HVDC Transmission (Introduction to HVDC and Historical Developments,Advantages and Disadvantages )

Historical developments:

Evolution of power systems

late 1870s	Commercial use of electricity
1882	First electric power system (generators, under ground cables, fuse, and load mostly of lamp loads (incandescent lamps) were developed by Thomas alwa Edison at pearl street station in new York. It was a dc system of 110 v load, 59 customers, supplying an area of 1.5 km radius.
1884	Motors were developed by frank Sprague ( father of electric traction)
1886	Limitation of dc become apparent As it has high losses and more voltage drop Transformation of voltage is also required Transformers and ac distribution (150 lamps) was developed by William Stanley of westing house
1888	Nikola testla developed poly phase systems and had patents of generators, motors, transformers and transmission lines. Westing house bought it.
1889	First ac transmission system in USA between Willamette falls and Portland oregaon. Single phase 4000 v and over 21 km in length.
1890s	Controversy on whether industry should standardize ac or dc, Edison advocated dc and westing house ac, the main advantage of using ac is in Voltage increase, simpler and cheaper generators and motors.
1893	First 3 phase line 2300 v, 12 km in California. Ac was chosen at Niagara falls (30 km)
1922 1923 1935 1953 1965 1966 1969 1990's	Early voltage (highest) 165kv 220kv 287kv 330kv 500kv 735kv 765kv 110kv Standards are 115,138,161,230 kv- high voltage 345,500,765kv- Extra high voltage Earlier frequencies were 25,50,60,125,133 Hz; USA-60Hz and some countries-50 Hz
	HVDC Transmission system A system of HVDC transmission was designed by a French engineer, Rene Thury when the ac system was in their infancy.
1880-1911	At least 11 Thury systems were installed in Europe. The prominent was mouteirs   to Lyons (France) in 1906. 180 km of 4.5km underground cable of 4.3MW, 57.6 kv, 75 A. DC series generators were used Constant current control mode of operation
1920	Transverter were developed. It is poly phase transformer commutated by synchronously rotating bus gear but not used commercially.
1938	All the thury systems were dismantled
1950s	Mercury arc valve
1954	First HVDC transmission between Sweden and Gotland island by cable.
Historical background of HVDC	The most significant contribution to HVDC came when the Gotland Scheme in Sweden was commissioned in 1954 to be the World's first commercial HVDC transmission system. This was capable of transmitting 20 MW of power at a voltage of -100 kV and consisted of a single 96 km cable with sea return. With the fast development of converters (rectifiers and inverters) at higher voltages and larger currents, d.c. transmission has become a major factor in the planning of the power transmission. In the beginning all HVDC schemes used mercury arc valves, invariably single phase in construction, in contrast to the low voltage poly phase units used for industrial application. About 1960 control electrodes were added to silicon diodes, giving silicon-controlled-rectifiers (SCRs or Thyristors). In 1961 the cross channel link between England and France was put into operation. The a.c. systems were connected by two single conductor submarine cables (64km) at ± 100kV with two bridges each rated at 80MW. The mid-point of the converters was grounded at one terminal only so as not to permit ground currents to flow. Sea return was not used because of its effect on the navigation of ships using compasses. The link is an asynchronous link between the two systems with the same nominal frequency (60Hz). The Sakuma Frequency Changer which was put into operation in 1965 interconnects the 50Hz and the 60Hz systems of Japan. It is the first d.c. link of zero length, and is confined to a single station. It is capable of transmitting 300 MW in either direction at a voltage of 250 kV. In 1968 the Vancouver Island scheme was operated at +250 kV to supply 300 MW and is the first d.c. link operating in parallel with an a.c. link. In 1970 a solid state addition (Thyristors) was made to the Gotland scheme with a rating of 30MW at - 150kV. Also in 1970 the Kings north scheme in England was operated on an experimental basis. In this scheme transmission of power by underground d.c. cable at ± 200 kV, 640 MW is used to reinforce the a.c. system without increasing the interrupting duty of a.c. circuit breakers. The first converter station using exclusively Thyristors was the Eel River scheme in Canada. Commissioned in 1972, it supplies 320 MW at 80 kV d.c. The link is of zero length and connects two a.c. systems of the same Nominal frequency (60Hz).
	HVDC Transmission system in India One of the most exciting new technical developments in electric power system in the last three decades has been “High Voltage Direct Current transmission”. From the first of HVDC links to the recent, the voltage has increased from 100 KV to 800 KV, the rated power from 20 MW to 6300 MW and the distance from 96 km to 1370 km. Preceding and accompanying this rapid growth of Direct Current Transmission were developments in High Voltage, High power valves, in control and protection system, in DC cables and in insulation for overhead DC lines.

Limitations of HVAC Transmission	Advantages of HVDC transmission
Reactive power loss	No reactive power loss
stability	No stability problem
Current carrying capacity	No charging current
Skin and Ferranti effect	No skin and Ferranti effect
Power flow control is not possible	Power control is possible
	Requires less space as compared to ac for same voltage rating and size
Disadvantages of HVDC Transmission	Ground can be used as return conductor
Cost of terminal equipments is high	Less corona loss and radio interference
Introduction of harmonics	Cheaper for long distance transmission
Blocking of reactive power	Asynchronous operation possible
Point to point transmission	No switching transient
Limited overload capacity	No transmission of short circuit power
Huge reactive power requirements at the converter terminals	No compensation problem
	Low short circuit current
	Fast fault clearing time