HVDC System Operation &
Maintenance
V.Diwakar
Dy.Manager
HVDC Kolar
Existing HVDC in INDIA
BIPOLE SYSTEMS:
RIHAND- DADRI (DELHI) 1500 MW
BIPOLE (1991)
TALCHER - KOLAR 2500 MW BIPOLE
(2001)
BALIA - BHIWADI 2500 MW BIPOLE
(2010 )
NER –AGRA 6000MW AT +/- 800KV DC
( Proposed)
BACK-TO-BACK SYSTEMS:
VINDHYACHAL 2 X 250 MW BACK TO
BACK(1989)
CHANDRAPUR 2 X 500 MW BACK TO
BACK(1997)
VIZAG 2 X 500 MW BACK TO
BACK(1999)
SASARAM 1 X 500 MW BACK TO
BACK(2002)
Advantages of HVDC

Why HVDC rather than HVAC?
Long distances make HVDC cheaper
 Improved link stability
 Fault isolation
 Asynchronous link
 Cable Transmission
 Low Right of Way (RoW)

Cost comparison of ac and dc transmission
Cost of AC Line
Cost
Break even distance
Cost of DC Line
Cost of DC terminal
Cost of AC terminal
 500 – 700 km
Distance in km
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
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
Basic Configuration - HVDC
DC
AC SYSTEM A
TERMINAL A
Ld
TRANSMISSION
LINE
P d = V d Id
Id
TERMINAL B
Ld
Vd
FILTER
FILTER
AC SYSTEM B
12-Pulse Convertor Bridge
Y

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
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
HVDC Control
Id
U1
AC System A
Simplified HVDC System diagram
U2
AC System B
HVDC Control
Id
U1
AC System A
U2
AC System B
HVDC Control
Id
Features
=
=
U1
U2
Power Direction
U1
U2
Change of Power Direction
•Id in One direction
•Magnitude of power is
controlled by controlling
the voltage difference on
the link
•Power direction is
reversed by reversing the
voltage
HVDC EQUIPMENTS
What are the Special
Components of HVDC?
MAIN COMPONENTS OF HVDC
Converter Transformer
2. Valve Hall
3. AC Harmonic Filters
4. Shunt Capacitors
5. DC Harmonic Filters
6. Smoothing Reactors
7. DC Current / Voltage measuring devices
8. Valve Cooling / Ventilation System
1.
Basic Components of HVDC Terminal
Converter Xmers
AC Harmonic
400 kV
filters
DC Line
Smoothing Reactor
DC
Filter
Electrode
station
AC Shunt
Capacitors
Valve Hall
-Thyristors
Valve Cooling
/ Ventilation
system
-Control & Protection
-Telecommunication
CONVERTER TRANSFORMER
400KV SIDE
BUSHING
STAR
BUSHINGS
DELTA
BUSHING
CONVERTER TRANSFORMERS
 Three Singe Phase Transformers for each Pole
 Each Transformer is of Three Windings
 Winding -1 connected to 400KV side in Star
 Winding -2 connected to one six pulse bridge in Star
 Winding -3 connected to second six pulse bridge in Delta
 Easy transportation
FEATURES OF CONVERTER
TRANSFORMERS
 Automatic onload tap changer control with
appropriate make and break capacity
 Extra insulation due to DC currents
 Proper conductors and magnetic shunts to take care
of the extra losses due to harmonic currents
 Very rugged and reliable OLTC as tap-changing is a
integral means of conversion process and control.
Converter Transformer Ratings
•Type of converter transformer
: Single phase three windings
•Rated power of line / star / delta winding (MVA) :
•Rated current of line / star / delta winding (A):
•Rated
Voltage
of
400/√3/210.3/√3/210.3
Line/star/delta
397/198.5/198.5
1719/1635/944
winding
(No-load):
•Tap changer (voltage range)
•Tap changer steps
: -5 % to +20 %
: 16 to -4 (21 steps)
•Tap changer current capacity
: 2X2000A
•Cooling arrangement
: ODAF
Converter Transformer Ratings
 No load losses – 192KW
 Load losses -
760KW @75°C
 Oil type – Napthanic, Shell Diala
 Bushings





Line side – oil filled
Valve side – Y – SF6 filled
Valve side – D – RIP condenser
Total weight – 461 Ton
Oil weight – 118.7 Ton
Converter Transformer Connection
Valve Hall
1-ph 3 winding
Converter
Transformer
D
Y
R
D
Y
Y
D
Y
B
Outdoor
Converter Transformer Cooling control
 Automatic daily changeover of cooling pumps and fans
 5 groups of fans and pumps
Each group – One oil circulating pump & 3 cooling fans
4 groups will be in service with 2 fans each
One redundant group – changeovers every day
Extra fans will switch ON when winding temperature > 75ºC
Redundant group will switch ON when winding temperature >85ºC
WTI Alarm - 115ºC
WTI Trip - 130ºC
OTI Alarm - 85ºC
OTI Trip - 95ºC









