cae-betin Wood section, due to the cumulative impacts of nearby
windfarms on that same area.
4.9 SP Manweb has estimated the costs of undergrounding at this section,
including an estimate (very roughly) of the lifetime maintenance cost,
and identified the combination of the capital cost and the estimated
lifetime cost to be in the region of an additional £13.6m, which is over
half the cost of the total scheme as an overhead line. This figure could
increase to approximately £20m if rock formations are encountered.
For the reasons given in NPS EN-5 Paper (Appendix 05a to the
Updated ES (Volume 3a) (CD/SPM/ES/01)), SP Manweb‟s view is that
undergrounding in the context of the Llandinam Scheme is not justified.
16
5. SELECTION OF WOOD POLE DESIGN (CONSIDERATION OF
TRIDENT AND HDWP TECHNOLOGY)
5.1 Based on the outcome of the network design studies performed by Dr
Beddoes (SPM/NETWORK/POE/BEDDOES/001A), it is proposed to
install a wood pole overhead line (rather than a steel lattice tower line)
between Welshpool and Llandinam Repowering Wind Farm substation.
5.2 Initially two wood pole options were considered, Trident and HDWP.
This is also described in the Alternatives Paper (Volume 5 of the
Updated ES (CD/SPM/ES/01)).
HDWP
5.3 The wood poles carry a single circuit containing three phase conductors
with an under slung aerial earth wire. The three phase conductors are
made of an aluminium alloy; the earth conductor is aluminium with steel
reinforcement and contains a fibre optic circuit. This earthwire
incorporates a fibre optic cable for protection signalling and
communication purposes known as Optical Ground Wire (OPGW). The
primary circuit conductors have an overall diameter of 20mm whilst the
earth conductor has a diameter of 14mm.
5.4 The engineering specification of the overhead line is in accordance with
the OHL-03-132 Issue 2 Technical Guidance for the Design and
Analysis of SP 132kV Single Cct, 4-Wire Heavy Duty Wood Pole OHL
(Appendix 3). Typical design sketches showing construction details are
shown in Appendix B of that document (Design Sketches).
Trident
5.5 The wood poles carry a single circuit containing three phase
conductors. There is no earth wire with this design and the Trident
design is therefore referred to as unearthed. The three phase
conductors are made of an aluminium alloy. The primary circuit
conductors have an overall diameter of 20mm.
17
5.6 Existing wood pole overhead lines are primarily build at low level
altitude and intermediate supports can be single pole support
structures. Design support structures are calculated taking into account
environmental conditions such as wind and ice loading. These factors
are influenced by altitude. For the Trident design, support structures
above 250m sea level are typically dual pole wood support structures.
In the case of the Llandinam Scheme, if it could be designed to ENA TS
43-50 (Trident), the last 13km towards the windfarm, from Cefn Gwyn
including the section adjacent to the Kerry ridge, would likely be
constructed with dual pole wood pole structures. This is important as
many objectors to date have just focussed on the single pole structure
of the Trident series of poles.
Need for an earth wire
5.7 I have already explained the need to protect the overhead line and high
voltage equipment at the Llandinam Repowering Wind Farm substation
by the provision of a reliable communication circuit between the
Welshpool Grid and Llandinam Repowering Wind Farm substation.
5.8 Although two options were initially identified, Trident and HDWP, the
unearthed Trident design in 2009 and 2010 was not capable of carrying
a protection communication circuit. HDWP has a separate earth wire,
designed to carry fault current, but which can also be used to carry an
additional protection communication circuit. HDWP was therefore
selected and formed the basis of the Application. This HDWP design
was assessed in the December 2009 ES (CD/SPM/ES/02) and the
December 2010 Addendum (CD/SPM/ES/03). Objectors in December
2013 have raised a question querying whether an initial proposal for
what they term “single T-pylons” was unilaterally changed by SP
Manweb to be HDWP. I assume that this reference to “single T-pylons”
is a reference to single Trident wood pole structures. Paragraphs 5.9 to
5.21 below respond to the selection of HDWP in place of Trident.
18
5.9 In response to the Application more generally, objectors have over a
number of months and years suggested that in the event of the need for
the connection being demonstrated, then SP Manweb should consider
whether the line design could be changed to the unearthed Trident
design. They argue that the Trident design has potentially less
environmental impact due to its lighter construction and potentially
longer span lengths.
