High Voltage Direct Current (HVDC) System Studies
Determination of Project Assumptions & Scope
Engaged in a small team to investigate and perform detailed system studies to find the optimal connection point for an East Coast 2 GW HVDC link to accommodate increased power transfers from Scotland to England and associated power transfers in the north of England. The system studies used National Grid's ELLA power system simulation tool.
The project's remit was to consider system access arrangements, cost of implementation, the optimal amount of system reinforcements and the ability to accommodate the short term 6 hour cyclic thermal ratings of cables and continuous rating of the HVDC link without due restrictions under outage conditions of the main interconnected transmission system, (MITS).
Studies were undertaken to observe the effect of blocking the East Coast HVDC link to mitigate thermal overloads on the wider system.
In total, thirty six, (36), system outages were considered in the studies.
Prior to commencing studies, in collaboration with colleagues, defined project scope and assumptions on study criteria to include the following:-
Study assumed a Gone Green year 2020 generation and demand background data set to be used, and a maximum peak winter demand of 57.1 GW. Assumed 73% available plant output margin for conventional plant and 60% plant margin for wind generation. The proposed 2020 network configuration model was assumed including where appropriate, re conductoring of existing circuits, series capacitor compensation, the West Coast 2 GW HVDC link and those circuits upgraded or modified for projects associated with Transmission Investments for Renewable Generation, (TIRG).
The southern end landing points of the HVDC link were at Blyth, Brine Field, Hartlepool, Hawthorn Pit, Humber Area, Lackenby, Saltholme and Tod Point substations, with the northern end landing point at Peterhead 275 kV substation.
The study was as per existing SQSS standards, and the HVDC link was classed as a transmission circuit and not generation.
The study considered the effect on the existing internal interconnector double circuits connecting Scotland with north England, classed as boundaries B6 and B7, (SPT to NGET).
Each boundary study was to be set up to the required transfer condition under agreed generation backgrounds, (Gone Green).
Where possible, Quadrature Booster optimisation was carried out to ensure maximum power transfers across the boundaries B6 & B7 as well as the HVDC link.
Each study performed pre fault analysis on an intact system or a system with a planned N-1 outage, and assumed pre fault conditions were met. A 84% pre fault rating on over head circuits for thermal loading was assumed. Thermal overloads on affected circuits were noted, as well as the percentage of this overload, (> 100%).
Each study performed post fault analysis of the HVDC link in service, (non blocking), for credible N-2 and N-D outages. A 100% post fault continuous rating on over head circuits for thermal loading was assumed. Thermal overloads on affected circuits were noted, as well as the percentage of this overload, (> 100%).
Each study also performed post fault analysis of the HVDC link offline, (blocked), for credible N-2 and N-D outages, and checked that power flows across the remainder of the network were compliant.
Each study had to consider steady state voltage compliance limits, voltage step change, switching operations, fault conditions affecting system voltage, reactive power both dynamic and static requirements on the network assessed under conditions stated, and MVar exchange from AC system to HVDC system and vice versa.
Additional study requirements such as the dataset for maximum and minimum fault levels as per ER/G74 standard for light loads, N-3 outages, highest transformer impedance and circuit breaker derating factors were taken into consideration.
Further work on stability studies was undertaken, including dynamic dataset preparation, transient and dynamic stability under various network outages and fault conditions, temporary over voltage analysis for HVDC link blocking and switching conditions.
Four studies were proposed and subsequently simulated using ELLA; Part 1 considered a required boundary power transfer of 5.5 GW for Boundary B7 under a gone green background, with a corresponding flow on Boundary B6 of 3.3 GW (AC circuits), with the effects of blocking the East Coast HVDC link with the West Coast HVDC link remaining in service during the blocking of the East Coast 2GW link. The total flow of 7.3 GW with both HVDC links in service was also studied.
Study Part 2 considered a small change in power flows on the East Coast HVDC link from 2.0 GW to 2.2 GW and a corresponding change on the West Coast HVDC link from 2.0 GW to 1.8 GW to see the effect on the main interconnected transmission system (MITS), at boundary 6. The study was based on an AC transfer of 4.6 GW on the AC interconnectors alone.
