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