RIIO-T2 Engineering Justification Papers
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RIIO-T2 Engineering Justification Paper: SPT-RI-224 Coylton SGT1(2) Reinforcement SPT-RI-224 Coylton SGT1(2) Reinforcement Name of Coylton SGT1(2) Reinforcement Scheme/Programme Primary Investment Driver Load Scheme reference/ SPT20035 mechanism or category SPT20036 Output references/type LRT2SP2014 Cost £7.579 Delivery Year 2023 Reporting Table B0.7 Load Master Data B4.2a Scheme Summary B4.5 Scheme Asset Data B4.5a Scheme Asset Data B4.6 Scheme Output Profile Outputs included in RIIO No T1 Business Plan Spend apportionment T1 T2 T3 0.359 7.220 0.000 Issue Date Issue No Amendment Details December 2019 Issue 1 First issue of document Page 1 SPT20035 Issue 1 RIIO-T2 Engineering Justification Paper: SPT-RI-224 Coylton SGT1(2) Reinforcement Table of Contents 1. Introduction .................................................................................................................................... 3 2. Background Information.................................................................................................................. 3 3. Optioneering ................................................................................................................................... 5 4. Detailed Analysis ............................................................................................................................. 5 5. Conclusions ..................................................................................................................................... 7 6. Future Pathways – Net Zero ............................................................................................................ 7 Page 2 SPT20035 Issue 1 RIIO-T2 Engineering Justification Paper: SPT-RI-224 Coylton SGT1(2) Reinforcement 1. Introduction Coylton substation is situated in the south west of Scotland approximately 12km East of Ayrshire town. The substation connects both a significant level of embedded generation but connects wider transmission generation in the south west Scotland area. In order to facilitate the generation connected and contracted at Maybole and Coylton 132kV GSPs (Approximately 370MW) it is proposed to replace the existing 275/132kV 120MVA transformers with 2 x 240MVA units providing 240MVA of Firm capacity at connecting into the Coylton/Maybole GSP group. The remainder of the generation shall be managed via commercial contracts and protections schemes on a Non-Firm basis. Works proposed are scheduled for completion in 2022 in line with requirements from associated generation sites. 2. Background Information Table 1 shows the connected and contracted generation at Maybole GSP. Maybole Generator Power (MW) Coylton SGT Access Grants CHP 12 REDACTED Straid Wind Farm (BEGA) 1 REDACTED HV/LV/FIT 5.2 REDACTED Hadyard Hill 99.9 REDACTED Assel Valley (BEGA) 29.95 REDACTED Minimum Demand 7.6 Total 140.45 Table 1: Maybole GSP Connected and Contracted Generation Similarly, Table 2 shows the connected and contracted generation at Coylton GSP. Coylton Generator Power (MW) Coylton SGT Access HV/LV/FIT 15 REDACTED Gallow and Polwat 22 REDACTED Garlaff 5 REDACTED Harehill 15 REDACTED Minimum Demand 18.2 Total 38.8 Table 2: Coylton GSP Connected and Contracted Generation From Table 1 and Table 2, there is a total of 205.05 MW connected or contracted to connect between Coylton and Maybole GSPs which will require firm access on the Coylton SGTs. The existing system is shown in Figure 1: Page 3 SPT20035 Issue 1 RIIO-T2 Engineering Justification Paper: SPT-RI-224 Coylton SGT1(2) Reinforcement To Hunterston To Strathaven X120 2 1 T T To Meadowhead G G S 105 S SGT4 205 F 25 F75 F35 H20 H85 Kilmarnock South No . 1 No. 2 To Ayr A V M 9 8 f o g n i Coylton t SGT2 120MVA a r (New) r e m m u s L40 L50 SGT1 120MVA t l u a f - L65 L2510 L35 e r P 380 120 280 1305 805 Grid 1 Grid 2 Pre-fault summer rating of89 MVA 120 220 320 To Hadyard Hill Coylton GSP Embedded (99.9 MW) Grid 1 Grid 2 Generation Maybole Maybole GSP Embedded Generation Figure 1: Schematic of the Existing Network Page 4 SPT20035 Issue 1 RIIO-T2 Engineering Justification Paper: SPT-RI-224 Coylton SGT1(2) Reinforcement 3. Optioneering The options considered for this project are shown in Table 3: Option Status Reason for rejection 1 Do nothing Rejected Does not comply with legal and licence obligations 2 Coylton SGT1 and SGT2 reinforcement Proposed 3 Reconductor 132kV Kilmarnock South to Proposed Maybole/Coylton T point 4 Coylton 275/33kV GSP Proposed Table 3: Overview of Options Considered Option 2 involves replacing the Coylton SGT1 and SGT2 120MVA transformers with 240MVA units. The total cost of the works associated with this option is approximately £7.579m. Option 3 involves the reconductoring the 132kV circuit between Kilmarnock South and Maybole/Coylton T point (15km OHL and 1 km underground cable). The OHL would be replaced with LARK HTLS conductor, and the cable with 2000mm Cu XLPE. The estimated cost for these works is £8.0m. In addition for Option 3 only, the Kilmarnock South to Meadowhead 132kV circuit (12km OHL and 1km underground