(Associate Professor) HVDC Network as Infrastructure for Smart SAARC Power Grid Netra Gyawali, PhD (Associate Professor) IOE, Pulchowk Campus, TU

Contents Background Key Attributes of High Voltage Direct Current (HVDC) Transmission HVDC Transmission: Configuration and Modalities HVDC Transmission: World Picture HVDC Transmission: SAARC Context HVDC Network in SAARC: Possibilities Conclusions

Background Requirement of Modern Transmission GRID Effective ( Functions as desired) Speed and accuracy Efficient (Low Loss) Asset Management (Optimum use the asset) Resilience Interoperability Accommodate Large Scale Renewable Power

Key HVDC Attributes No reactive losses Provision for high cable length Lower electrical losses Accommodate Renewable Power BTB connection Better Voltage Ride through Capability The Power Flow on an HVDC link is Fully Controllable (Fast and Accurate) The operator or automatic controller determines how much power flows via the link and in which direction Irrespective of the interconnected AC system conditions Connecting different frequencies. E.g. Japan and Brasil: 50Hz grid connected to 60Hz grid by back-to-back (BTB) HVDC. Connecting two non-synchronous networks. E.g. UCTE and the Russian grid, France and UK Losses: R*I², but I is lower because no Q

Key HVDC Attributes An HVDC Link is asynchronous The ac voltage and frequency in the two ac networks can be controlled independently of each other No need for common frequency control The HVDC link can be used to improve the dynamic conditions in both of the interconnected ac networks (power system damping) Can be controlled independently of AC system variations HVDC links do not increase the Short Circuit Level of the connected systems Faults and oscillations don’t transfer across HVDC interconnected systems Firewall against cascading outages

Key HVDC Attributes HVDC can transport energy economically and efficiently over longer distances than ac lines or cables Increased Transmission Capacity in a fixed corridor Up to 3 times more power per tower, therefore narrower rights of way

Key HVDC Attributes

Key HVDC Attributes Source: IEEE Magazine 2008

Key HVDC Attributes

HVDC Transmission: Concept Source: IEEE Magazine 2008

HVDC Configurations

HVDC Transmission: Concept Natural Commutation Based HVDC Thyristor or mercury-arc valves Reactive power source needed Large harmonic filters needed

HVDC Transmission: Concept VSC Based HVDC Natural Commutation Based HVDC IGBT valves P and Q (or U) control Can feed in passive networks Smaller footprint Less filters needed

HVDC Transmission: Configuration Source: IEEE Magazine 2008

Decrease voltage at station B or increase voltage at station A Decrease voltage at station B or increase voltage at station A. power flows from A B Normal direction Source: VG Rao 2005

NORMAL POWER DIRECTION Source: VG Rao 2005

REVERSE POWER OPERATION

HVDC Transmission: Working

HVDC Transmission: Working

Overview of HVDC applications

HVDC Transmission: World Picture

HVDC Transmission: Some Examples Norway Netherland Line Type submarine cable Type of current HVDC Total length 580 km (360 mi) Power rating 700 MW AC Voltage 300 kV (Feda), 400 kV (Eemshaven) DC Voltage ±450 kV 700 MW http://search.abb.com/library/ABBLibrary.asp?DocumentID=9AKK101130D1756& LanguageCode=en&DocumentPartID=&Action=Launch

HVDC Transmission: Some Examples The first HVDC Light transmission Commissioning year: 1997 (Sweden) Power rating: 3 MW No. of poles: 1 AC voltage: 10 kV (both ends) DC voltage: ±10 kV Length of DC overhead line: 10 km Main reason for choosing HVDC Light: Test transmission

VSC HVDC example: troll (north sea) HVDC Transmission: Some Examples VSC HVDC example: troll (north sea) Commissioning year: 2005 Power rating: 2 x 42 MW AC Voltage:132 kV at Kollsnes, 56 kV at Troll DC Voltage: +/- 60 kV DC Current: 350 A Length of DC cable:4 x 70 km Main reason for choosing HVDC Light: Environment, long submarine cable distance, compactness of converter on platform

Brazil Argentina HVDC line

HVDC Transmission Philippines

HVDC Transmission: Some Examples

HVDC Network in SAARC (BTB Link) NR ER ER SR SR HVDC LINK CONNECTING REGION CAPACITY (MW) Vindyachal North – West 2 x 250 Chandrapur West – South 2 x 500 Vizag – I East – South 500 Sasaram East – North SR SR Source power grid India

HVDC LINKS IN SAARC (India)

HVDC IN INDIA Bipolar HVDC LINK CONNECTING REGION CAPACITY (MW) LINE LENGTH Rihand – Dadri North-North 1500 815 Chandrapur - Padghe West - West 752 Talcher – Kolar East – South 2500 1367 Source power grid India

SAARC HVDC Link: Possibilities India-Pakistan Nepal-India Srilanka-India Bangladesh-India Bhutan-India Afghan-Pakistan

Conclusions HVDC transmission has number of benefits for bulk power transmission; namely efficiency, resilience, interoperability etc. In short distance, BTB HVDC provides smart link for frequency conversion and renewable power integration. In SAARC Country, the development of HVDC is only limited to India. For cross-border transmission link, HVDC is a good candidate. Combining with FACTS technology, HVDC provides a infrastructure of the future Smart Transmission Grid for SAARC.

References Understanding Facts: Concepts and Technology of Flexible AC Transmission Systems, Narain G. Hingorani, Laszlo Gyugyi Flexible AC transmission systems, Song & Johns Thyristor-based FACTS controllers for electrical transmission systems, Mathur Vama

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