HVDC System Operation & Maintenance

Presentation on theme: "HVDC System Operation & Maintenance"— Presentation transcript:

1 HVDC System Operation & Maintenance
V.Diwakar Dy.Manager HVDC Kolar

2 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)

3 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) 2

4 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

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

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

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

8 HVDC Convertor Operation
Basic HVDC link 6-pulse diode bridge Thyristor rectifier Inverter operation Valve voltage waveform HVDC link voltage profile 2

9 Basic Configuration - HVDC
TRANSMISSION AC SYSTEM A TERMINAL A LINE TERMINAL B AC SYSTEM B Pd = Vd Id L d I L d d Vd FILTER FILTER 2

10 12-Pulse Convertor Bridge
Y  2

11 6-Pulse Thyristor Ld I d 1 3 5 L i s A E 1 L i s B V ' d V d L i s C 4
2 I d 2

12 Ideal No-Load Condition
1 3 C A V d B 2 2

13 Effect of Control Angle
1 3 u u u C A V d B 2 2

14 DC Terminal Voltage 120 º RECTIFICATION 240 º 180 º 300 º 60 º 0.866
240 º 180 º 300 º 60 º 0.866 E LL 2

15 DC Terminal Voltage 120 º INVERSION 240 º 180 º 300 º 60 º 0.866 E . 2
240 º 180 º 300 º 60 º 0.866 E LL 2

16 Valve Voltage and Valve Current
120 180 A u 0.866 240 60 F C D B E K G J L H N M 300 P S E LL R Q RECTIFICATION =15º +u 2

17 Valve Voltage and Valve Current
M Q 120 º 180 º R N P u 240 º 120º B F S A C E D H 60 º J K G L INVERSION =15º 60º 0.866 E LL 2

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

19 HVDC Control

20 HVDC Control

21 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

22 What are the Special Components of HVDC?
HVDC EQUIPMENTS What are the Special Components of HVDC?

23 MAIN COMPONENTS OF HVDC
Converter Transformer Valve Hall AC Harmonic Filters Shunt Capacitors DC Harmonic Filters Smoothing Reactors DC Current / Voltage measuring devices Valve Cooling / Ventilation System

24 Basic Components of HVDC Terminal
Converter Xmers DC Line AC Harmonic filters Smoothing Reactor 400 kV DC Filter Electrode station AC Shunt Capacitors Valve Hall -Thyristors Valve Cooling / Ventilation system -Control & Protection -Telecommunication

25 CONVERTER TRANSFORMER

26 CONVERTER TRANSFORMER
400KV SIDE BUSHING STAR BUSHINGS DELTA BUSHING

27 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

28 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.

29 Converter Transformer Ratings
Type of converter transformer : Single phase three windings Rated power of line / star / delta winding (MVA) : /198.5/198.5 Rated current of line / star / delta winding (A): /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

30 Converter Transformer Ratings
No load losses – 192KW Load losses - 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 – Ton

31 Converter Transformer Connection
Valve Hall 1-ph 3 winding Converter Transformer D R Y D Y Y D B Y Outdoor

32 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

33 Converter Transformer internal connection

34 CONVERTER VALVES

35 HVDC VALVE HALL LAYOUT

36 VALVE HALL

37 MULTIPLE VALVE UNIT Multiple Valve Unit D Y Y

38 Circuit Diagram of the Converters for Pole 1

39 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 kg All dimensions in mm

40 Valve Structure Valve Section / tier Single Valve Quadra Valve

41 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

42 Components in one valve
Population at Talcher Population at Kolar Thyristor 84 78 Snubber Capacitor Snubber Resistor Valve Reactor 24 Grading Capacitor 6 Grading Resistor Valve arrester 1 TE card

43 Components in one Pole Component Population at Talcher
Population at Kolar Thyristor 1008 936 Snubber Capacitor Snubber Resistor Valve Reactor 288 Grading Capacitor 72 Grading Resistor Valve arrester 144 TE card