cable) would need to be reinforced to give a minimum summer pre-fault rating of 146MVA, which is estimated to cost a further £3.5m. The existing 275/132 kV 120MVA transformers currently are not matched for impedance as such share load unevenly resulting a total capacity of 190MVA between the two transformers. As part of these proposed works one SGT unit at Coylton 275kV substation would be replaced increasing the capacity to the full 240MVA. The cost of the proposed reinforcement is £3m. This brings the total cost of Option 3 to £14.5m. At present, Keirs Hill WF (57.6MW) and Sanquhar WF (20.7MW) are contracted with firm transmission access at Coylton GSP based on a new 275/33kV GSP with a predicted capital cost of £12m payable by the developers. Option 4 would remove the Coylton GSP generation from the Coylton/Maybole 132kV network. However, there is still ~190MW of generation contracted at Maybole GSP, and the Kilmarnock South to Maybole/Coylton T point circuit would still need reinforced to provide a minimum summer pre-fault rating of 152MVA. The cost for these works alone is estimated to be £8m. 4. Detailed Analysis Option 1 is not a viable solution, as pursuing it would result in a lack of capacity at the Coylton SGT 1 and SGT2 and in an overload on the Kilmarnock South/Maybole/Coylton 132kV circuit. Option 3, given the large number of circuits which would need to be reconductored, is the least viable from an economic perspective. Similarly, Option 4 requires reconductoring, albeit of a smaller number of Page 5 SPT20035 Issue 1 RIIO-T2 Engineering Justification Paper: SPT-RI-224 Coylton SGT1(2) Reinforcement circuits. This still gives Option 4 a large economic disadvantage. Option 2, due to the fact that only two transformers need to be replaced, is the most economically advantageous and therefore the preferred solution. Therefore, it is proposed to replace the existing Coylton SGT1(2) 120MVA transformers with 240MVA units and also replace the associated busbars, apparatus and 275kV cabling as required to match the 240MVA SGT rating. Also at Kilmarnock South, the overload tripping for CB 205 is proposed to be reconfigured to trip if there is an overload detected on the Kilmarnock South to Coylton/Maybole circuit. Although this circuit is proposed to be operated normally open at Kilmarnock South substation, this overload protection scheme permits the ESO to operate the circuit closed with protection to prevent any overloads and permit increase network flexibility. A schematic of the new system, as proposed, is shown in Figure 2: KILMARNOCK SOUTH TO HUER TO STHA 1000MVA KILT 2 To Meadowhead TORI 224 Works SGT4 KILT 1 N/O 1) Replacement of Coylton SGT1(2) with 240MVA units. AYR 1) 275/132 kV 132/33kV 240MVA 60MVA COYLTON 805 Coylton T Maybole T Marks Hill Areceloch Kilgallioch 1) 132/33kV 60MVA Kendoon 99MW MAYBOLE GSP ~10MW min D AUCHENCROSH Hadyard Hill Figure 2: Schematic of the Proposed Works In addition, the retention of the Kilmarnock South to Coylton/Maybole 132kV circuit is required to ensure following an N-2 outage scenario, restoration to one third of the group demand is completed within three hours. It follows, for the loss of the two 400kV infeeds to Kilmarnock South or the two 275kV infeeds to Coylton that Coylton and Maybole GSPs will be isolated, and the Kilmarnock South 132kV circuit will provide the required third supply. At Kilmarnock South, CB 205 is required to be operated ‘normally open’ to ensure the Kilmarnock South to Coylton/Maybole circuit is not overloaded under intact and outage network conditions. This is required as the generation contracted at Maybole and Coylton 132/33kV substations will flow through the lower impedance 132kV network rather than through the 275/132kV transformers at Coylton substation. Page 6 SPT20035 Issue 1 RIIO-T2 Engineering Justification Paper: SPT-RI-224 Coylton SGT1(2) Reinforcement 5. Conclusions In order to cope with the amount of generation contracted at Maybole and Coylton substations, Coylton SGT1 and SGT2 must be uprated from 120MVA to 240MVA. This will ensure that there is sufficient capacity at Coylton substation and also that the 132kV circuit from Kilmarnock South to Maybole/Coylton Tee point is not overloaded. The total cost associated with these works is £7.579m and the completion time will be by 2023, when several generators will be connected. Project Summary: Forecast Costs – £7.579m o SPT funded – £7.579m Timing of Investment – 2019/2023 Outputs: o Addition – 2 x 275/132kV 240MVA Transformers and associated protection, control and civil works. o Disposal – 2 x 275/132kV 120MVA transformers o Modification to existing Kilmarnock South 132kV Overload protection scheme. 6. Future Pathways – Net Zero Primary Economic Driver The primary driver for investment for the proposed works is the provision of connection to the generation sites. Payback Periods As the proposed scheme works are the lowest capital expenditure that also provides capacity to the generation schemes a full CBA has not been undertaken for these works. This paper has considered various capital cost options and the justification is based on the lowest cost.