challenging substation design

7/31/2019 Challenging Substation Design

1/11

[email protected] 1

SC B3

SUBSTATION DESIGN IN A CHALLENGING REGULATORY ENVIRONMENT

C. Twomey

ESB International

Ireland

SUMMARY

ESB (Electricity Supply Board) Networks has an extensive (15+) programme of 110kV/MV

substations to be built within a regulated budget by 2010.

A comprehensive cost-reduction study was undertaken which included a review of current

practice in a number of other utilities and an enquiry to a wide range of manufacturers based

on an open functional specification.

The tenders received were evaluated against a full range of cost factors including material

cost, installation costs and lifetime costs.

The outcome of the study was a decision to standardise on the use of 110kV gas-insulated

equipment (either hybrid modules or conventional GIS) for new 110kV substations and alsoto use this equipment as far as possible in extensions or refurbishment of existing AIS

substations.

A further outcome was a decision to replace conventional buildings with prefabricated

enclosures for various functions e.g. 38kV GIS, MV switchboards, control/relay rooms,

battery rooms, store rooms where it makes economic sense to do so.

KEYWORDS

Hybrid, substations, cost reduction, prefabricated equipment

103 CIGRE SC B3 Berlin 2007http : //www.cigre-berlin-2007.org


2/11

[email protected] 2

Background

The Irish electricity system had a maximum demand of 5042 MW at the end of 2006. The

network which is owned by ESB contains four 400kV stations, twenty seven 220kV stations

and approximately one hundred and thirty 110kV stations. The 400kV network comprises two

lines connecting a 900MW generating station on the west coast to the main load centre of the

capital city of Dublin on the east coast. The 220kV network is the main transmission networkto which about 66% of generation is connected. In addition, due to the dispersed pattern of

development in Ireland much of the 110kV network outside Dublin is operated as part of the

transmission system (with about 16% of generation capacity including most of the wind

generation connected to it) rather than as a sub-transmission system.

The historical transformation ratios to distribution voltages are 110/38kV and 38/10kV. In the

mid 1990s it was decided to introduce a new voltage level of 20kV with the long term aim of

moving to a single MV voltage replacing both the 38kV and 10kV levels.

At this stage most of the 10kV network with the exception of urban cabled networks has been

upgraded to 20kV. The original intention was to freeze the 38kV system with all future

transformation to be directly from 110kV to 20kV. However due to the dispersed nature of the

load it has proved uneconomic to do this in all cases so a certain amount of 110/38kVdevelopment has continued.

Since 1996 Ireland has undergone an unprecedented rate of economic development with

demand for electricity growing continuously. The average rate of load growth since 1996 has

been of the order of 5% and this rate of load growth is still continuing at present.

Meeting this load growth has required a corresponding network development effort from

ESB.

During this period one 400kV station, six 220kV stations and over thirty 110kV stations have

been built. The ongoing construction programme includes the construction of at least four

110kV stations per year.

Traditionally ESB carried out all detailed design in house and used ESB staff for allconstruction work. Meeting the concentrated workload of this programme in addition to an

extensive refurbishment of the MV network could only be done through the extensive use of

installation contractors and also a limited introduction of turnkey projects for a series of urban

110kV/MV GIS stations.

This process was also complicated by the need to respond to the change in environment from

a single national vertically integrated utility to a liberalised regulated system mandated by EU

legislation which has taken place over this period.

ESB is at present operating in its second 5 year (2005-2010) price review period which has

imposed significant cuts in allowed capital and operating costs.

This has resulted in a challenge to:

- Deliver the required programme

- Review critically every aspect of the historical project delivery method

- Maintain an absolute commitment to quality

- Reduce the project delivery cycle

To meet these requirements a comprehensive cost reduction study was undertaken. This study

covered the whole field of various issues associated with the substation construction project


3/11

[email protected] 3

life cycle. The initial stage of the study identified the following areas as being the most

promising for cost reduction.

1) Use of prefabricated equipment and buildings

2) Reduction in site dimensions

3) Reduction in construction time

4) Reduction in engineering costs5) Optimisation of individual design issues

6) Reduction in life cycle costs

7) Use of mobile plant

8) Review of site purchase commercial issues

9) Review of construction contract arrangement

10)Review of material purchase tender strategy

This paper will describe the outcome from the work carried out in areas 1-6.