5.10 Subsequent improvements in overhead line conductor technology have
led to a conductor that can carry an integrated protection
communication circuit. Optical fibres are incorporated in the design of
the phase conductor. This conductor design is known as Optical Phase
Conductor (“OPPC”). Therefore a Trident pole can now carry a
communication circuit. As a result, SP Manweb has considered the use
of the Trident design again as part of the Updated ES (CD/SPM/ES/01).
5.11 An electrical fault at a substation can cause very high current to flow.
This current is trying to find the path of least resistance back to its
source. In an unearthed design (Trident) all this current has to find its
way back to the source via the general mass of earth which in effect is a
return conductor, and thus relies upon the general make up of the
ground. The resistivity of the ground determines how easy it is for this
current to flow. A low resistivity indicates a material that readily allows
the movement of electric current.
5.12 When a current flows through a resistance a voltage is set up. When
high voltage equipment faults and current flows to the general mass of
earth a fault develops (earth fault). The magnitude of this earth fault
current is dictated by the amount of energy that is available at the point
of the fault and the resistance in the earth return path. The earth fault
current is highest at the point of the fault and declines with distance
from this source. A voltage (potential) is created in the ground
surrounding the point of fault and the ground rises in potential
compared to a remote earth (ie. a voltage difference may be present at
the ground where the fault occurs compared with a point some distance
19
away which is at a different potential; general mass of earth is to be
taken at 0 Volt). This voltage is commonly referred to as Rise Of Earth
Potential (“ROEP”).
5.13 The ROEP may be so high that a person could be injured due to the
voltage developed between the position on the ground of his or her two
feet (“step potential”), or between the ground on which the person is
standing whilst touching a metal object (“touch potential”). Any
conducting object in contact with the surrounding substation ground,
such as telephone wires, fences, or metallic piping, may also be
energised at the ground potential in the substation. This transferred
potential is a hazard to people and equipment outside the substation
(“transfer potential”).
5.14 An earth fault at a substation supplied via an unearthed design,
combined with highly resistive ground at the substation, can result in a
very high ROEP. At Llandinam Repowering Wind Farm substation
measurements show that the resistivity of the ground is very high. The
prospective earth fault current combined with this highly resistive
ground causes an extremely high ROEP.
5.15 The substation and associated equipment can be designed to ensure
there are no dangerous touch or step potentials for personnel within, or
at, the boundary of the substation compound. To ensure that no
members of the public are subjected to dangerous voltages, the
substation area may have to be increased to ensure all dangerous
voltages are controlled within the substation compound.
5.16 The location of the point of connection, the Llandinam Repowering
Wind Farm substation, has been identified by the customer. The
customer has made a plot of land available of approximately 35m by
100m. The substation compound that contains the 132kV and 33kV
switchgear is about 30m by 45m. The immediate area surrounding the
land made available by the customer is uniform and the resistivity of the
20
ground is unlikely to vary - resulting in no significant increase, or
reduction, in the ROEP.
5.17 For the Trident design the extent of the substation compound (the
controlled area) would have to be so large to overcome ROEP issues
that it would be impracticable to safeguard the public, since the
compound would encompass third party buildings. It may not be
possible to control the touch and step potentials if the substation
compound overlaps these third party buildings and therefore may
present a hazard to third parties.
5.18 SP Manweb has a duty to design and operate installations that
minimise the ROEP and hence eliminate dangerous touch and step
potentials. There are no practical solutions to significantly reduce
ground impedance values to reduce the ROEP to acceptable limits
around the substation, nor would it be practical to establish a large
exclusion zone from the perimeter of the main substation earth system
(and, in any event, the efficacy of such an exclusion zone is dubious: it
could be deliberately breached). As a result, the use of a Trident
overhead line design cannot be recommended on the grounds of public
safety.
5.19 The high resistivity of the ground at the Llandinam Repowering Wind
Farm substation and the resulting ROEP confirmed the need to
incorporate an earth conductor within the proposed overhead line
design. An earthed construction ensures that in case of an earth fault
not all the fault current is flowing through the ground and part of it will
flow through the earth return conductor back to its source. There is
therefore less current flowing to earth and the inherent local ROEP has
been lowered, reducing the area subjected to high ROEP values.
