General Overview Of HVDC Transmission System - CASA-1000
General Overview of HVDCTransmission System
WHAT IS HVDC ? High Voltage Direct Current Transmission Only Active Power Flow is associated with HVDC: P. High Voltage Alternative Current Transmission Both Active and Reactive Power (Var) Flows with AC: P and QHVDC1-Phase( )HVAC3-Phase
What is HVDC ?Basic Image : DC vs. AC Transmission DC1-Phase ( ge/PowerDistance Voltage/Power – Decrease (Loss) Angle – No stance Voltage/Power – Decrease (Loss) Angle – Change (Reactive Power)
WHAT IS HVDC ?Sending SideDirect CurrentId (Vs-Vr)/R ACRVs–Receiving SideVrRSending VoltageVsReceiving VoltageVr Basic Power Flow Equations Only Governed by Ohm’s LawVs (Vs Vr )Power RAC
WHAT IS HVAC ?Sending SideVsReceiving SideX(Reactance)VsLθVr Basic Power Flow Equations Power VrVs Vrsin θX Governed by Reactance- Var from Inductance & Capacitance
HVDC Advantages (1) Long-Haul Over Head Line ( 500 1000km)Bulk Power Transmission ( 1 2 GW) No limitation of stability (Free from stability & capacitance limitation) HVDC transmission line has less right of way requirement& less expensive in construction (HVDC 2-phase; HVAC 3phase) Lower transmission loss because of no reactive loss Lower insulation/clearance of conductor (DC Voltage isabout 71% of the AC Peak Voltage. AC is defined by RMS) Power transmission between asynchronous AC systems
HVDC Advantages (2) Fast Power Flow control Enhancement of AC system stability Supplying more active power where AC system is at thelimit of its Short Circuit Capability
HVDC Disadvantages HVDC is generally less reliable and has lower availabilitythan HVAC. Mainly due to the extra conversion equipment and maintenancedifficulty. Tapping for Multiple grids is difficult. HVDC circuit breakers are difficult Some mechanism must be included in the circuit breaker to forcecurrent to zero Pollution deterioration of Outdoor Insulator is faster Static Charge effect AC Filters are required to absorb harmonic component Clean room (Dust free) for Thyristor Valve is necessary
Comparison HVDC with HVAC#ItemHVDCHVAC1Long-Haul OHLBulk Transmission CapacityHigh( 1 2GW)Limited2Long-Haul Transmission StabilityNo LimitLimited3Right-of-Way for BulkTransmission OHLLowHigh4Long-Haul Transmission LossLowHigh5Insulation / ClearanceLowHigh6System ConnectionAsynchronousSynchronous7Power Flow ControlEasy and FastDifficult6Multiple terminal (Tapping)Difficult and CostlySimple and Easy7Short Circuit LimitationEffectiveNot Effective8Pollution Effect More Pronounced Higher insulator creepage isrequiredRelatively less
Why HVDC rather than HVAC ? Cheaper in Long-Haul Bulk Power transmission Asynchronous link Accurate Control of power flow – both magnitudeand direction Fault isolation Improved link stability
Comparison of Right of Way for 2 GW400 500 kV AC Lines 100 m400 500 kV DC Line 50 m1 2GW Bulk Power Transmission
Cost comparison of HVDC & HVACOHL TransmissionCostTotal AC CostBreak-Even DistanceTotal DC CostAC Line CostDC terminal CostDC Line CostAC terminal Cost600 800 kmDistance
Types of HVDC Transmission system Monopole System: One pole, one set of conductor for transmission andcurrent return path is through earth. Mainly used for submarine cable transmission.AC1AC2SubmarineDC Cable(HVDC Line)Earth/Water(Return Path)
Types of HVDC Transmission system Bipolar System: Two poles, two set of conductors in transmission line, one positivewith respect to earth & other negative The mid point of Bi-poles in each terminal is earthed via anelectrode line and earth electrode. In normal condition power flows through lines & negligible currentthrough earth electrode. (in order of less than 10 Amps.)AC1HVDC LineOHL/Cable ( )Neutral LineReturn Path ( 0)HVDC LineOHL/Cable (–)AC2
Types of HVDC Transmission system Back To Back: Usually bipolar without earth return.Converter & inverters are located at the same place.No HVDC Transmission line.Provides Asynchronous tie between two different AC networkPower transfer can be in either directionAC1AC2
