text:
Talk:High-voltage direct current

Back from DC to AC
Right now, I think it doesn't get clear enough how the HVDC is put back to AC. An explanation would be great, especially see Static inverter plant - i think that would be a good reference. Thanks, --Abdull 09:22, 22 July 2005 (UTC) It is much like the inverter you connect to a 12 volt battery, but much larger components and many of them connected in series.Ccpoodle (talk) 18:13, 7 January 2009 (UTC)

Corona discharge
Corona dicharge does not depend on an electromagnetic field neccessarily ( unless you are talking about RF corona when of course it does) So, to keep thing simple and improve accuracy, I ve changed electromagnetic to electric. Any comments. Please reply here initially. I watch this page. Light current 16:41, 5 August 2005 (UTC) "electrostatic field" is possibly still better than electric field. Ccpoodle (talk) 18:17, 7 January 2009 (UTC)
 * FYI, static electric fields are electromagnetic fields, and so are static magnetic fields. There is no such thing as a pure magnetic or electric field for all observers. If you ever see what you think is a pure one, you should know that your view is only due to your unique point of view as an observer with a particular velocity. Change velocity and any "pure" magnetic field you were looking at, will now have an electric component, and any pure electric field picks up a magnetic component. So each one is just an aspect of the other, and will show both faces to another observer in a different reference frame. Which is why the one EM field that always has two aspects, is called electomagnetic. S  B Harris 00:03, 27 April 2012 (UTC)

Advantages of HVDC
I don't really understand one of the advantages of HVDC: Reducing I²R losses and line cost since HVDC transmission requires less copper conductor (i.e 2 conductors one is +ve another is -ve). Less copper means more resistance, not less, so at a given I, the losses should increase! -- CyrilB 13:24, 18 April 2006 (UTC)

 * Right. Thinner wire generally has more resistance and more I²R loss effects at the same amplitude RMS current (which is the peak value for DC, and 0.707 x Peak for AC) in simple, constant-load-demand, low voltage circuits.

 * To compare AC transmission systems to DC it helps to assume static conditions, normalize loads, and convert the three AC phases to three equivalent DC circuits. Besides the 1/0.707 AC-to-DC current ratio, AC networks require another form of current because its loads and transmission lines cause the demand and generation of significant reactive power. The reactive power results in apparent power that has more current associated with it. See the Copper Losses section below.

 * You can argue Conservation of Energy in which the imaginary reactive phasor or component of AC isn’t "used" but this additional resultant current must still be transported by the utility. In Northern California the apparent power -- vector sum of the reactive and resistive powers -- is billed by PGE to industries, which are major contributors of reactive loads. These charges are PGE's adjustments for low (true and displacement) power factors, which cause higher apparent power and higher currents. PGE's residential customers aren’t directly charged for this though PGE's aggregate costs for apparent power in the transmission line chain are billed in the "Transmission and Distribution" section of the bill.

 * Though there's reactance in wires carrying DC and capacitance in underwater DC lines, reactances encountered in DC systems are mostly at the end points at conversion stations and are not as significant as those in AC.

 * AC's higher currents entail larger-sized cables, conductors, transformers, and switchgear. AC's higher peak voltages are also 1/.707 higher than equivalent DC voltages so, reactive power aside, insulation for HVAC has to be designed for 41% higher instantaneous voltage values.
 * DonL (talk) 16:01, 19 May 2012 (UTC)
 * It ain't necessarily so ... The design of HVDC insulation, especially outdoors, has to take into account creep stress and the behaviour of ionised particles under HVDC stress on contaminated or wet insulator surfaces.  The surface creep stress phenomenon with HVDC insulation can lead to highly non-linear voltage distribution across the surface, causing a phenomenon that is sometimes called "dry-band arcing". This can lead to severe stress on porcelain bushings that sometimes leads to failure.  The capacitive properties of an insulator or bushing when exposed to an HVAC stress leads to much more even surface stress distribution than occurs with HVDC, meaning that a shorter total creepage path length is acceptable.  Anyway, the operating experience with HVDC, particularly in areas where insulator pollution occurs (such as coastal regions of New Zealand) is that you often need much longer surface creepage lengths for HVDC than for HVAC insulation for an equivalent operating voltage.  This usually means that the total length of the insulator is also considerably greater than would be required for HVAC.  Marshelec (talk) 08:43, 31 May 2012 (UTC)

Hmm... I didn't exactly understand this either. Perhaps what the other user meant to imply was that, by using bipolar DC transmission, the effective transmission voltage would be twice the transmission voltage (versus ground), and by using DC you'd also reduce line reactive, skin effect, and corona losses. The combination should allow smaller conductors to be used versus a HVAC transmission system of similar power handling capability?? Bert 14:26, 18 April 2006 (UTC)

 * Bert- Yes, for similar power handling, HVDC allows smaller conductors for a number of reasons. And the effective DC voltage in bipolar DC is “double” in the way I think you described. I think in the event of a failure some bipolar DC systems temporarily halve the total voltage, and use earth as a conductor, while the still-working leg of now-unipolar system would carry the same steady-state condition current before the fault. Some countries don't allow HVDC transmission sytems to carry ground currents, which contribute to corrosion of nearby metal objects buried underground. There may also be safety considerations. Earth soil is a lousy ground conductor anyway.
 * DonL (talk) 19:54, 30 April 2012 (UTC)
 * Actually the ground is an outstandingly good conductor - effectively infinite. The problem is getting a good grip on the ground with a suitable ground electrode !! It can be difficult to get the electrode resistance down to a suitably low level.  The HVDC Inter-Island scheme in New Zealand has operated almost continuously in monopolar mode with ground return current for several years.  At one end of the link there is a buried land electrode, and the other end uses a set of electrodes buried along a seashore.  Electrolytic action occurs at both electrodes, and extended periods of operation with large ground return currents can lead to considerable maintenance requirements, particularly at the land electrode.  Ground return current is not permitted in many jurisdictions, but it has been a feature of the New Zealand scheme since first commissioning in 1965.  The safety issues of ground return current in the New Zealand scheme are minor, and easily controlled.  The key benefits are the avoidance of a metallic return conductor for monopolar operation (which would have been uneconomic/impractical in the context of the New Zealand scheme Marshelec (talk) 08:43, 31 May 2012 (UTC)

I think the I²R=P refers to power lost in charging and discharging of the line vs. ground(mono) or other conductor (bipolar)   —Preceding unsigned comment added by 81.166.130.9 (talk) 09:24, 3 May 2009 (UTC)

Yes, this para needds to be re-written. Its confued. Fact 1 -The I2R losses are identical for AC and DC. P(lost) = I2R and P (lost) = V2 (square)/R

The losses are identical if Vac RMS = Vdc. There is no difference.

Fact 2 - The V in V2/r is NOT the total V applied to the line (refrecned to ground). Rather, its the voltage DROPPED across the line. Its not relative to ground, instead its the V dropped across the 2 ends of the line itself.

