HVDC - Science topic

Interesting

Yes, detecting faults in HVDC systems using travelling waves and analysing them with wavelet transforms in MATLAB is a valid approach. However, you're right, the transient nature of DC faults can make it challenging. Here's why and some alternative techniques to consider:

Monopolar HVDC system simulation:

1. Power System Model:

- AC Grid: Represented by a synchronous generator and connected to a local AC bus.

- DC Link: Modeled as a transmission line with an inductor and a capacitor representing the line impedance and energy storage, respectively.

- Rectifier: Modeled as a controlled current source that converts AC power to DC power.

- Inverter: Modeled as a controlled voltage source that converts DC power back to AC power.

2. Control Structure:

- Rectifier Control: The control strategy in the rectifier is typically based on regulating the DC voltage. It involves a feedback loop that adjusts the rectifier firing angle to maintain a desired DC voltage level.

- Inverter Control: The control strategy in the inverter is usually aimed at regulating the AC voltage and frequency. It involves a feedback loop that adjusts the inverter firing angle and frequency to match the AC grid conditions.

- DC Link Control: The control of the DC link involves regulating the DC current and maintaining the DC voltage within a specified range. This can be achieved using proportional-integral (PI) controllers or more advanced control techniques.

3. Simulation Steps:

- Define the power system model, including the AC grid, DC link, rectifier, and inverter.

- Implement the control structure for the rectifier, inverter, and DC link.

- Specify the initial conditions and parameters for the simulation.

- Run the simulation to observe the dynamic behavior of the Monopolar HVDC system under different operating conditions and disturbances.

To implement this simulation, you can use software tools such as MATLAB/SIMULINK, PSCAD, or other power system simulation software that supports HVDC modeling.

Good luck: partial credit AI

There are several ways to mitigate the harmonics on the HVDC converter station. However, the most common methods are:

1. Using AC harmonic filters. They create low-impedance paths to ground for specific harmonic frequencies which should be mitigated, and

2. Canceling out harmonics by using different converter configurations. Typically, 12 or 24 pulse bridges are deployed. 12 pulse bridge, for example, consists of two six-pulse bridges connected in series or parallel, with their AC connections supplied from a converter transformer that produces a 30° phase shift between the bridges.

Dear Md. Asaduzzaman Jabin,

I suggest you see the links on the topic.

Best regards

Dear Til Kristian Vrana

Please take a look at these sites

Best regards

Dear Hamed Hanifi

welcome!

It is the firs time that I read your comment on my post on your question.

I think such projects as Desertec are very required and strategic. However they need intensive cooperation and transparency in dealing with the project as well as fairly distributing its benefits to all partners.

I would like that you read the essay in the link:https://www.ecomena.org/desertec/

Best wishes

You may find useful information and examples in CIGRE Technical Brochures 368, 492, and 831.

Best regards, Giulio Santagostino

Fault classification and location in Bipole HVDC transmission systems with a dedicated metallic return wire is a currently research topic. If you can find EMTP based test case, you can just create different types of faults at different locations such as along the line, bus, inside the converter, AC side, etc, and capture the transient responses. You can just feed the captured snapshots after faults and feed to a ANN based classifier available in Matlab, you can come with a results which more likely can be published in a reputed electrical in engineering conference.

I believe there is an autotune feature in this model.

I think I have a useful book for your requirements. Send me your contact information.

Corona is there because of the ionization around a charge carrying conductor. Since the negative terminal of a DC link carries negative charge, it repels the negative charge around the conductor reducing the chances of ionization and hence less corona is observed around it.

The following link may help for MMC-HVDC transmission.

Hi Im tuning 4 VSC stations for a HVDC grid, modulus optimum and symmetrical optimum. works????

The important aspects are power losses and electromagnetic interferences caused by corona. Both problems are described in numerous publications.

Here is the full-text of the paper.

Try to contact him via Reseachgates messages

this may help.

AC-DC !