5.20 The proposed earthed HDWP line ensures that the ROEP is
significantly reduced to an acceptable level and the area surrounding
the substation compound is safe for the public. The perimeter fence
enclosing the substation compound ensures the substation compound
21
is controlled as far as is reasonable practicable. The earthing system, a
buried copper mesh embedded within the substation, is designed so
there is no danger to personnel from touch or step potentials. The
positioning of the perimeter fence has been designed to ensure there is
no danger to public adjacent to, and outside, the perimeter fence.
5.21 In conclusion, it is recommended that the HDWP design for the
overhead line is progressed as the most appropriate design to meet the
earthing needs for the connection within acceptable safe limits.
22
6. TECHNICAL AND COST CHARACTERISTICS OF CONNECTION ALTERNATIVES.
Estimate of cost for the Llandinam Scheme and combined with the
SP Mid Wales Connections Project.
6.1 The alternatives listed below were considered in the Alternatives Paper
(Volume 5 of the Updated ES (CD/SPM/ES/01)) and Dr Beddoes' proof
of evidence (SPM/NETWORK/POE/BEDDOES/001A). This section
should be read alongside Dr Beddoes evidence (section 6). I deal here
with the technical and cost implications only of the alternatives
proposed.
6.2 The estimated costs of the alternatives have been compared against
the LSC (identified above as between £21 – 24m) or, where the
alternative involves a connection through the currently proposed SP Mid
Wales Connections Project, against a combined cost for the Llandinam
Scheme with the SP Mid Wales Connections Project in so far as it
relates to the CC1 corridor of that scheme. This later scenario is termed
the "status quo" in the Alternatives paper (Volume 5 of the Updated ES
(CD/SPM/ES/01)).
6.3 The combined costs of the Llandinam Scheme and the SP Mid Wales
Connections Project is referred to as the (LS/MWC). The LS/MWC is
estimated to amount to between £48m to £52m.
Technical and cost considerations of accommodating a connection on existing 33kV customer connection using current 33kV infrastructure.
6.4 Dr Beddoes concludes (SPM/NETWORK/POE/BEDDOES/001A) that
the connection of any additional generation at the Llandinam
Repowering Wind Farm substation, using the existing 33kV customer
connection, cannot be accommodated on the current 33kV network
infrastructure. As such, the costs of this alternative are not considered.
Technical and cost considerations of accommodating a
connection on existing 33kV customer connection using current
and new 33kV infrastructure – Newtown Grid.
23
6.5 An alternative means to connect 90MVA of embedded generation at the
Llandinam Repowering Wind Farm substation is by installing a new
33kV circuit between the Wind Farm and Newtown Grid.
6.6 In order to connect the Llandinam Repowering Wind Farm at 33kV into
the nearest 132kV network at Newtown (a distance of 12km) an
additional five new 33kV circuits would be required based upon a circuit
capacity of 20MVA each.
6.7 This would result in a total of 60km (5 x 12km) of new 33kV overhead
lines running in parallel through the Severn Valley or 5 new 33kV cable
circuits installed in roads and verges.
6.8 It would be very difficult to construct 5 overhead lines running in parallel
taking into account the necessary spacing between them. Typically a
distance of 12 meters is required between the lines and a similar
distance outside the lines, which results in a 70 meter corridor.
6.9 33kV circuits that are installed underground close together have to take
account of mutual heating effect of the ground surrounding the cables.
Typical spacing of 500mm between circuits would apply and result in
having to excavate one or two wide trenches in road or verge.
6.10 The Newtown Grid substation compound would need to be increased in
size to accommodate the new circuits and associated switchgear, which
in turn would require additional land and necessary permissions. The
current grid transformer at Newtown Grid Substation would need to be
changed as its power rating would be exceeded.
6.11 Several existing 33kV circuits in the Newtown / Welshpool area would
also need to be replaced as they would exceed their thermal capability.
6.12 As discussed in Dr Beddoes' evidence
(SPM/NETWORK/POE/BEDDOES/001A), the majority of the 132kV
overhead line between Newtown and Oswestry Grid (referred to as the
BU circuit) would need to be reinforced.