Study Part 3 was a local generation sensitivity analysis study. As there is significant proposed generation developments in the North East of England, the optimum connection point needs to fully consider future reinforcements required to accommodate not only the requirements of the HVDC link at the time of proposed connection, but also consideration must be given to the impact on reinforcements required to accommodate future contracted generation.
The studies in part 3 considered the effect of new generation developments connected at Blyth 400 kV and Brine Field 400 kV locations. Both pre fault and post fault analysis was undertaken, with thermal overloads on affected circuits were noted, as well as the percentage of this overload, (> 100%).
Study Part 4 considered if the connection points at Saltholme, Lackenby and Tod Point were discounted on economic grounds due to environmental factors, difficulties in planning outages to accommodate new circuits, a number of further studies were performed to establish if, at additional expense, what additional transmission assets would be required to connect the HVDC link at each co respective location.
Pre fault, (N-1 outage) and post fault, (N-2/N-D outage) studies were performed, with the indicated transfer, outage condition, overloaded circuits, and overload percentage % shown in study results.
At Lackenby, a separate 400 kV gas insulted substation, (GIS) was proposed/studied, looped into the existing Lackenby/Thornton 400 kV circuit. For Tod Point / Saltholme locations, a joint solution was proposed with an additional 400kV substation at Saltholme, and the HVDC link connecting at Tod Point 400 kV, with new 400kV circuits connecting the various 400 kV substations.
An examination of original cable distances between 275 kV substations in the North East ring was undertaken, to calculate potential 400 kV circuit lengths into upgraded 275 kV substations for all study scenarios.
Using the 2010 Seven Year Statement, (SYS), Appendix B, circuit parameters of a generic 275 kV and 400 kV circuits using standard conductor sizes including GAP were calculated for all expected cable distances on proposed network upgrades and study scenarios, and were later used in ELLA to model the modified circuit parameters.
The project's remit was to consider system access arrangements, cost of implementation, the optimal amount of system reinforcements and the ability to accommodate the short term 6 hour cyclic thermal ratings of cables and continuous rating of the HVDC link without due restrictions under outage conditions of the main interconnected transmission system, (MITS).
Studies were undertaken to observe the effect of blocking the East Coast HVDC link to mitigate thermal overloads on the wider system.
In total, thirty six, (36), system outages were considered in the studies.
Prior to commencing studies, in collaboration with colleagues, defined project scope and assumptions on study criteria to include the following:-
Study assumed a Gone Green year 2020 generation and demand background data set to be used, and a maximum peak winter demand of 57.1 GW. Assumed 73% available plant output margin for conventional plant and 60% plant margin for wind generation. The proposed 2020 network configuration model was assumed including where appropriate, re conductoring of existing circuits, series capacitor compensation, the West Coast 2 GW HVDC link and those circuits upgraded or modified for projects associated with Transmission Investments for Renewable Generation, (TIRG).
The southern end landing points of the HVDC link were at Blyth, Brine Field, Hartlepool, Hawthorn Pit, Humber Area, Lackenby, Saltholme and Tod Point substations, with the northern end landing point at Peterhead 275 kV substation.
The study was as per existing SQSS standards, and the HVDC link was classed as a transmission circuit and not generation.
The study considered the effect on the existing internal interconnector double circuits connecting Scotland with north England, classed as boundaries B6 and B7, (SPT to NGET).
Each boundary study was to be set up to the required transfer condition under agreed generation backgrounds, (Gone Green).
Where possible, Quadrature Booster optimisation was carried out to ensure maximum power transfers across the boundaries B6 & B7 as well as the HVDC link.
Each study performed pre fault analysis on an intact system or a system with a planned N-1 outage, and assumed pre fault conditions were met. A 84% pre fault rating on over head circuits for thermal loading was assumed. Thermal overloads on affected circuits were noted, as well as the percentage of this overload, (> 100%).
