Basics of hvdc

1. V G RAO
HVDC / KOLAR

2. 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.
REASONS FOR AC GENERATION AND TRANSMISSION

3. – 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
COMPARISION OF HVAC & HVDC SYSTEMS

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
USE OF AC
• HVDC and HVAC
SHOULD CO-
OPERATE FOR
OPTIMUM
EFFICIENCY

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
Terminal Cost AC
Terminal Cost DC
Line Cost DC
Line Cost AC
Break Even Distance

19. HVDC BIPOLAR TRANSMISSION SYSTEM
2 DOUBLE CIRCUIT HVAC TRANSMISSION SYSTEMS
2000 MW HVDC VIS- A- VIS – HVAC 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-Back
Up to600MW
Back-to-Back Station
AC AC
50 Hz 60 Hz

24. Types of HVDC
HVDC representsthe most economical solution to
transmit electrical energy over distances greater
than approx. 600 km
Solution: HVDC Long Distance
Up to3000MW
Long Distance Transmission
AC AC
DCline

25. Types of HVDC
HVDC is an alternative for submarine transmission.
Economical evenfor shorter distances such as a few
10km/miles
Solution: HVDC Cable
Up to600MW
Long Submarine Transmission
AC AC
DCcable

26. HVDC BIPOLAR LINKS IN INDIA
NER
ER
SR
NR
NER
ER
SR
NR
RIHAND-DELHI -- 2*750 MW
CHANDRAPUR-PADGE – 2* 750 MW
TALCHER-KOLAR – 2*1000 MW
ER TO SR
SILERU-BARASORE - 100 MW
EXPERIMENTAL PROJECT
ER –SR

27. HVDC IN INDIA
Bipolar
HVDC LINK CONNECTING
REGION
CAPACITY
(MW)
LINE
LENGTH
Rihand –
Dadri
North-North 1500 815
Chandrapur -
Padghe
West - West 1500 752
Talcher –
Kolar
East – South 2500 1367

28. ASYNCHRONOUS LINKS IN INDIA
NER
ER
SR
NR
NER
ER
SR
NR
VINDYACHAL (N-W) – 2*250 MW
CHANDRAPUR (W-S)– 2*500 MW
VIZAG (E-S) - 2*500 MW
SASARAM (E-N) - 1*500 MW

29. HVDC IN INDIA
Back-to-Back
HVDC LINK 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

31. BASIC PRINCIPLES
OF
HVDC TRANSMISSION

32. AC Transmission Principle

33. HVDC Transmission Principle

34. Direct current is put to use in common life for driving our
portable devices, UPSs, battery systems and vastly in
railway locomotives.
USE OF DC
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 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

36. 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
The Evolution of Thyristor Valves in HVDC

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
3
6
CiLs
4
E1 Ls
Ls
Bi
iA
1
2
I
V'd
5
Vd
IddL
d

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. • 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
Operation of Converter

46. Ideal No-Load Condition
B
2
A
1
C
3
Vd

47. Effect of Control Angle
B
A
2
C
1

u u
Vd
u
3
 

48. RECTIFIER VOLTAGE

49. INVERTER VOLTAGE

50. DC Terminal Voltage
120 º
RECTIFICATION
0
240 º180 º 300 º 120 º60 º 180 º
0.866E . 2LL
E . 2LL

51. DC Terminal Voltage
120 º
INVERSION
0
240 º180 º 300 º 120 º60 º 180 º
0.866E . 2LL
E . 2LL

52. DC Voltage Verses Firing Angle
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
0 30 60 90 120 150 180
Vd
alpha
Vd=Vac*1.35*(cosalpha-uk/2)

53. Valve Voltage and Valve
Current
120 180
A
u
0.866
240120
u
60
FC
D
B E
180
A
u
60 60
K
G J L
H
N
M
300
0
P
u
S
E . 2LL
60R
Q
RECTIFICATION
 =15º
+u  E . 2LL