Existing standard designs

110/38kV (Station dimensions are 90m x 84m)- 110kV: Single stranded busbar with AIS equipment. The station is laid out and

equipment rated where appropriate for an ultimate development of six feeders, two

63MVA transformers and a sectionaliser bay. All disconnectors are manually operated.

- 38kV: single tubular or solid busbar with phases in a vertical formation. The layout

allows for an ultimate development of six feeders, two transformer bays, a house

transformer bay and a sectionaliser bay.

The initial station development is frequently in the form of a tail-fed 31.5MVA transformer

with a small number of 38kV bays. The station may be then extended by a 110kV loop-in

with the installation of a busbar. A second transformer could follow in due course and the

transformers could eventually be replaced by 63MVA units.

110kV/MV (Station dimensions are 63m x 37m)

- 110kV: A tubular copper busbar with AIS equipment. The station is laid out as a H-type

layout of two feeder bays and two 20MVA transformer bays with a sectionaliser bay. All

disconnectors are manually-operated. The transformer secondary voltage is selectable as

10kV or 20kV. The design of the station allows for a possible uprating to 31.5MVA

transformers. It does not allow for additional bays.

- MV (where MV is 10kV or 20kV): Single busbar metal-enclosed switchgear rated for

operation at 10kV or 20kV in a building sized for an ultimate capacity of 20 feeders. The

initial installation is fitted with the number of feeders immediately required.

110kV/MV (Station dimensions are 34m x 34m)

- 110kV: Single busbar GIS. The normal initial layout is two feeders and two 20MVA

transformer bays and a sectionaliser bay with space left to add an additional feeder at

each end of the busbar. The transformer secondary voltage is selectable as 10kV or 20kV.

The design of the station allows for a possible uprating to 31.5MVA transformers.

- MV (where MV is 10kV or 20kV): Single busbar metal-enclosed switchgear rated for

operation at 10kV or 20kV with space for an ultimate capacity of 20 feeders. The initial

installation is fitted with the number of feeders immediately required.


4/11

[email protected] 4

The HV & MV equipment is installed indoors with transformers either indoors or in open-

topped enclosures.

All HV or MV equipment is bought on the open market in the form of 3-5 year framework

contracts for each item.

The default standard is that of an AIS station. GIS is normally used only in urban areas or in

high pollution locations e.g. coastal generating stations.

ESB experience with the two technologies may be summarised as:

AIS GIS (25 year history)

Advantages Lowest material prices as best value option

is bought for each item

Excellent service history

Freedom from long-term dependence on

any particular supplier as layouts allow for

use of equipment from any supplier in new

construction or in individual itemupgrading or replacement

Short construction time

Small site size

Disadvantages Normal AIS maintenance issues,

particularly with disconnectors

High initial cost

Large site size Corrosion issues on exposed

flanges

Construction time Awkward to extend or

modify once the particular

equipment has gone out ofproduction.

Cost reduction study

The cost reduction study focussed on the AIS 110kV/MV station as this comprises the vast

majority of currently foreseen new station construction. As this is already a very basic H

arrangement it was not considered worthwhile to look at alternative configurations.

The process began with a research phase in liaison with various manufacturers to identify

possible options. Many different designs are available on the market today as suppliers,

recognising the current pressures on utilities, are promoting various approaches to costreduction.

Nothing was ruled out at this stage so information was collected from suppliers and visits

were made in conjunction with suppliers to utility substations in 7 countries France,

Germany, Hong Kong, Italy, Japan, Portugal and UK.

ESB itself has experience since 2000 with some of these new solutions in the form of:


5/11

[email protected] 5

- Compact AIS on a single frame used in the refurbishment of a generation-associated

110kV station in a restricted site (Fig. 1)

- GIS modules used in the extension of a small generation-associated 110kV station on a

very restricted site (Fig. 2)

Fig. 1 Compact AIS on a single frame Fig. 2 GIS modules

- GIS modules used to provide 110kV mobile bays (Fig. 3)

- GIS modules used as part of relocatable capacitor banks (Fig. 4)

Fig. 3 110kV mobile bay Fig. 4 Relocatable 110kV capacitor bank

- GIS modules used by IPP contractors in the connection of new wind farms and of a new

generation station to the ESB network

Layout studies were carried out using:

- Existing AIS (as a baseline)

- Rotating circuit breakers

- Withdrawable circuit breakers


6/11

[email protected] 6

- Outdoor GIS

- GIS modules

- Compact AIS on single base frame

Possible layouts proposed by suppliers in their publicity layouts were reviewed and modified

in cases where it was felt that they were based in over-optimistic assumptions. A particular

example of this was proposed layouts for adjacent bays using open terminal connections usinga bay spacing based on electrical clearances rather than maintenance clearances.