So the I2R arguements re HVDC being efficient are bunk.

However, HVDC is better for specific reasons 1) No Losses due to Line Impedence. Z is immaterial to HVDC 2) No Capacitance Losses. Line only needs ot be charged once on startup. 3) Crona losses are less because Vpeak for AC is > Vdc for identical power transfer. —Preceding unsigned comment added by 61.95.167.91 (talk) 06:00, 10 July 2009 (UTC)

 * Fact 1 is correct -- I²R is I²R, except equal power transmission in an AC system requires more currrent.
 * Fact 2 is also correct for power lost as heat in the transmission line itself.
 * HVDC does have losses in the 6- and 12-pulse rectification and inversion processes though not as much as step-up and step-down transformer losses in AC sytems.
 * DonL (talk) 20:13, 30 April 2012 (UTC)

Yay!, armchair critics. You can talk all you like about corona discharge and what-ever, with HVDC, I've never seen it in 20 years as a chopper pilot/Line Mechanic over here. The guy above me that says there is no line impedance had better do his maths again, all wires have a finite resistance, even at DC voltages.
 * Well, I've stopped my car under Bipole II on a hot dry day on the way back from the brother-in-law's cottage, and pointed out to my wife the crackling sound in the air. It was daylight, so I couldn't see any glow...but if the wind isn't too high, you can hear something. I believe I also noted a crackling sound when I took pictures of the HVDC crossing lines in North Dakota, in a very bumpy cow pasture. Again, daylight, don't know if any visible glow happens. Also, pages 15-9 through 15-11 of my very old Std. Hbk. for EE says the average annual corona loss for a +/-400 kV line was around 2.3 kW/km.  --Wtshymanski (talk) 21:18, 22 October 2011 (UTC)

Copper Losses
The additional copper in AC lines is used to transmit the reactive power due to inductance. Since DC lines are not subject to reactive power, you can use less copper. Ac power lines act as a transmitting antenna, so there is significant 60 hertz electromagnetic energy lost, plus small skin effect losses. Three phase ac requires at least three conductors. HVDC monopole one conductor, bipolar two conductors. The voltage can be 140% or more higher without serious arcing, corona losses and environmental hazard. Higher voltage means less current and/or more power capacity. Is HVDC more vulnerable to EMP = electromagnetic pulse than properly transposed ac power lines? Ccpoodle (talk) 01:39, 8 January 2009 (UTC). Rubbish, All HV stuff uses ACSR wire, this is aluminium outer and a steel centre tensioning wire or pure aluminium wire Trumpy (talk) 11:52, 22 October 2011 (UTC)

Itaipu converters
I don't want do edit this page, but I'm afraid the second Itaipu converter is located at Sao Paulo, not at Brasilia. Take a look at http://www.transmission.bpa.gov/cigresc14/Compendium/Itaipu%20Pictures.pdf. Brasilia is not shown, but it is at the heart of the country, while Sao Paulo is much closer to Foz do Iguacu, where Itaipu is located.

Alvaro Augusto alvaro@daelt.sh06.com

lack of costing information
This stuff is all irrelevant without cost informatn and comparison with AC. Also what about losses? Cam;t see them anywhere yetEngineman 18:48, 8 April 2007 (UTC)

Wave effects
I’ve heard HVDC lines are better for long-distance transitions because the ac current reflects from the end points when the length of the line approaches 1/2 of the wavelength of the power. Given a 50 Hz line, the length is c/ν = (3e8 m/s) / (50 s-1) = 6e6 m = 6 thousand km, and if the line is exactly 3000 kilometers in length, the potential difference at the recipient’s end will be exactly zero. Is that true? Zero and double voltage is for a theoretical transmission line loaded at the characteristic impedance. The voltage is however different at the half wave length and quarter wave length points of ac power lines, but not by enough to cause serious problems in most cases. Ccpoodle (talk) 02:05, 8 January 2009 (UTC)

---isn't that true for any EM wave? find the equivalent LC of the circuit thus made and see if it can resonate. I think it has more to do with mixing of circuits and no phase matching needed which make HVDC easier

12-pulse system grammar
"Between each" makes no sense. I tried to correct the grammar of that section, and hope that in the process I didn't change the intended meaning. Please, would somebody who is familiar with the subject verify that the rewording is accurate? D021317c 00:46, 10 June 2007 (UTC)

Why is that non-existent source credited on this page? He may not want to be named, but it is the same as an unsourced comment as far as articles go... (#11)

Credibility
I read  (e.g. 50 hz is used in Canada while 60 hz is used in the United States)  and was made very sad. I'd like to think that someone who's bold enough to edit an article can speak with some reliability about the topic he or she chooses to edit; but if you're missing on the fundamentals, it really undercuts the reliability and credibility of the whole process. --Wtshymanski (talk) 13:24, 21 May 2008 (UTC)
 * Most of Canada uses 60 hertz. Parts of Quebec, or other locals far North may use 50 hertz. The phase likely is not synchronized everywhere. Ccpoodle (talk) 02:18, 8 January 2009 (UTC)
 * Sorry, completely incorrect. There are no 50 Hz grids in Canada, and the 25 Hz generation at Niagara Falls has been shut down. Quebec is its own synchronous grid, and Canadian regions are synchronous in the NERC areas. Isolated communities in Canada are necessarily not on a grid, but are all 60 Hz. --Wtshymanski (talk) 14:38, 8 January 2009 (UTC)

why?
"HVDC cables can carry more power for the same thickness of cable compared with AC lines"

Can we have an explanation in the article for why this is?

Rtdrury (talk) 06:21, 24 July 2008 (UTC)

 * Added. Because AC cabling must be rated for peak voltage, while only the RMS voltage is usable (71% of peak). RMS does not apply to DC, so there is a built-in 29% greater efficiency of DC vs single-phase AC.
 * I don't know how three phase AC compares to DC, since 3 phase uses 3 wires but DC only uses two. It would appear that DC of much higher voltage can function in place of 3 phase, due to the lack of the 3rd wire that allows for much greater spacing of the two DC wires, and therefore perhaps a higher working voltage.
 * Also, I don't know how capacitive coupling is figured into AC line ratings. It may be that the insulation ratings for AC have to be some margin higher than peak for safe AC line operation, and this margin may not be necessary for DC, so the DC line efficiencies could possibly be higher yet than the basic gain vs RMS of 29%.
 * DMahalko (talk) 03:27, 8 April 2009 (UTC)
 * Capacitance mostly isn't a problem, except for underwater cables. That is why they are more often HVDC. Yes AC has to work to peak voltage, but as others above note, there are problems with insulators for DC. If you reverse the voltage once in a while, that might go away. AC has reactive power loss and skin effect, which DC doesn't have. The converters need to handle reactive power, though, so the problem doesn't completely go away. Gah4 (talk) 22:11, 18 January 2022 (UTC)
 * Capacitance mostly isn't a problem, except for underwater cables. That is why they are more often HVDC. Yes AC has to work to peak voltage, but as others above note, there are problems with insulators for DC. If you reverse the voltage once in a while, that might go away. AC has reactive power loss and skin effect, which DC doesn't have. The converters need to handle reactive power, though, so the problem doesn't completely go away. Gah4 (talk) 22:11, 18 January 2022 (UTC)

Costs and reliability of sources
I took out the link to the breathless article claiming HVDC underground costs no more than overhead lines. The author of that piece seems (how to put it gently?) ill-informed, at the very best. He seems unaware that every HVDC converter must also have a power transformer (or two), and that because of their multiple windings and special construction they are more costly per MVA than an equivalent AC line transformer. He seems also uninformed about the relative costs of digging in a cable vs. overhead lines. Yes, overhead right of way is expensive too, but you don't get to bury cables along the highway for free either. Buried cables always cost several times as much as an overhead run...that's why we don't bury cables more often.

