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High Voltage Engineering - Science topic

High Voltage Engineering are it is a special application field of Electrical Engineering, specially becoming more popular and demanding due to Power Transmissions at Ultra High Voltage level.
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Following the success of ISH2023 at the University of Strathclyde, Glasgow, I am pleased to share with everyone that the papers have now been published in the IET Proceedings. The next Symposium (ISH2025) will be in Tokyo and I look forward to welcoming all of you there.
However, we wish to increase participation by more researchers in the area of High Voltage Engineering. Any suggestions please?
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You can buy any paper published on the IET webpage.
Regards
Siew
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I want to explore the following topic :
Is it possible to simulate the phenomenon of Water Treeing in COMSOL ?
Water Treeing is the phenomenon of partial breakdown of the Dielectric Medium in an Insulator Material between two electrodes (or conductors) due to a group of factors (like presence of humidity, contamination, or impurities).
What I want to know is; whether someone has done this before, or someone know about reports or articles where these "Trees" have been simulated? In practice, these phenomena are interested tipycally for polymers like; Polyethylene, Polypropylene, other Eleastometers, etc.
I would like to perform a simulation of one of this Water Trees ocurring inside an insulator materal in a power transmission cable operating on standar condicionts under Medium Voltage.
I would like to predict the pattern and the direction of the path taken by the breackdown, the size and shape of the "Tree" and the duration from the initial point 'till the time when the breackdown reach the other conductor.
Hope someone knows more about this
Best Regards !:)
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Yes! here is my research implementing electrical tree in comsol
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why dc capacitor charge faster than it discharges? Can we control charging and discharging time?
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why does discharge time is obviously shorter than the charge time for most of the supercapacitors? What is the phenomenon behind this?
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I have a power supply which is consists of a flyback and a circuit.
It is a dual output power supply that have 3 wires in output(a. ground wire, b. 4kv, c. 8kv).
in put voltage is 220v and the power of this power supply is 50 watts.
I need to simulate this power supply in ltspice or any similar software so I need to know the specs of the flyback transformer.
how can I find the specs of this transformer without destroying it? :D
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Dear Ju Cheng ,
To see the list of the specifications of the flyback transformer please refer to the paper in the link:
Best wishes
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I compensate my series resistance 75-80%, I have sodium currents that range from 0.5 to 6 nA, and my pipettes are 1.5-3 megaohms.
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If we talk about an inward current (like sodium current in cardiomyocites), should we then put another minus in the equation?
For instance I have a desired voltage of -50 mV and a peak current of 2nA...
Then Vm= (-50mV) - (- 2nA * 2megohms of residual Rs after compensation)
Then Vm= -50- (-4mV) = -46mV
Is this correct?
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Are there any models to predict when an "Electrical Tree" or a "Water Tree" will occur inside an electrical insulator (dielectric materials as Polyethylene, Polypropylene, etc.) working on its normal operating conditions for Medium Voltage or High Voltage applications ? i.e. the Electric Insulator material covering the conductor cable in underground power cables (MV and HV)
Are there any theoretical or empirical models to predict these phenomena ? When treeing will occur along the life of an electrical power cable?
Regards !
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I’m using COMSOL for circuit breaker PSS-1 2D time-dependent simulation. I have coupled all moduls: Heat Transfer in Fluids, CFD-Modul, Electric Currents, Magnetic Fields, Moving Mesh
in HT-Modul I use 3 HeatSources for Simulation of radiation, Joule-Heat(ec volumetric los), enthalpy transport.
in CFD Modul I use Force for Lorenz-Force consideration
EC and MF moduls are coupled with external current density.
