glenrothes 275kv switchgear replacement - ofgem ... · 2 background information .....4 3...

Issue Date Issue No Amendment Details

December 2019 Issue 1 First issue

Glenrothes 275kV switchgear replacement - OFGEM justification paper

Name of Scheme/Programme

Glenrothes 275kV switchgear replacement project

Primary Investment Driver Asset Health (Lead asset – Circuit Breaker) Scheme reference/ mechanism or category

SPNLT 2041 (Circuit-Breaker replacement)

Output references/type NLRT2SP2041 (275kV Circuit-breaker air insulated (OD) / 275kV Switchgear others)

Cost £ 1.81 m Delivery Year 2025 Reporting Table C0.7 / C2.2a_CI / C2.2a_AP / C2.3 / C2.4b / C2.5 / C2.5a Outputs included in RIIO T1 Business Plan

No

OFGEM RIIO-T2 justification paper:

Glenrothes 275kV switchgear replacement Issue 1

Table of contents 1 Introduction .................................................................................................................................... 3

2 Background Information ................................................................................................................. 4

3 Optioneering ................................................................................................................................... 6

4 Detailed analysis ............................................................................................................................. 7

4.1 Scope ....................................................................................................................................... 7

4.2 Sustainability: .......................................................................................................................... 7

4.3 Innovation: .............................................................................................................................. 7

4.3.1 Reuse of existing concrete assets ................................................................................... 7

4.3.2 Disconnecting Circuit Breaker (DCB) ............................................................................... 8

4.4 Total cost / construction timescales ....................................................................................... 8

4.5 CBA results .............................................................................................................................. 8

5 Conclusion ....................................................................................................................................... 9

6 Future Pathways – Net Zero ......................................................................................................... 10

6.1 Primary Economic Driver ...................................................................................................... 10

6.2 Payback Periods .................................................................................................................... 10

6.3 Pathways and End Points ...................................................................................................... 10

6.4 Asset Stranding Risks ............................................................................................................ 10

6.5 Sensitivity to Carbon Prices ................................................................................................... 10

6.6 Future Asset Utilisation ......................................................................................................... 10

6.7 Whole Systems Benefits........................................................................................................ 10

7 Outputs included in RIIO T1 Plans ................................................................................................. 10

8 Appendix: Drawings ...................................................................................................................... 11



1 Introduction

The existing system at Glenrothes 275kV s/s comprises of a single bus section circuit breaker with incoming supply from Tealing and Westfield 275kV s/s. The arrangement also includes 2 off 275/33kV 120MVA units which support the distribution network in Fife region thru 33kV outdoor substation located in same compound area.

Glenrothes 275kV s/s is also part of the MITS (Main interconnected transmission system) and responsible for critical power flow between SPEN (thru WFIE2) and SHETL (thru TEAL2) transmission networks (please refer to the GSN drawing in the appendix).

The principal driver for the proposal is the condition of the 1 off JW420 bulk oil Circuit Breaker which will have EoL modifier scores of 10.65 at end of RIIO-T2 period (without any intervention) with critical operational and maintenance issues, and so has been identified for replacement in the RIIO-T3 period.

The condition of the non-lead assets – disconnectors/earthing switches, busbars, insulators and structures have also been assessed and in all cases, intervention is required.

In line with above, the proposed 275kV outputs to be delivered in this project for the selected option are:

- 275kV Circuit Breaker disposal: 1 unit - 275kV Circuit Breaker addition: 1 unit

The delivery of the project is proposed over 1 outage season. This involves replacement of lead as well non-lead assets.



2 Background Information

This paper supports a proposal to replace the existing 1 off JW420 bulk oil circuit-breakers and associated non-lead assets at Glenrothes 275kV substation. Based on the values determined in accordance with the NOMS methodology, the circuit-breaker has an EoL modifier of 10.65 (at end of RIIO-T2 period without any intervention) and identified for replacement during the RIIO-T2 period.

This is also in line with SP Transmission’s strategy at staged replacement and sequential phasing out of bulk oil circuit-breaker over different price control period.

The options for retaining and refurbishing the circuit-breakers has been assessed and determined not to be technically or economically viable, as detailed in report SWG-05-0911.

Please find below details of the circuit-breakers identified for replacement.

SPEN corporate asset ID

Asset Description Manufacturer Model Year of manufacture

EoL (at end of RIIO T2)

Risk £

14163449 GLRO275OCBS10 AEI/METRO VICKS JW420 1974 10.65

£ 1,164,262.14

A detailed site review and technical assessment of the condition of the non-lead assets has been carried out by SP Transmission as part of this project’s development.

Condition assessment of the Switchgear and equipment 275kV Disconnectors / earth switches have shown internal corrosion along with deterioration of internal electrical and mechanical components. Control relays and contactors are prone to failure resulting in non-operation of respective switchgear. Other issues experienced include failure of the mag bolt circuit and motor burn out. Only limited spares are available for this type of switchgear with SP Transmission.