Converter
Transformer
internal connection
HVDC VALVE HALL LAYOUT
MULTIPLE VALVE UNIT
Grd
Quadruplevalve
Valve
Arrester
AC
Multiple
Valve
Unit
D
Y
Y
AC
DC
Circuit Diagram of the Converters for Pole 1
Valve Tower side view
1. AC Terminal
2. DC Terminal
3. Cooling Water Inlet
4. Cooling Water Outlet
5. Fiber Optic Cables Tubes
6. Thyristor Module
7. Insulator
8. Arrester
9. Screen
• Max. length of fibre optic cables in quadruple valve Lmax =
17.5m
• Weight of quadruple valve without arresters: approx. 19300
kg
• All dimensions in mm
Valve Structure
Valve Section / tier
Single Valve
Quadra Valve
Hierarchy of
valve structure
Each Thyristor level consists
•Thyristor
•Snubber circuit – to prevent high
dv/dt
•Snubber Capacitor
•Snubber Resistor
•Valve Reactor – to prevent high
di/dt
•Grading Resistor – to equilize the
potential across all the levels in a
valve – static equalizing
•Grading capacitor – dynamic
equalizing
Components in one valve
Component
Thyristor
Snubber Capacitor
Snubber Resistor
Valve Reactor
Grading Capacitor
Grading Resistor
Valve arrester
TE card
Population
at Talcher
Population
at Kolar
84
84
84
24
6
84
1
84
78
78
78
24
6
78
1
78
Components in one Pole
Component
Thyristor
Snubber Capacitor
Snubber Resistor
Valve Reactor
Grading Capacitor
Grading Resistor
Valve arrester
TE card
Population Population
at Talcher at Kolar
1008
936
1008
1008
288
72
1008
144
1008
936
936
288
72
936
144
936
Thyristor Module
GRADING CAPACITOR
SNUBBER CAPACITOR
SNUBBER RESISTOR
COOLING PIPE-PEX
THYRISTOR
TE CARD
FIBRE OPTICS
Thyristor Modular Unit top view
Block Diagram of Thyristor Electronic
1 Light Receiver
2 Light Transmitter
3 Thyristor Voltage Detection
4 Logic
5 Gate Pusle Amplifier
6 Back Up Trigger Circuit
(BTC)
7 Energy Supply
Thyristor T1501 N75 T - S34 (1)
Features:
• High-power thyristor for phase control
• Ceramic insulation
• Contacts copper, nickel plated
• Anode, Cathode and gate pressure
contacted
• Inter digitised amplifying gate
Applications:
• HVDC-Transmissions
• Synchro- drivers
• Reactive-power compensation
• Controlled Rectifiers
Internal Structure of Thyristor
Valve Reactor - Dimensional Drawing
Valve Reactor - Electrical and Mechanical
Ratings
• Voltage-time area
 = 80mVs ±10%
• Saturated part of main inductance
LH = 0.55 mH ±10%
• Reactor current
ID max = 1270 A
Current and Voltage Characteristic of the Valve Reactor
Grading Capacitor - Dimensional Drawing
Grading Capacitor - Electrical and
Mechanical Ratings
• Capacity
C = 2.4 µF ±3%
• Nominal voltage
UN = 58 kV
• Periodical max. voltage
Umax = 88 kV
• Short time max. impulse voltage
Us = 8700 V
• Nominal effective current
IN = 1 A
• Periodical max. current
Imax = 100 A
• Operating frequency
f = 50/60 Hz
• Cooling type
self-cooling
• Weight
approx. 25 kg
• Impregnation
SF6 gas
Snubber Circuit Resistor
Resistance R
45 
Tolerance
± 3%
Cooling
Water
Snubber Circuit Capacitor
X
View X
Capacitance
1.6 µFd
Tolerance
+/-5%
Insulation
SF6
DC Smoothing Reactors
Smoothing Reactor - Purpose
 Connected in series in each converter with each