MF:full field, ”in plane“ field, gauge A-fixing
boundary conditions: walls
initial values: T=293K, P=1atm(with hydrostatic correction), DC terminal 100A and ground.
between electrodes T=10000K or I tryed to use Gauss-Pulse function (quasi same effect)
Solver: fully coupled
Method: High-nonlinear Newton
Goal: to simulate plasma in switching device correct and watch internal thermo-hydrodynamics and V-A characteristics of circuit breaker.
when I start to calculate my modell, I receive no convergence in both Stationary and Time-Dependent cases.
when somebody need a comsol-file, just ask it
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Agreed with the link provided by dear Ijaz Durrani
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Can someone suggest me the latest, novel and most ongoing active research activities and research topics in Electrostatic Precipitation and High Voltage Power Supply Design?
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A most of topics ,you find it in this link:
Best regards
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Especially for the non-condenser bushing. I'm studying FEM analysis.
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Material type
Climate
Rated voltage levels
.
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In High Voltage Engineering by Naidu & Kamaraju(3rd edition) the following is seen in Chapter 3, Conduction and breakdown in Liquid Dieletrics,
Section 3.4.5 Conclusions:
Vb=Adn
Where: d=gap length, A= a constant, and n= a constant, n<1
Now, what is the electric field?
Is it E=Vb/d = (Adn)/d
OR
Is it E= dV/dd = (nA dn-1)
As you can see the answers will be very different!!
ERB
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I need some theoretical literature on ferroresonance choke and high voltage choke. 
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Capacitive Voltage Transformers: Transient Overreach Concerns and Solutions for Distance Relaying By: Daqing Hou and Jeff Roberts
HV transformers and chokes
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as you know for making the phases of transmission lines symmetric we transpose the lines,i want the suitable Distancefor transposing
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The suitable distance is n(1/3) distance of line,
n : The number of transpositions across each line length.
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My Requirement is to create an equation to calculate the distribution line power loss with distance and solve it to get an optimum distance. all other variables can be predefined within the equation, (i.e. voltage drop of cable, cable resistance, tem, X axis distances to side roads, Y axis distances from loads,) - finally calculate X* Figure attached will clarify the X, Y-axis and Rectangles indicate loads. Circled X is the power source (Battery Bank with 3-phase inverter) Note - Distribution system is a 3-phase line system, cable parameters are known (50mm or 70mm ABS), Ignore street light conductor in cable parameters, for the equation , pls consider on its capability of calculating loads up to 10 homes in a lane and 10 lanes (needs at least 100 homes for this system) this equation can be solved using any software means necessary, thus not focusing on that, will you be able to provide me the equation within 2 days
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The x distances are determined based on the locations of the source and loads as well as the available routes. Provided that correct cables are selected, what exactly would you like to optimize? Anyway, the power loss in a specfic cable #i = 3*I^2*r*xi where r is the cable resistance per unit length. The overall power loss in the x's = sum of the previous equation over all x sections.
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Since the wind turbine has a tall structure, it is more affected by lightning than others. We can distinguish several paths of lightning current to the wind turbine generator and to protect these systems might be the redirection of the discharge current into the earth through the grounding system is the solution. Even without the possibility of being struck by lightning, wind turbines contain sensitive electronic equipment. Is the electromagnetic field (E and B) generated during the current flow (in the down-conductor) can cause damage? if yes, how to solve this problem?
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Generally the tollest structures more venerable to direct and indirect lightening stroke, hence should be protected by earthing rod on top ...
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I think there are two methods are available to improve HVDC circuit breaker which means make the dc current artificially zero.
They are 1)LC oscillation method 
                2)Add external voltage source method
If you know any methods other than above two then give me your answers.
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Hi Nithya
I hope the attached document can help you in this regard
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Some experts told that HVDC is better transmission system.
HVDC eliminates the problems of AC system as well as economical benefits.
On the other hand, the initial cost of the LFAC (low frequency AC Transmission) system is lower than HVDC system. 
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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:
  1. Long distance inter-area bulk power transactions, that in AC would "collect" excessive reactive power burden due to line capacitance, and be associated with consequent poor transmission efficiency is perhaps the major motivation to switch to DC ! Cases in point being the several high capacity links in the North America.
  2. Almost as a follow-up of #1, we have the requirement of transmission across submarine cable routes, between several utilities in Europe. (Cable routes are almost always more capacitive than OHT's !!)