It would be a good practice when picking external links to make sure that the linked material is credible, authoritative, and well-informed; not some puff piece written by an "expert" who wouldn't know the difference betweeen a kw and a kwh. --Wtshymanski (talk) 14:26, 12 March 2009 (UTC)
 * I've taken it out again, for reasons described above. Neutral point of view, sure, but this article is just plain wrong. --Wtshymanski (talk) 16:17, 4 April 2009 (UTC)
 * As with underwater lines, buried cables also have extra capacitance. But yes it costs more to bury them. Electrolysis complicates buried DC lines, though. Gah4 (talk) 22:15, 18 January 2022 (UTC)
 * As with underwater lines, buried cables also have extra capacitance. But yes it costs more to bury them. Electrolysis complicates buried DC lines, though. Gah4 (talk) 22:15, 18 January 2022 (UTC)

TEXAS joins EAST grid?
Due to Texas wind farms now feeding presumably the USA EAST grid is it correct to still list TEXAS as being a grid unto itself? —Preceding unsigned comment added by 151.198.55.135 (talk) 18:20, 3 May 2009 (UTC)

File:4263517 High voltage direct current system.png
Can be used, a explanatory image, to improve the article.

Requirement of harmonic filters
This scheme has no harmonic filters at one terminal. Can a machine delivering reactive power make harmonic filters obsolete?

Intermediate Switching Stations
Inga-Shaba has intermediate switching stations. Under which circumstances is such equipment sensitive?

Photo Request
Can someone please make a photograph of the crossing of HVDC CU and Square Butte situated at 47.04667°N, -100.09694°W? It would be the unique chance to take a photograph showing 2 different HVDC lines!

 * I have posted a request at Wikipedia talk:WikiProject North Dakota. —EncMstr (talk) 16:26, 7 October 2009 (UTC)
 * Done. --Wtshymanski (talk) 02:41, 3 June 2010 (UTC)

inherent properties of the transmission line
what inherent properties of the transmission line is used now in a.c. networks  to regulate the power? Wdl1961 (talk) 22:03, 15 October 2009 (UTC)
 * Shorthand for "phase angle divided by series impedance". The point is that load flow through an AC line doesn't require real-time communication links between the ends like a DC link needs. --Wtshymanski (talk) 01:16, 16 October 2009 (UTC)
 * the question is what determines the power generation (kw) in the sources in the net. it is not the property of the transmission line.Wdl1961 (talk) 01:33, 16 October 2009 (UTC)
 * Not talking about the generation end, just about flow through the network. The main idea is that for a DC link you must coordinate the converters at both ends, whereas for an AC link the power flow is a consequence of the impedance of the line and the phase angles at each end. This means that *every* DC  link must have coordination, where as most AC lines don't need anything special to control power flow ( or rather, that power flow is a consequence of the system properties and not specifically commanded for each line).  Sometimes you find phase-angle shifting transformers on one parallel AC line to balance load flow along parallel paths but this is the exception. --Wtshymanski (talk) 13:10, 16 October 2009 (UTC)
 * exactly . the property of a transmission line is a small part of the system property, not the governing factor except for some nebulous upper limit. Wdl1961 (talk) 13:59, 16 October 2009 (UTC)
 * An example would clarify what I'm concerned about. Suppose you have two substations connected by a 138 kV line built in 1959, with all its hardware rated for 1000 amps (for discussion purposes). Suppose a second line is built 50 years later, in parallel with the first between the same two busses, rated 2000 amps. The new line will have very close to the same impedance as the first (has to, it will be about the same phase/phase spacing, etc. because of the voltage class). Unless something is installed to manipulate the phase angle between the voltages at the end of the lines, there's no way to ensure that the lines divide current according to their ratings - no way to ensure the new line carries 2/3 of the current. With DC, the magnitude ( and direction) of power flow can be directly manipulated - you basically give the converter stations an assignment, and they will change firing angles and tapchanger settings to make it come about.  I suppose hypothetically you could have X megawatts flowing east to west down an AC line and the parallel DC line could be ordered to send X megawatts back west to east.  This sort of flexibility isn't possible with AC. This is NOT talking about generation, which is regulated by frequency droop as the earlier edit described.
 * The stability limit for a line is not a nebulous upper limit - if the phase angle between terminal voltages hits 90 degrees, you cannot ship any more power over the line. Prudence dictates that this limit is not approached due to momentary load fluctuations and contingencies of losing generation or a line. --Wtshymanski (talk) 15:22, 16 October 2009 (UTC)
 * basically the power generated is determined by the frequency on the net and therefore on transmission lines .stability is achieved  with droop controlling the generators . problem is each time another factor is mentioned  one is wrong  in the margin . therefore it is advisable keep it simple or write an articel on control and stability. also it is possible to run ac in a circle .Wdl1961 (talk) 16:01, 16 October 2009 (UTC)

here are a few references about control of HVDC. these do not appear to use properties of transmission lines

Stability analysis of HVDC control loops The influence of HVDC control loops on the dynamic stability of an overall HVDC- HVAC system is discussed. The eigenvalue decomposition is used for the ...

cat.inist.fr/?aModele=afficheN&cpsidt=1795072 - - Similar pages ANFIS based HVDC control and fault identification of HVDC converter of ANFIS for HVDC control is given in Section 4. Section 5 presents use .... train ANFIS based control, training data is obtained from HVDC system, ...

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[hal-00407666, v1] HVDC Control Strategies to Improve Transient ... 27 Jul 2009 ... First, the HVDC control settings are unchanged during the disturbance. ... This paper focuses on four control strategies for the HVDC- ...

