HVDC TRANSMISSION SYSTEMPresented by: Sagnik Roychowdhury 3rd yearDepartment of Electrical EngineeringCollege: Future Institute Of Engineering & ManagementClass Roll No:62University Roll No:14801610062
Introduction• Beginning• History of HVDC Transmission• Advantages of HVDC over AC Transmission• Disadvantages• Costs of High Voltage DC Transmission• Component & Diagram• Corona Discharge• The Future prospect• Applications• Conclusion• Bibliography
Beginning1. Uses direct current for transmission of electrical power.2. Should be used over long distance.3. Can be used underwater.
Continued….• The modern form of HVDC transmission uses technology developed extensively in the 1930s in Sweden at ASEA.• Early commercial installations included one in the Soviet Union in 1951 between Moscow and Kashira, and a 10–20 MW system between Gotland and Mainland Sweden in 1954.
High Voltage DC Transmission• Full form of HVDC is High Voltage Direct Current.• Two AC systems having different frequencies can be linked up together by means of HVDC link.• HVDC technology is used to transmit electricity over long distances.
Why DC Transmission?• Losses are less.• Two conductors required.• Less Expensive.• Can be used over long distance.
History of HVDC Transmission • Electromechanical (Thury) Systems • Mercury Arc valves • Thyristor Valves• Capacitor –Commutated Converters(CCC)
Electromechanical (Thury) SystemsFirst Power transmission:Betwwen Miesbach-MunichTime:1882Capacity:2.5 kWThury System:• series-connected motor-generator sets used.Moutiers-Lyon System for 8000 kW 200 km distance. René Thury• Used eight series-connected generators with dual commutators.• Between 1906 to 1936 Fifteen Thury systems were in operation by 1913.
Mercury Arc valves• Between 1920 to 1940• In 1932 GE tested first mercury-vapor valves.• Elbe-projest in 1941.• Fully static mercury arc valve to commercial service in 1954.
Continued…• Required an external circuit to force the current to zero and thus turn off the valve.• In HVDC applications, the AC power system itself provides the means of "commutating" the current to another valve in the converter.• Also known as LCC.
Thyristor Valves• Since 1976, new HVDC systems have used only solid-state devices, in most cases thyristor valves.• Thyristors require an external circuit (in HVDC applications, the AC power system itself does this) to turn them off.• On March 15, 1979, a thyristor based direct current connection between Cabora Bassa and Johannesburg (1410 km, ±533 kV, 1920 MW) was turned on.
Capacitor –Commutated Converters(CCC)• To overcome the limitations of LCC, CCC was introduced.• It is conventional.• LCC using thyristor valves, where series capacitors are inserted into the AC line connections, either on the primary or secondary side of the converter transformer.• The series capacitors partially offset the “commutating inductance” of the converter and help to reduce fault currents.• Reducing the requirment of reactive power by allowing ‘extinction angle’ to be used at an inverter.
ADVANTAGES• Occupies less space.• Less expensive.• Synchronization of two AC power supply.• Does not transmit short circuit current.
DISADVANTAGES• Complexity of control.• Inability to use transformers to change voltage levels.• High cost of convention equipment.• The difficulty of breaking DC current which results in high cost of DC currents.
Costs of High Voltage DC Transmission• The manufacturers do not state the exact cost of a particular project.• Depends on power rating, circuit length, overhead vs. underwater route, land costs, and AC network improvements required at either terminal.
Corona Discharge• Corona discharge is the creation of ions in a fluid (such as air) by the presence of a strong electric field.• Both AC and DC transmission lines can generate coronas, in the former case in the form of oscillating particles, in the latter a constant wind. Pdc=P0+K(E-EC)2 kW/km
The Future Prospect• Next 25 years HVDC market will be dominated by “force commutated converter”.• However, the force-commutated converters using capacitive commutation never outgrew niche use, due to the rapid emergence of the second trend today, in favour of “self-commutated converters” which use more complicated semiconductor devices which can be directly turned off by gate action.
Continued….• These self-commutated devices include the insulated gate bipolar transistors (IGBT) and variants of the thyristor such as the integrated gate-commutated thyristor(IGCT), and gate turn-off thyristor (GTO).• Self-commutated converters, more commonly known as "Voltage-Sourced Converters" started to appear in 1997 with the experimental Hellsjön–Grängesberg project in Sweden, and by the end of 2011, this technology had captured a significant proportion of the HVDC market.
Applications• Long distance bulk power transmission.• Under ground or under water cables.• Asynchronous interconnection of two AC power supplies.
Application of HVDC in INDIA• Rihand-Delhi and Chandrapur- Padghe were the first long distance HVDC projects in INDIA.• In 1990 ,Rihand-Delhi (Singrauli) thermal power complex with a combined power generation of several thousand MW was put in to service. It covers over a distance of 814km.• In 1998,the 1500 MW transmission Chandrapur- Padghe was putting to service. It covers over distance of 736 km.
Conclusion• With the HVDC systems, the power flow can be controlled rapidly and accurately as to both power level and direction. This possibility is often used in order to improve the performance and efficiency of connected AC networks.• Using HVDC to inter connect two points in a power grid, in many cases is the best economic alternative, and further more it has excellent environmental benefits.• The HVDC technology is used to transmit electricity over long distances by overhead transmission lines or submarines cables.• HVDC overland links are usually bipolar, on overhead lines. Compared to AC , DC transmission has several advantages.
Bibliography• GOOGLE.COM• WIKIPEDIA.COM• A COURSE IN POWER SYSTEM by J.B.Gupta