Hi Aung,

Nice to be participating in one of your discussions after considerable time!

It is true that the genesis of HVDC as an accepted technology is rooted in long distance transmission problems. There are some well known (I would say, almost classic !) aspects that are known to have contributed to the evolution - some of these are commonly cited in HVDC texts:

But with all this, one must not overlook a genesis of HVDC that facilitates power transactions between networks functioning at different base frequencies. The so called back-to-back (or B2B) links need not involve long distance at all ! They simply uses the feature of AC-to-DC-to-AC conversion, which can operate with different frequencies at the two ends.

If I am not wrong, The B2B concept has origins in Japan, though it has thereafter been implemented successfully by many nations and utilities.

Hope that helped !

With best wishes.

-Sanjay

With advent in semi conductor technology conversion from AC to DC and again from DC to AC is very reliable, economical, efficient hence modern high power long distance transmission HVDC is in used, and found more economical and efficient...

Hi ,

you know , that depends on distance and bulk power transmission.

Each has its own merits and demerits.

with HVDC ,you know its very complicated to give firing pulses to converter  stations and maintenanace and losses are also more.

Its better to use EHVAC OR UHVAC like 745KV lines .

Hope it helps//

Mainly it depends on the distance of transmission and the amount of power to be transmitted. Also depends of the application: Offshore transmission, interconnection between two asynchronous AC systems(50/60) Hz.. etc.

Offshore wind power plants maybe the only feasible transmission is HVDC due to the high charging currents produced in case of AC underwater transmission.

However, i think HVDC technology is moving faster that will replace most of HVAC systems.

It is mainly related to the  capacitive effects in the transmission lines

If the line is long and/or the conductors are separate by a short distance (e.g. submarine cables), the equivalent line capacitance per phase is  large. For instance if you assume a PI representation CLC of the line, the capacitance in each extreme of the PI representation is large and  will draw a large steady state sinusoidal current for 50/60Hz operation.

However in a dc transmission system, the steady state current in the equivalent capacitances is not a problem.

This is a very simplified answer. There are other issues, for instance those  already mentioned by Abouzeid.

http://new.abb.com/systems/hvdc/why-hvdc

Hello Desai,

Thanks a lot for your good comments.

Yes, of course, I think HVDC is more appropriate for very long transmission line.

Have a nice day!

Hello Vissamraju,

Big thanks for your kind comments.

I agree that both has advantages and disadvantages.

So, do you want to mean that the higher voltage level, the more benefits?

Good day to you!

Hello Abouzeid, 

Great thanks for your valuable answers.

I agree with you.

So, do you mean the future large grid will be HVDC?

Very nice time!

Hello Cardenas,

Thank you so much for your very simplified answer.

Great Day!

Hello Eedara,

Thanks a lot for your shared link.

Good day!

There can not be a general answer to the question. Advantages vary depending being on applications. As on date both have to coexist even though with developments in semiconductor technologies HVDC will be slowly replacing HVAC but not eliminate.

Hello Raghavan,

Big thanks for your good answer!

Nice day!

Thank you for your quick acknowledgement.

I recommend the above post of Dr. Rajagopalan Raghavan, I agree with him.

Regards, Emad

Hello Dr. Rajagopalan Raghavan & Dr. Emad,

Great thanks!!!!!!!!!!!!!!!

Dear Aung Ze Ya,

HVDC is better than HVAC, in simple terms, HVDC does not have frequency component hence, synchronization of power will be very simple unlike in AC  where it has to satisfy the conditions like V, F and phase sequence should be same.

Like this there are many advantages are there with respect to HVDC.

I'm a bit surprised that all your respondents are thinking of HVDC vs HVAC solely in terms bulk power transmission at EHV.  I don't see any such bias in your original question.  May I point out there's a fundamental difference in the topologies of HVDC and HVAC transmission/distribution networks?  DC forms current loop(s); AC a set of voltage nodes.  Consequently it's much easier to (a) to transform voltage levels in an AC system, and (b) connect/disconnect loads and other plant. Just think of the complexity of kit needed to plug a kettle into a DC loop, and the safety issues.