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there is more.Wdl1961 (talk) 01:26, 20 October 2009 (UTC)

 * One more time. WP:AGF and all that. Suppose I have two different transmission lines. One is a set of HVDC inverters. The other is just an AC line. I can walk up to the controls of the inverters and dial in any transmission level I want, from 0 to + or - the full rating of the ivnerters - the power flow in that line is independantly controllable.  For an AC line, I have nothing to manipulate - the power flow through that line depends only on the phase angle difference between the two busses at the ends of the line, and the line impedance (which is fixed and which is the inherent property of the transmission line). There's nothing to manipulate, the power flow through that AC line falls out as a consequence of the behavior of the system. That's a key difference between AC and HVDC transmission because you can use the power flow setting of an HVDC link to stabilize a whole system, whereas once the phase angles at the ends of an AC line hit a 90 degree difference, the line cannot help send power where its needed any more.  The only way you can independantly control flow on an AC line is to add a phase-shifting transformer, but most AC lines don't have this. --Wtshymanski (talk) 14:28, 9 November 2009 (UTC)
 * yes but that is not used to regulate power generation . all these electrical engineers do not know this and do not put the required equipment or adjust the phase angle of the generator in the system for normal operation .read the refs pls!Wdl1961 (talk) 14:49, 9 November 2009 (UTC)
 * But, once again, this isn't talking about power *generation* (power leaving the generator terminals), but the flow in one branch of the network. Not the tide rising in the sea, but the ripples in one part of the harbor. And you (indirectly) do adjust the phase angle of the internal voltage of generators automatically to regulate power flow - one increases load delievered by a generator essentially by opening up a valve to increase the speed of the prime mover, which increases the phase angle of the internal voltage with respect to the network and thereby increases power flow from the generator. But you don't have a valve to turn on a transmission line and must accept whatever flow comes out of the difference in phase angles at its ends. You are conflating two different things - power generation in one or more generators, and power flow in one branch of a network.  Note that all your references talk about controlling flow on a DC link - because it *can* be independantly controlled. Not so for AC. --Wtshymanski (talk) 15:39, 9 November 2009 (UTC)
 * pls refer to equivalent circuits and parallel impedances etc. in eng handbooks.Wdl1961 (talk) 16:32, 9 November 2009 (UTC)

regulation and control goes from zero to max cap sim to a gaspedal .max  cp is limit. Wdl1961 (talk) 02:08, 19 January 2010 (UTC)
 * This isn't even English. Once again, the power over an AC line is given by the products of the sending and receiving voltages and the sine of the angle between them, divided by the reactance. In an AC line that is part of a network, you don't (easily) get to manipulate any of these variables (unless you go to tap changing transformers or phase-shifting transformers or series capacitors,etc.). In an HVDC link, the amount of power sent over the line is dialled in up to the thermal limits of the equipment - you must coordinate both ends of the link, though.  This is what I've been trying to convey for the last several months and which you apparently don't or won't understand. This is a critical difference and advantage to an HVDC link as it can stabilize parts of a network that are otherwise drifting toward the stability limit - when delta hits 90 degrees, you can't send any more power over an AC link, but phase angle between the buses doesn't affect an HVDC link.  Here's a picture of the equation I'm referring to.

thumb|right|200px| Stability equation 14-56 out of Fink and Beaty.
 * You wouldn't happen to be from Boise, would you? --Wtshymanski (talk) 04:56, 19 January 2010 (UTC)

 * In a utility which has transmission lines from several directions serving a large load center, phase shifting transformers are the standard, to prevent some lines being overloaded while others were far below capacity. Series inductors could also be used to hold back flow which would otherwise overload a line. In the example above of an old line rated at 1000 amps parallel with a new line rated at 2000 amps, wouldn't the new line have larger conductors, with less resistance? And why would it have the same conductor configuration (like 2 spaced conductors rather than more?). This should cause it to carry more of the load automatically. The utility would run a load flow study and use inductors or phase shifters to regulate the flow. If different lines connect different generating stations to a load center, the generators can be used to balance the flow on the lines, or the lines would be designed to aid in economic dispatch of generation, since the generators are typically more expensive than the lines. An AC transmission line would have high speed communications for relaying purposes, to trip in high speed for a fault on the line. There would be metering for load flow purposes, telemetered to a system dispatch center. HVDC systems have inherent control of current flow in fault conditions, unlike AC systems. Basically I agree with Wtshymanski here. Edison (talk) 14:34, 19 January 2010 (UTC)
 * Resistance, being so much smaller than reactance, has little effect on power flow in this sort of case. Resistance, conductor spacing, reactance, etc. are what I was referring to as "inherent properties of the line" which someone objected to; phase shifting transformers and inductors are external measures to override these properties, as I said. With a pair of HVDC converters, you can tell it "Go to 83% of rated power" and it will send that much power over the line, (broadly) independently of the voltages or phase angles at either end. Yes, long AC lines have communication *for protection* but this doesn't affect power transfer over the line (aside from interrupting it). AND IT'S GOT NOTHING TO DO WITH GOVERNOR DROOP! (Sorry....must go lie down now...)--Wtshymanski (talk) 14:47, 19 January 2010 (UTC)
 * I have an example in my own back yard (practically). Manitoba is tied to Ontario on the east, and to Minnesota on the south. The tie to Ontario is small, 300 or 400 MVA maximum capacity. The 500 kV to the US is much stiffer. Both sides are part of MAPP so are synchronous, but the Ontario link goes around the north side of Lake Superior, while the American end is tied through a much stiffer system to the south. The only way to control exports at the Whiteshell link to Ontario is through phase-shifting transformers. See  for example. If either link was HVDC, we wouldn't need to worry about the phase difference between the two links. Recall that during the Great Blackout of August 2003 that one of the reasons the effects rippled on up into Northern Ontario was that power flows change direction around the Great Lakes - it's all one big loop. --Wtshymanski (talk) 15:02, 19 January 2010 (UTC)

quote """In contrast to AC systems, realizing multiterminal systems is complex, as is expanding existing schemes to multiterminal systems. Controlling power flow in a multiterminal DC system requires good communication between all the terminals; power flow must be actively regulated by the inverter control system """"  how is this done,not how it is not done???Wdl1961 (talk) 15:41, 19 January 2010 (UTC)
 * And in English your question is? I'm having a hard time translating from garble. Didn't you just post a large number of references to how HVDC systems are controlled? And now you're asking how DC converters are controlled? --Wtshymanski (talk) 22:39, 19 January 2010 (UTC)

,

try for ac current(i) = voltage / impedance(i)    i=1,2,3,4,---,n. usually the voltage is regulated instantly by powerplants.Wdl1961 (talk) 20:00, 31 January 2010 (UTC)

 * impedance = x+iy where i =  $$\sqrt{-1}$$       Wdl1961 (talk) 17:04, 18 March 2010 (UTC)

Back to back
It is possible to go from one frequency to another without rectification. It is used in motor drives. Wdl1961 (talk) 15:18, 1 November 2009 (UTC)
 * That's a cycloconverter and has nothing to do with HVDC transmission. --Wtshymanski (talk) 04:56, 19 January 2010 (UTC)

 * Back to back is not distance transmission, it is connection.Wdl1961 (talk) 18:06, 14 March 2010 (UTC)

Costs of high voltage DC transmission
Am I the only one who cannot parse this?:

"For an 8 GW 40 km link laid under the English Channel, the following are approximate primary equipment costs for a 2000 MW 500 kV bipolar conventional HVDC link... "

The cited reference cannot be "reasonably well relied upon" given that the quotation is pretty well garbled. What is the point it is trying to make? An anonymous reference is no reference at all, because it is unverifiable.