44 Thyristor Module GRADING CAPACITOR SNUBBER CAPACITOR SNUBBER RESISTOR
COOLING PIPE-PEX THYRISTOR TE CARD FIBRE OPTICS

45 Thyristor Modular Unit top view

46 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

47 Thyristor T1501 N75 T - S34 (1) Features: Applications:
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

48 Internal Structure of Thyristor

49 Valve Reactor - Dimensional Drawing

50 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

51 Grading Capacitor - Dimensional Drawing

52 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

53 Snubber Circuit Resistor
Resistance R 45  Tolerance ± 3% Cooling Water

54 Snubber Circuit Capacitor
X View X Capacitance 1.6 µFd Tolerance +/-5% Insulation SF6

55 DC Smoothing Reactors

56 DC Smoothing Reactors

57 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

58 DC Smoothing Reactor ratings
Two Smoothing Reactors per pole Inductance - 125mH Nominal DC Voltage – 500KV Max DC Voltage – 515KV BIL – 950/1425KV

59 DC Smoothing Reactor ratings
Continuous current A Continuous Over load current A Type – Air Cored Dry type Forced Air Cooled reactors for 2500A Location : Outdoor Total mass – 30 Ton Temperature Class - F

60 HARMONIC FILTERS

61 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 Predominant harmonics – 12,24,36

62 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

63 AC Filters - Kolar ITEM 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 4.503 3.759 LV-Reactor L2 7.751 204.2 LV-Resistor R2 1500

64 12/24 Double Tuned Filter – 120 MVAr
C1=2.374µF L1=16.208mH R1=420Ω C2=4.503 µF L2=7.751mH Impedance Graph

65 12/24 Double Tuned Filter – Sectional view
Capacitor Stack CT Resistor Reactor Reactor

66 3/36 Double Tuned Filter – 97 MVAr
C1=1.85µF L1= mH R1=300Ω R2=1500 Ω C=23.759µF L2=204.2mH Impedance Graph

67 3/36 Double Tuned Filter – Sectional view
Capacitor stack CT Resistor Reactor Reactor C=23.759µF

68 Shunt Capacitor – 138 MVAr No harmonic filtering
Supplies MVAr to the grid Switched into the circuit for voltage control purpose Capacity – 138 MVAr C1=2.744 µF L1=1.602 mH

69 Shunt Capacitors-Voltage Improvement

70 DC Filter

71 DC Filter 12/24 TYPE C1=1800 nF L1=14.71 mH R1=400 Ω C1=5700 nF

72 DC Filter 12/36 TYPE C1=1800 nF L1=7.21 mH R1=400 Ω C1=3300 nF

73 DC MEASURING DEVICES

74 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

75

76

77 Example for the Use of the Hybrid Optical Sensor

78 Functional Concept

79 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

80 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

81 Hybrid-Optical Measuring Device
Measuring Shunt Sensor Head Box Composite Insulator incl. Fiber Optics Connection Box

82 Sensor Head Box with Sensors

83 Assembly of Shunt

84 OPTODYN Sensor Analoge Input Signal from Shunt Optical Data Link
Optical Power Supply Link

85 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

86 DC Voltage Measurement

87 DC Voltage Measurement

88 KOLAR SINGLE LINE DIAGRAM

89 THANK YOU

90 VALVE COOLING SYSTEM

91 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.

92 Design Basis Kolar Station Talcher Station
Maximum Dry Bulb One Hour Average 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 Water Outlet Temperature Average 620C Water Conductivity <0.5μS/cm Redundant Circulating Pumps One of two Spray Water Storage for 24hrs The cooling system is designed as follow The design of the cooling systems are identical for one single pole and valid for both stations.

93 Flow Diagram 09 12 10 08 03 02 11 01 04 05 07 06

94 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

95 Valve Hall Ventilation system Flow Diagram
AIR INLET 5m ABOVE GROUND LEVEL

96 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

97 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

98 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.

99 Electrode station - Layout

100 EARTH ELECTRODE Conductor type ACSR “Bersimis”
Double bundle - 2 x Sq.mm Length – 32 Kms DC resistance at 20°C – ( / 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

101 PLCC SCHEMATIC Pole 1 DC Line Pole 2 DC Line KOLAR REPEATER TALCHER BT
PLCC PANELS PLCC PANELS PLCC PANELS BT BT BT BT PLCC PANELS PLCC PANELS PLCC PANELS Pole 2 DC Line KOLAR REPEATER TALCHER BT= BALANCING TRANSFORMER