V G RAO HVDC / KOLAR
REASONS FOR AC GENERATION AND TRANSMISSION Due to ease of transformation of voltage levels (simple transformer action) and rugged squirrel cage motors, ALTERNATING CURRENT is universally utilised. Both for GENERATION and LOADS and hence for TRANSMISSION. Generators are at remote places, away from the populated areas i.e. the load centers They are either PIT HEAD THERMAL or HYDEL Turbines drive synchronous generators giving an output at 15-25 kv. Voltage is boosted up to 220 or 400 KV by step-up transformers for transmission to LOADS. To reach the loads at homes/industry at required safe levels, transformers step down voltage.
COMPARISION OF HVAC & HVDC SYSTEMS CONVENTIONALLY POWER TRANSMISSION IS EFFECTED THROUGH HVAC SYSTEMS ALL OVER THE WORLD. HVAC TRANSMISSION IS HAVING SEVER LIMITATIONS LIKE LINE LENGTH, UNCONTROLLED POWER FLOW, OVER/LOW VOLTAGES DURING LIGHTLY / OVER LOADED CONDITIONS,STABILITY PROBLEMS,FAULT ISOLATION ETC CONSIDERING THE DISADVANTAGES OF HVAC SYSTEM AND THE ADVANTAGES OF HVDC TRANSMISSION, POWERGRID HAS CHOOSEN HVDC TRANSMISSION FOR TRANSFERRING 2000 MW FROM ER TO SR
HVDC: USE less current Direct current : Roll along the line ; opposing force friction (electrical resistance ) AC current will struggle against inertia in the line (100times/sec)- cuurent inertia inductance-reactive power
Better Voltage utilisation rating
DC has Greater Reach Distance as well as amount of POWER determine the choice of DC over AC
DC The alternating current in a cable leaks current (charging movements) in the same manner as a pulsating pressure would be evened out in an elastic tube.
DIRECT CURRENT CONSERVES FOREST AND SAVES LAND Fewer support TOWER, less losses
CONTROLLING or BEING CONTROLLED By raising the level in tank ;controlled water flow
CONTROLLING or BEING CONTROLLED ZERO IF Vr=VI=10V
HVDC leads to Better Use of AC TRANS SYS. FORCE HAS TO BE APPLIED IN RIGHT POSITION
HVDC provides increase power but does not increase the short circuit POWER
HVDC LEADS TO BETTER HVDC and HVAC SHOULD CO- OPERATE FOR OPTIMUM EFFICIENCY USE OF AC
HVDC LEADS TO BETTER USE OF AC If two networks are connected by an AC link, it can be in-efficient
ADVANTAGES OF HVDC OVER HVAC TRANSMISSION CONTROLLED POWER FLOW IS POSSIBLE VERY PRECISELY ASYNCHRONOUS OPERATION POSSIBLE BETWEEN REGIONS HAVING DIFFERENT ELECTRICAL PARAMETERS NO RESTRICTION ON LINE LENGTH AS NO REACTANCE IN DC LINES
ADVANTAGES OF HVDC OVER HVAC TRANSMISSION STABILISING HVAC SYSTEMS -DAMPENING OF POWER SWINGS AND SUB SYNCHRONOUS FREQUENCIES OF GENERATOR. FAULTS IN ONE AC SYSTEMS WILL NOT EFFECT THE OTHER AC SYSTEM. CABLE TRANSMISSION.
