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HVDC System Operation HVDC System Operation & Maintenance& Maintenance
V.DiwakarV.Diwakar
Dy.ManagerDy.Manager
HVDC Kolar 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 DC terminal
Cost of AC terminal
Cost
Break even distance
Distance in km
Cost of AC Line
Cost of DC Line
500 – 700 km
Modes of Operation
DC OH Line
Converter Transformer
ThyristorValves
400 kV AC Bus
AC Filters,Reactors
Smoothing Reactor
Converter Transformer
ThyristorValves
400 kV AC Bus
AC Filters
Smoothing Reactor
Bipolar
Current
Current
Modes of Operation
DC OH Line
Converter Transformer
ThyristorValves
400 kV AC Bus
AC Filters,Reactors
Smoothing Reactor
Converter Transformer
ThyristorValves
400 kV AC Bus
AC Filters
Smoothing Reactor
Monopolar Ground Return
Current
Modes of Operation
DC OH Line
Converter Transformer
ThyristorValves
400 kV AC Bus
AC Filters,Reactors
Smoothing Reactor
Converter Transformer
ThyristorValves
400 kV AC Bus
AC Filters
Smoothing Reactor
Monopolar Metallic Return
Current
Basic Configuration - HVDC
DC
TRANSMISSION LINE
Pd = Vd Id
FILTER
Vd
AC SYSTEM A TERMINAL A
Ld Id
FILTER
TERMINAL B
Ld
AC SYSTEM B
12-Pulse Convertor Bridge
Y
Ideal No-Load Condition
B
2
A
1
C
3
Vd
Effect of Control Angle
B
A
2
C
1
u u
Vd
u
3
DC Terminal Voltage
120 º
RECTIFICATION
0240 º180 º 300 º 120 º60 º 180 º
0.866E . 2 LLE . 2 LL
DC Terminal Voltage
120 º
INVERSION
0240 º180 º 300 º 120 º60 º 180 º
0.866E . 2 LLE . 2 LL
AC System A AC System B
U1 U2
Id
Simplified HVDC System diagram
HVDC Control
AC System A AC System B
U1 U2
Id
HVDC Control
Id
Change of Power Direction
Power Direction
U1 U2
HVDC Control
Features
•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
U1 U2
HVDC EQUIPMENTSHVDC EQUIPMENTS
What are the Special Components of HVDC?
MAIN COMPONENTS OF HVDCMAIN COMPONENTS OF HVDC
1. Converter Transformer2. Valve Hall3. AC Harmonic Filters4. Shunt Capacitors 5. DC Harmonic Filters6. Smoothing Reactors7. DC Current / Voltage measuring
devices8. Valve Cooling / Ventilation System
Converter Xmers
Valve Hall
-Thyristors
Smoothing Reactor
Basic Components of HVDC TerminalBasic Components of HVDC Terminal
400 kV
DC Line
-Control & Protection
-Telecommunication
AC Shunt Capacitors
DC Filter
AC Harmonic filters
Valve Cooling / Ventilation system
Electrode station
CONVERTER TRANSFORMERCONVERTER TRANSFORMER
STAR BUSHINGS
400KV SIDE BUSHING
DELTA BUSHING
CONVERTER TRANSFORMERSCONVERTER TRANSFORMERS
Three Singe Phase Transformers for each PoleEach 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
Automatic onload tap changer control with appropriate make and break capacity
Extra insulation due to DC currentsProper 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.