  3. Another follow up of #1, which additionally brought forth possible stability issues with regard to AC over long distances ! A good example is the hydro generation in the Brazilian Andes that by plan and design, was expected to provide for industrial loads close to the Brazilian coast - leading to the classic Itaipu HVDC station (a project by ABB, if I am not wrong), and a volley of concepts related to unit connected converters.
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
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Which formulas can help me calculate the maximum distance of HVAC submarine cables? 
By how much does shunt compensation increase maximum distance of HVAC cable?
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I suggest you to read the IEEE paper I Co-authored:
Power Transfer Capability of HVAC Cables for Subsea Transmission and Distribution Systems
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I am doing high frequency modelling of the substation equipments for lightning studies. please help me to model VSC valve in detail.In addition to this help in grounding part also..
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Hi J.A . Jardini,
                     I am unable to obtain the B4-57 repórt. If you have please send to my mail id: a.jagadeesh06@gmail.com
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I'm trying to measure the leakage current along an insulator energize with HVDC (the effect of space charges is been considered).
-          Can I connect a picoammeter to the ground electrode? If yes, please how do I protect the picoammeter so as not to damage it?
Or
-          Can I connect a voltage divider (with 5kohms and 50ohms connected in series) at the ground electrode, measure the voltage across the 50ohms with a picoscope and from there I can use V=IR to get my current? If yes, please how do I protect the picoscope from getting damaged?
Thanks.
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It is preferable to avoid ohmic connections by resistances. I propose to use a follower Aop (high impedance input amplifiers) to measure the current.
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How to protect the electrical installations in the aircraft in case of lack of ferroresonance or other similar? (fault currents of high-frequency)
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Dear Zeashan Khan, 
Thank you for your answer. I undrestand, but how to protect the transformer in these cases. Do you have an idea about it?
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Caught in the vicinity of metro lines high currents, causing severe corrosion in oil and gas installations Here are tips to solve the problem. thank you
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What is rate of corrosion sir
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Mathematical analysis of current waveform
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I have research about inductance of toroidal transformer, On my research, i'am using magnetostatic when the model are given steady current (or DC), then i got question from my friend, because we know that transformer are device that working with AC current, do you think that is worth if we do simulation with DC current to the toroidal transformer, if you want to know more about transformer? or i just change the current to AC?
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yeah you can simulate the designed transformer to get the knowledge about the inductance and resistance of the hardware. 
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In  of calculation or analysis of pre breakdown of insulation related article. 
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Partial discharge (PD) is a pre-breakdown phenomenon/symptom that due to the insulation degradation can cause failures in the high voltage (HV) power components. U can read this paper that elaborate the PD activity on XLPE power cable and the sensor development technique for PD detection.
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During bad weather and pollution atmosphere how I can measure electromagnetic interference between them.
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Salam aalaykum
You can found many informations concerning this field published by Dr Farid Dawalibi in IEEE.
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Hi,
I am designing a water cooling system for high power IGBTs, but I don't know how to do that, such as selecting heat sink, velocity of water etc.
If I have known the losses of IGBTs, thermal impedance of IGBTs, ambient temperature, how to design a proper water cooling system.
Best regards,
Yi
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Hi Hussein A Kazem,
Thanks for your suggestion. I will read those two books.
Best regards,
Yi
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Rework activities are done by manufactures in order to get good results at partial discharge test. 
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Dear Mehmet,
First, you have to determine the location of partial discharge and then take measures to eliminate them when possible and economically more convenient.
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I am wondering if there is any potential damage/fault can be caused by low-frequency electrical resonance within a power grid or system due to internal or external inductive and capacitive components.
If this is possible, what would be some good examples to prove this point?
Thanks so much!
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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.
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Hi all
Is there any expressions or explanation of corona effects in high-frequency ?
I need theorical or experimental works.
Thank you,
Omar
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Oh! OK, I think that I had chose wrong keywords in my web search.