This section has nothing to say, except there is no reliably sourced data on HVDC costs. --Albany45 (talk) 13:14, 8 June 2010 (UTC)
 * See above. You know what to do. --Wtshymanski (talk) 20:48, 8 June 2010 (UTC)

 * Deleted section. Info on commercial suppliers might be useful somewhere else. --Albany45 (talk) 02:47, 10 June 2010 (UTC)

Quoted by Lawrence Berkeley National Laboratory
While trolling through the Web on a quest for cheap references, I found. It appears to rip off quote extensively from an earlier version of this article. We must be doing something right if it's worth putting on Governor Schwartzenegar's desk. Pity they garbled it somewhat. --Wtshymanski (talk) 20:48, 8 June 2010 (UTC)

Graphics of HVDC in Europe
There seems to be a mismatch between the descriptions to

http://upload.wikimedia.org/wikipedia/commons/thumb/a/ab/HVDC_Europe.svg/350px-HVDC_Europe.svg.png  "On the main article" and http://upload.wikimedia.org/wikipedia/commons/thumb/5/51/HVDC_Europe_annotated.svg/400px-HVDC_Europe_annotated.svg.png  "Annotated version"

"Under construction" and "Under consideration" are switched. I think the annotated version has it right, but could someone more familiar with the article take a look at this?

Thanks, Satan_Klaus —Preceding unsigned comment added by 84.160.50.191 (talk) 11:08, 7 August 2010 (UTC)
 * I've all ready changed it. BritNed is allmost finisched (the green line between Britan and the Netherlands. You can look at the website or the articles assosiated with the shown lines (which largely don't exist for the proposed projects): http://en.wikipedia.org/wiki/List_of_HVDC_projects#Europe Pcmadman (talk) 02:54, 20 September 2010 (UTC)

Hello, I think one more European connection can be added to the map as the SIEMENS company have launched in 2011 the Inelfe-Baixas project on the French-Spanish border with a 2x1000 MW HVDC PLUS (AC 400 kV, DC +/-320 kV) station. 212.160.202.180 (talk) 07:31, 15 December 2011 (UTC)

One additional issue with the map. The France / Spain inter-connector is now built and operational http://www.ree.es/en/activities/unique-projects/new-interconnection-with-france — Preceding unsigned comment added by Jfparis (talk • contribs) 14:08, 17 February 2017 (UTC)

AC network interconnections
The "AC network interconnections" section is missing citation, which makes it hard to veryfie, and is not usable as a reference.

81.225.97.154 (talk) 18:25, 31 October 2010 (UTC) Gego/XAREN

Rewrite sentence
Could someone who understands the subject rewrite "At such operation mode, it is possible that transmission can be continued, if one conductor fails, however with greater losses and possibly with less transmission capacity, if ground electrodes or lines are not designed for the load of both poles." This sentence does not make much sense, there are a few too many clauses that appear disjointed. 192.16.184.140 (talk) 10:49, 22 November 2010 (UTC)
 * Fixed. --Wtshymanski (talk) 17:58, 9 March 2011 (UTC)

Update image
Now that the second cable from the south of the UK has been opened, perhaps the images should be updated. Esn (talk) 05:25, 4 May 2011 (UTC)

BBC?
BBC is mentioned, but after a a short confusion about what BBC has to do with high voltage, a quick check reveals the current name of that company is ABB. Article aslo meantions ASEA a lot, that too is now ABB. Is this article really the right place for a history lesson? 83.227.1.122 (talk) 08:59, 8 September 2011 (UTC)
 * Well...yes. Anyone who wants to know what happened to Brown Boveri or ASEA only has to click on the link to eventually get the ABB story; we should report HVDC projects with the manufacturer's names as they were at the time the project was built. It's confusing to refer to a congolomerate that didn't exist until decades after the project was built. --Wtshymanski (talk) 13:15, 8 September 2011 (UTC)

Siemens info from
I am not an expert in this area, but found further detailed info (in pretty much this format) at http://www.energy.siemens.com/fi/pool/hq/power-transmission/HVDC/HVDC_Proven_Technology.pdf some of which may be added whist avoiding copyright infringement. Particularly thought that the figures were informative 1-1, 1-2 and section 4. Would an expert in this area be able to compare and see if useful additions may be made to improve the quality of this article. Thanks --DrSteveEllis (talk) 11:22, 26 September 2012 (UTC) Figures 1-1 and 1-2 would certainly be useful. They would need to be re-drawn in order to avoid copyright but that would not be difficult. Clampower (talk) 20:13, 3 October 2012 (UTC)

Applications
I have just made quite a large number of text changes to improve clarity, but could not help noticing that the section "Applications" right at the very end seems to be in the wrong place. Shouldn't it be moved to somewhere near the start of the article? Clampower (talk) 20:13, 3 October 2012 (UTC)

 * Applications are discussed throughout the article. If you're talking about real world PROJECTS there's a list of them which I've put in as a section, rather than just a "see also". It's at List of HVDC projects. When you check it out you'll see why we didn't shoehorn it into the article, as it's large and rather amazing. The current "applications" section is really a little section on theory of future applications, so I've retitled it. And no, since this is an article about the technology itself, we don't discuss this stuff till the end. Just as an article on automobiles would discuss particular models of automobiles (as examples) until near the end, and certainly wouldn't contain a list of them, as it's too long. And future automobile plan and theory goes at the end, since it's the future and isn't yet real. S  B Harris 02:26, 4 October 2012 (UTC)

I quite agree that "the future" needs to be discussed at the end of the article. My point is just that quite a lot of what is currently in the first two sub-sections under "Applications" is NOT about the future, but actually about the past and present. Things like the ability to inter-link 50Hz and 60Hz networks, efficiently carry power long distances from remote generating sources etc, have been known (and used) for decades. So my point is just that I think those bits ought to appear earlier in the article, around the same point as the section on "advantages and disadvantages". Anything future-looking, like multi-terminal DC grids, using HVDC to transport solar energy from Africa to Europe etc, should rightly be at the end.Clampower (talk) 11:42, 4 October 2012 (UTC)

 * Agree. Okay, go ahead and add the ability to connect grids of differing frequencies up toward the front. I think it should be even mentioned in the lede as a neat "feature." The "applications" section as it was, really looked forward to a time when all grids of the world would be connected in some way by HVDC links. S  B Harris 19:53, 4 October 2012 (UTC)
 * The entire Applications section could be removed, with a selection of the most relevant content relocated into the sections earlier in the article about "Advantages". The specific applications of HVDC that are described in the current Applications section are all instances where HVDC has been chosen because of the benefits it provides.  I think this re-arrangement would be an improvement, and eliminate the current duplication of content. Marshelec (talk) 05:19, 14 October 2012 (UTC)