FEATURES OF CONVERTER FEATURES OF CONVERTER TRANSFORMERSTRANSFORMERS
•Type of converter transformer : Single phase three windings
•Rated power of line / star / delta winding (MVA) : 397/198.5/198.5
•Rated current of line / star / delta winding (A): 1719/1635/944
•Rated Voltage of Line/star/delta winding (No-load): 400/√3/210.3/√3/210.3
•Tap changer (voltage range) : -5 % to +20 %•Tap changer steps : 16 to -4 (21 steps)•Tap changer current capacity : 2X2000A
•Cooling arrangement : ODAF
Converter Transformer RatingsConverter Transformer Ratings
Converter Transformer RatingsConverter Transformer Ratings
No load losses – 192KWLoad losses - 760KW @75°COil type – Napthanic, Shell DialaBushings
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 Converter Transformer Connection Connection
Y
Y
Y
D
D
D1-ph 3 winding
Converter Transformer
Valve Hall
Outdoor
RR
YY
BB
Converter Transformer Cooling control
Automatic daily changeover of cooling pumps and fans5 groups of fans and pumps
Each group – One oil circulating pump & 3 cooling fans4 groups will be in service with 2 fans each One redundant group – changeovers every dayExtra fans will switch ON when winding temperature > 75ºCRedundant group will switch ON when winding temperature >85ºCWTI Alarm - 115ºCWTI Trip - 130ºCOTI Alarm - 85ºCOTI Trip - 95ºC
Converter Transformer
internal connection
HVDC VALVE HALL LAYOUTHVDC VALVE HALL LAYOUT
MULTIPLE VALVE UNIT
AC
DC
ValveQ uadrup leva lve
A rrester
AC
G rd
Multiple
Valve
Unit
DD
YYYY
Circuit Diagram of the Converters for Circuit Diagram of the Converters for Pole 1Pole 1
Valve Tower side view
1. AC Terminal2. DC Terminal3. Cooling Water Inlet4. Cooling Water Outlet5. Fiber Optic Cables Tubes
6. Thyristor Module7. Insulator8. Arrester9. 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 StructureValve Structure
Valve Section / tier Single Valve Quadra Valve
Hierarchy of Hierarchy of valve structurevalve structure
Each Thyristor level consistsEach Thyristor level consists
•ThyristorThyristor
•Snubber circuit – to prevent high Snubber circuit – to prevent high dv/dtdv/dt
•Snubber CapacitorSnubber Capacitor
•Snubber ResistorSnubber Resistor
•Valve Reactor – to prevent high Valve Reactor – to prevent high di/dtdi/dt
•Grading Resistor – to equilize the Grading Resistor – to equilize the potential across all the levels in a potential across all the levels in a valve – static equalizingvalve – static equalizing
•Grading capacitor – dynamic Grading capacitor – dynamic equalizing equalizing
Components in one valveComponents in one valve
Component Population at Talcher
Population at Kolar
Thyristor 84 78
Snubber Capacitor 84 78
Snubber Resistor 84 78
Valve Reactor 24 24
Grading Capacitor 6 6
Grading Resistor 84 78
Valve arrester 1 1
TE card 84 78
Components in one PoleComponents in one Pole
Component Population at Talcher
Population at Kolar
Thyristor 1008 936
Snubber Capacitor 1008 936
Snubber Resistor 1008 936
Valve Reactor 288 288
Grading Capacitor 72 72
Grading Resistor 1008 936
Valve arrester 144 144
TE card 1008 936
Thyristor Module
SNUBBER CAPACITOR
SNUBBER RESISTOR
THYRISTOR
TE CARD
COOLING PIPE-PEX
GRADING CAPACITOR
FIBRE OPTICS
Thyristor Modular Unit top view
Block Diagram of Thyristor Block Diagram of Thyristor ElectronicElectronic
1 Light Receiver2 Light Transmitter3 Thyristor Voltage Detection4 Logic
5 Gate Pusle Amplifier6 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 ThyristorInternal Structure of Thyristor
Valve Reactor - Dimensional Valve Reactor - Dimensional DrawingDrawing