Thank you again
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     It's well known that in high voltage transformers, the contents of harmonics in the applied voltage are induced by the non-linear behavior in the saturated part of the magnetizing curve of the testing transformer core. In addition, non-sinusoidal magnetization current causes a distortion of the secondary voltage. Is there any solution in order to improve the applied voltage signal and decrease its harmonic components ?
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Hi Youcef
I suggest to use a low frequency filter (LC circuit) with high voltage inductance and capacitor which could help you to eliminate odd harmonic components.
Good luck
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I'm obtaining the thickness of insulation in shielded power cables and I find as a reference a standard Japanese (JEC-3408 - High voltage tests for extra high voltage cross-linked polyethylene cables and connection parts) but i would like to know, the equivalent standard in the IEEE or IEC.
Do somebody know the equivalent standard in the IEEE or IEC ?
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Personally, my research works are based on the IEC 60502 standard which I highly recommend it for you (Power cables with extruded insulation and their accessories for rated voltages from 1 kV (Um = 1,2 kV) up to 30 kV (Um = 36 kV)) ... best regards
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hi.The high-voltage transmission lines, in some places, high balls or Yayyn be installed in Dersim. what is the reason?
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hi
im agree to mr ramezali
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We know for Bose-Hubbard model in simple lattice, the ground state could be Mott insulator with integer number of particles per site and it is a commensurate phase. When the lattice is a superlattice, there appears fractional-filling Mott insulators with rational number of particles per site. I want to know is the fractional-filling Mott insulator is also commensurate.
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maybe i can help you but need more explanation what you want exactly!
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I think this method is used for measuring partial discharges. Please share relevant material for the same. Thank you.
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maybe i can help you but need more explanation what you want exactly!
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I have found that distribution transformer failure differs from altitude to altitude. One of the main reason being frequent lightning in some locations. Therefore, there is a need for different lightning arrester for different locations of transformer.
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The insulation level is affected by both the altitude and humidity.  The altidute  correction factor in the standards is for  2000 m above the sea level.  Check the altidute/humidity condition at the transofrmer location. It could be necessary to chance the LA type.
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We are facing a line tripping problem in the 132 kV single source transmission line. The fault is temporary. As we restore the line again after 15-20 minutes the fault does not exist and line works well.
As the fault occur protection relay (earth fault and short circuit fault) operate at sending and receiving end. The fault current at the sending end and receiving end are in 5 kilo ampere (kA) range and  100 mili ampere (mA) respectively. 
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It is important to see the waveform recorders in failure to analyze the characteristics of the fault. In transmission lines to equal or higher levels of 230 kV, the angle between the voltage and current is a good indicator of the fault impedance (type).
Some elements that can cause these types of failures are:
- Approach with other low voltage circuits .
- Approach with vegetation
- Failure arrester
- Contamination in electrical insulators
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1. Expecting the complete internal architecture of current transformer rated at EHV level.
2. Site tests & Lab tests conducted on current transformer
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Dear Sir,
You can find qualified informations about these topics in the book Stanley E. Zocholl - Analyzing and Applying Current Transformers – publisher: Schweitzer Engineering Laboratories, Inc., 2004 (and many other sources). Some producers gives also informations in theirs leaflets about magneto-optic current transformers (MOCTs) based on Faraday effect.
Regarding the tests, the dedicated international standards are: “IEC 61869-1 Instrument transformers – Part 1: General requirements” and “IEC 61869-2 Instrument transformers – Part 2: Additional requirements for current transformers”.
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I was searching for co-axial/tri-axial cables for our test facility which can carry a current of 60A at voltages ~55kV DC (which are supposed to be modulated at 5kHz continuously). 
I observed that the typical co-axial/tri-axial cables are rated like this:
"45kV Pulse or AC and 150kV DC"
I didn't understood what is deciding factor by which we de-rate an dielectric for a AC and DC application.
--
Thanks 
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I think a study on Skin effect and current densities of equi-dimensional cable under AC & DC may help the concern ...