Definitely it should be used several applications in control room for weather hazard on power system. SCADA system will be first source of information from power system and in control room can be used like base source for other application in control room. Smart grid applications in control room should have Intelligent Alarm Processing system, IAP. That application are feed from SCADA system and have special algorithm. With that, application will give in real time root cause analyses, which means it will be exactly pointed the first disturbance, which cause cascading event or blackout. Performance metrics for that application is running in real time, second or two delay in comparison with SCADA time. In circumstances like cascading events large amount of signals are inflow in SCADA and it is hard to recognized important signals for dispatcher in control room. Other applications in control room are weather applications. Lightning Location Detection system, LLS is crucial part of smart grid applications in control room. With that applications it is possible to track in real time storms and it is possible to do predictions where and when storms move. Performance metrics for that application is also real time, only few seconds’ delay after SCADA events. Complex LLS system use SCADA like source for own algorithm, beside the detection from lightning sensors. Blackout prediction is a complex process for Transmission System Operators, TSOs. It runs on various time horizons, yearly, monthly, daily, hourly and in almost second range. Energy Management System, EMS have state estimator which is operate each minute or more often in control center. In addition, it start calculations on topology change and calculate N-1 security constrain.

Ok with my pleasure

I agree with Prof. Abdelhalim Zekry

Good chance

Regards

Thanks, I will be back soon.

Omar Hazem MOHAMMED

Number of modules or valves = Operating voltage of converter / voltage rating of each module.

Normally the number pairs will be six to twelve...

Actually 1.2/50 microseconds is waveform of voltage impulse, not current impulse. Waveform of lightning current impulses, for example, for surge arrester testing is 8/20 microseconds. (30/60 or 45/90 microseconds for switching current impulses).

me too

Dear Saber,

What do you judge in your question is correct. It is so that the filters are designed to suppress the harmonics starting with the first harmonic after the fundamental. If you designed the filters at both sides at 50 Hz fundamental frequency in both sides it will work well at the 60Hz side as it will cuts off at an mealier frequency. But you can not use the 60 Hz side filter in both sides.

Best wuishes

whenever calculating rms values of the IGBTorThyristor current conduction period of individual switches are taken into consideration having said that i want to say that usually IGBTmodules or STAKPAK or thyristor valves are being used ,the total switching losses can be calculated by summing all the individual losses

Dear Affan,

You can find several examples for HVDC systems with relevant models in the Simscape Power Systems Examples of Matlab 2017. The directory to follow is listed below with a fig attached as reference.

Matlab>Simulink>Simscape>Power Systems>Specialized Technology>Facts>

Sufficiently answered,

A caution, earlier empirical formulae were voltage regulation based / loss based / temperature rise based/criteria applicable for radial lines, single m/c infinite source or long lines with ideal voltage sources. In integrated network with FACTS controllers, voltage and line length relationships have lost significance. For HVDC for example length is no limit and voltage options are based on choice of device and over all economy.

For cables, yes reactive power continues to dictate length and reactive compensation, and mechanical handling etc.

There are different types of earth electrode connections besides well type. There are separate earth connections with many earth switches in between and all separate earth connections converge into one main electrode connection. Off-course the connection of separate earthing depend upon specific topology. I would recommend you reading this document for more details.

2. http://cigre.ru/research_commitets/ik_rus/b4_rus/library/ALSTOM_HVDC_for_Beginners_and_Beyond.pdf

3. http://www.skb.com/publication/2485831/R-14-34.pdf

Did you try this link:

we have been using AC system and HVAC system for the past 100 years. Now with the significant improvements in DC and the FACTS devices, Thyristors etc, the HVDC is becoming viable for long distance power transfer, the break even would be 700 kms and 1000 MW transfer which does not required reactive power compensation, requires less number of conductors and reduced losses. the greatest advantages would be to reduce the loop flows in the AC system if planned carefully. I think Germany is utilizing multi terminal HVDC systems effectively to mitigate the wind and solar variability. 

Hi Nithya

I hope the attached document can help you in this regard

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

There are other related Authors on the particular.

All major grid planning suites facilitate power flow with HVDC links, e.g. PowerFactory, NEPLAN, PSS/E, Simpow. In addition, you can use open source programs like MATPOWER (running on MATLAB). Most of these programs even also support transient stability simulation (rms) with HVDC links.

PSCAD does not have any load flow module, but is most powerful for electromagnetic transient simations (emt).

I have to maximize hvdc transmission power. 

Hi

In HVDC systems, Converter control parameters can determine the power flow. for example Control firing angle of converters.base reference in hvdc systems is:

Power System Stability and Control 1st Edition

by Prabha Kundur (Author) chapter10

thanks guys

Very important are the transient stability, oscillation produced in power system, reason why we cannot run system, at unity p.f (though it is efficient and economica) even with online fast computer control (instrumentation, protection and control) at load dispatched center.

PSCAD with ETAP is a good choice. I would prefer using MATLAB & SIMULINK with its power system toolkit.