Valve Reactor - Electrical and Valve Reactor - Electrical and Mechanical RatingsMechanical 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 Grading Capacitor - Electrical and Mechanical RatingsMechanical 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 ResistorSnubber Circuit Resistor
Resistance R 45
Tolerance ± 3%
Cooling Water
Snubber Circuit CapacitorSnubber Circuit Capacitor
X
View X
Capacitance 1.6 µFd
Tolerance +/-5%
Insulation SF6
DC Smoothing ReactorsDC Smoothing Reactors
Smoothing Reactor - PurposeSmoothing 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
•Two Smoothing Reactors per pole
•Inductance - 125mH
•Nominal DC Voltage – 500KV
•Max DC Voltage – 515KV
•BIL – 950/1425KV
DC Smoothing Reactor DC Smoothing Reactor ratingsratings
•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
DC Smoothing Reactor ratingsDC Smoothing Reactor ratings
HARMONIC FILTERSHARMONIC FILTERS
Conversion process generates – HarmonicsAC 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 generatorsOver heating and extra losses in motors Instability in the converter controlInterference with telecommunication
systemsOver voltages due to resonance
AC Filters AC Filters - - KolarKolarITEM A B C
Filter sub bank DT 12/24 DT 3/36 Shunt C
Rating (3 ph., 400 kV) MVAr 120 97 138
No.of 3 phase Banks - 6 3 5
HV-Capacitor C1 μF 2.374 1.85 2.744
HV-Reactor L1 mH 16.208 5.444 1.602
HV-Resistor R1 ohms 420 300 -
LV-Capacitor C2 μF 4.503 3.759 -
LV-Reactor L2 mH 7.751 204.2 -
LV-Resistor R2 ohms - 1500 -
12/24 Double Tuned Filter – 120 MVAr12/24 Double Tuned Filter – 120 MVAr
C2=4.503 µF
R1=420Ω
L2=7.751mH
L1=16.208mH
C1=2.374µF
11 13 23 25
Impedance Graph
Capacitor Stack
ResistorReactorReactor
12/24 Double Tuned Filter – Sectional 12/24 Double Tuned Filter – Sectional viewview
CT
3/36 Double Tuned Filter – 97 MVAr3/36 Double Tuned Filter – 97 MVAr
C1=1.85µF
R1=300ΩL1=15.444 mH
C=23.759µFR2=1500 Ω
L2=204.2mH 3 35 37
Impedance Graph
Capacitor stack
ResistorReactor
C=23.759µF
Reactor
3/36 Double Tuned Filter – Sectional view3/36 Double Tuned Filter – Sectional view
CT
Shunt Capacitor – 138 MVArShunt Capacitor – 138 MVAr
C1=2.744 µF
L1=1.602 mH
•No harmonic filteringNo harmonic filtering
•Supplies MVAr to the gridSupplies MVAr to the grid
•Switched into the circuit for Switched into the circuit for voltage control purposevoltage control purpose
•Capacity – 138 MVArCapacity – 138 MVAr
Shunt Capacitors-Voltage Shunt Capacitors-Voltage ImprovementImprovement
DC FilterDC Filter 12/24 TYPE12/24 TYPE
C1=1800 nF
R1=400 ΩL1=14.71 mH
L2=8.19 mH
C1=5700 nF
DC FilterDC Filter 12/36 TYPE12/36 TYPE
C1=1800 nF
R1=400 ΩL1=7.21 mH
L2=12.68mH
C1=3300 nF
DC MEASURING DEVICESDC 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
66 UdL 4
Line 1
Pole1
4UdN
2 4 8
Electrode lines
2 4 8UdN 8
411Nos (4 HV+7 LV)
Pole204 Nos ( 2 HV+2 LV)
Line 2
6 UdL 46
Current Measuring Devices
Voltage Dividers
DC Current Measuring Device (OPTODYN) Lay out at HVDC Kolar
IdH
IdN
IdN Idee1
IdL
IdE
Idee2
Idee3
IdE
IdLIdH
Example for the Use of the Hybrid Optical Sensor
Iron C ore Induc tive C T S hun t R ogow sk i A ir C ore C T H V /E H V -L ine
C apac itiveV o ltage D iv ide r
R es is tanceV o ltage D iv ide r
Induc tive V o ltageTrans fo rm er G round Leve l
O PTO DYN TM
Functional ConceptFunctional Concept
Analog/ Digital
Digital/ Optical
Optical Energy
Electrical EnergyId
Shunt
Sensor Head at high voltage level
Optical Energy
Electrical Energy
Power fibre
Signal fibre
Optical
Digital
Power supply
Fibre optical cable