54. Valve Voltage and Valve
Current
M Q
120 º 180 º
R
N
P
u
240 º120º
R
Q
180 º
u
0
B
F
SA
C
E
D
H
60 º
J
K
G L
INVERSION
=15º
60º60º
u u
60º
0.866E . 2LL
E . 2LL




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

56. • 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, 5th and 7th harmonics
are reduced and filtering higher order
harmonics is easier
• Higher pulse number than 12 is not
economical
12-Pulse Convertor Bridge

57. DC VOLTAGE AT α = 15º

58. DC VOLTAGE AT α = 90º

59. DC VOLTAGE AT α = 165º

60. HVDC Link Voltage Profile
I R
DC CABLE or O/H LINE
I Ed r
d
RECTIFIER
dio R
V
I X
2
d c
cos
rI Ed
L I X
2
d c
cos
Vdio I
INVERTER


VdR=VdioR cos-Id Xc+Er VdI=VdioI(cos-Id Xc+Er
2 2

61. Control of DC Voltage
V 1 V 3 V 5
V 2V 6V 4
Phase A
Ud
Phase B
Phase C
Id
Power FlowAC System DC System
V 1 V 3 V 5
V 2V 6V 4
Phase A
Ud
Phase B
Phase C
Id
AC System DC SystemPower Flow
30 60 90 120 150 180
0
+Ud
-Ud
160
5
Rectifier
Operation
Inverter
Operation

Rectifier Operation Inverter Operation

62. Relationship of DC Voltage Ud and Firing
Angle α
30 60 90 120 150 180
0

+Ud
-Ud
160
Limit Inv
5
Limit Rect.
Rectifier
Operation
Inverter
Operation
tw
o
60=
Ud
o
30=o
0=
o
90= o
120= o
150=
-Ud
tw
Ud
Ud

63. How does HVDC
Operate?

65. NORMAL POWER DIRECTION

66. REVERSE POWER OPERATION

67. Schematic of HVDC

68. Modes of Operation
DC OH Line
Converter
Transformer
Thyristor
Valves
400 kV
AC Bus
AC Filters,
Reactors
Smoothing Reactor
Converter
Transformer
Thyristor
Valves
400 kV
AC Bus
AC Filters, shunt
capacitors
Smoothing Reactor
Bipolar
Current
Current

69. Modes of Operation
DC OH Line
Converter
Transformer
Thyristor
Valves
400 kV
AC Bus
AC Filters,
Reactors
Smoothing Reactor
Converter
Transformer
Thyristor
Valves
400 kV
AC Bus
AC Filters
Smoothing Reactor
Monopolar Ground Return
Current

70. Modes of Operation
DC OH Line
Converter
Transformer
Thyristor
Valves
400 kV
AC Bus
AC Filters,
Reactors
Smoothing Reactor
Converter
Transformer
Thyristor
Valves
400 kV
AC Bus
AC Filters
Smoothing Reactor
Monopolar Metallic Return
Current

71. Kolar
Chintamani
Cudappah
Hoody
Hosur
Salem
Udumalpet
Madras
B’lore
+/- 500 KV DC line
1370 KM
Electrode
Station
Electrode
Station
TALCHER
400kv System
220kv system
KOLAR
TALCHER KOLAR
SCHEMATIC

72. Sharing of Talcher Power
• Tamil Nadu - 636 MW
•
• A.P. - 499 MW
•
• Karnataka - 466 MW
• Kerala - 330 MW
• Pondicherry - 69 MW
32%
23%
17% 3%
25%
T.N. A.P.
Karnataka Kerala
Pondy

73. KOLAR SINGLE LINE DIAGRAM

74. • 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
TACLHER-KOLAR ± 500 kV HVDC TRANSMISSION SYTEM

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. 3865.61 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 1.25 pu per pole
• Half an hour 1.3 pu per pole
• Five Seconds 1.47 pu per pole

77. 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

78. 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

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. – 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 .
SYSTEM CAPACITIES

81. TALCHER-KOLAR HVDC & EHVAC SYSTEM