Comparative cost estimates were produced using budget prices from suppliers (where

available) or cost information from ESB records or experience. These estimates also used the

suppliers estimates for the effort required to install the equipment modified where

appropriate to reflect ESB experience.

The study showed that savings of the following order appeared to be feasible:

Total Project cost: 0% to 19%

Required site area: 25% to 46%

Construction time: 25% to 42%

Use of standard prefabricated modules over a series of stations should lead to a reduction in

detailed design costs for subsequent stations. It will certainly lead to a reduction in

procurement (as opposed to material) costs due to most of the 110kV equipment in a station

being bought on a single order.

The level of saving achievable was highly dependant on the cost of land. In general the

equipment cost was higher than the AIS equipment but this additional cost was

counterbalanced by the reduced land cost, reduced civil works cost and the impact of the

shorter construction time.

As mentioned above many of these stations would be under the operational control of theTransmission System Operator so close contact was maintained with this organisation during

the study.

The best results seemed to be obtainable from the use of Mixed Technology Switchgear

(MTS) either in the form of GIS modules with an AIS busbar or GIS modules using a GIS

busbar i.e. outdoor GIS.

These designs appeared to offer the lowest lifetime cost due to all operating contacts being

enclosed under SF6 rather than exposed to atmosphere, assuming of course that the GIS

corrosion issues previously experienced by ESB have indeed been solved as claimed by the

various suppliers.

They also have the advantage of being offered by most or all of the main suppliers. This

should ensure competitive pricing and also provides insurance that the design layout will not

be dependant on a single supplier.

One possibility raised by the lower visual profile of this equipment compared to traditional

AIS was the possibility of using it in semi-urban locations where previously the only suitable

alternative was indoor GIS in an expensive building.


7/11

[email protected] 7

Pilot Project

The next step was to confirm the results of the study with actual tendered prices.

An enquiry using a basic functional specification was issued in December 2005 as a pilot

project for the next 3 planned green-field semi-urban stations. Tenders were received for all ofthe equipment types covered in the feasibility study. The tender evaluation process confirmed

the conclusions of the study.

A graphical representation of the evaluation outcome is given below in Fig 5, based of course

for Irish civil works and labour costs. The minimum and maximum savings achievable at land

prices of300 and 500 per sq. m. are given.

Fig. 5 Variation in Station cost with land price

The consistent level of saving achieved compared to the traditional AIS can be clearly seen as

can the increased percentage saving achieved as land costs increase.

As can be seen from Fig. 5 there are very small differences in station cost resulting from the

use of any of the tendered options. These small differences emphasise the importance of

careful evaluation to ensure that the selected option is the best fit to a utilitys particular

requirements.

The reduction in site dimensions achieved compared to a traditional cable-connected AIS

110kV/MV station is shown below in Fig 6.


8/11

[email protected] 8

Fig. 6 Reduction in site dimensions

Orders were issued for:

- MTS of the GIS busbar type (for two stations of the basic H type, see Fig 7)

- MTS of the AIS busbar type (for one larger station requiring four transformer bays, see Fig

8).

Fig. 7 MTS (GIS Busbar type) Fig. 8 MTS (AIS Busbar type)

Feedback from the planning permission process has been favourable to date due to the

reduced visual impact of the smaller switchgear and also from the decision to change to a 3m

high boundary wall rather than the previously-used combination of a 2.8m high palisade fence

and extensive landscaping. See Fig. 9


9/11

[email protected] 9

Fig. 9 Elevation of MTS Station Frontage

The smaller site size was also helpful during site acquisition negotiations with developers.

Main enquiry

The experience and information gained during the pilot project was used in the preparation of

a detailed specification for a full term contract. One outcome from the pilot project was a

decision to restrict the scope of the enquiry to MTS type equipment only. As many of the

stations would be part of the transmission system the specification was also signed off by the

TSO.

An enquiry was issued to cover the equipment required by ESB for substations up to 2010 and

tender evaluation is in progress at present.