ABB and SEL are the leading protection relay manufacturers operating in the GOOSE/IEC61850 space.  RuggedCOM, recently became a Siemens subsidiary, supply the first IEC61850 grade switches.  You should be able to find white papers from each of these companies implying what the minimum lags that their devices transmit at, and you can maybe make assumptions based on those documents.

Arm overcurrent protection turning IGBTs off after the threshold be passed

hello Orlando Nina Ali

i think the attachment is beneficial for you.

have a nice day 

Ms Sanjoy

Thanks for your advice and your time

I will review that information

Thanks for your valuable answers

Thanks for your valuable answers

Conceptual base for corona effect: local electric field exceeding the critical value, free charges and ionization process.

Possibilities to reduce corona effect: Lower applied voltage, larger diameter of the conductors, optimized arrangement and diameter of conductors when in bundle, suitable condition of the conductors surface (smooth, without nicks or burrs or scrapes), the condition of the hardware surface, its position and shape (rounded rather than sharp edges and no protruding bolts with sharp edges).

It depends on the technology. The line-commutated-converter (LCC)-based HVDC can change the power direction by shifting the firing angle, whereas the voultage-source-converter (VSC)-based HVDC do not need to reverse voltage polarity, only the current need to be changed.

regards.

Dear Samuel,

That’s not the way I see it.

At first glance, it seems that DG is much better than HVDC however, the transmission network of a country can be connected to the grids of its neighboring countries using HVDC technology and as a result, such interconnected systems can provide so many technical and economic benefits for each country at a macro level.

Furthermore, the private investments on DG installation seem a time-consuming and lengthy process.

What is your idea?

Dear Inno Davidson,

Please read the abstract for the article:  HVDC tapping station: power tapping from a DC transmission line to a local AC network

The authors describe a new concept for tapping off a small amount of power from a high voltage direct current (HVDC) transmission line to a local network. The proposed new concept for a series tapping implies power conversion in two steps from the line to a local AC network. This will make it possible to the use a single phase transformer between the DC line potential and ground. The converter bridge connected in series in the DC transmission is of the current source line-commutated type, while the other two converters are of the voltage-source forced-commutated type. The basic functions of the converter are described and illustrated by the results from simulations with the EMTP program.

Check the link for full paper download.

Regards

VSC -HVDC is basically converting AC to DC and then DC to the AC. FACTS devices are basically  for the increase in transfer capability,  improvement in transient stability voltage stability etc. In VSC-HVDC both controllers are series-series connected. None of the controllers inject any voltage either in series or parallel. FACTs devices are basically injecting the voltage in phase with with  terminal voltage, in loss or perpendicular with the current. Therefore in my view VSC-HVDC shall not be included in the FACTS category.

Dear Mohammad

you can try MATLAB, PSCAD, EMTP-rv, Neplan

good luck

Thanks for your valuable answers

Thanks for your valuable answers

Both are complementary technologies:

The role of HVDC is to interconnect ac systems where a reliable ac interconnectionwould be too expensive :-Independent frequency and control. -Lower line cost . -Power control, voltage control and stability control possible

 The large market potential for FACTS is within AC system on a value added basis where : -The existing steady-state phase angle between bus node is reasonable. -The cost of FACTS solution is lower than the HVDC cost . -The required FACTS controller capacity is lesser than the transmission rating

Active filters are frequently considered for HVDC systems because they provide superior harmonic performance and avoid problems which are often encountered in passive filter applications,but also more costly!

Maybe my  paper could help you,:

This paper presents a comparison between HVDC link and an HVAC link in a 29 Bus multimachine system, based on load flow analysis using Newton-Raphson method for the AC link case, and sequential method for the HVDC link case.

Thanks, Ali, I mistakenly assumed no grounding loop exists in the system, so the high impedance grounding will not shift the grounding potential.

Now I realize the grounding loops may be formed by AC side filters and dc grounding or cable parasitic capacitors, which will increase the insulation requirement for components in a high impedance grounding system.

Thanks again Vyas,

But i want some good journals like IEEE Transactions, Elsevier Journals and Taylor and Francis Journals.

I dont think that k=1.2 is to allow blanking time between switching ON a switch after turning OFF another switch of the same leg. Because by cheking the model both switches of the same leg change at the same time after the "Relational Operator".