I would think the great benefit of no inductance reactance of HVDC in case of long distance above 80Km without the possibility of installing substation In the case of offshore wind farms, or to send power to very long distances from generation to consumers.   Otherwise, I would stick of HVAC due to cost.

Hello Badachi,

I'm very delighted for your good answer.

Many Thanks!!!

Nice Day!!!

Hello Toal,

Thanks a lot for your valuable answer.

Good Day!

Hello Sampaio,

I have great pleasure for your good answer.

Big Thanks!

Nice Day!

Hi Aung,

Nice to be participating in one of your discussions after considerable time!

It is true that the genesis of HVDC as an accepted technology is rooted in long distance transmission problems. There are some well known (I would say, almost classic !) aspects that are known to have contributed to the evolution - some of these are commonly cited in HVDC texts:

But with all this, one must not overlook a genesis of HVDC that facilitates power transactions between networks functioning at different base frequencies. The so called back-to-back (or B2B) links need not involve long distance at all ! They simply uses the feature of AC-to-DC-to-AC conversion, which can operate with different frequencies at the two ends.

If I am not wrong, The B2B concept has origins in Japan, though it has thereafter been implemented successfully by many nations and utilities.

Hope that helped !

With best wishes.

-Sanjay

Dear Aung Ze Ya ,

look the link, may be useful.

http://www.electricaleasy.com/2016/02/hvdc-vs-hvac.html

https://ijeir.org/administrator/components/com_jresearch/files/publications/IJEIR-183.pdf

Regards, Shafagat

Hello Prof. Sanjay,

I am heartfelt appreciate for your very great answer.

Big Big Thanks!!!!!!!!!!!!!!!!!!!!!!!!!

Have a Good Day!

Hello Shafagat,

Thanks a lot for your valuable sharing.

Have a Nice Day!

hvdc is better than hvac as only one parameter to be taken into consideration

Hello Lone,

Thanks a lot for your good answer.

HVDC systems offer several operational and special technical advantages over HVAC transmission systems. HVDC power has no frequency, hence minimal problems of harmonics, oscillations or transients; they actually damp out transients. All angular stability problems disappear and even connection of systems at different frequency is feasible. The problems of cable charging current are eliminated. Thus cables can readily be used for underwater crossings. For weak AC grids, voltage source converter-based HVDC systems offer better controllability and grid flexibility for integrating intermittent renewable energy sources such as: wind and solar-power. Using power electronic switching devices or FACTS controllers, precise and fast power control in either direction is easier to achieve in HVDC than in HVAC systems as dc power is minimally affected by reactance. The ease of power flow control in HVDC lines makes it easy to achieve the maximum power and thermal capacity of transmission lines. It is also simple to control active power transfer at a predetermined level or even to modulate this to improve system damping. HVAC is suitable for short transmission lines.

I suggest folks are taking a very narrow focus to answering this question.  A transmission link, whether AC or DC, is only part of the overall electricity supply system.  The question is not which is "better", but which is more suited to the specific system requirements.  AC or DC, each brings particular attributes to the system, and should be evaluated accordingly.

On a more fundamental basis, it is interesting to consider whether each leads to a radically network topology. If Edison had won the "war of the systems", would we now be operating in a current loop world, and what changes would we see?  Would we be using domestic plugs that make/break a current loop, and appliances that have to be rated for the full loop current? Would that have stifled the expansion of domestic electric consumption? Would it have encouraged plasma generating sources?  Something to mull over in the early hours when counting sheep doesn't work.

Hello Davidson,

Big Thanks for your excellent answer.

Have a Nice Day!

Hello James Toal,

Thank you so much for your thoughtful answer.

Have a Great Day!

obviously HVDC is better in many ways

Hello Kumar,

Yes, of course!

Thanks!