Each study performed post fault analysis of the HVDC link in service, (non blocking), for credible N-2 and N-D outages. A 100% post fault continuous rating on over head circuits for thermal loading was assumed. Thermal overloads on affected circuits were noted, as well as the percentage of this overload, (> 100%).
Each study also performed post fault analysis of the HVDC link offline, (blocked), for credible N-2 and N-D outages, and checked that power flows across the remainder of the network were compliant.
Each study had to consider steady state voltage compliance limits, voltage step change, switching operations, fault conditions affecting system voltage, reactive power both dynamic and static requirements on the network assessed under conditions stated, and MVar exchange from AC system to HVDC system and vice versa.
Additional study requirements such as the dataset for maximum and minimum fault levels as per ER/G74 standard for light loads, N-3 outages, highest transformer impedance and circuit breaker derating factors were taken into consideration.
Further work on stability studies was undertaken, including dynamic dataset preparation, transient and dynamic stability under various network outages and fault conditions, temporary over voltage analysis for HVDC link blocking and switching conditions.
Four studies were proposed and subsequently simulated using ELLA; Part 1 considered a required boundary power transfer of 5.5 GW for Boundary B7 under a gone green background, with a corresponding flow on Boundary B6 of 3.3 GW (AC circuits), with the effects of blocking the East Coast HVDC link with the West Coast HVDC link remaining in service during the blocking of the East Coast 2GW link. The total flow of 7.3 GW with both HVDC links in service was also studied.
Study Part 2 considered a small change in power flows on the East Coast HVDC link from 2.0 GW to 2.2 GW and a corresponding change on the West Coast HVDC link from 2.0 GW to 1.8 GW to see the effect on the main interconnected transmission system (MITS), at boundary 6. The study was based on an AC transfer of 4.6 GW on the AC interconnectors alone.
Study Part 3 was a local generation sensitivity analysis study. As there is significant proposed generation developments in the North East of England, the optimum connection point needs to fully consider future reinforcements required to accommodate not only the requirements of the HVDC link at the time of proposed connection, but also consideration must be given to the impact on reinforcements required to accommodate future contracted generation.
The studies in part 3 considered the effect of new generation developments connected at Blyth 400 kV and Brine Field 400 kV locations. Both pre fault and post fault analysis was undertaken, with thermal overloads on affected circuits were noted, as well as the percentage of this overload, (> 100%).
Study Part 4 considered if the connection points at Saltholme, Lackenby and Tod Point were discounted on economic grounds due to environmental factors, difficulties in planning outages to accommodate new circuits, a number of further studies were performed to establish if, at additional expense, what additional transmission assets would be required to connect the HVDC link at each co respective location.
Pre fault, (N-1 outage) and post fault, (N-2/N-D outage) studies were performed, with the indicated transfer, outage condition, overloaded circuits, and overload percentage % shown in study results.
At Lackenby, a separate 400 kV gas insulted substation, (GIS) was proposed/studied, looped into the existing Lackenby/Thornton 400 kV circuit. For Tod Point / Saltholme locations, a joint solution was proposed with an additional 400kV substation at Saltholme, and the HVDC link connecting at Tod Point 400 kV, with new 400kV circuits connecting the various 400 kV substations.
An examination of original cable distances between 275 kV substations in the North East ring was undertaken, to calculate potential 400 kV circuit lengths into upgraded 275 kV substations for all study scenarios.
Using the 2010 Seven Year Statement, (SYS), Appendix B, circuit parameters of a generic 275 kV and 400 kV circuits using standard conductor sizes including GAP were calculated for all expected cable distances on proposed network upgrades and study scenarios, and were later used in ELLA to model the modified circuit parameters.
Hawthorn Pit Landing Point
Undertook system studies assuming a HVDC link landing point at Hawthorn Pit substation, for both boundaries B6 and B7. Developed base file data and case file data, outage lists, (N-1, N-2, N-D), including scenarios with 2nd 400kV circuit for each respective boundaries.
A brief optioneering report was written to consider pre study scenarios prior to commencing each study for Hawthorn Pit, with a results table prepared in advance.
