Transcript Document

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
USE OF AC
• HVDC and HVAC
SHOULD COOPERATE FOR
OPTIMUM
EFFICIENCY
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-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
NR
NER
NER
ER
ER
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
SR
SR
HVDC IN INDIA
Bipolar
HVDC LINK
CONNECTING CAPACITY
LINE
REGION
(MW)
LENGTH
Rihand –
Dadri
North-North
1500
815
Chandrapur Padghe
West - West
1500
752
Talcher –
Kolar
East – South
2500
1367
ASYNCHRONOUS LINKS IN INDIA
NR
NR
NER
NER
ER
ER
VINDYACHAL (N-W) – 2*250 MW
CHANDRAPUR (W-S)– 2*500 MW
VIZAG (E-S)
- 2*500 MW
SASARAM (E-N)
- 1*500 MW
SR
SR
HVDC IN INDIA
Back-to-Back
HVDC LINK CONNECTING CAPACITY
REGION
(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
Ld
1
E1
Ls
iA
Ls
iB
3
5
V'd
Ls
Vd
iC
4
6
Id
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
Vd
B
2
Effect of Control Angle
1

u
3

u

u
C
A
Vd
B
2
RECTIFIER VOLTAGE
INVERTER VOLTAGE
DC Terminal Voltage
RECTIFICATION
120 º 180 º 240 º 300 º
0
60 º 120 º 180 º
0.866 E . 2
LL
E . 2
LL
DC Terminal Voltage
INVERSION
0.866 E . 2
LL
120 º 180 º 240 º 300 º
0
60 º 120 º 180 º
E . 2
LL
DC Voltage Verses Firing Angle
1
Vd
0.8
0.6
0.4
0.2
alpha
0
-0.2 0
30
60
90
120
-0.4
-0.6
-0.8
-1
Vd=Vac*1.35 *(cos alpha-uk/2)
150
180
Valve Voltage and Valve Current
RECTIFICATION
 =15º
+u

u
Q
A
120 180
S
240
300
u
u
B
R
0
P
u
EG J L N
D
H
M
K
C F
60
60
60
60
E . 2
LL
A
120 180
0.866 E . 2
LL
Valve Voltage and Valve Current
INVERSION
 =15º
60º
60º
60º
u
u
u
L
G
u
Q
E

D
J
P
N
F H K
M
Q
0.866 E . 2
LL
C
AS
R
120º 180 º 240 º
B
0
R
60 º 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, 5th and 7th 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 
Vdio I
cos 
Id Xc
2
Id E r
Id R L
Id X c
2
IdEr
DC CABLE or O/H LINE
VdR=VdioR cos-Id Xc+Er
2
VdI=VdioI(cos-Id Xc+Er
2
Control of DC Voltage
Rectifier Operation
AC System
Power Flow
Inverter Operation
DC System
AC System
DC System
Power Flow
Id
V1
V3
Id
V5
V1
Phase A
V3
V5
Phase A
Phase B
Phase B
Ud
Phase C
Ud
Phase C
V4
V6
V2
V4
V6
V2
+Ud
Rectifier
Operation
160

0
5
-Ud
30
60
90
120
150
Inverter
Operation
180
Relationship of DC Voltage Ud and Firing
Angle α
 Rect. Limit
+Ud
Rectifier
Operation
160

0
5
30
60
90
120
150
180
Inverter
Operation
-Ud
Ud
 = 0o
 = 30o
 = 60o
 Inv
Limit
Ud
wt
 = 90o
Ud
 = 120o
 = 150o
wt
-Ud
How does HVDC
Operate?
NORMAL POWER DIRECTION
REVERSE POWER OPERATION
Schematic of HVDC
Modes of Operation
Bipolar
Smoothing Reactor
Thyristor
Valves
DC OH Line
Smoothing Reactor
Thyristor
Valves
Current
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
Thyristor
Valves
Thyristor
Valves
Converter
Transformer
400 kV
AC Bus
AC Filters,
Reactors
Smoothing Reactor
Current
Converter
Transformer
400 kV
AC Bus
AC Filters
Modes of Operation
Monopolar Metallic Return
Smoothing Reactor
DC OH Line
Thyristor
Valves
Thyristor
Valves
Converter
Transformer
400 kV
AC Bus
AC Filters,
Reactors
Smoothing Reactor
Current
Converter
Transformer
400 kV
AC Bus
AC Filters
TALCHER KOLAR
SCHEMATIC
TALCHER
Electrode
Station
Electrode
Station
KOLAR
+/- 500 KV DC line
1370 KM
400kv System
B’lore
Hoody
Cudappah
220kv system
Hosur
Salem
Udumalpet
Kolar
Madras
Chintamani
Sharing of Talcher Power
• Tamil Nadu - 636 MW
•
• A.P.
- 499 MW
•
• Karnataka - 466 MW
• Kerala
- 330 MW
• Pondicherry - 69 MW
3%
17%
32%
23%
25%
T.N.
Karnataka
Pondy
A.P.
Kerala
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