24
6.13 The existing conductor is not capable of carrying the required current
and requires upgrading to 300 mm2 Upas. This is not an option with the
current conductor supporting structures that are not capable of
supporting the 300mm2 Upas conductor. The only practicable solution
would be an offline rebuild in parallel with the existing circuit. The
rebuild will have to be capable of supporting a 300mm2 Upas conductor.
This would either be a new woodpole line or a steel lattice tower line.
6.14 The total estimated cost of this alternative is £30.5m above the LSC
defined in section 3.36.
6.15 Taking into account the above and the introduction of additional 33kV
circuits to provide capacity, this option is not considered to be a feasible
technical design solution which meets the needs of the current and
future network, and does not demonstrate the maintenance of an
efficient, co-ordinated and economical system of electricity distribution.
Technical and cost considerations of accommodating a
connection on existing 132kV network – Newtown Grid.
6.16 Newtown Grid (12km from Llandinam) is the nearest 132kV connection
point to the Llandinam Repowering Wind Farm.
6.17 As discussed in Dr Beddoes' evidence
(SPM/NETWORK/POE/BEDDOES/001A) and section 6.13 above, the
majority of the 132kV BU circuit would need to be rebuilt to
accommodate the generation power flows on the 132kV network.
6.18 The Newtown Grid substation compound would need to be increased in
size to accommodate equipment such as disconnectors, circuit breaker,
cable termination structures and surge arresters. The extension of
Newtown Grid substation would require additional land and necessary
permissions.
6.19 This alternative is not considered efficient and would cost £9.8m above
the LSC.
25
6.20 The introduction of additional generation onto the Newtown Grid 132kV
BU circuit is therefore not considered a feasible technical design
solution which meets the needs of the current and future network. It
does not demonstrate the maintenance of an efficient, co-ordinated and
economical system of electricity distribution.
Technical and cost considerations of accommodating a
connection on existing 132kV network – Carno Grid / Circuit.
6.21 Given that a connection within the local 33kV network and a 132kV
connection at Newtown is not viable, the next nearest 132kV connection
point is Carno Grid. Carno Grid substation is 15km from Llandinam
Repowering Wind Farm and connected at 132kV to Oswestry Grid via
the 132kV line referred to as the MB line, the nearest point to the
Carno 132kV circuit is 12km.
6.22 Reinforcement / rebuilding of the MB circuit has been considered, but
additional upstream 132kV circuit reinforcement as described in 6.13 of
this paper (132kV Oswestry to Newtown circuit) would also be
necessary in order to accommodate any additional generation to the
Carno MB 132kV circuit. A new overhead line of approximately 83km
would have to be constructed.
6.23 For the reasons set out above, this alternative is not considered efficient
at a cost of £22.4m above the LSC.
6.24 The introduction of additional generation onto the Carno 132kV MB
circuit is therefore not considered a feasible technical design solution
which would meet the needs of the current and future network. It does
not demonstrate the maintenance of an efficient, co-ordinated and
economical system of electricity distribution.
Technical and cost considerations of accommodating a
connection on existing 132kV network – Welshpool Grid via an
underground cable.
26
6.25 An alternative to the proposed overhead line would be to install an
underground cable between Welshpool Grid and Llandinam
Repowering Wind Farm substation.
6.26 The underground cable would have to be installed in roadways or in
verges and the route would comprise approximately 40km of
underground cable buried at a depth of about 1m in a trench of about
1m wide.
6.27 The capital costs for this alternative would be £38.8m above the LSC -
based on new cable (40km) plus associated substation works. SP
Manweb considers that, as the cost would be a multiple of the LSC, this
would not be an economical means of providing the required
connection.
Alternative network 400kV infeeds
6.28 The nearest 400kV connection from Llandinam Repowering Wind Farm
would be north west of Shrewsbury, approximately 55km in distance.
Such a long connection at 400kV would be more expensive than the
shorter Llandinam Scheme connected at 132kV.
6.29 The proposed Llandinam to Welshpool 132kV connection makes more
efficient use of the existing and available local Distribution Network
capacity.