Studies were performed for a connection at 275 kV into the existing Hawthorn Pit 275 kV substation, for a connection at 400 kV with the existing 400 kV single circuit out of Hawthorn Pit 400 kV substation, for a connection at 400 kV utilising the existing 400 kV single circuit out of Hawthorn Pit 400 kV and an additional upgraded 275 kV circuit to 400 kV giving 2 circuits, finally upgrading those two 400 kV circuits from 4 GW to 6 GW using GAP conductors. (All study assumptions were taken into account including the blocking and non blocking of the link).
A brief optioneering report was written to consider pre study scenarios prior to commencing each study for Hawthorn Pit, with a results table prepared in advance.
Studies were performed for a connection at 275 kV into the existing Hawthorn Pit 275 kV substation, for a connection at 400 kV with the existing 400 kV single circuit out of Hawthorn Pit 400 kV substation, for a connection at 400 kV utilising the existing 400 kV single circuit out of Hawthorn Pit 400 kV and an additional upgraded 275 kV circuit to 400 kV giving 2 circuits, finally upgrading those two 400 kV circuits from 4 GW to 6 GW using GAP conductors. (All study assumptions were taken into account including the blocking and non blocking of the link).
Lackenby Landing Point
Undertook system studies assuming a HVDC link landing point at Lackenby substation, for both boundaries B6 and B7. Developed base file data and case file data, outage lists, (N-1, N-2, N-D), including scenarios with 2nd 400kV circuit via Saltholme or Norton for each respective boundaries.
A brief optioneering report was written to consider pre study scenarios prior to commencing each study for Lackenby, with a results table prepared in advance.
Studies were performed for a connection at 400 kV into the existing Lackenby 400 kV substation, for a connection at 400 kV but using a reconductored GAP line to increase the rating of the circuits to 6GW, for a connection at 400 kV with the Norton to Lackenby 400 kV line upgraded, (GAP), and finally upgrading Saltholme 275 kV substation to 400 kV and turn in 400 kV circuits to this substation. (All study assumptions were taken into account including the blocking and non blocking of the link).
A brief optioneering report was written to consider pre study scenarios prior to commencing each study for Lackenby, with a results table prepared in advance.
Studies were performed for a connection at 400 kV into the existing Lackenby 400 kV substation, for a connection at 400 kV but using a reconductored GAP line to increase the rating of the circuits to 6GW, for a connection at 400 kV with the Norton to Lackenby 400 kV line upgraded, (GAP), and finally upgrading Saltholme 275 kV substation to 400 kV and turn in 400 kV circuits to this substation. (All study assumptions were taken into account including the blocking and non blocking of the link).
Tod Point Landing Point
Undertook system studies assuming a HVDC link landing point at Tod Point substation, for both boundaries B6 and B7. Developed base file data and case file data, outage lists, (N-1, N-2, N-D), including scenarios with 400kV circuit upgrade for each respective boundaries.
An examination of original cable distances between 275 kV substations in the North East ring was undertaken, to calculate potential 400 kV circuit lengths into Tod Point substation.
A proposal for a 'dive under' circuit modification using the existing Lackenby to Norton circuit was considered. A brief optioneering report was written to consider pre study scenarios prior to commencing each study for Tod Point, with a results table prepared in advance.
Studies were performed for a connection at 275 kV into the existing Tod Point 275 kV substation, for a connection at 400 kV using a dive under for connection with the adjacent Lackenby to Norton 400 kV circuit, for a connection at 400 kV but using reconductored GAP conductors to increase rating to 6GW, for a connection at 400 kV but at Saltholme, retaining Tod Point at 275kV, and finally for a connection at 400 kV midway between Tod Point and Saltholme. (All study assumptions were taken into account including the blocking and non blocking of the link).
An examination of original cable distances between 275 kV substations in the North East ring was undertaken, to calculate potential 400 kV circuit lengths into Tod Point substation.
A proposal for a 'dive under' circuit modification using the existing Lackenby to Norton circuit was considered. A brief optioneering report was written to consider pre study scenarios prior to commencing each study for Tod Point, with a results table prepared in advance.