Prefabricated enclosures

A parallel process was carried out to investigate the benefits achievable from replacing

conventional concrete buildings by prefabricated enclosures delivered with all internal wiring

completed. The perceived benefits are a reduction in civil work and a reduction in site

construction time.

ESBs previous experience with prefabricatedenclosures was of containers built to ESB design

used to provide distributed control and protection

(one container per bay) facilities in a number of

new and refurbished 220/110kV stations

equipped with digital control systems. (See Fig.

10)

Fig. 10 Distributed control & protectioncontainer

The first step in the process was to include an option with the current MV switchboard

contract for a number of the boards to be delivered prewired in suitable enclosures for use in

38V/MV stations. Matching enclosures were also delivered to the assemblers of ESB control

and protection cabinets for installation and interwiring of the control and protection cabinets.


10/11

[email protected] 10

The first installation of this equipment was carried out in early 2007. See Figs. 11 & 12

Fig. 11 Side view of MV enclosure Fig. 12 End view of control & MV enclosures

As in the case of the 110kV HV equipment the experience gained in this pilot project is being

used to prepare detailed specifications for an enquiry for all of the enclosures required for use

in 38kV and in 110kV stations. Particular issues of concern are the durability of the structuresin Irelands notoriously wet and humid climate and the maintenance of the existing level of

security provided by conventional buildings.

The durability issue is addressed by an explicit requirement for a 45 year lifetime and for a

very high quality surface treatment which was assessed as being adequate by a metallurgy

expert.

Security was addressed by a requirement for a 3mm thick steel external skin and for

appropriately specified doors, windows and external fittings

It is expected that the enquiry process will be completed during 2007 and a decision will be

taken then on which of the enclosure requirements will be fulfilled by prefabricatedenclosures and which will be more economically met by conventional buildings.

Conclusions

A full review of existing practice has resulted in design changes which are expected to

produce cost savings of up to 18% in 110kV substation construction. These savings should be

obtained without a need for any dramatic changes in operational practice.

As suppliers are continuing to innovate in this area it is expected that further savings will be

achievable in the future. Further studies will be carried out before the next term contract

enquiry to ensure that these savings are captured.

One particular approach which looks very promising is the disconnecting circuit breaker. As it

now appears that this product will be offered by more than one supplier in the near future it

will become more attractive as ESB is normally quite wary of getting into a situation where a

particular layout is dependant on a single supplier.


11/11

[email protected] 11

BIBLIOGRAPHY

[1] M. Bues, E. Mikes; Compact optimised GIS, Modular Hybrid Substation bays, Mobile

GIS substations; CIGRE SC A3 & B3 Colloquium, Paper 120, Tokyo, Japan 2005

[2] M. Blundell, D. Roby, C. Piazza; Compact integrated bay modules for new 145kVsubstations; CIGRE SC A3 & B3 Colloquium, Paper 121, Tokyo, Japan 2005

[3] P. Ponchon et al.; Application of gas-insulated modules (GIM) to EHV substations;

Paper B3-215, CIGRE Session, Paris, 2004

[4] S. Pohler et al.; Mixed Technology HV switchgear and substations; Optimised service

strategies; Paper B3-204, CIGRE Session, Paris, 2004

[4] A.D Georgopoulos et al.; A 170kV compact switchgear module application at Komotini

open-air substation in northeastern Greece; Paper 23-204, CIGRE Session, Paris, 2002

[5] P. Roussel et al.; Technical and economical evaluation of new air-insulated substation

concepts; Paper 23-205, CIGRE Session, Paris, 2002

[5] V. Colloca et al.; Environmentally friendly, low cost HV/MV distribution substations

using new compact HV and MV equipment; CIRED 2001

[6] Y. Doin et al.; Compact Substation : a comprehensive solution ; Paper 23-103, CIGRESession, Paris, 2000

[7] B. Pokarier et al.; First new integrated switchgear substation in service; Paper 23-104,

CIGRE Session, Paris, 2000

[8] D. Helbig et al.; Highly integrated switchgear: an innovative concept to reduce life cycle

costs; Paper 23-108, CIGRE Session, Paris, 2000

[9] P. Roussel et al.; Innovative switchgear design for modern substations: CAIS solution;

CIGRE SC 23 Colloquium, Paper 7, Zurich, Switzerland, 1999

challenging substation design

Documents