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When doing analyses with ambient plasma sources (e.g., DART, LTP), there is typically a high background due to junk in the air getting ionized (such as vacuum oil, plasticizers, detergents, etc). Has anyone found a good way to reduce that background signal?  It can interfere significantly with any analysis you do.
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As far as I know, the only way to reduce background is to keep your experiment in clean air. We take great care to use only the cleanest air - either blow top grade bottled air over your experiment or install special air conditioning for the whole lab with positive pressure to avoid contamination from outside. Neither of these solutions is cheap. I hope someone else has a more affordable suggestion...
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See these sentences in one technical report: "Reconnection of these inductive loads with an out–of–phase residual voltage present of more than .25 per unit can result in transient currents high enough to trip overcurrent devices and/or transient torque high enough to damage the load equipment".
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Some references indicates that the motor should not be subjected to a reclose when the phasor difference between the source volts/Hz and the motor residual volts/Hz exceeds 1.33 per unit volts/Hz. I do have some photos of destructive effect on the rotor bars (double cage rotor) - par 4.2.6 - Novel Method of Improving Squirrel Cage Induction Motor Performance by using Mixed Conductivity Fabricated Rotors (MCFR) posted on Research Gate
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The goal is to make the initial study for HVDC link back to back , want to do the basic design of the station Back to Back , to model and simulate
I want this study as a reference to plan the station and its final design study
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Ms Sanjoy
Thanks for your advice and your time
I will review that information
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Suppose there is a logic gate and it has two inputs.I want both the inputs to be "high" i.e logic 1, can i have two different voltage values at these two inputs? e.g 3v on one and 4v on another?
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Dear Purnima
I think it will work provided both the values are well above the threshold value for logic '1' voltage. Assume the two inputs made of two mosfet , if 3V can create a channel for conduction then it is certainly possible for 5V or any other voltage in error margin
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Corona current is usually calculated from Ic=sigma*Electric field = ion mobility*space charge*Electric field. In Maxwell, E is available, mobility is constant, the problem in finding the value of space charge density. My application is: electrostatic precipitator (wire-cylindrical or wire-duct).
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Mohamed Bendib, thank you, if possible simplify the solution in steps.
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Can we say connect a single phase customer(instead of all, just a few customers in a LV Distribution network) to all 3 phases but use some sort of relay to select one at any time and then switch the customer at the customer's end to a different phase to control Voltage Unbalance?
Can we preset for certain times?
And if yes then what sort of problems we would face when switching phase? will there be a short time interval where the customer's appliances will be out of power or can we neglect that time? Or may be it is a slow transition?
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Dera Karam, your question is very interesting. So far anybody has discuss this question. There is not commercial equipment for this function. I think the cost of equipment and the assembly at last is a problem.    
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i want to run avalanche transistor
but i can bias this transistor for this section
please help me to run it 
best regard
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Hello,
I just found an interesting document that talks about biasing transistors such as the 2N5551 for avalanche mode.  I have attached it to this message, see Section 2 - Avalanche Transistors.  Later in the document, they talk about screening/selecting 2N5551s on the basis of their collector voltage, see Section 4.3 - 2N5551.  You will also see that they discuss how transistors with same part number, say 2N5551, from different manufacturers are built differently, see Fig. 1, which shows the 2N3700 made by two different companies - the construction is quite different.
Regards,
Tom Cuff
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VSC HVDC
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Dear Sunil,
maybe this file can help you
good luck
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I want to study the dynamic behavior of a complex power system, including some HVDC links. In which simulation software can I study this?
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Dear Mohammad
you can try MATLAB, PSCAD, EMTP-rv, Neplan
good luck
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In order to avoid selection of oversized distribution transformers, it is required to optimize its selection based on their chargeability.
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It is not needed to select transformer on short time load above the rated, till the remaining life consuming cost on basis of hot spot temperature, is not used totally for a day, refer my papers on microprocessor/ computer based optimum utilization of transformer capacity.... 
