DEPARTMENT OF ELECTRICAL
ENGINEERING
IFTM UNIVERSITY
MORADABAD
A
Presentation
On
HVDC System
Guide By:Mr. Vinod Shrivastava
Assistant Professor
Submitted By:Ankit Kumar-15049028
Ankit Kumar-15049029
Ankit Kumar-15049030
Ankit Kumar-15049031
Ankit Kumar-15049032
HVDC stands for High Voltage Direct Current
and
is today a well-proven technology employed for
power transmission all over the world.
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HVDC technology is used to transmit electricity
over long distances by overhead transmission
lines or submarine cables.
It is also used to interconnect separate power
systems, where traditional alternating current
(AC) connections can not be used.

Non-synchronous

Long undersea cable

Long-distance
HVDC links can be broadly
classified
into:
 Monopolar links
 Bipolar links
 Homopolar links

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It uses one conductor .
The return path is provided by ground or water.
Use
of this system is mainly due to cost considerations.
A metallic return may be used where earth resistivity is too high.
This configuration type is the first step towards a bipolar link.

If one pole is isolated due to fault, the other pole can
operate with ground and carry half the rated load (or
more using overload capabilities of its converter line).

Each
terminal
has
two converters of equal
rated voltage, connected in
series on the DC side.
 The junctions between the
converters is grounded.



It has two or more conductors all having the same
polarity, usually negative.
Since the corona effect in DC transmission lines is
less for negative polarity, homopolar link is usually
operated with negative polarity.
The return path for such a system is through ground.
1.
2.
3.
4.
5.
6.
7.
Converters
Smoothing reactors
Harmonic filters
Reactive power supplies
Electrodes
DC lines
AC circuit breakers
Components of HVDC [2]

Objectives of Control
◦
◦
◦
◦
Efficient and stable operation.
Maximum flexibility of power control without
compromising the safety of equipment.
Principle of operation of various control
systems.
Implementation and their performance during
normal and abnormal system conditions.

Direct current from the rectifier to the inverter
Id
V dor cos
R cr
V doi cos
Rl
R ci

Power at the rectifier terminal

Pdr
V dr I d
Power at the inverter terminal
Pdi
V
di
Id
Pdr
RLId
2
Schematic diagram of control [2]



Internal voltages V dor cos and V doi cos can used be
controlled to control the voltages at any point on
the line and the current flow (power).
This can be accomplished by:
◦ Controlling firing angles of the rectifier and
inverter (for fast action).
◦ Changing taps on the transformers on the AC
side (slow response).
Power reversal is obtained by reversal of polarity of
direct voltages at both ends.



Power control
To transmit a scheduled power, the corresponding
current order is determined by:
Po / V d
I ord
Bridge/converter unit control
Determines firing angles and sets their limits.
Pole control
It coordinates the conversion of current order to a
firing angle order, tap changer control and other
protection sequences.
BLOCK DIAGRAM OF CONTROL IMPLEMENTATION[2]
HVDC links can stabilize AC system frequencies and
voltages and help with unplanned outages.


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Renewable electricity superhighways in Smaller
use.

A 500 V,1500 W,810Km bipolar HVDC transmission line
is set up between Rihand & Delhi.

In Vindhyachal back to back link is laid for exchange of
power between Northern & Western regions.
scale
•For equivalent transmission capacity, a
DC line has lower construction costs than
an AC line.
•A double HVAC three-phase circuit with 6
conductors is needed to get the reliability
of a two-pole DC link.
•DC requires less insulation.
•For the same conductor, DC losses are
less, so other costs, and generally final
losses too, can be reduced.
•An optimized DC link has smaller towers
than an optimized AC link of equal
capacity.
Price vs distance [2]
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Reactive power requirement
System stability
Short Circuit Current
Independent Control of ac system
Fast change of energy flow
Lesser Corona Loss and Radio interference
Greater Reliability.
•
•
•
DC lines and cables are cheaper than ac lines or
cables.
The towers of the dc lines are narrower, simpler
and cheaper compared to the towers of the ac
lines.
Line losses in a dc line are lower than the losses in
an ac lines.
Cost vs distance
[1]
Distance vs losses [1]
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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.
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.
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
application of HVDC.
 Very large investments in e.g in China and India shows
that high-voltage direct current will very important in the
future, especially in big, new-industries countries.
 Recent studies indicate that HVDC systems are very
reliable.
 The data collected from 31 utilities says that forced
unavailability of energy due to the converter station is
1.62%.

The scheduled unavailability of energy is about 5.39%.
[1] Lips H P. “Aspects of multiple in feed of HVDC
inverter station into a common AC system”, IEEE
Trans. on Power Apparatus Sys. vol .2,pp 135-141,
1973
[2] Xiao Wang, Boon-Tech Ooi. "High Voltage Direct
Current Transmission System Based on Voltage
Source Converters", IEEE Trans.on HVDC Sys.
vol.1,pp. 325-332,1990
[3] R. N. Nayak, R. P. Sasmal, Y. K. Sehgal, et al, "AC/DC
interactions in multi-infeed HVDC scheme: a case
study," IEEE Power India Conference, pp. 5-9, 2006
Thank you!