HVDC Technology Line Commutated Converters
Transcription
4/16/2014 1 HVDC Technology Line Commutated Converters Michael Bahrman, P.E., IEEE PES T&D, Chicago, April 15, 2014 2 Topics • • • • • • • • • • Line Commutated Converter ‐ LCC Effective short Circuit Ratio ‐ ESCR Configurations and operating modes Conversion principles Reactive power Capacitor Commutated Converter – CCC Converter arrangements Converter station layout and equipment Control & protection Questions? 1 4/16/2014 3 HVDC technology Line Commutated Converters ‐ LCC HVDCHVDC-CSC Converter Transformers AC Filters AC DC Filters DC Outdoor Indoor Thyristor Valves HVDC Classic • Current source converters (CSC) • Line-commutated converter (LCC) with thyristor valves • Requires ~50% reactive compensation (35% HF) • Converter transformers • Minimum short circuit capacity > 2 x Pd, > 1.3 x Pd with capacitor commuted converter (CCC) 4 Short Circuit Ratio What’s the deal? • • • • • • AC Network SN WF SWF? QHF ± QSH Commutation performance Voltage stability Dynamic performance Dynamic overvoltage, DOV Low order harmonic resonance, fres = f1 (S/Q) Rule of thumb – ESCR > 2 LCC, > 1.3 CCC; where ESCR = (SN+SG+SSC+SWF‐Q)/PDC QHF ± QSH T G SG SC SSC 2 4/16/2014 5 HVDC in bipolar operation Single 12p CSC per pole with metallic return switching BPS BPS GRTS MRTB NBS NBS NBGS NBGS BPS = DC breaker DC disconnect, closed DC disconnect, open DC breaker, closed DC breaker, open BPS • MRTB – metallic return transfer breaker, used for switching from ground return to metallic return • GRTS – ground return transfer switch, used for switching from metallic return to earth return in preparation for restarting pole (NRTS for systems with continuous metallic neutral) • BPS – bypass switch, used to provide metallic return path • NBS – neutral bus switch, used to commutate spill current from healthy pole for neutral bus fault • NBGS – neutral bus ground switch, used to help clear faults on electrode line (or metallic neutral 6 HVDC monopolar earth return operation Temporary during emergencies or maintenance Idp1 Idp1=Ig = DC breaker DC disconnect, closed DC disconnect, open DC breaker, closed DC breaker, open 3 4/16/2014 7 HVDC monopolar metallic return operation During converter outages or degraded line insulation Idp1 Ig = 0 Idp1 = DC breaker DC disconnect, closed DC disconnect, open DC breaker, closed DC breaker, open 8 Commutation in a controlled bridge Rectifier operation Id uR uS uT IR 1 3 5 IS Ud IT 4 6 2 u uT U d U di 0 cos U di0 3 3 2 π uR X cId uS U v 4 4/16/2014 9 Reactive power characteristics LCC • • • HVDC Classic: Reactive compensation by switched filters and shunt capacitor banks • • • Converter stations appear as a reactive load, i.e. lagging power factor Both rectifier and inverter operation exhibit lagging power factor, i.e. current lags voltage Lagging power factor is due to phase control and commutating reactance Typically reactive power demand = 55% of station rating at full load Reactive power compensation – typically 35% of station rating from ac filters the balance from shunt banks Shunt reactors sometimes used at light load to absorb excess from filters 10 Conventional HVDC technology LCC and CCC Commutation capacitor, CC LCC circuit • • • • • CCC circuit CC located between converter transformers and thyristor valves ‐ reduces transformer rating, increases valve voltage rating CC provides part of the commutation voltage and reactive support. Reduces probability for commutation failure for remote faults CC location reduces bank exposure to ac network faults, simplifies commutation capacitor protection, reduces MOV energy Reduces amount of shunt compensation, raises ac network resonance frequency, reduces dynamic overvoltage, lowers minimum ESCR Reduces variable O&M with shunt bank switching and transformer LTC operations 5 4/16/2014 11 CCC principles of commutation Inverter operation • Commutation Margin, ´ • Apparent Margin ac • Commutation margin increases with +Id or -Uac 12 HVDC converter arrangements Thyristor Module Gate Unit Single Double Valve Valve Quadruple Valve Thyristor HVDC Classic • Current source converter • Line commutated • Thyristor valves • Thyristor modules • Electrically triggered Heat Sink 6 4/16/2014 13 Layout of bipolar HVDC station ± 500 kV, 3000 MW 14 HVDC converter station 6400 MW, ± 800 kV with series converters 7 4/16/2014 15 Thyristor Valve Installation 16 Layout of HVDC quadruple thyristor valve Saturable Reactor Module TCU TCU Thyristor Module = 9 thyristor positions TCU Derivative Feeding Capacitor DC Grading Resistor TCU Thyristor Thyristor Control Unit Damping Resistors TCU Damping Capacitors TCU Derivative Feeding