i The Future of Electric Power Transmission MOD
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i MOD nc Some thoughts on…. The Future of Electric Power Transmission i MOD nc Enhancing Capacity of today’s Systems: Improve Capacity thru 1. Better using intrinsic characteristics of transmission lines 2. Adding equipment to achieve greater flows Series compensation Reactive power sources Phase angle shift Increasingly dependent on power electronics ….“FACTS” i MOD nc Current-activated Tension Adjuster i MOD nc Distributed Reactive Drop Compensation Series quadrature voltage adjuster: i MOD nc Enhancing Capacity of todays System: Improve Capacity thru 1. Better using inherent characteristics of transmission lines 2. Adding equipment to achieve greater flows Series compensation Reactive power sources Phase angle shift Increasingly dependent on power electronics ….“FACTS” i MOD nc How many MW/ft2? 25’ 250 ft2 10’ ii MOD MODnc Poynting Vector Analysis nc S = E xH 25’ 2 S max E max = Zi E max = 30 250 ft2 kV cm S max = 12,000 MW m 2 = 1,115 P = 278,810 MW MW ft 2 10’ i MOD How are we doing? nc 138 kV ~ 200 MW (0.08%) i MOD nc High Phase Order Transmission 3 phase 6 phase 12 phase Infinite phase order in tin la su g condu cting i MOD nc It Works….but imagine the substation! 3 phase 6 phase 12 phase i MOD nc 1. ACCR i MOD nc Potential for Current & Voltage Uprating Reconductoring allows: 1. Current uprating by reducing sag 2. Voltage uprating by creating extra clearance and room for more insulators. (Light weight allows bundling) i MOD nc 2. High Surge Impedance Loading Construction X reduced C increased Voltage (kV) 69 138 230 500 SIL (MW) Normal HSIL 9-12 10-40 40-50 50-120 120-130 130-440 950-1,000 1,000 - 2,000 MOD nc i 3. HVDC Conversion Advantages: 1. Full time-utilization of insulation 2. DC Operating advantages Obstacles: 1. High cost per incremental kW 2. Bi-pole system leaves 1/3 of a valuable line investment idle MOD nc i 3. Tri-pole HVDC An extra conductor….. Why not an extra bridge? DC 1 2 AC AC A B C 1-pole Converter A B C 3 AC 1-pole Converter A B C 1-pole Converter i MOD nc Symmetrical Bi-Pole Asymmetrical HVDC Modulation modulation options 1.00 Pole 1 Pole 2 -1.00 Conductor 3 Conductor 3 is idle except in emergencies i MOD nc Symmetrical CurrentAsymmetrical Modulation Modulated modulation HVDC options One pole reversible, in current & voltage: 1.37 Pole 1 Pole 2 -1.37 1.00 Pole 3 -1.00 Pole 3 alternately relieves current from pole 2…then pole 1 i MOD nc Symmetrical Asymmetrical Asymmetrical Modulation Modulation modulation options One reversible pole: PoleThe 1 tri-pole system:1.37 1. Carries 37% more power than a bi-pole on the same 3-conductor system. 2. Reduces losses, for the same power, by 20% Pole 2 3. Can loose any conductor or pole, act like a -1.37 bi-pole, and still transmit 73% of its maximum power. 4. Needs no ground return. 1.00 Pole 3 -1.00 Pole 3 alternately relieves current from pole 2…then pole 1 i MOD nc Symmetrical CurrentAsymmetrical Modulation Modulated modulation HVDC options 1.37 Pole 1 Pole 2 -1.37 1.00 Pole 3 -1.00 i MOD nc Symmetrical Transitional Transitional Modulation Ramps ramps options Ramp holds constant DC Power 1.0 I1 0.5 -0.5 I2 -1.0 0.5 I3 -0.5 178 180 182 o Modulating Pole regulated to hold neutral current to zero 4 of a 6 minute period = 4 seconds i MOD nc Symmetrical Transitional Transitional Modulation Ramps ramps options Constant-polarity currents overlap. providing time to reverse modulating pole polarity I1 I2 I3 T (Detailed control simulation demonstrated by Dennis Woodford) i MOD nc Symmetrical Transitional Transitional Modulation Ramps ramps options Simulation (By Dennis Woodford) of the transition with example control logic: Power (MW) Pole 1 Power (MW) Pole 2 Power (MW) Pole 3 Total Tri-pole power (MW) i MOD nc Symmetrical Economics Transitional Modulation - AC ramps Conversion options Issues: 1. Tri-pole terminals are 10% to 20% more expensive per kW 2. This premium is offset by higher DC/AC power ratio…lower cost per incremental kW 3. Tri-pole makes 37% better use of prior transmission line investment 4. Tri-pole losses are lower 5. Tri-pole has 50% higher redundancy. nc Symmetrical 500kV kVModulation Conversionoptions Example AA500 conversion example Different ways to bring loading up to thermal capacity 350 Loss / Mile / Phase = kW i MOD 300 Conductor Thermal Limit 250 385 kV Tri-Pole 200 436 kV Bi-pole 150 100 436 kV Tri-Pole 500 kV AC 50 0 0 500 1000 1500 2000 2500 3000 Power Transfer = MW 3500 4000 nc Symmetrical The Transmission case for Modulation “promoting” line “promotion” options 230 kV St. Clair Curve for 500 kV and 230 kV: 5,000 4,500 4,000 Loading - MW i MOD 3,500 3,000 2,500 2,000 1,500 500 kV 1,000 230 kV 500 0 0 100 200 300 Miles 400 500 600 nc Symmetrical 230 Transmission kV Promotion Modulation line “promotion” options Convert the 230 to tri-pole HVDC, feed terminals from the 500 kV Bus (If the 230 kV can be spared from its own network) 1,400 1,200 Loading - MW i MOD 500 kV AC 200 kV Tri-pole HVDC 1,000 2000 a. 800 600 400 230 kV AC 200 0 0 100 200 Miles 300 i MOD nc Symmetrical What The case about Modulation for new new HVDC tri-pole options circuits? lines MCM/2 MCM /////\\\\\/////\\\\\/////\\\\\/////\\\\\/////\\\\\/////\\\\\ /////\\\\\/////\\\\\/////\\\\\/////\\\\\/////\\\\\/////\\\\\ /////\\\\\/////\\\\\/////\\\\\/////\\\\\/////\\\ Bi-pole w Ground Return Tri-pole without Ground Return MW = 1.00 R = .5 MW = 1.37 R = .78 All towers have approximately equal wind & weight loading….approximately the same cost in $/mile i MOD nc Symmetrical HVDC The case options Modulation for new – all tri-pole equal options MW lines 100% i MOD nc 90% 80% 4 Pole + G 3 Pole 70% 3 Pole + G All options suspended from a single tower. Redundancy 60% 2 Pole + G 4 Pole 50% Weight Loading Wind Loading Average of Weight & Wind Loading 40% All cases are relative to the 2-pole case without ground return. 30% All Cases represent the same MW rating 20% 10% 3 Phase AC 2 Pole 0% 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 Tower Cost Index 1.8 1.9 2.0 i Symmetrical KeyConclusion technical Modulation / economic options issues MOD nc It’s worthwhile reviewing the basics of conductor configuration and use…e.g. “bundled circuits” DC will play a bigger role in future systems. Tri-pole appears to have cost and reliability advantages both for conversion and for new lines where metallic ground return is used. Higher voltage bi-directional valves are needed both multi-terminal and tri-pole applications. Reliability criteria need to better accommodate internal circuit redundancy.
