HVDC and its System Benefits IEEE PES General Meeting July 2014 (PSACE) Economic Systems Panel Session : “System Economic/Technical Benefits of Unconventional Transmission Provision: Transmission Switching, Embedded HVDC, and Others” HVDC and its System Benefits Neil Kirby – Alstom Grid Gaylord National Resort & Convention Center National Harbor, MD

Agenda HVDC Technology HVDC Functions Embedded Applications of HVDC

HVDC Technology

HVDC Technology Classic Line-Commutated Converters Based on Thyristors Need AC System Voltage present to operate Very limited control of Reactive Power Require AC filters to reduce generated harmonics Very high power capability 1100 kV 11000 MW Links in operation Approx 130 by end of 2015

HVDC Technology Voltage Source Converters Based on Transistors or similar Create their own AC Voltage from DC source Dynamic, Independent and Simultaneous control of MW and Mvars Limited harmonics Limited, increasing capacity +/-320kV (cable limit) 1100MW Links in operation Approx 30 by end of 2015

VSC vs. LCC HVDC Line-Commutated Converter (LCC) HVDC Voltage-Sourced Converter (VSC) HVDC VDC_A VDC_B IDC Power flow A → B Power flow B → A VDC_A VDC_B IDC Power flow A → B Power flow B → A VDC_A VDC_B VDC_A VDC_B IDC With LCC multi-terminal difficult for the network operator as a change in power direction at one terminal necessitates DC voltage reversal, hence, a Global network impact With VSC current direction changes not DC voltage therefore only a Local change

HVDC Functions

“Traditional” Applications Asynchronous interconnections, Bulk power transfer, Water crossings, etc Control Modes Power, Frequency, Swing Damping, AC Voltage, Reactive Power Both VSC and LCC are capable

Stability Improvement Steady-State vs. Dynamic Dynamic Voltage/Reactive Power Control Power Stability in Parallel AC lines Angular Stability Oscillatory Stability HVDC Can Reduce Stability Margins Allows use of Line Rating up to Thermal Capacity

DC Link Control Power Control Constant Real Power VSC can also control Mvar at each terminal Dynamic Linear AC Voltage Control STATCOM Functionality Even if DC power transfer is zero LCC can only control MW Coarse Control of Mvar through Filter Switching Here, a power level is ordered. Current order = (power demand/voltage order) Mvar MW Mvar

DC Link Control Frequency Control Constant Frequency VSC and LCC VSC can also control Mvar and AC voltage at each terminal Here, a power level is ordered. Current order = (power demand/voltage order) Mvar MW Mvar

DC Link Control Power Modulation Control Preset response Control system adjusts power to offset phase error P time Mvar MW Power Oscillation Damping controls oscillations in an adjacent line, Following a disturbance. The principle is to add an antiphase amount of DC power, so as to damp the AC power oscillations. Multimodal tuning methods are used from Transient Stability analysis. Mvar

DC Link Control Power Modulation Control Preset response Control system adjusts power to offset phase error P time Mvar MW Mvar

DC Link Control Power Modulation Control Preset response Control system adjusts power to offset phase error P time Mvar MW Phase error is a good measurement of power swing and is used to produce An antiphase signal to damp out the oscillation Mvar

DC Link Control Power Runback / PDO Preset response from Transient Stability Analysis Control system adjusts power flow to defined value P time Mvar MW Power is reduced from rectifier side to promote stability, in the same manner as as reduction of load to alleviate the effects of PV instability Mvar

DC Link Control Power Runback / PDO Preset response from Transient Stability Analysis Control system adjusts power flow to defined value P time Mvar MW Power is reduced from rectifier side to promote stability, in the same manner as as reduction of load to alleviate the effects of PV instability Mvar

DC Link Control Reactive Power Control VSC Offers Linear Reactive Power Control, independent of Real Power MW MW MW Power is reduced from rectifier side to promote stability, in the same manner as as reduction of load to alleviate the effects of PV instability Mvar Mvar