Electrode line article needs a hand
If you are knowledgeable about HVDC, please take a look at the electrode line article which needs a hand (expansion and references). Katana (talk) 20:41, 30 October 2012 (UTC)
 * The Electrode Line article has had exactly 1 edit since I wrote this, and it is an excellent large and referenced expansion by Clampower - good job and case closed. Katana (talk) 14:43, 12 April 2013 (UTC)

Sunrise Powerlink
Sunrise Powerlink is an AC line! — Preceding unsigned comment added by 91.46.154.156 (talk) 18:31, 9 December 2012 (UTC)
 * If anyone has any clue where to look for a citable reference on this point, per WP:V, please join in the discussion at Talk:Sunrise Powerlink, and eventually help fix the {cn} tag I just added here. --Nigelj (talk) 20:15, 9 December 2012 (UTC)

Symmetrical Monopole
Cross Channel is still considered a "bipole" even though ground return is not possible, because each end (of each bipole) contains two completely independent converters. A fault in one converter does not shut down the entire bipole (as would happen for NorNed) because the bipole can still operate with the faulted converter bypassed and its HV cable used as the neutral return. Clampower (talk) 19:29, 14 December 2012 (UTC)

Dead link
Hi there. I am completely new to wikipedia, but I found a dead link (currently referece 25 to a pdf of ABB) and I think I found the new location of the reference. I don't know how the procedure is to fix that, but I wanted to let you know, in case someone has the time to fix that. the new location is http://new.abb.com/docs/default-source/default-document-library/hybrid-hvdc-breaker---an-innovation-breakthrough-for-reliable-hvdc-gridsnov2012finmc20121210_clean.pdf?sfvrsn=2 — Preceding unsigned comment added by 129.132.125.221 (talk) 09:17, 13 January 2014 (UTC)
 * Thank you ... I have updated the link.  Dwpaul   Talk   17:29, 13 January 2014 (UTC)

Correctly summarizing material
Per this edit, Wikipedia is not a reliable source and the claim that this was the "AC system of George Westinghouse and Nikola Tesla" is incorrect. The Westinghouse AC system was based on the work of many engineers, not just Tesla, including the early work of Lucien Gaulard, John Dixon Gibbs and the developments of Westinghouse engineers William Stanley (who developed the first AC transformer), Vladimir Zworykin, Oliver B. Shallenberger, Stephen Timoshenko, and Benjamin Garver Lamme. Westinghouse started installing AC systems in 1886, two full years before Tesla got into the business and the company was eating Edison lunch by 1887, that led into the War of Currents (given a start date of December 1887 (Empires Of Light By Jill Jonnes, page 419). The "War" was a battle of lighting businesses, AC Arc vs DC incandescent (The 100 Most Significant Events in American Business: An Encyclopedia By Quentin R. Skrabec, page 86) so Tesla's July 1888 licensing of his induction motor patents to Westinghouse didn't come into it. The "War" was over by either: 1890 (Edison Machine entered AC biz), or the 1891 International Electro-Technical Exhibition, or the 1892 merger of Edison Electric into GE and the ouster of Edison...... take your pick. Tesla's AC motor was still on the back burner at Westinghouse at that point (George Westinghouse: Gentle Genius By Quentin R. Skrabec page 127). The Tesla induction motor patent did become important to the Westinghouse system in later patent battles but that was after the "War" and a motor is only one quarter of a system, you also have to have lighting, generators, and transformers - none of which were invented by Tesla. Fountains of Bryn Mawr (talk) 04:14, 5 February 2015 (UTC)

Applications of HVDC transmission technology
I add on one more important applications especially for now and the future, which is the integration of renewable resources such as wind into the main transmission grid. One of the challenges of renewable power generation like wind and solar power is that it can be interrupted, and this variability affects the stability of the power produced. HVDC is so far the best technology for integrating more intermittent forms of renewable energy into the local power grid, particularly over long distances. This is especially significant for large scale offshore wind projects, or large scale solar power production. — Preceding unsigned comment added by (talk) Shenyawang (talk) 01:42, 28 April 2015 (UTC)01:41, 28 April 2015 (UTC)

Rio Madeira line
This article's lead contains some misleading and out-of-date information. Here is the link from which I get my information: (as of June 14, 2015) there are 32 of the total planned 50 turbines operational. (Each with 71.5 MW capacity ...doing the math...) that's 2288 MW (so far, that dam is scheduled for completion in Nov 2016). There are also 3 other hydroelectric dams planned, only one of which is in construction. (I don't know if the others will contribute to the HVDC transmission, based on the claim that a total of over 6000 MW will be transmitted, I assume so -but the total MW claimed seems a bit high to me). The lede needs to change to reflect this information. That is the lede states "which consists of two bipoles of ±600 kV, 3150 MW each..." which is clearly not correct. I know almost nothing about HVDC transmission, but I'm guessing that only one bipole is operational. (No idea about whether both have been constructed).FWIW216.96.78.101 (talk) 17:34, 14 June 2015 (UTC)

External links modified
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Effiency of different technologies
In the article, one should make a comparision on the effiency of HVDC converters and inverters using mercury arc valves, thyristors and IGBTs. Which percentage of the transmitted power is required to steer these different valve types? How depends the amount of steering power from the load current? What is their lose, when the valve is conducting? — Preceding unsigned comment added by 93.236.153.175 (talk) 22:30, 27 September 2018 (UTC)

What late completion date?
Hi Wtshmansky, I was slightly worked up in my last revert on the "late completion date" question. Sorry about that. Maybe we can discuss here. 98.216.244.217 (talk) 09:04, 27 January 2019 (UTC)

We can go around and around on the edit summaries with me repeating myself and you playing WP:ICANTHEARYOU. Let's talk about it here instead. I see you're one of those rapid-fire editors who likes to make multiple edits per minute. Does that allow you to pay any attention to what you're doing? I'm thinking you're not paying attention.

If you want to mention that a war caused a delay, you need to provide sources that at least mention a delay in construction. The current source doesn't mention a delay in completion (probably because it's an unreliable PR sheet from a company who had a hand in building it!). Find a better source before replacing the material, see WP:burden. It also needs to be worded better to explain what delay it's talking about.

Mainly, find a ref that actually does the job. If you want to replace, you need to find at least one reliable secondary source (not a PR sheet) that says there was a delay in the construction caused by a Mozambique war -- and says it in a way that makes it notable to the HVDC subject. That's a tall order, but that's what you need to satisfy inclusion requirements and WP:burden. Reactionary WP:ICANTHEARYOU reverts don't cut the mustard.