The recommendation for the Switchgear and equipment make 275kV Disconnectors / Earth switch is that it would be possible to refurbish them and make them operational for the expected design life of refurbished bay (40 years). However for refurbishing and reusing existing disconnectors, a substantial amount of work is required to be carried out by a specialist contractor. This involves rebuilding main contacts, sand blasting arcing rings, painting, replacing earth cables, rewiring and painting mechanism boxes, replacing contactors, relays, fuses, heaters and mechanism boxes to be tested in workshops. There is an element of added cost and time for refurbishment that needs to be reflected in the overall project timescales and costs. The costs and timescales to refurbish the disconnectors and mechanism boxes when compared with the costs and timescales to replace them indicate that replacement is the most economic option.

Accordingly the associated Switchgear and equipment RCP Disconnectors have been considered for replacement.

1 SWG-05-091 Operational issues with AEI JW420 Circuit-breaker



The two line entry RCP Disconnectors (Hapam make) were found to be in a good condition and considered for reuse without any intervention.

A site condition assessment report for these non-lead assets, along with condition assessment of other assets at the site can be supplied as required. Recommendations from this report have been included within the options considered.

The existing 275kV control building has been surveyed to determine if repair or refurbishment works are necessary and to assess the space available to accommodate replacement protection and control equipment. In line with the survey carried out, only minor repair works and building service upgrades are envisaged within the options considered.

The LVAC board along with Battery chargers have recently been replaced as part of Blackstart works and considered to be reused without any intervention.



3 Optioneering

The following is a summary of the options considered for this project. The respective associated drawings for each of these options are available for review if required.

Option Status Reason for rejection

Baseline option: Works deferred to RIIO T3. Scope of works similar to option 1

Proposed -

1 Option 1: Insitu AIS rebuild

Proposed -

2 Option 2: GIS rebuild

Rejected

Option not technical feasibly or commercially logical. The scope of works involves only changing one bus section AIS circuit-breaker for which AIS like for like replacement is the only possible option.

Based on engineering design studies to determine the costs of the options identified as addressing the asset condition issues, the following 2 options have been considered for further review for this project:

- Baseline: Works deferred to RIIO T3. Scope of works similar to option 1 - Option 1: Insitu AIS replacement in RIIO T2



4 Detailed analysis

As the scope, and costs associated with the proposed options are the same, with the only difference being the delivery schedule, a common description for both the options has been included here.

4.1 Scope

The existing JW420 bulk oil circuit breaker is proposed to be replaced in situ with a new live tank 300kV circuit breaker. Please find below the scope of works:

- Replace existing bus section S10 – JW420 Circuit Breaker with a live tank 300kV Breaker. - 6 off 275kV Current transformer to be added. - Reuse existing JW420 circuit breaker foundation for new 300kV live tank and CT units. - Insitu replacement of disconnectors S14, S18, H23 and H13. - Scope to reuse existing disconnector structures / foundations subject to onsite assessment

along with review of concrete testing result for each asset. - Replace the 2 off high level 3 ph Post insulators / bus bar arrangement. - Replace existing LVAC board and building services board to suit the new switchgear. - Existing access roads, cable trenches, below ground earth etc. to be reused. - Repair and refurbish existing civil assets that are proposed to be reused. Note this is subject

to further on site concrete testing and assessment of final loads on the existing structure.

4.2 Sustainability:

This project involves removal of bulk oil 275kV circuit-breaker thereby reducing the associated environmental risks with this asset.

The option also includes reuse of existing concrete foundation which is in line SP Transmission’s sustainability policy for RIIO T2 period.

4.3 Innovation:

The following innovation schemes were considered for this option:

Serial no. Description Associated project (s) Conclusion

1.2.4.2 Reuse of existing concrete assets

NIA_SPT_1606 Considered for further review

- 275kV Disconnecting Circuit Breaker (DCB) - Considered for further

review

4.3.1 Reuse of existing concrete assets

As described earlier within this option reuse of existing JW420CB foundations have been considered. Note this is subject to results of concrete testing and further analysis in regards to the expected loading on the civil structures with the new arrangement within the substation.



4.3.2 Disconnecting Circuit Breaker (DCB)

Use of Disconnecting Circuit Breaker has been reviewed for this specific project and considering the additional operational maintenance cost and the requirement for both SGT1 / SGT2 being on outage during the 6 year maintenance cycle has been deemed to be technically / commercially not viable.

4.4 Total cost / construction timescales

Please find below the costs and construction timescales for the 2 options considered:

Baseline: Works deferred to RIIO T3. Scope of works similar to option 1

Option 1: Insitu AIS rebuild

Cost £ 1.81 m £ 1.81 m

Construction timescales 1 outage season 1 outage season

Note that the costs have been built up from individual costs for each element and included in a bill of quantities. The bill of quantities has been engineered from the design layouts developed for each option. The basis of individual unit costs has been the SP Transmission MoSC (Manual of Standard Costs) tool which makes reference to costs incurred during previous similar projects.