Digital control/ protection systemSIMADYN D
Control/ Protection system at ground level
Redundancy Concept
Id
Shunt
Sensor Head Pole control System 1
Sensor Head
Sensor Head
Sensor Head
Protection System 1
Protection System 2
Pole control System 2
common composite insulator and fibre optic cable ground level; control buildinghigh voltage level; switchyard
• complete redundancy from sensor head via FO cable to control/ protection equipment
• only one Analog/ Digital conversion per signal path
• direct digital signal processing
Comparision to Comparision to Conventional SolutionConventional 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 kgNo additional Post InsulatorsNo electromagnetic interference (EMI) due to fibre optic linksFull redundancy up to the measuring locationExcellent dynamic performance
Picture 2
a
s
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 DIAGRAMKOLAR SINGLE LINE DIAGRAM
THANK YOU
System DescriptionSystem Description
The Valve Cooling System is a single closed The Valve Cooling System is a single closed loop deionised water system. Heat transfer to the loop deionised water system. Heat transfer to the ambient is provided by dry coolers. The Valve ambient is provided by dry coolers. The Valve Cooling System is for one pole and works Cooling System is for one pole and works independent of other cooling and air conditioning independent of other cooling and air conditioning systems.systems.
Spray water will be used if the water Spray water will be used if the water temperature rises above controller set point value.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
01
02
03
04
05
0607
08
09
10
11
12
94
• 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
VALVE COOLING MAIN PUMPVALVE COOLING MAIN PUMP
Valve Hall Ventilation system Flow DiagramValve Hall Ventilation system Flow Diagram
AIR INLET 5m ABOVE GROUND LEVEL
•It is inductive voltage It is inductive voltage transformer transformer
•Oil filled – Oil type Shell Oil filled – Oil type Shell Diala DDiala D
•Make – Trench.Make – Trench.
•Primary/secondary Primary/secondary voltage ratio – 400√3/110 voltage ratio – 400√3/110 √ √ 33
VALVE TIMING PTVALVE TIMING PT
VALVE TIMING PTVALVE TIMING PT
•Inductive Voltage Transformer - Connected to converter Inductive Voltage Transformer - Connected to converter transformer 400 KV sidetransformer 400 KV side
•Pole control gets the zero crossings of the Voltage on line side Pole control gets the zero crossings of the Voltage on line side and uses this as the reference for generating firing signals for and uses this as the reference for generating firing signals for the valvesthe valves
•This PT is used only for firing signal generation – not used for This PT is used only for firing signal generation – not used for any protection taskany protection task
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 STATIONELECTRODE STATION
Electrode station - LayoutElectrode station - Layout
EARTH ELECTRODE EARTH ELECTRODE
Conductor type ACSR “Bersimis”Double bundle - 2 x 725.2 Sq.mmLength – 32 KmsDC resistance at 20°C – (0.0421 / 2 ) ohms / kmElectrode resistance < 0.3 ohmsElectrode – Double ring of diameter 450/320mEach 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 sectionsCurrent 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
TALCHERTALCHERKOLARKOLAR REPEATERREPEATER
PLCC PANELS
PLCC PANELS
PLCC PANELS
PLCC PANELSPLCC
PANELS
PLCC PANELS
BTBT
BTBT
BT= BALANCING TRANSFORMER
PLCC SCHEMATICPLCC SCHEMATIC
Pole 1 DC Line Pole 1 DC Line
Pole 2 DC Line Pole 2 DC Line