98.216.244.217 (talk) 23:31, 27 January 2019 (UTC)

I fixed the biggest problem which was that a "late completion date" wasn't established as a thing in the text before it was suddenly referred to, and then it wasn't even mentioned by the ref. Service interruptions resulting from the war were mentioned by the ref so I changed it to that. It's still off topic, non-notable, ideological digression. It's still supported only by a self-published public-relations propaganda that even has "pressrelease" in its URL. But, at least the wording doesn't stand out as much as it did before for correction or removal. 98.216.244.217 (talk) 05:00, 29 January 2019 (UTC)

Ambiguous/Misleading efficiency comparison
"Depending on voltage level and construction details, HVDC transmission losses are quoted as less than 3% per 1,000 km, which are 30 to 40% less than with AC lines" This is a terribly ambiguous phrasing. It could either mean that AC has losses of 33%-43% per 1000km, or losses of 4%-5% per 1000km. OliverKlozoff (talk) 01:03, 28 June 2020 (UTC)
 * You could be more specific in which claims you are discussing, but I suspect that I agree. Gah4 (talk) 01:53, 28 June 2020 (UTC)
 * Ok, for one, it says: if the HVDC line can operate continuously with an HVDC voltage that is the same as the peak voltage of the AC equivalent line. Note the if.  As noted below about circuit breakers, arcing is a problem, so the DC system has to be arranged so that arcs don't start, or if they do, there is a way to stop them.  Gah4 (talk) 08:33, 28 June 2020 (UTC)
 * Ok, for one, it says: if the HVDC line can operate continuously with an HVDC voltage that is the same as the peak voltage of the AC equivalent line. Note the if.  As noted below about circuit breakers, arcing is a problem, so the DC system has to be arranged so that arcs don't start, or if they do, there is a way to stop them.  Gah4 (talk) 08:33, 28 June 2020 (UTC)

Capacitor-commutated converters (CCC)
Which HVDC schemes use Capacitor-commutated converters (CCC)? — Preceding unsigned comment added by 2003:DF:1F25:7650:D7B:5B87:6F99:D1FE (talk) 20:41, 4 November 2020 (UTC)

Qualifiers
The first sentence of the lead says, "A high-voltage, direct current (HVDC) electric power transmission system (also called a power superhighway or an electrical superhighway) uses direct current (DC) for the controlled bulk transmission of electrical power, in contrast with the more common alternating current (AC) systems." It is unclear to me what we're trying to accompliish with the "controlled bulk" qualifiers here. recently added "controlled". It would seem that we could make things easier for readers by leaving out these qualifiers. If they need to remain, there needs to be some further explaination of this jargon. ~Kvng (talk) 13:47, 1 October 2021 (UTC)

 * HVDC systems are controlled, unlike AC interconnectors. And that's a crucial difference. For example, historically the USA's Eastern and Western interconnections were AC linked. This made the overall system horribly unstable. When they were replaced with HVDC in 1975, or so, the system immediately stabilised. And that's because the generators were hunting trying to stabilise the phaze, and the interconnection was giving variable power based on the phase angle. With HVDC they can just set it to some value, and either side will stabilize itself around it. GliderMaven (talk) 17:31, 1 October 2021 (UTC)
 * OK, I now see this is connected to the 3rd paragraph of the lead. But controlled in the first sentence of the lead is a forward reference and is not helping readers. I have removed it. ~Kvng (talk) 18:00, 4 October 2021 (UTC)

Change ABB to Hitachi?
The ABB Power Grid unit (originally part of ASEA) was sold to Hitachi two years ago. Should we switch all references to ABB to Hitachi instead? jax (talk) 10:22, 9 September 2022 (UTC)
 * No, becauase ABB was the company name at the time. Thei article is about high voltage direct current transmission, not what company owns what other company. --Wtshymanski (talk) 00:18, 17 September 2022 (UTC)

Bundling of conductors.
An overhead line strung with a bundle of stranded conductors (or indeed any stranded cable) behaves in the same way as a solid conductor of equivalent cross sectional area. The varying magnetic field of alternating current forces the current to the outside of the strands or solid conductor if it is larger in diameter than twice the skin depth. The advantage of stranded cables is solely that they are easier to handle, transport and install because they are much more flexible (and possibly cheaper to make).

If more current capacity is required compared with a single cable (stranded or otherwise) that can carry the current without significantly exhibiting the skin effect (roughly 27 mm or so for the normally encountered utility frequencies in copper conductors), then separate multiple conductors are employed.

Although not relevant to this case, Litz wire does carry the current distributed in all the strands of the bundle, but only because the strands are insulated from each other which changes everything. The magnetic field cannot force the current through the insulation (though, of course, it will try). 109.152.150.247 (talk) 18:28, 14 February 2023 (UTC)

 * Note: This was posted in response to a revert that was made in error. The post can remain for information to anyone interested. 109.152.150.247 (talk) 13:28, 17 February 2023 (UTC)

title: Talk:High-voltage direct current


text:
Bokeh

In photography, bokeh ( or  ; ) is the aesthetic quality of the blur produced in out-of-focus parts of an image, whether foreground or background or both. It is created by using a wide aperture lens.

Some photographers incorrectly restrict use of the term bokeh to the appearance of bright spots in the out-of-focus area caused by circles of confusion. Bokeh has also been defined as "the way the lens renders out-of-focus points of light". Differences in lens aberrations and aperture shape cause very different bokeh effects. Some lens designs blur the image in a way that is pleasing to the eye, while others produce distracting or unpleasant blurring ("good" and "bad" bokeh, respectively). Photographers may deliberately use a shallow focus technique to create images with prominent out-of-focus regions, accentuating their lens's bokeh.

Bokeh is often most visible around small background highlights, such as specular reflections and light sources, which is why it is often associated with such areas. However, bokeh is not limited to highlights; blur occurs in all regions of an image which are outside the depth of field.

The opposite of bokeh—an image in which multiple distances are visible and all are in focus—is deep focus.

Etymology
The term comes from the Japanese word boke (暈け/ボケ), which means "blur" or "haze", resulting in boke-aji (ボケ味), the "blur quality". This is derived as a noun form of the verb bokeru, which is written in several ways, with additional meanings and nuances: 暈ける refers to being blurry, hazy or out-of-focus, whereas the 惚ける and 呆ける spellings refer to being mentally hazy, befuddled, childish, senile, or playing stupid. Jisaboke (時差ボケ) (literally, "time difference fog") is the term for jet lag. Nebokeru (寝ぼける) is a verb denoting the actions or condition of someone who is half-asleep, or nodding off. Tobokeru means playing dumb, and toboketa kao refers to a poker face. The related term bokashi (暈かし) means intentional blurring or gradation; that is a noun form of the transitive verb bokasu (暈す), which means to make something blurry, rather than to be blurry.

Use abroad
The English spelling bokeh was popularized in 1997 in Photo Techniques magazine, when Mike Johnston, the editor at the time, commissioned three papers on the topic for the May/June 1997 issue; he altered the spelling to suggest the correct pronunciation to English speakers, saying "it is properly pronounced with bo as in bone and ke as in Kenneth, with equal stress on either syllable".