Alternative network 400kV infeeds – Mid Wales
6.30 As discussed in the Alternatives paper (Volume 5 of the Updated ES
(CD/SPM/ES/01)) at section 6.1, National Grid has committed to the
provision of a Grid Entry Point (GEP) in Mid Wales in order to provide a
connection for the proposed Mid Wales wind farms that are being
connected by SP Manweb via the SP Mid Wales Connections Project.
6.31 The location of the GEP as Cefn Coch was only confirmed last year
with a more detailed announcement on the draft route and substation
site location within Cefn Coch announced very recently. In considering
27
whether the SP Mid Wales Connections Project would provide a
suitable 132kV connection for the Llandinam Repowering Wind Farm,
SP Manweb has noted that the distance from the Llandinam
Repowering Wind Farm to the proposed GEP substation is no different
to that of the Llandinam Scheme.
6.32 However, the integration of the Llandinam Repowering Wind Farm into
the GEP substation would necessitate, due to existing contracted Mid
Wales generation, the installation of an additional 132kV circuit between
the GEP substation and SSA C (wood pole or steel tower line) to
ensure that suitable circuit capacity is provided.
6.33 The following alternatives to connect the Llandinam Repowering Wind
Farm via the SP Mid Wales Connections Project have been considered
and should be read alongside the Alternatives Paper (Volume 5 of the
Updated ES (CD/SPM/ES/01)) and section 6 of Dr Beddoes' proof of
evidence (SPM/NETWORK/POE/BEDDOES/001A).
Alternative 4a (two 132kV HDWP overhead lines, one in CC1 and a
second line in CC2):
6.34 The alternative overhead line construction for both circuits is HDWP,
the second circuit would be strung with 200mm2 Poplar conductor.
6.35 This connection would require an additional Supergrid transformer and
a new 132kV bay comprising of disconnectors, circuitbreaker, surge
arresters, associated busbar supports and protection equipment.
6.36 The total estimated costs for this alternative would be £6m above the
LS/MWC.
Alternative 4b (two 132kV HDWP overhead lines in CC1):
6.37 The alternative overhead line construction for both circuits is HDWP,
the second circuit would be strung with 200mm2 Poplar conductor.
28
6.38 This connection would require an additional Supergrid transformer and
a new 132kV bay comprising of disconnectors, circuitbreaker, surge
arresters, associated busbar supports and protection equipment.
6.39 The total estimated costs of this scheme would be £8.2m above the
LS/MWC.
Alternative 4c (two 132kV HDWP overhead lines in CC2):
6.40 The alternative overhead line construction for both circuits is HDWP,
the second circuit would be strung with 200mm2 Poplar conductor.
6.41 This connection would require an additional Supergrid transformer and
a new 132kV bay comprising of disconnectors, circuitbreaker, surge
arresters, associated busbar supports and protection equipment.
6.42 The total estimated costs of this option would be £3.9m above the
LS/MWC.
Alternative 4d (a double circuit steel tower pylon) in CC1:
6.43 The alternative overhead line construction for the Llandinam
Repowering Wind Farm is based upon a steel lattice L4 tower
construction strung with 300mm2 Upas conductor. This conductor type
is the smallest conductor size taking into account other connected
parties on the shared tower line (all parties share both circuits on one
double circuit tower line).
6.44 The connection would require an additional Supergrid transformer and a
new 132kV bay comprising of disconnectors, circuitbreaker, surge
arresters, associated busbar supports and protection equipment.
6.45 In terms of costs, the total estimated costs of this option would be
£6.7m above the LS/MWC. For Celt Power the estimated Llandinam
apportioned cost is in the order of 75% of the LSC.
Alternative 4e (a double circuit steel tower pylon) in CC2):
29
6.46 The alternative overhead line construction for the Llandinam
Repowering Wind Farm is based upon a steel lattice L4 tower
construction strung with 300mm2 Upas conductor. This conductor type
is the smallest conductor size taking into account other connected
parties on the shared tower line (all parties share both circuits on one
double circuit tower line).
6.47 This connection would require an additional Supergrid transformer and
a new 132kV bay comprising of disconnectors, circuitbreaker, surge
arresters, associated busbar supports and protection equipment.
6.48 The total costs of this alternative would be £0.7m above the LS/MWC.
For Celt Power the estimated Llandinam apportioned cost is in the order
of 70% of the LSC.