4.5 CBA results

Please find below the NPV values from the CBA carried between the 2 proposed options:

Option NPV (Inc monetised risk)

Baseline option Do nothing in RIIO T2 period, works deferred to RIIO T3 period £ 37.04

Option 1 Relocate 4 off 400kV bays to HUNE substation £ 42.18



5 Conclusion

Replacement of the JW420 units is part of an ongoing strategy aimed at replacing end of life bulk oil circuit breakers on the network and reducing the risks associated.

The 2 options proposed have been reviewed in terms of scope, costs, timescales, construction risks and feasibility.

The main issue with the Baseline option is the timescale considered (2031), with the existing JW420 units required to be in service till then. As explained in SWG-05-0912, AEI JW420 275kV bulk oil circuit breakers have numerous issues like possibility of bushing failures, failure in latch mechanism or failure of interphase drive rods etc. which if left unchecked can end in catastrophic failure of these units. Along with the associated network risks, there’s also an element of H&S risks associated with failure of these units which needs to be considered before finalising any option. An ENA SOP was issued in 2019 with respect to catastrophic failures of JW420s experienced by another network operator. It is considered that further life extension of JW420s is not feasible.

The potential impact on the MITS to deliver power transfer due to the long and unpredictable maintenance durations of these circuit breakers also need to be taken into account.

The East Coast Phase 2 upgrade NOA project (please see EJP_SPNLT2034 for further details) considers the uprating of Glenrothes to 400kV operation. However, the proposal retains the existing 275kV bus section arrangement and so this proposal is compatible with the future development of the site.

Accordingly, and in line with the results of CBA analysis, Option 1: In situ replacement within RIIO T2 period is the preferred option for this project.

- Forecast costs: £ 1.81 m - Timing of investment: 2025 - Declared outputs: Addition – 1 unit / Disposal – 1 unit - Lifetime risk benefit: Lr£43.620m

2 SWG-05-091 – Operational issues with AEI JW420 Circuit-breaker



6 Future Pathways – Net Zero

6.1 Primary Economic Driver

The primary driver for this investment is asset condition and risk. The investment does not have a strong reliance on environmental benefits.

6.2 Payback Periods

The CBA indicates that a positive NPV results in all assessment periods (10, 20, 30 & 45 years) which is consistent with the lifetime of the intervention. Consumers benefit from reduced network risk immediately on completion of the project.

6.3 Pathways and End Points

The network capacity and capability that result from the proposed option has been tested against and has been found to be consistent with the network requirements determined from the ETYS and NOA processes. Additionally, the proposed option is consistent with the site-specific capacity requirements from SPT’s Energy Scenarios.

6.4 Asset Stranding Risks

Electricity generation, demand and system transfers are forecast to increase under all scenarios. The stranding risk is therefore considered to be very low.

6.5 Sensitivity to Carbon Prices

Carbon price sensitivities have been applied using the higher case CBA template. The CBA outcome is influenced by losses and is sensitive to carbon prices.

6.6 Future Asset Utilisation

It has been assessed that the preferred option is consistent with the future generation and demand scenarios and that the risk of stranding is very low.

6.7 Whole Systems Benefits

Whole system benefits have been considered as part of this proposal. The capacity and capability of the preferred option is consistent with the provision of whole system solutions.

7 Outputs included in RIIO T1 Plans

N/A



8 Appendix: Drawings

275/33kV

H11

120MVA

SUPERGRID T1

H13

L11

H21

SUPERGRID T2

H23

3T4

SUPERGRID 1

33kV

6T4

SUPERGRID 2

ACCESS ROAD

EARTHING

SUPERGRID T1

TRANSFORMER TRANSFORMER

EARTHING

SUPERGRID T2

WESTFIELD TEALING

L13

S14 S10 S18

120MVA

275/33kV

S11BS11A

L131

L21

L23L231

DateChecked

Approved

Drawn

Project

Copyright property of SP PowerSystems Ltd. Scale Size A4

Drawn

Approved

TRS No.

Checked

TitleDate

Status

Location

Date

Date

Drg. No. Rev.

Voltage

Rev FOR ISSUE SP2070170 2.0

SWITCHGEAR NUMBERING FOR

GLENROTHES 275KV SUBSTATION

GSN105(B)

GLENROTHES 275KV

NTS

PMR 08/09/95

WC 12/01/96

CC 27/08/96

2.0 21/01/14

PMR

DJBSA

WESTFIELD: L13, L11 & CVTs REPLACED, L131 & CTs ADDED.

TEALING: L23, L21 & CVTs REPLACED, L231 & CTs ADDED.

glenrothes 275kv switchgear replacement - ofgem ... · 2 background information .....4 3...

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