The spellings bokeh and boke have both been in use since at least 1996, when Merklinger had suggested "or Bokeh if you prefer." The term bokeh has appeared in photography books as early as 1998. It is sometimes pronounced.

Bokeh and lens design
Though difficult to quantify, some lenses have subjectively more pleasing out-of-focus areas. "Good" bokeh is especially important for macro lenses and long telephoto lenses, because they are typically used in situations that produce shallow depth of field. Good bokeh is also important for medium telephoto lenses (typically 85–150 mm on 35 mm format). When used in portrait photography (for their "natural" perspective), the photographer usually wants a shallow depth of field, so that the subject stands out sharply against a blurred background.

Bokeh characteristics may be quantified by examining the image's circle of confusion. In out-of-focus areas, each point of light becomes an image of the aperture, generally a more or less round disc. Depending on how a lens is corrected for spherical aberration, the disc may be uniformly illuminated, brighter near the edge, or brighter near the center. A well-known lens that exhibited the latter "soap-bubble" characteristic was that produced by Hugo Meyer & Co., more recently revived by Meyer Optik Görlitz.

Lenses that are poorly corrected for spherical aberration will show one kind of disc for out-of-focus points in front of the plane of focus, and a different kind for points behind. This may actually be desirable, as blur circles that are dimmer near the edges produce less-defined shapes which blend smoothly with the surrounding image. The shape of the aperture has an influence on the subjective quality of bokeh as well. For conventional lens designs (with bladed apertures), when a lens is stopped down smaller than its maximum aperture size (minimum f-number), out-of-focus points are blurred into the polygonal shape formed by the aperture blades. This is most apparent when a lens produces hard-edged bokeh. For this reason, some lenses have many aperture blades and/or blades with curved edges to make the aperture more closely approximate a circle rather than a polygon. Minolta has been on the forefront of promoting and introducing lenses with near-ideal circular apertures since 1987, but most other manufacturers now offer lenses with shape-optimized diaphragms, at least for the domain of portraiture photography. In contrast, a catadioptric telephoto lens renders bokehs resembling doughnuts, because its secondary mirror blocks the central part of the aperture opening. Recently, photographers have exploited the shape of the bokeh by creating a simple mask out of card with shapes such as hearts or stars, that the photographer wishes the bokeh to be, and placing it over the lens.

Lenses with 11, 12, or 15 blade iris diaphragms are often claimed to excel in bokeh quality. Because of this, the lenses do not need to reach wide apertures to get better circles (instead of polygons). In the past, wide aperture lenses (f/2, f/2.8) were very expensive, due to the complex mathematical design and manufacturing know-how required, at a time when all computations and glass making were done by hand. Leica could reach a good bokeh at f/4.5. Today it is much easier to make an f/1.8 lens, and a 9-bladed lens at f/1.8 is enough for an 85 mm lens to achieve great bokeh.

Some lens manufacturers including Nikon, Minolta, and Sony make lenses designed with specific controls to change the rendering of the out-of-focus areas.

The Nikon 105 mm DC-Nikkor and 135 mm DC-Nikkor lenses (DC stands for "Defocus Control") have a control ring that permits the overcorrection or undercorrection of spherical aberration to change the bokeh in front of and behind the focal plane.

The Minolta/Sony STF 135 mm f/2.8 [T4.5] (with STF standing for smooth trans focus) is a lens specifically designed to produce pleasing bokeh. It is possible to choose between two diaphragms: one with 9 and another with 10 blades. An apodization filter is used to soften the aperture edges which results in a smooth defocused area with gradually fading circles. Those qualities made it the only lens of this kind on the market from its introduction in 1999 to 2014. In 2014 Fujifilm announced a lens utilizing a similar apodization filter in the Fujinon XF 56mm F1.2 R APD lens. Sony added the Sony FE 100 mm F2.8 STF GM OSS in 2017.

The 'Sigma YS System Focusing' 135 mm f/2.8 also has an extra manually-moved component, intended to compensate for aberration at close-focus distances. It can be re-purposed for defocus control.

In 2015, Meyer Optik USA Inc. launched a Kickstarter campaign to produce the Trioplan f2.9/50, a new lens based on one originally produced by Hugo Meyer & Co.; both lenses exhibit a characteristic "soap-bubble" bokeh.

The use of anamorphic lenses will cause bokeh to appear differently along the horizontal and vertical axes of the lens, becoming ellipsoidal compared to those in a spherical lens.

In 2016, Apple Inc. released the iPhone 7 Plus which can take pictures with "Portrait Mode" (a bokeh like effect). Samsung's Galaxy Note 8 has a similar effect available. Both of these phones use dual cameras to detect edges and create a "depth map" of the image, which the phone uses to blur the out-of-focus portions of the photo. Other phones, like the Google Pixel, only use a single camera and machine learning to create the depth map.

In 2017, Vivo released a smartphone with dual front lenses for selfies with bokeh. The first, a 20 MP lens, uses a 1/2.78" sensor with f/2.0 aperture, while the second, an 8 MP f/2.0 lens, captures depth information. Bokeh can be made with a combination of both lenses, and shots can be refocused even after they are captured, adding bokeh effects with different depths.

In early 2018, the Honor 9 Lite smartphone was released with quad cameras (two dual-lens). Both the front and back cameras have a 13 MP main lens and a 2 MP lens for capturing bokeh depth information.

Emulation

Bokeh can be simulated by convolving the image with a kernel that corresponds to the image of an out-of-focus point source taken with a real camera. Unlike conventional convolution, this convolution has a kernel that depends on the distance of each image point and – at least in principle – has to include image points that are occluded by objects in the foreground. Also, bokeh is not just any blur. To a first approximation, defocus blur is convolution by a uniform disk, a more computationally intensive operation than the "standard" Gaussian blur; the former produces sharp circles around highlights whereas the latter is a much softer effect. Diffraction may alter the effective shape of the blur. Some graphics editors have a filter to do this, usually called "Lens Blur". Accurate bokeh simulation requires running the blur in linear, HDR space. For low dynamic range images, an artificial neural network may be used to reconstruct the HDR light.

An alternative mechanical mechanism has been proposed for generating bokeh in small aperture cameras such as compacts or cellphone cameras, called image destabilisation, in which both the lens and sensor are moved in order to maintain focus at one focal plane, while defocusing nearby ones. This effect currently generates blur in only one axis.

Some advanced digital cameras have bokeh features which take several images with different apertures and focuses and then manually compose them afterward to one image. More advanced systems of bokeh use a hardware system of 2 sensors, one sensor to take photo as usual while other ones record depth information. Bokeh effect and refocusing can then be applied to an image after the photo is taken.

Other applications
In 2009, a research group at MIT Media Lab showed that the bokeh effect can be used to make imperceptibly small barcodes, or bokodes. By using barcodes as small as 3 mm with a small lens over them, if the barcode is viewed out of focus through an ordinary camera focused at infinity, the resulting image is large enough to scan the information in the barcode.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Bokeh