Types of HVDC Transmission system Multi Terminal System: Three or more terminals connected in parallel, some feed power andsome receive power from HVDC Bus. Provides Inter connection among three or more AC network.AC1AC2AC3
HOW HVDC WORKS
Basic Diagram of HVDC SystemTERMINAL ADCTERMINAL B(Converter)LINE(Converter)AC 1IdLdAC 2LdPd Vd IdVdFILTERFILTER
6-Pulse Convertor Bridge (Valve)Id135462DC OutputY YAC Input
12-Pulse Convertor Bridge (Valve)DC OutputY YY AC Input
HVDC Thyristor Valve (1)SingleValveDoubleValveQuadruple Valve(Multiple Valve Unit : MVU)
HVDC Thyristor Valve (2)ThyristorDriveUnitThyristorModuleMultiple Valve Unit
HVDC Converter Transformers & FiltersConverter TransformerAC Filters
HVDC Station (3000MW)
BIPOLE HVDCMODES OF OPERATION
BASIC HVDC Single Line DiagramSmoothing ReactorThyristorValvesDC Filter:DC OH LineSmoothing ReactorDC Filter:ConverterTransformerConverterTransformerDC Filter:AC BusAC FiltersThyristorValvesDC Filter:AC BusAC Filters
Modes of Operation (1)BipolarCurrentCurrent
Modes of Operation (2)Monopole Ground ReturnCurrentCurrent
Modes of Operation (3)Monopole Metallic ReturnCurrentCurrent
Basic Power Flow Equations . DC terminal Cost AC terminal Cost Cost Break-Even Distance Distance AC Line Cost DC Line Cost 600 800 km Total AC Cost Total DC Cost : Types of
HVDC Applications HVDC Technology Line Commutated Converters Voltage Sourced Converters Recent Developments DC Grid Cigre Activities in HVDC 2 Advantages of HVDC Sample HVdc and HVac Tower Configurations Smaller towers 6.4m 6.9m 28.3m 7.8m 4.6m 169. m 8.5m 13m 11.3m 25.9m 1 7 m HVDC towers are smaller and simpler .
such as IGTO, IGBT and HVDC light etc., and then the power system will be improved. The main idea of FACTS and HVDC can be explained by the basic power flow concept for transmission in fig 2. Figure 2: Basic power flow diagram for power transmission 2. Development of HVDC HVDC has been introduced in the second half of the past
Enabling technology for HVDC and FACTS Power Cables Product or complete system Key product for HVDC and FACTS Service and upgrading. HVDC Technologies . HVDC Light Transmission - Voltage Source Converters. HVDC Light Cable Development 1997 Hellsjön 95 mm2 Al /- 10 kV, 3 MW 2000 Directlink 630 mm2 Al
Further, a better HVDC and HVAC line losses was formulated [7]. In this paper, the technical aspects of HVDC transmission have been introduced in Economic Dispatch (ED). This paper provides an improved formulation of ED with HVDC incorporating the cost incurred due to the technical challenges associated with adopting HVDC technology.
will require, among other technologies, DC-DC conversion systems. The advantages of HVDC over HVAC technology in relation to transmission distance are given. The different HVDC configurations and topologies of HVDC converters are elucidated. In this context, the HVDC grids are a promising alternative for the expansion of the existing AC grid.
High voltage AC (HVAC) used across the world tends to be fussy over longer distances and it creates various environment issues. Therefore, HVDC use is been propound. III. LITERATURE 2)REVIEW Literature review deals with the different types of HVDC system configurations and the components that are used in the HVDC system. A.Types of HVDC Systems
This is a two part series on HVDC Transmission. Part 1 of this series looked at specific applications where HVDC Transmission excels, other applications that may not be as suitable, and the geographic area in the U.S. Grid where they have, and will continue to be used extensively. Part 1 also looked at the technology used to implement HVDC lines.
This paper discusses the HVAC transmission system and HVDC operation system at stable condition, also shows the fault current result at faults due to HVAC and HHDC system to be used with transmission system. Figure1. Characteristic Curves for the Relations between Cost with Distance for HVDC and HVAC. 2. STABILITY IN HVAC AND HVDC SYSTEMS