Studies were performed for a connection at 275 kV into the existing Tod Point 275 kV substation, for a connection at 400 kV using a dive under for connection with the adjacent Lackenby to Norton 400 kV circuit, for a connection at 400 kV but using reconductored GAP conductors to increase rating to 6GW, for a connection at 400 kV but at Saltholme, retaining Tod Point at 275kV, and finally for a connection at 400 kV midway between Tod Point and Saltholme. (All study assumptions were taken into account including the blocking and non blocking of the link).
Tod Point & Saltholme Landing Point
Undertook system studies assuming a HVDC link landing point at both Tod Point and Saltholme substations, for both boundaries B6 and B7. Developed base file data and case file data, outage lists, (N-1, N-2, N-D), including scenarios with 400 kV circuit upgrade for each respective boundaries.
A brief optioneering report was written to consider pre study scenarios prior to commencing each study for a combined landing point at Tod Point and Saltholme, with a results table prepared in advance.
Studies were performed for a connection at 275 kV at both Tod Point and Saltholme existing 275 kV substations, for a connection at 400 kV at both Tod Point and Saltholme substations upgraded to 400 kV, including a further study with the 400 kV circuits restrung with GAP conductors to bring circuit rating to 6GW.
A brief optioneering report was written to consider pre study scenarios prior to commencing each study for a combined landing point at Tod Point and Saltholme, with a results table prepared in advance.
Studies were performed for a connection at 275 kV at both Tod Point and Saltholme existing 275 kV substations, for a connection at 400 kV at both Tod Point and Saltholme substations upgraded to 400 kV, including a further study with the 400 kV circuits restrung with GAP conductors to bring circuit rating to 6GW.
Potential Connection Points in England and Wales Study Report
Wrote document into 'Potential Connection Points in England and Wales Study Report'. The scope of this document included suggested system reinforcements at each landing point, such as turning in lines, re conductoring lines with new increased thermal ratings, upgrading 275 kV circuits to 400 kV including overhead lines, new substations and interbus 400/275kV transformers, and HVDC line blocking.
The report also considered each landing point system study, a basic overview of existing infrastructure, the ease of connection of the HVDC into MITS, minimal system changes, the distance to coast for offshore cables, all pre fault analysis results, all post fault analysis results, required system reinforcements and a summary of findings.
Collated results from colleagues as well from my own study results for Hawthorn Pit, Lackenby, Saltholme and Tod Point substations, and updated HVDC Link boundary transfer overload tables to show worst case network overloads.
Includes outage between substations or tee points, a trip number identification, the boundary transfer capacity (MW), overload status and location of overload circuits, the percentage overload %, the circuit rating in MVA, overload power flow (MW), for both HVDC non blocking (in service), blocking (offline) scenarios.
Created system development diagrams for north east area using common SYS Picasso symbols for lines, substations, inter bus transformers, HVDC converters, overhead line tower construction style type, (L2, L6, L8 etc), and switch disconnectors, for existing and proposed network with landing points.
Included all study results for parts 1, 2, 3 and 4.
The report also considered each landing point system study, a basic overview of existing infrastructure, the ease of connection of the HVDC into MITS, minimal system changes, the distance to coast for offshore cables, all pre fault analysis results, all post fault analysis results, required system reinforcements and a summary of findings.
Collated results from colleagues as well from my own study results for Hawthorn Pit, Lackenby, Saltholme and Tod Point substations, and updated HVDC Link boundary transfer overload tables to show worst case network overloads.
Includes outage between substations or tee points, a trip number identification, the boundary transfer capacity (MW), overload status and location of overload circuits, the percentage overload %, the circuit rating in MVA, overload power flow (MW), for both HVDC non blocking (in service), blocking (offline) scenarios.
Created system development diagrams for north east area using common SYS Picasso symbols for lines, substations, inter bus transformers, HVDC converters, overhead line tower construction style type, (L2, L6, L8 etc), and switch disconnectors, for existing and proposed network with landing points.
Included all study results for parts 1, 2, 3 and 4.