ADVANTAGES OF HVDC OVER HVAC TRANSMISSION CHEAPER THAN HVAC SYSTEM DUE TO LESS TRANSMISSION LINES & LESS RIGHT OF WAY FOR THE SAME AMOUNT OF POWER TRANSMISSION
COST: AC vs DC Transmission Line Cost AC Line Cost DC Terminal Cost DC Terminal Cost AC Break Even Distance
2000 MW HVDC VIS- A- VIS HVAC SYSTEMS HVDC BIPOLAR TRANSMISSION SYSTEM 2 DOUBLE CIRCUIT HVAC TRANSMISSION SYSTEMS
AC
DC
DC
Types of HVDC HVDC is the unique solution to interconnect asynchronous systems or grids with different frequencies. Solution: HVDC Back-to to-back Back-to-Back Station Up to 600 MW AC AC 50 Hz 60 Hz
Types of HVDC HVDC represents the most economical solution to transmit electrical energy over distances greater than approx. 600 km Solution: HVDC Long Distance Long Distance Transmission Up to 3000 MW AC AC DC line
Types of HVDC HVDC is an alternative for submarine transmission. Economical even for shorter distances such as a few 10km/miles Solution: HVDC Cable Long Submarine Transmission Up to 600 MW AC AC DC cable
HVDC BIPOLAR LINKS IN INDIA NR NER ER RIHAND-DELHI -- 2*750 MW CHANDRAPUR-PADGE 2* 750 MW SR SR TALCHER-KOLAR 2*1000 MW ER TO SR SILERU-BARASORE - 100 MW EXPERIMENTAL PROJECT ER SR
HVDC IN INDIA Bipolar HVDC LINK CONNECTING REGION CAPACITY (MW) LINE LENGTH Rihand Dadri Chandrapur - Padghe Talcher Kolar North-North 1500 815 West - West 1500 752 East South 2500 1367
ASYNCHRONOUS LINKS IN INDIA NR NER ER VINDYACHAL (N-W) 2*250 MW CHANDRAPUR (W-S) 2*500 MW SR SR VIZAG (E-S) - 2*500 MW SASARAM (E-N) - 1*500 MW
HVDC LINK HVDC IN INDIA Back-to-Back CONNECTING REGION CAPACITY (MW) Vindyachal North West 2 x 250 Chandrapur West South 2 x 500 Vizag I East South 500 Sasaram East North 500 Vizag II East South 500
BASIC PRINCIPLES OF HVDC TRANSMISSION
AC Transmission Principle
HVDC Transmission Principle
USE OF DC Direct current is put to use in common life for driving our portable devices, UPSs, battery systems and vastly in railway locomotives. DC AS A MEANS OF TRANSMISSION This has been possible with advent of High power/ high current capability thyristors & Fast acting computerised controls
Important Milestones in the Development of HVDC technology Hewitt s mercury-vapour rectifier, which appeared in 1901. Experiments with thyratrons in America and mercury arc valves in Europe before 1940. First commercial HVDC transmission, Gotland 1 in Sweden in 1954. First solid state semiconductor valves in 1970. First microcomputer based control equipment for HVDC in 1979. Highest DC transmission voltage (+/- 600 kv) in Itaipú, Brazil, 1984. First active DC filters for outstanding filtering performance in 1994. First Capacitor Commutated Converter (CCC) in Argentina-Brazil interconnection, 1998 First Voltage Source Converter for transmission in Gotland, Sweden,1999
The Evolution of Thyristor Valves in HVDC High Voltage Thyristor Valve History Highlights 1967 First Test Valve: 2 parallel 35 mm Thyristors @ 1650 V 1969 World's First Contract for an HVDC System with Thyristor Valves 2 parallel 35 mm thyristors @ 1650 V for 2000 A 1975 World's First Contract for Watercooled HVDC Thyristor Valves 2 parallel 52 mm thyristors @ 3500 V for 2000 A 1980 World's First Contract for HVDC System with 100 mm Thyristors no parallel thyristors @ 4200 V for 3600 A 1994 First HVDC Contract Using 8kV Thyristors 100 mm thyristors @ 8000 V 1997 First Thyristor Valve with Direct-Light-Triggering 100 mm thyristors with breakover protection @ 8000 V for 2000 A 2001 First complete HVDC System using Direct-Light-Triggered Thyristors with integrated breakover protection @ 8000 V
