Due to ease of transformation of voltage levels (simple transformer action) and rugged squirrel cage motors, ALTERNATING CURRENT is universally

Transcription

1 V G RAO HVDC / KOLAR

2 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 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.

3 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

4 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

5 Better Voltage utilisation rating

6 DC has Greater Reach Distance as well as amount of POWER determine the choice of DC over AC

7 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.

8 DIRECT CURRENT CONSERVES FOREST AND SAVES LAND Fewer support TOWER, less losses

9 CONTROLLING or BEING CONTROLLED By raising the level in tank ;controlled water flow

10 CONTROLLING or BEING CONTROLLED ZERO IF Vr=VI=10V

11 HVDC leads to Better Use of AC TRANS SYS. FORCE HAS TO BE APPLIED IN RIGHT POSITION

12 HVDC provides increase power but does not increase the short circuit POWER

13 HVDC LEADS TO BETTER HVDC and HVAC SHOULD CO- OPERATE FOR OPTIMUM EFFICIENCY USE OF AC

14 HVDC LEADS TO BETTER USE OF AC If two networks are connected by an AC link, it can be in-efficient

15 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

16 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.

17 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

18 COST: AC vs DC Transmission Line Cost AC Line Cost DC Terminal Cost DC Terminal Cost AC Break Even Distance

19 2000 MW HVDC VIS- A- VIS HVAC SYSTEMS HVDC BIPOLAR TRANSMISSION SYSTEM 2 DOUBLE CIRCUIT HVAC TRANSMISSION SYSTEMS

20 AC

21 DC

22 DC

23 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

24 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

25 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

26 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 MW EXPERIMENTAL PROJECT ER SR

27 HVDC IN INDIA Bipolar HVDC LINK CONNECTING REGION CAPACITY (MW) LINE LENGTH Rihand Dadri Chandrapur - Padghe Talcher Kolar North-North West - West East South

28 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

29 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

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31 BASIC PRINCIPLES OF HVDC TRANSMISSION

32 AC Transmission Principle

33 HVDC Transmission Principle

34 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

35 Important Milestones in the Development of HVDC technology Hewitt s mercury-vapour rectifier, which appeared in Experiments with thyratrons in America and mercury arc valves in Europe before First commercial HVDC transmission, Gotland 1 in Sweden in First solid state semiconductor valves in First microcomputer based control equipment for HVDC in Highest DC transmission voltage (+/- 600 kv) in Itaipú, Brazil, First active DC filters for outstanding filtering performance in First Capacitor Commutated Converter (CCC) in Argentina-Brazil interconnection, 1998 First Voltage Source Converter for transmission in Gotland, Sweden,1999

36 The Evolution of Thyristor Valves in HVDC High Voltage Thyristor Valve History Highlights 1967 First Test Valve: 2 parallel 35 mm 1650 V 1969 World's First Contract for an HVDC System with Thyristor Valves 2 parallel 35 mm 1650 V for 2000 A 1975 World's First Contract for Watercooled HVDC Thyristor Valves 2 parallel 52 mm 3500 V for 2000 A 1980 World's First Contract for HVDC System with 100 mm Thyristors no parallel 4200 V for 3600 A 1994 First HVDC Contract Using 8kV Thyristors 100 mm 8000 V 1997 First Thyristor Valve with Direct-Light-Triggering 100 mm thyristors with breakover 8000 V for 2000 A 2001 First complete HVDC System using Direct-Light-Triggered Thyristors with integrated breakover 8000 V

37 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)

38 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

39 SINGLE PHASE HALF WAVE RECTIFIER

40 SINGLE PHASE FULL WAVE RECTIFIER

41 SINGLE PHASE FULL WAVE BRIDGE RECTIFIER

42 6-Pulse Convertor Bridge L d I d L s i A E 1 L s ib V' d V d L s ic Id

43 Voltage and Current of an Ideal Diode 6 Pulse Converter Alpha = 0 Overlap = 0

44 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

45 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

46 Ideal No-Load Condition 1 3 C A V d B 2

47 Effect of Control Angle 1 3 C α u α u α u A V d B 2

48 RECTIFIER VOLTAGE

49 INVERTER VOLTAGE

50 DC Terminal Voltage RECTIFICATION 120 º 180 º 240 º 300 º 60 º 120 º 180 º E. 2 LL E. 2 LL

51 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

52 DC Voltage Verses Firing Angle Vd alpha Vd=Vac*1.35 *(cos alpha-uk/2)

53 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

54 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

55 12-Pulse Convertor Bridge Y Commonly Used in HVDC systems

56 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

57 DC VOLTAGE AT α = 15º

58 DC VOLTAGE AT α = 90º

59 DC VOLTAGE AT α = 165º

60 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

61 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 Inverter 180 Operation 160 α

62 Relationship of DC Voltage Ud and Firing Angle α +Ud α Rect. Limit Rectifier Operation 0 -Ud 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

63 How does HVDC Operate?

64

65 NORMAL POWER DIRECTION

66 REVERSE POWER OPERATION

67 Schematic of HVDC

68 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

69 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

70 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

71 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

72 Sharing of Talcher Power Tamil Nadu MW A.P. Karnataka MW MW 23% 17% 3% 25% 32% Kerala MW T.N. Karnataka Pondy A.P. Kerala Pondicherry - 69 MW

73 KOLAR SINGLE LINE DIAGRAM

74 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

75 Project Highlights KEY DATES AWARD OF HVDC TERMINAL STATION PKG - 14TH MAR 2000 AWARD OF HVAC PACKAGE - 27TH APR 2000 APPROVED PROJECT COST - RS CR THIS IS THE FIRST OF SUCH SYSTEM WHERE THE ENTIRE GENERATION IN ONE REGION IS EARMARKED TO ANOTHER REGION.

76 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

77 SYSTEM CAPACITIES BIPOLAR MODE OF OPERATION MW MONO POLAR WITH GROUND RETURN MW MONO POLAR WITH METALLIC RETURN MODE MW DEBLOCKS EACH POLE AT P min 100 MW POWER DEMAND AT DESIRED LEVEL POWER RAMP RATE MW /MIN POWER REVERSAL IN OFF MODE

78 SYSTEM CAPACITIES OVER LOAD CAPACBILITIES RATED POWER MW LONG TIME OVER LOAD POWER 8/10 HOURS MW SHORT TIME OVER LOAD 5 SEC MW

79 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

80 SYSTEM CAPACITIES MONOPOLAR GROUND RETURN 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 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.

81 TALCHER-KOLAR HVDC & EHVAC SYSTEM

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