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I am currently using fiber optic in my system and need to know the standard leakage current in order to calibrate the system.
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Leakage cuurent (LC) depends on conductivity of pollution layer, insulator shape, pollution distribution. If you consider a IEEE standard insulator, you must consider that the pollution is uniform.
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There are some inventions made in between 2000 and 2010 about sensing and measuring electrostatic fields. Mainly they deal with solid states (semiconductors) or MEMS Technology (to implement so called field mills). I look for a miniaturized sensor for fields between 1kV/m and 1000 kV/m. Does anybody know products on the market in size of a Computer chip  or would somebody be interested in a cooperation to develop a sensor?
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We know that high voltage engineering is a very traditional subject. Judging from the present condition, it seems that American universities seldom conduct researches on this area now. However, in Europe and Japan, there are still many researchers in this area. Maybe it is because some large companies like ABB, SIEMENS, ALSTOM, and TOSHIBA, etc. have the motivation to make products with higher voltage level and larger capacity and all theses companies are in the mentioned regions. My question is, are there any institutes, especially universities, doing research related with high voltage or electrical insulation in the USA?  
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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/.
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Hello.
Please see the attached images which shows our capacitively gas discharge circuit. HV box has single output of 30 kV.
Before thyratron (fast electrical switch) is on, everything looks clear and no need to worry. But after thyratron is on, among 30 kV or 0, which voltage is right on the HV box side? Although this circuit have works so far. I've always confused this.
I guess the best scenario is the HV side becomes 0 zero and I've believed this way but...why and how?
If this circuit is bad, how can HV side be automatically cut when thyratron is on so the box is protected from , for example, huge current drawing from the box to ground by electrical short?
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When the thyratron is ON, the voltage on its anode is close to 0. The HV of 30 kV is applied mainly to the charging resistor (or inductance) - inside the HV unit. All is in accordance with Ohm's law. Generally, a limiting resistor (limits the current of HV device) is always present in such systems.
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Hi, everyone
I am wondering where I can find the complete data of IEEE 39bus system, especially the base voltage of both sides of the transformer(since 345KV is only provided for the high-voltage side). Thanks
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Hello.
Let's say we have narrow sapphire tube (~300 um width and few cm length) which is filled with gas and discharged capacitively with high voltage of ~ 30 kV. With sub atm pressure, we can get order of 10^18 cm^(-3) plasma density and plasma temperature (both electron and ion are in equilibrium due to such a high density) is about 1~2 eV. This is actually for plasma waveguide for intense laser.
I've always worrying melt down of dielectric material due to direct contact of plasma although it have been reported as successful waveguide.
Is it possible that temperature is significantly reduced within very thin sheath possibly formed in proximity to the dielectric wall? Is it possible that temperature there can be even lower than material melting point?
Please give me any comments on this.
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In our similar experiments (preionization of the channel for a main discharge), the allumina walls get chared (3mm Inner Diameter). Which results in some ablation of the material and such effect  adds measurable amount of added pressure and contaminants to the plasma channel. 
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The condition for the occurrence of partial discharge (PD) is commonly associated to the increase of the local electric field up to exceed a critical value. In general, nothing is mentioned about the availability of electric charges as complementary condition for PD occurrence. Rigorously speaking, is it not necessary also to consider the need of free local electric charges as additional condition for PD occurrence?
Complementary to the question, I would like to pose a situation where a cavity is located deep inside a solid insulating body far from electrodes in a high voltage equipment. Such situation I had in mind when I thought about this question. It is a condition where a relative small volume of gas is confined with very low or none availability of electric charges, but with great possibility of being stressed by high local electric field. Should we worry about PD in such case?
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A few details as possible clarification of some of the above comments (I am sure these points were considered in developing he comments, but I thought that it would be useful to articulate them):
1.  Partial breakdown (partial discharge) means that the entire insulation system has not broken down, or a puncture has not occurred in solid insulation.  However, this does not mean that a complete breakdown (sparkover) does not occur within the voids themselves in solid insulation.