If DC is required to be used for transmission & since our primary source of power is A.C, the following are the basic steps: 1. CONVERT AC into DC (rectifier) 2. TRANSMIT DC 3. CONVERT DC into AC ( inverter)
Purpose & function of Thyristor Valve Connects AC phases to DC system Conduct High Current currents upto 3000A without the requirement of paralleling of thyristors Block High Voltage Blocks high voltage in forward and reverse direction up to 8KV Controllable thyristor triggering /conduction possible with the gate firing circuits Fault tolerant and robust
SINGLE PHASE HALF WAVE RECTIFIER
SINGLE PHASE FULL WAVE RECTIFIER
SINGLE PHASE FULL WAVE BRIDGE RECTIFIER
6-Pulse Convertor Bridge L d I d 1 3 5 L s i A E 1 L s ib V' d V d L s ic 4 6 2 Id
Voltage and Current of an Ideal Diode 6 Pulse Converter Alpha = 0 Overlap = 0
Operation of Converter Each thyristor conducts for 120º Every 60º one Thyristor from +ve limb and one Thyristor from ve limb is triggered Each thyristor will be triggered when voltage across it becomes positive Thyristor commutates the current automatically when the voltage across it becomes ve. Hence, this process is called natural commutation and the converters are called Line Commutated converters
Operation of Converter Triggering can be delayed from this point and this is called firing angle α Output voltage of the converter is controlled by controlling the α Rectifier action If α > 90º negative voltage is available across the bridge Inverter action Due to finite transformer inductance, current transfer from one thyristor valve to the other cannot take place instantly This delay is called over lap angle µ and the reactance called commutating reactance. This also causes additional drop in the voltage
Ideal No-Load Condition 1 3 C A V d B 2
Effect of Control Angle 1 3 C α u α u α u A V d B 2
RECTIFIER VOLTAGE
INVERTER VOLTAGE
DC Terminal Voltage RECTIFICATION 120 º 180 º 240 º 300 º 60 º 120 º 180 º 0 0.866 E. 2 LL E. 2 LL
DC Terminal Voltage INVERSION 0.866E. 2 LL E. 2 LL 120 º 180 º 240 º 300 º 60 º 120 º 180 º 0
DC Voltage Verses Firing Angle 1 0.8 0.6 0.4 Vd 0.2 0-0.2 alpha 0 30 60 90 120 150 180-0.4-0.6-0.8-1 Vd=Vac*1.35 *(cos alpha-uk/2)
Valve Voltage and Valve Current RECTIFICATION α =15º α+u α 0.866E. 2 u LL Q 120 B A 180 D C u 240 EG F u H S 300 R 0 u P J L K M N 60 E. 2 LL A 120 180 60 60 60
Valve Voltage and Valve Current INVERSION γ=15º u Q γ 60º 60º u u G E J D F H C 60º u L P N K M Q 0.866E. 2 LL R 120º 180 º 240 º B A S 0 60 º α R 120 º 180 º E. 2 LL
12-Pulse Convertor Bridge Y Commonly Used in HVDC systems
12-Pulse Convertor Bridge Commonly adopted in all HVDC applications Two 6 pulse bridges connected in series 30º phase shift between Star and Delta windings of the converter transformer Due to this phase shift, 5 th and 7 th harmonics are reduced and filtering higher order harmonics is easier Higher pulse number than 12 is not economical
DC VOLTAGE AT α = 15º
DC VOLTAGE AT α = 90º
DC VOLTAGE AT α = 165º
HVDC Link Voltage Profile RECTIFIER INVERTER Vdio R cos α Vdio I I dxc 2 I der I drl I dxc 2 cos γ I der DC CABLE or O/H LINE V dr =V dior cosα-i d X c +E r V di =V dioi (cosα-i d X c +E r 2 2
Control of DC Voltage Rectifier Operation Inverter Operation AC System Power Flow DC System AC System Power Flow DC System I d I d V 1 V 3 V 5 V 1 V 3 V 5 Phase A Phase A Phase B U d Phase B U d Phase C Phase C V 4 V 6 V 2 V 4 V 6 V 2 +Ud 0 -Ud 5 Rectifier Operation 30 60 90 120 150 Inverter 180 Operation 160 α
Relationship of DC Voltage Ud and Firing Angle α +Ud α Rect. Limit Rectifier Operation 0 -Ud 5 30 60 90 120 150 180 Inverter Operation 160 α Ud o α= 0 α= 30 o o α= 60 α Inv Limit Ud ωt Ud o α= 90 o α= 120 o α = 150 ωt -Ud
How does HVDC Operate?