DC Link Control AC Voltage Control VSC Offers Linear Reactive Power Control, independent of Real Power MW MW MW Power is reduced from rectifier side to promote stability, in the same manner as as reduction of load to alleviate the effects of PV instability kV kV

Embedded Applications of HVDC

Nelson River, Canada Hydro electric power transmitted over 900km of OHL supplying half of Manitoba load 4000MW, ±500kV Double Bipole with series bridges BP1 originally commissioned 1972-77 with mercury arc BP2 added in two stages 1978 & 1985 (by German HVDC Group) BBC (now ABB) AEG (now Alstom) Siemens BP1 re-valved with thyristors & uprated in 1993 BP3 coming soon First HVDC link with: AC system damping 4 - terminal operation Hudson Bay Lake Winnipeg Limestone 1330 MW Longspruce 980 MW SASKATCHEWAN Nelson River MANITOBA ONTARIO Kettle 1272 MW Winnipeg

Nelson River HVDC Effect of Damping Controls Damping OFF Hz 64 62 60 58 10 20 30 0.2 0.1 -0.1 -0.2 t (sec) 10 20 30 Damping ON Hz 64 62 60 58 t (sec) 0.2 0.1 -0.1 -0.2 Kettle Generator Speed Manitoba Equivalent Machine Frequency

Pacific Intertie / Intermountain Intermountain Power Project (IPP) Path 27 (Delta, UT – Adelanto, CA) Pacific DC Intertie (PDCI) Path 65 (Celilo, OR – Sylmar, CA) 2 Embedded HVDC Pacific DC Intertie 3100 MW / 500 kV Intermountain Power Project 2400 MW / 500 kV Both run parallel with many AC lines Swing Damping

Alberta, Canada Under Construction 2 Embedded HVDC Improve Power Flows EATL 1000 MW /500 kV WATL Improve Power Flows N-S S-N Under Construction West Alberta Tie Line (WATL) East Alberta Tie Line (EATL)

New Embedded HVDC In Europe France-Spain 2 x 1000 MW U/G Cable Improve power flows across border Germany Multiple Parallel N-S HVDC Corridors Closing down Nuclear in South Adding new Offshore Wind In North

New Embedded HVDC In Europe Sweden 2 x 720 MW Cable / Line Improve N-S Power Flows Reduce Energy Price Differential Phase 1 Phase 2

HVDC Cost Benefit Analysis 55 k$/MVAr 0.4 .. 0.7 $/MVAr/h 0.4 .. 0.7 $/MVAr/h + 6 $/MVAr/h 1.2 k$ per year and MW capacity Ref: Cigre Publication : Report 492 – Table 4.11 (….. EUR to USD converted at 1.347)

Overlay grid - Supergrid Renewables unevenly distributed Wind in NW Europe Solar in N Africa and S Europe Hydro can be used for storage HVDC bringing efficiency and stability Efficiency over long distances Oscillation damping “Firewalls” to blackout Right of way complicated Cable underground/water vs. overhead lines 3000km So back to the concept of the Supergrid. In terms of offshore wind power and Mediterranean/north african solar power, HVDC connections will allow the connection of these renewable sources to be shared across country and continental boundaries. This meshed DC and AC grid with multi-terminal interconnections known as a Supergrid is already underway in many areas of the world, notably Europe, India, Brazil, China and the Middle East. Future is multi-terminal meshed DC and AC Grid

Supergrid / DC Grid “DC Grids” – Multiple converters connecting AC power networks to a DC power network DC circuit breaker, to interrupt DC fault current in 2 ms DC – DC voltage converter, equivalent to an AC transformer Fault protection system, detect and discriminate faulted sections Control system, dispatch of power from multiple terminals Existing AC grid DC Grid

References & Further Reading Cigre Report 492 “Voltage Source Converter (VSC) HVDC for Power Transmission – Economic Aspects and Comparison with other AC and DC Technologies” European Supergrid Program – “Friends of the Supergrid” http://www.friendsofthesupergrid.eu/ “High Voltage Direct Current Transmission” by J. Arrillaga, Publisher IET (UK) Power & Energy Series. ISBN 0 85296 941 4