6.49 In response to comments from statutory consultees, SP Manweb has
considered two additional alternatives, 4f and 4g, these being
alternatives introduced on the basis of a presumed reduction in the level
of generation in SSA C to that which could be accommodated in a
single 132kV connection using 300mm2 Upas conductor (rating of
176MVA). These options are described in section 6.4 of the Alternatives
Paper (Volume 5 of the Updated ES (CD/SPM/ES/01)).
Alternative 4f (a connection provided by a 132kV HDWP overhead
line in CC1 able to carry 176MVA of generation capacity):
6.50 The alternative overhead line construction for the Llandinam
Repowering Wind Farm substation is HDWP strung with 300mm2 Upas
conductor.
6.51 The Llandinam connection, including other contracted parties to the Mid
Wales hub is included within the cost estimate for the SP Mid Wales
Connections Project.
6.52 The total costs of this option would be £24m less than the LS/MWC as
generation would be capped such that only one 132kV overhead line
would be provided. For Celt Power the estimated apportioned
30
Llandinam Repowering Wind Farm project connection cost is in the
order of 60% of the LSC.
Alternative 4g (as alternative 4f but in CC2):
6.53 The proposed overhead line construction for the Llandinam Repowering
Wind Farm substation is HDWP strung with 300mm2 Upas conductor.
6.54 The Llandinam connection, including other contracted parties to the Mid
Wales hub is included within the cost estimate for the SP Mid Wales
Connections Project.
6.55 The total costs of this option would be £26m less than the LS/MWC as
generation would be capped such that only one 132kV overhead line
would be provided. For Celt Power the estimated apportioned
Llandinam Repowering Wind Farm project connection cost is in the
order of 55% of the LSC.
6.56 From an engineering design and a costs perspective, the Llandinam
Scheme is the preferred option.
6.57 A summary of the costs of the alternative options is shown below in Table 1.
31
Accommodate on existing network £,000,000
33kV
Current and new 33kV infrastructure – Newtown Grid 30.5 Above LSC132kV
Newtown Grid 9.8 Above LSC
Carno Grid / Circuit 22.4 Above LSCWelshpool Grid via an underground cable 38.8 Above LSCAlternative network 400kV infeeds – Mid Wales
Alternative 4a 6 Above LS/MWC
Alternative 4b 8.2 Above LS/MWC
Alternative 4c 3.9 Above LS/MWC
Alternative 4d 6.7 Above LS/MWC
Alternative 4e 0.7 Above LS/MWC
Alternative 4f 24 Below* LS/MWC
Alternative 4g 26 Below* LS/MWC
Table 1 summary of the costs of the alternative options.
*Assumes not all contracted generation associated with the SP Mid Wales
Connection Project is consented
32
7. CONCLUSIONS
7.1 I have described how SP Manweb has approached the development of
its proposal for a 132kV wood pole overhead line between the proposed
Llandinam Repowering Wind Farm substation and Welshpool Grid.
7.2 I have explained the engineering requirements and variation in costs for
the alternatives listed compared to the Llandinam Scheme and (where
relevant) the combined costs of the Llandinam Scheme and the SP Mid
Wales Connections Project.
7.3 I have highlighted that undergrounding small sections of overhead line
could give rise to unwarranted adverse impacts both on operational
performance and construction costs.
7.4 Following representations on the project, SP Manweb has been asked
to consider the use of a Trident design rather than the HDWP design to
further mitigate environmental impacts. In section 5 of this paper I have
explained the technical reasoning behind the decision to maintain the
HDWP design, due to the need for an aerial earth connection that limits
the ROEP at the proposed Llandinam Repowering Wind Farm
substation.
7.5 There are no practical solutions to significantly reduce the ground
impedance values to reduce the ROEP to acceptable limits around the
proposed Llandinam Repowering Wind Farm substation, nor would it be
practical to establish and maintain an exclusion zone from the perimeter
of the main substation earth mat. As a result, use of the Trident design
for all or part of the route cannot be recommended on the grounds of
safety.
7.6 To limit the ROEP to manageable levels the overhead line arrangement
must be of an earthed design.
7.7 HDWP is an earthed design and ensures that SP Manweb adheres to
its licence obligation to develop a safe, efficient, coordinated and
economical system.