NORMAL POWER DIRECTION
REVERSE POWER OPERATION
Schematic of HVDC
Modes of Operation Bipolar Smoothing Reactor DC OH Line Smoothing Reactor Thyristor Valves Current Thyristor Valves Converter Transformer Converter Transformer Current 400 kv AC Bus AC Filters, Reactors 400 kv AC Bus AC Filters, shunt capacitors
Modes of Operation Monopolar Ground Return Smoothing Reactor DC OH Line Smoothing Reactor Thyristor Valves Thyristor Valves Converter Transformer Current Converter Transformer 400 kv AC Bus AC Filters, Reactors 400 kv AC Bus AC Filters
Modes of Operation Monopolar Metallic Return Smoothing Reactor DC OH Line Smoothing Reactor Thyristor Valves Thyristor Valves Converter Transformer Current Converter Transformer 400 kv AC Bus AC Filters, Reactors 400 kv AC Bus AC Filters
TALCHER KOLAR SCHEMATIC TALCHER Electrode Station KOLAR +/- 500 KV DC line 1370 KM Electrode Station B lore Cudappah Hoody 400kv System Hosur Salem Madras Udumalpet Kolar 220kv system Chintamani
Sharing of Talcher Power Tamil Nadu - 636 MW A.P. Karnataka - 499 MW - 466 MW 23% 17% 3% 25% 32% Kerala - 330 MW T.N. Karnataka Pondy A.P. Kerala Pondicherry - 69 MW
KOLAR SINGLE LINE DIAGRAM
TACLHER-KOLAR ± 500 kv HVDC TRANSMISSION SYTEM Project Highlights FOR TRANSMITTING 2000 MW OF POWER FROM NTPC TALCHER STPS -II AND FOR SHARING AMOGEST SOUTHERN STATES THE 2000 MW HVDC BIPOLAR TRANSMISSION SYSTEM IS ENVISAGED AS EAST SOUTH INTERCONNECTOR II (ESICON II). THIS IS THE LARGEST TRANSMISSION SYSTEM TAKEN UP IN THE COUNTRY SO FAR THE PROJECT SCHEDULE IS QUITE CHALLENGING AGAINST THE 50 MONTHS FOR SUCH PROJECTS, THE PROJECT SCHEDULE IS ONLY 39 MONTHS SCHEDULED COMPLETION BY JUNE 2003
Project Highlights KEY DATES AWARD OF HVDC TERMINAL STATION PKG - 14TH MAR 2000 AWARD OF HVAC PACKAGE - 27TH APR 2000 APPROVED PROJECT COST - RS. 3865.61 CR THIS IS THE FIRST OF SUCH SYSTEM WHERE THE ENTIRE GENERATION IN ONE REGION IS EARMARKED TO ANOTHER REGION.
Salient Features Rectifier Talcher, Orissa Inverter Kolar, Karnataka Distance 1370 km Rated Power 2000 MW Operating Voltage ±500 kv DC Reduced Voltage ±400 kv DC Overload Long time, 40 C Half an hour Five Seconds 1.25 pu per pole 1.3 pu per pole 1.47 pu per pole
SYSTEM CAPACITIES BIPOLAR MODE OF OPERATION -- 2000 MW MONO POLAR WITH GROUND RETURN --- 1000 MW MONO POLAR WITH METALLIC RETURN MODE --- 1000 MW DEBLOCKS EACH POLE AT P min 100 MW POWER DEMAND AT DESIRED LEVEL POWER RAMP RATE -- 1 300 MW /MIN POWER REVERSAL IN OFF MODE
SYSTEM CAPACITIES OVER LOAD CAPACBILITIES RATED POWER -- 2000 MW LONG TIME OVER LOAD POWER 8/10 HOURS -- 2500 MW SHORT TIME OVER LOAD 5 SEC- 3210 MW
HARMONIC FILTERS AT TALCHER TOTAL FILTERS 14 DT 12/24 FILTERS EACH 120 MVAR - 7 NOS DT 3/36 FILTERS EACH 97 MVAR - 4 NOS SHUNT REACTORS 138 MVAR- 2 NOS SHUNT CAPCITORS 138 MVAR- 1 NOS DC FILTERS DT 12/24 & DT 12/36 1 No per pole. AT KOLAR TOTAL FILTERS 17 DT 12/24 FILTERS EACH 120 MVAR - 8 NOS DT 3/36 FILTERS EACH 97 MVAR - 4 NOS SHUNT CAPCITORS 138 MVAR- 5 NOS DC FILTERS DT 12/24 & DT 12/36 1 each pole
SYSTEM CAPACITIES MONOPOLAR GROUND RETURN - 1000 MW POWER CAN BE TRANSMITTED THROUGH THIS MODE WHERE THE RETURN PATH IS THROUGH THE GROUND WHICH IS FACILITATED THROUGH A EARTH ELECTRODE STATION SITUATED AT ABOUT 35 KMS FROM THE TERMINALS AND CONNECTED BY A DOUBLE CIRCUIT TRANSMISSION LINE. MONOPOLAR METALLIC RETURN - 1000 MW POWER CAN BE TRANSMITTED THROUGH THIS MODE WHERE THE RETURN PATH IS THE TRANSMISSION LINES OF OTHER POLE. BALANCED BIPOLAR MODE 2000 MW CAN BE TRANSMITTED THROUGH THIS MODE WHERE WITH ONE +VE AND OTHER VE.
TALCHER-KOLAR HVDC & EHVAC SYSTEM