this presentation is prepared my friend about high voltage direct current that is very important in electrical engineering.

1. AAMIR SOHAIL 12063122-025
SECTION(B) SEMESTER 5TH
University of Gujrat (Pakistan)

2.  HVDC Definition.
 Introduction to HVDC.
 HVDC working.
 HVDC transmission principle.
 HVAC transmission principle.
 Comparison of HVAC & HVDC.
 Advantages & Disadvantages of HVDC.

3.  HVDC stands for high voltage direct current transmission.
 A high-voltage, direct current (HVDC) electric power
transmission system uses direct current for the bulk
transmission of electrical power, in contrast with the more
common alternating current (AC) systems

4.  First commercial application of HVDC between Swedish
mainland and the island of Gotland in 1954.
 Underwater link of 90 km and 20 MW.
 After the advent of thyristor convertor, New Brunswick and
Quebec 320 MW back-to-back DC interconnection
commissioned in 1972.

5.  With reduced size, cost and improved reliability of power
electronic converters, has made HVDC transmission more
widespread.
 In North America, total HVDC transmission capacity in 1987
was 14,000 MW

11.  AC Transmission Principle

12.  HVDC Transmission Principle

13. CONVENTIONALLY POWER TRANSMISSION IS
EFFECTED THROUGH HVAC SYSTEMS ALL OVER
THE WORLD.
 HVAC TRANSMISSION IS HAVING SEVER
LIMITATIONS LIKE LINE LENGTH ,
UNCONTROLLED POWER FLOW, OVER/LOW
VOLTAGES DURING LIGHTLY / OVER LOADED
CONDITIONS,STABILITY PROBLEMS,FAULT
ISOLATION ETC

14.  HVDC Use less current
 DC roll along the line ,
opposing force friction.
 AC current will struggle against
inertia in the line (100times/sec)-
current inertia –inductance-
reactive power

15.  Better Voltage utilization rating

16.  DC has Greater Reach.
 Distance as well as amount
of POWER determine the
choice of DC over AC.

17.  DC conserves Forest and saves land.
 Fewer support TOWER, less losses.

18. Line controlled power flow is possible very precisely.
ASYNCHRONUS OPERATION possible between regions
having different ELECTRICAL parameters.
 No restriction on line length as no reactance in DC.

19. Stabilizing HVAC SYSTEMS –Dampening of power swings
and sub synchronous frequencies of GENERATOR.
Faults in one AC system will not effect the other AC system .
Cable transmission.

20.  Cheaper than HVAC SYSTEM due to less TRANSMISSION
LINES & LESS RIGHT OF WAY for the same amount of
power transmission.

24.  If DC is required to be used for transmission
since our primary source of power is A.C,
the following are the basic steps:
1. CONVERT AC into DC (rectifier)
2. TRANSMIT DC
3. CONVERT DC into AC ( inverter)

25.  Due to ease of transformation of voltage levels (simple
transformer action) and rugged squirrel cage motors,
ALTERNATING CURRENT is universally utilized.—
Both for GENERATION and LOADS and hence for
TRANSMISSION.
 Generators are at remote places, away from the populated
areas i.e. the load centers
 They are either PIT HEAD THERMAL or HYDEL

26.  Turbines drive synchronous generators giving an output at 15-
25 kV.
 Voltage is boosted up to 220 or 400 KV by step-up
transformers for transmission to LOADS.
 To reach the loads at homes/industry at required safe levels,
transformers step down voltage

27.  In a number of applications HVDC is more effective than AC
transmission.
 Undersea cables, where high capacitance causes additional AC
losses. (e.g. 250 km Baltic Cable between Sweden and
Germany)
 Long power transmission without intermediate taps, for
example, in remote areas
 Power transmission and stabilization between unsynchronized
AC distribution systems

28.  Connecting a remote generating plant to the distribution
grid
 Reducing line cost: 1) fewer conductors 2) thinner
conductors since HVDC does not suffer from the skin
effect
 Facilitate power transmission between different countries
that use AC at differing voltages and/or frequencies
 Synchronize AC produced by renewable energy sources

29.  The disadvantages of HVDC are in conversion, switching and
control.
 Expensive inverters with limited overload capacity.
 Higher losses in static inverters at smaller transmission
distances.

30.  The cost of the inverters may not be offset by reductions in
line construction cost and lower line loss.
 High voltage DC circuit breakers are difficult to build because
some mechanism must be included in the circuit breaker to
force current to zero, otherwise arcing and contact wear would
be too great to allow reliable switching.

31.  Costs vary widely depending on power rating, circuit length,
overhead vs. underwater route, land costs, and AC network
improvements required at either terminal.