2. Complete breakdown of a void can occur even when the total average applied field across the entire insulation is relatively low - consider the different in dielectric constants of the insulation and the gas or vacuum within the void.  The electric field within the void in enhanced compared with the electric field in the solid insulation.
3. The enhanced field within the void may result in the mechanisms described in previous comments: avalanche - which requires free electrons to initiate the avalanche, field emission - which does not rely on the availability of free electrons.
The possibility of void (complete) breakdown in practice is discussed in previous comments.
Regards, GG
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Hello all,
I am working with the Pulse Discrimination in micro-EDM (RC Circuit). Their is a very general concept of a class of contributing and non-contributing pulses which are being discriminating on the basis of the charging and discharging location of capacitor. I would like to know the exact theory behind deciding the threshold for such contributing and non-contributing pulses in details. If possible, refer me some publications as i am unable to find it out from my end. Thank You
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RC generators are pulse power sources on the basis of discharges from a stored capacity. The charging curve corresponds to an exponential function, ie an initial rapid voltage rise is followed by a very slow approach to the charging voltage. The ignition timing is determined by the gap conditions and can be done at very different starting voltages. These altered times lead to very different pulse energies (w = C / U 2 * 2) and the dependence of the pause duration of the ignition voltage. The highest efficiency of machining is achieved at about 72% of charging voltage.
In the micro-EDM You must note that the capacity of its "switching capacity" corresponding plus the parasitic capacitances of the electrode assembly and the supply line.
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Dear all,
through litterature, two options exist :
- with SiO2 thin layer : provides a current barrier that can spread space charge region and thus yields higher breakdown voltage 
- without SiO2 thin layer : to avoid instability caused by space charge region spreading that may be difficult to control 
In case we need SiO2, how can we control it (Piranha clean, low temperature oxidation ...) ?
In case we do not need SiO2, how can we get rid of native oxide ? And I've also read that SIPOS annealing forms a very thin layer SiO2 at the interface so it may be dificult to completely avoid it.
What is your feeling about that ?
Thanks for help !
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Thanks for reply and advice. Have you heard of a thin oxide layer formed during SIPOS annealing ? Is it even thinner than native oxide so that it cannot alter SIPOS properties ?
Thanks again
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I work in HVDC systems ,its converters needs transformer in each side of HVDC link ,this transformer must be performed by a tap changer control, i need to know, what is the purpose of this tap changer and the difference than transformer turns ratio.
thanks in advance
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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). 
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When we pass the current through coil heat generated is calculated by Current^2*Resistance*time.So heat generated in coil depends on current,resistance and time. Like, on which factors heat generated due to spark gap depends??
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Your question is not framed clearly. Are you talking about the arc struck between two conductors? Spark and arc are different. Arc is  continuous between the two surfaces. Spark is a discontinuous phenomenon.
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how should load be connected  directly with 3-Phase AC  high voltage generator that has no  neutral wire? Should three loads be connected; something like   L1 - L2 , L2 -L3 , L3 -L1 !
Moreover , there is voltage between all three phases. if  the voltage is measured only between L1-L2 i.e 100v , is that the actual voltage output of the generator? . Should the voltage is to be  read as L1-L2 +L2-L3 =>100V+100V= 200V?
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The voltages between L1-L2 = L2-L3 = L3-L1 are all measurements of line-to-line (or simply 'line') voltages, which may be 100V as you have stated. That is the voltage rating of the generator (alternator to be precise). Since there is no neutral, your supply system is a 3-phase 3-wire system. If your load is also rated at 100V each, then 3 such loads can be connected in "delta", ie one load from each set of one line to another.
However, if your load voltage is 100/(sqrt3) = 57.7V, then only you can connect three identical loads in "star" connection ie one end of each load to one line and the other end of all loads connected together (to form the 'star' point) without connection to any other terminal. In this mode, while the line-to-line voltage is still at 100V, the line-to-neutral (or 'phase') voltage of the load side is 57.7V. Note that there is no corresponding neutral on the alternator (supply) side and hence your supply system is still 3-phase 3-wire type.