Resistor 8 4/16/2014 17 HVDC thyristor module PROTECTIVE FIRING + UPF + URP Thyristors RECOVERY PROTECTION - UN S + & Q R 1 MONITORING TCU Heat sinks NORMAL FIRING + UDI & & + UPS POWER IP FP Cooling tubes Capacitors Compression springs Resistors Current connector 18 Valve Cooling System Single circuit system Outdoor dry, liquid‐to‐air coolers for valve heat dissipation • Same base design for HVDC, HVDC Light and SVC • High reliability – redundant pumps, coolers, control, monitoring and protection • Designed for ease of maintenance – redundancy permits repair or replacement of parts without requiring a converter or pole outage • • MAIN PUMPS D EAERATION VESSEL SHU NT VALVES M EXPANSION VESSEL CONVERTER VALVE OUTDOOR COOLERS MECH ANIC AL F ILTERS D EION IZER FILTERS REPLEN ISHMENT SYSTEM M ECH AN IC AL F ILTERS 9 4/16/2014 19 Transformer Converter Interface HVDC • • • • • Match valve voltage with system AC‐ side Provide impedance to limit the short circuit current to the valve Galvanically separate the AC‐ and DC‐ side (takes place inside transformer, between AC and DC winding) making it possible to connect the converters in series Converter transformers also carry harmonics, phase shift provides some harmonic cancellation MVA rating and transport limitations determine configuration 20 Harmonic Filters Conventional HVDC12‐pulse converter • • • • • • AC side current harmonics: fh=12n±1, i.e. 11th,13th,23rd,25th,. . . Typical ac filter performance criteria: THD<1.5%, Dh<1%, TIF < 45 DC side voltage harmonics: fh=12n Typical dc filter performance criteria: Ieq < 250ma Typically 35% of station rating in installed ac filters Harmonics diminish with increasing harmonic number 10 4/16/2014 21 Filter types Bandpass filter High-pass filter 100 10 1 0 10 20 Harmonic number 30 1 10 4 1 10 Impedance (ohms) 1 10 3 1 10 Impedance (ohms) Impedance (ohms) 4 1 10 Double-tuned filter 3 100 10 0 20 40 60 3 100 10 1 5 Harmonic number 10 15 Harmonic number 22 HVDC classic control principles • Two independent variables at each terminal – firing angle, ac voltage • Control of firing angle is fast, control of ac voltage is slow (LTC) • One end assigned to voltage control, the other end to current control • Higher level power control calculates current order – no need for speed for normal dispatch but can be fast for pole loss compensation or runback • Current (or voltage) order converted to firing angle and sent to control pulse generator • CPG synchronized to ac voltage via PLL for equidistant firing 11 4/16/2014 23 Firing angle limits and VDCOL • Firing angle limits – alpha min for rectifier operation, minimum commutation margin for inverter operation • Minimum firing voltage for rectifier operation for disturbances • Voltage dependent current order limiter for controlling dynamic reactive power demand during start‐up and disturbance recovery • VDCOL time constants – fast for decreasing voltage, slower for increasing voltage • VDCOL up time constant speed dependent on system strength Rio Madeira HVDC Project Challenges Rio Madeira - Total transmission project overview Hydro Power Plants 3300 and 3150 MW Complex Customer structure Technology – Very week network in NW Brazil. – Advanced technical solutions • Capacitor Commuted Converters – Replaces 2 Synchronous machines • Large three winding transformers (Largest HVDC transformers so far) • Deep hole electrodes Logistics – – Transport of transformers on river. Limited period of enough water in river Brazilian Custom Clearance © ABB Group April 16, 2014 | Slide 24 12 4/16/2014 Rio Madeira HVDC Project Two transformers moved into position ABB Araraquara Converter station (right) and Ahlstom station in the middle © ABB Group April 16, 2014 | Slide 25 Rio Madeira HVDC Project Porto Velho Bipole quadruple valves © ABB Group April 16, 2014 | Slide 26 13 4/16/2014 Rio Madeira HVDC Project Araraquara Bipole double valves © ABB Group April 16, 2014 | Slide 27 Rio Madeira HVDC Project Porto Velho Back to Back station © ABB Group April 16, 2014 | Slide 28 14 4/16/2014 Rio Madeira HVDC Project Porto Velho Back to Back © ABB Group April 16, 2014 | Slide 29 30 NorthEast – Agra (NEA800), India Power: 6000/8000*) MW * continuous overload DC‐voltage: + 800 kV Transmission: 1728 km Three‐station multi‐terminal bipole with OH‐lines, parallel‐connected 12‐pulse converters • In‐service: 2014‐15 • • • • BIPOLE 1 BIPOLE 2 ~432 km ~1296 km +800 kV 3000 MW 400 kV 3000 MW Pole 3 Pole 1 Pole 4 Pole 2 Bipole 2 Bipole 1 Agra 3000 MW 400 kV -800 kV 400 kV 3000 MW Pole 3 Pole 1 Pole 4 Pole 2 Bipole 2 Bipole 1 Alipurduar Biswanath Chariali 15 4/16/2014 31 Questions? 16
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