Dear Boya Zhang, I can tell you at least one USA university with research on HV engineering: Mississippi State University. Please check in its HV laboratory website:  http://www.ece.msstate.edu/hvl/.

hi

please see

You can model the system using PSCAD/EMTDC to confirm. 

Hello,

I recommend you study the following worthwhile paper. It gives you some hints to devise a mathematical model for your problem.

"Information Gap Decision Theory based OPF with HVDC Connected Wind Farms"

by Abbas Rabiee, Alireza Soroudi, Andrew Keane

Good luck,

Morteza Shabanzadeh

Inno, grid extension and reinforcement is a huge topic in Austria and Germany as a consequence of enhanced wind and solar power generation. More information on HVDC in Germany on: http://www.netzentwicklungsplan.de/en/search/site/hvdc ...unfortunately most data there is in german. Attached I also send you a list of HVDC projects.

Regards.

Dear Mr. Hamed, I guess you are refering to "on load tap changers" and not to simple "off load" ones. Indeed, HVDC systems require big power transformers, usually with 3 windings (primary, secondary, tertiary) and an on load tap changer, or "Jansen switch". This switch follows the load changes and changes the voltage level according to the terminal user. Although a much complicated system than the off load tap changer, it is required in this case. Irrelevant to your load, you have to keep a fixed voltage at your end terminal, of course under the specified tolerances (say +-5%). This end-voltage requires in turn a fixed DC voltage at both sides of the transmission line, or with other words a constant DC voltage drop. If the demand increases, an additional voltage drop is produced, therefore keeping the same voltage at the end, requires a higher voltage at the primary side or more turns in the primary winding. Here comes the "on load tap changer". An off load tap changer cant do that, because it is required a constant load monitoring, with switch on and off frequently. The switching produces a high current and arc, which can not be ceased in a simple off load tap changer. The on load is equiped with an arc eraser chamber (usually with insulation oil). 

Dear Amir,

Are you working with a single phase frequency inverter ? If it's the case you could just use a triangular wave form as a carrier and use two sine waves opposite one of the other in 180º. Each of these sine waves can vary between 0 and 1. 

One of the sine wave you use to the first leg of your H bridge converter and it's opposite you will use in the other leg.

The command sequence for the converter switches will be done naturally with the modulation.

Regards,

Leonardo

Dear Javier,

a thyristor will turn off naturally if the current goes down to zero and the trigger is off..

As your description said "turn-off at minimum current" I assumed you would turn off in zero current condition according to the diagram you added.

The datasheet value correlating to 10ms is given, because this refers to using the device in a 50Hz application. I'm sorry I didn't recognize the time scale in your figure was µs and not milliseconds.

Critical voltage slope for the device I linked to is 2kV/µs and with 7 in series, turns to about 14kV/µs. Thus, 50kV can be turned off in less than about 4µs.

A solution using High-Voltage IGBTs will be even more challenging and demand even more devices, series-connecting IGBTs is rarely done in the industry.

You would need 6.5kV switches, maximum current today is 750A.

Wow - at least 8 in series to achieve your 50kV but at least 27 in parallel will get you 216 modules per direction, 432 for the whole switch and controlling these will get even worse. The number of gate drivers alone scares me :-)

So yes - possible but challenging.

@Despoina Pitsa .... actually am unable to view the article as access to the jounal is not available .. can you share a printable version ?

Matrix converter usually comes with bulky filter which could be troublesome in HVDC application. Also there is no DC-bus in matrix converter.

If it is AC-AC converter, "Generalised analytical methods and current-energy

control design for modular multilevel cascade

converter" from Yun Wan shows such an application using modular multilevel converter you could achieve similar (see fig 3c)

Omar that is the purpose and function of the "fly-back" diodes. This allows the load current to transfer or commutate from the power transistor to the diode to allow the transistor to switch off. If not the transistor will be destroyed.

It is actually the load and stray or leakage inductance that causes the diode to conduct.

a major constraint when designing traditional AC transmission lines over long distances is the significant inductance such a line will have. The effects of both the line inductance and capacitance have to be compensated along the AC line and this adds costs for long distances.

A rough approximation of savings in line construction is about 30%. Furthermore, long-distance AC lines usually require intermediate switching stations and reactive power compensation which increases the overall AC transmission cost

The break-even distance, where the HVDC solution becomes more economical than an equivalent AC, greatly depends on land conditions and project specifications. The reasons for choosing HVDC are generally economic and not technical. Power system stability improvements and environmental circumstances may, however, also be reasons for using this technology.