pole
Decreases harmonic voltages and currents in the
DC line
Smooth the ripple in the DC current and prevents
the current from becoming discontinuous at light
loads
Limits crest current (di/dt) in the rectifier due to a
short circuit on DC line
Limits current in the bypass valve firing due to the
discharge of the shunt capacitances of the dc line
DC Smoothing Reactor ratings
•Two Smoothing Reactors per pole
•Inductance - 125mH
•Nominal DC Voltage – 500KV
•Max DC Voltage – 515KV
•BIL – 950/1425KV
DC Smoothing Reactor ratings
•Continuous current - 2000A
•Continuous Over load current - 2200A
•Type – Air Cored Dry type
•Forced Air Cooled reactors for 2500A
•Location : Outdoor
•Total mass – 30 Ton
•Temperature Class - F
HARMONIC FILTERS
 Conversion process generates – Harmonics
 AC side Harmonics- Current harmonics
 Generated harmonics – (12n ± 1) harmonics
 n = 1,2,3….
 Predominant harmonics – 11,13,23,25,35,37
 Additionally 3rd harmonics
 DC side Harmonics- Voltage harmonics
 Generated harmonics – (12n) harmonics
 n = 1,2,3….
 Predominant harmonics – 12,24,36
Disadvantages of Harmonics
 Over heating and extra losses in generators
 Over heating and extra losses in motors
 Instability in the converter control
 Interference with telecommunication systems
 Over voltages due to resonance
AC Filters - Kolar
ITEM
A
B
C
Filter sub bank
DT 12/24
DT 3/36
Shunt C
97
138
1.85
2.744
Rating (3 ph., 400 kV)
MVAr 120
No.of 3 phase Banks
-
HV-Capacitor C1
μF
HV-Reactor L1
mH
HV-Resistor R1
ohms
LV-Capacitor C2
μF
LV-Reactor L2
mH
LV-Resistor R2
ohms
6
2.374
16.208
420
4.503
7.751
-
3
5.444
300
3.759
204.2
1500
5
1.602
-
12/24 Double Tuned Filter – 120 MVAr
C1=2.374µF
L1=16.208mH
R1=420Ω
C2=4.503 µF
L2=7.751mH
11
23
25
13
Impedance Graph
12/24 Double Tuned Filter – Sectional view
Capacitor Stack
CT
Resistor
Reactor
Reactor
3/36 Double Tuned Filter – 97 MVAr
C1=1.85µF
L1=15.444 mH
R1=300Ω
C=23.759µF
R2=1500 Ω
L2=204.2mH
35
3
37
Impedance Graph
3/36 Double Tuned Filter – Sectional view
Capacitor stack
CT
Resistor
Reactor
Reactor
C=23.759µF
Shunt Capacitor – 138 MVAr
•No harmonic filtering
C1=2.744 µF
L1=1.602 mH
•Supplies MVAr to the grid
•Switched into the circuit for
voltage control purpose
•Capacity – 138 MVAr
Shunt Capacitors-Voltage Improvement
DC Filter 12/24 TYPE
C1=1800 nF
R1=400 Ω
L1=14.71 mH
C1=5700 nF
L2=8.19 mH
DC Filter 12/36 TYPE
C1=1800 nF
L1=7.21 mH
R1=400 Ω
C1=3300 nF
L2=12.68mH
DC MEASURING DEVICES
 Measurement on DC side for control, monitoring and
Protection
 AC CTs cannot be used on DC side – saturation
 DC current measuring devices – OPTODYNE




DC shunt – low value resistor
mV drop from the shunt will be taken for determining the current
To solve insulation problems – electrical signals are converted to
optical at the shunt and at control system converted to electrical
Supply for the conversion process is obtained from the control panels
in the form of optical power
 DC voltage divider
 Capacitive & resistor divider circuit
 Drop across the resistor scaled for determining the voltage
 Optical conversion process is same as the current measuring device
DC Current Measuring Device (OPTODYN) Lay out at HVDC Kolar
6
UdL
6
IdH
4
IdL
Line 1
Pole1
4
UdN
2
IdN
4
IdE
IdN
IdE
2
4
8
Idee1
Idee2
UdN
4
Idee3
8
8
Current Measuring Devices
11Nos
(4 HV+7 LV)
Voltage Dividers
04 Nos
( 2 HV+2 LV)
Pole2
IdH
6
Electrode
lines
Line 2
IdL
UdL
6
4
Example for the Use of the Hybrid Optical Sensor
Iron Core Inductive CT
Shunt
Rogowski Air Core CT
HV/EHV-Line
TM
OPTODYN
Ground Level
Capacitive
Resistance Inductive Voltage
Voltage Divider Voltage Divider
Transformer
Functional Concept
Shunt
Analog/ Digital
Digital/ Optical
Id
Electrical Energy
Optical
Signal fibre
Power fibre
Optical Energy
Digital
Digital control/
protection system
SIMADYN D
Optical Energy
Electrical Energy
Sensor Head at high voltage level
Fibre optical cable
Power supply
Control/ Protection system at ground level
Redundancy Concept
• complete redundancy from sensor head via FO cable to control/ protection
equipment
• only one Analog/ Digital conversion per signal path
• direct digital signal processing
Shunt
Sensor Head
Pole control System 1
Sensor Head
Pole control System 2
Sensor Head
Protection System 1
Sensor Head
Protection System 2
Id
common composite insulator
and fibre optic cable
high v oltage lev el; sw itchyard
ground lev el; control building
Comparision to
Conventional Solution
Comparison between Hybrid-Optical a
Conventional DC Measuring System
The weight of the new measuring
device is
reduced from 4,000 kg to 100 kg
No additional Post Insulators
No electromagnetic interference
(EMI)
due to fibre optic links
Full redundancy up to the measuring
location
Excellent dynamic performance
a
s
Picture 2
Hybrid-Optical Measuring
Device
Measuring Shunt
Sensor Head Box
Composite Insulator
incl. Fiber Optics
Connection Box
Sensor Head Box with Sensors
Assembly of Shunt
OPTODYN Sensor
Analoge Input
Signal from Shunt
Optical Data
Link
Optical Power
Supply Link
Summary
 Measures DC current quantities up to the range of 18,000 A
 High voltage insulation level up to 500 kV rated DC voltage
 Current measuring by a high precision shunt
 Light construction
 High insulation capability also under extreme environmental conditions
 Less pollution due to less electrostatic potential of silicon surface
 Hydrophobic silicon material reduces risk of leakage currents
 No electromagnetic interference by use of fibre optic cables
DC Voltage Measurement
DC Voltage Measurement
KOLAR SINGLE LINE DIAGRAM
THANK YOU
System Description

The Valve Cooling System is a single closed loop
deionised water system. Heat transfer to the ambient is
provided by dry coolers. The Valve Cooling System is for
one pole and works independent of other cooling and air
conditioning systems.

Spray water will be used if the water temperature
rises above controller set point value.
Design Basis
Kolar Station
Talcher Station
Maximum Dry Bulb One Hour Average
450C
450C
Minimum Dry Bulb One Hour Average
20C
00C
Total Cooling Capacity
4340kW
4053kW
Water flow
4140l/min
4350l/min
Water Inlet Temperature MAX
500C
500C
Water Outlet Temperature Average
620C
620C
Water Conductivity
<0.5μS/cm
<0.5μS/cm
Redundant Circulating Pumps
One of two
One of two
Spray Water Storage for
24hrs
24hrs
Flow Diagram
09
12
10
08
03
02
11
01
04
05
07
06
VALVE COOLING MAIN PUMP
•
•
•
•
•
Two centrifugal
circulating pumps
One pump - operating
Other pump - standby
Periodical automatic
pump changeover.
Changeover to the stand
by pump takes place in
case of failure of the
operating pump
Capacity of
– Motor – 45KW
– Pump – 265Cu.m/Hr
94
Valve Hall Ventilation system Flow Diagram
AIR INLET 5m ABOVE GROUND LEVEL
VALVE TIMING PT
•It is inductive voltage
transformer
•Oil filled – Oil type Shell
Diala D
•Make – Trench.
•Primary/secondary
voltage ratio – 400√3/110
√3
VALVE TIMING PT
•Inductive Voltage Transformer - Connected to converter
transformer 400 KV side
•Pole control gets the zero crossings of the Voltage on line side
and uses this as the reference for generating firing signals for the
valves
•This PT is used only for firing signal generation – not used for
any protection task
ELECTRODE STATION
 Converter requires reference ground for insulation coordination,
control & protection
 DC currents cause corrosion in metallic structures, hence generally
the grounding is done at a safe distance away from HVDC stations
(30 to 35 Km)
 Reliability of HVDC System


When one line is faulty then by using earth as return path 50% of rated Bipole
power can be transmitted.
When one pole trips other pole continues in ground return with over load capacity
of that pole thus providing transient stabilty / sudden loss of power
 Eliminates the requirement of a separate line as return path

During balance bipolar operation no current flows through the ground however it
provides a return path
 Located at Sidalagatta about 32 km from Kolar Station.
 Similar station exits at Talcher.
Electrode station - Layout
EARTH ELECTRODE
Conductor type ACSR “Bersimis”
Double bundle - 2 x 725.2 Sq.mm
Length – 32 Kms
DC resistance at 20°C – (0.0421 / 2 ) ohms / km
Electrode resistance < 0.3 ohms
Electrode – Double ring of diameter 450/320m
Each ring consist of a buried coke bed at approx. 2.5 m depth.
The outer ring is divided into six sections and the inner ring into
two sections
 Current is distributed by an overhead system to the feeding cables
of each electrode section. The cables are connected to the buried
electrode.
 The electrodes are equipped with detecting wells for monitoring the
temperature and humidity development of the soil








PLCC SCHEMATIC
Pole 1 DC Line
PLCC
PANELS
PLCC
PANELS
PLCC PANELS
BT
PLCC
PANELS
BT
BT
BT
PLCC
PANELS
PLCC PANELS
Pole 2 DC Line
KOLAR
BT= BALANCING TRANSFORMER
REPEATER
TALCHER