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What is the reason for producing high voltage by the ballast(choke) and what is the ballast actually made of?
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This article has a very clear picture to show how the fluorescent lights with starter work (and confirms Francesc Casanellas' explanation):
In short, when you have a choke and starter, the starter is in the current path only as long as the fluorescent tube is not conducting (gas not ionized yet). Then after the gas is ionized, the fluorescent tube shunts the current away from the starter.
I don't know if you are familiar with the old Kettering ignition system in cars (also called point ignition). During the starting phase, the starter in these fluorescent fixtures behaves very much like the points in the Kettering ignition. Current flows through the starter at first, and current flows through the choke (as current flows through the coil and the points in the car, while the points are closed). This current flow through the starter causes the starter to open soon, as a bimetallic strip heats up in the starter (much like the points open in the car after the distributor shaft rotates a little). When the starter is opened suddenly, just like when the points in the car's ignition are suddenly opened, the current flowing through the choke/coil cannot stop suddenly. So instead, voltage builds up until the current can force its way across the fluorescent tube, or the spark plug gap in the car. (There's a little extra detail in a car's coil, in which the spark plugs connect to a higher voltage secondary coil.)
In the fluorescent tube, if the gas in the tube does not ionize at the first attempt, then current will flow again through the starter, repeating the cycle.
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in transmission line reflected current and voltage is produced whenever there is a short or  open circuit condition . i want to know that physical significance of that thing  how it has come ? it is induced voltage or anything else  how can current flow in both directions means incident and reflected current.
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Reflection is a characteristic of any waves at the boundary. There is refraction, too. Transmission line is only a medium for waves traveling in 1-D.
Reflection occurs when the transmission line is not matched at the end. Short and open ciruits are two special cases. It could be better understood if you think of the em wave rather than circuit.  Solving the Maxwell equations will give the final answer.
Here is an anology. Consider a uniform channel with water flowing in constant speed. So water just travels smoothly before it knocks the end. In front of the water head there is no water yet, as water travels in limited speed. The flowing water will maitain a specific height as the channel restricts it to flow only in one direction.
If the channel is blocked at the end, you will notice water height increases as the water has to travel back (the open ciruict condition). If the end of the channel expands a lot (short circuit condition), you will notice the water height decrease, and this information travels back.
Back to the transmission line. If the line is uniform, it is easy to imagine that the ratio of the electric field over magnetic field (called impedance) is a constant. (In fact the wave should be a constant if you move at the speed of the wave (light speed)). At the end of the transmission line, if there exists diffrent line, the impedance might be different. So em field adjusts itself to satisfy the Maxwell equation. The change is called a reflection.
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I am trying to find out the maximum ramp rate (practically feasible) for the power reversal operation in a VSC-HVDC system. 
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if you are asking in the operations point of view, besides the physical/design limitations, it is usually capped by the transmission system operator's operations parameters such as frequency control. The rule of thumb is 10% per minute of the total capacity. 
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Dear researchers,
Experimental investigations are to be carried out on a prototype to determine the design stress levels.
Prototype : Chamber filled with SF6 gas. Conductor running longitudinally and isolated from the tank/chamber by the gas.
Objective: Determine the withstand voltage level with 50% probability through experimentation and establish the 90% withstand voltage level theoretically.
Reason : In up-down method of stressing the insulation, only 1 shot per group is to be applied and there is no mention in the IEC 60060-1 to determine the 90% withstand voltage level.
We know that the breakdown characteristics of SF6 follows weibull distribution. Could I determine the 50% withstand voltage level and extrapolate through curve fitting to obtain 90% withstand voltage level?
If yes, how do I  proceed after establishing 50% withstand voltage level? How to determine the maximum likelihood estimator and how is it helpful in this regard?
Thank you
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Of course, you can estimate the Weibull  percentiles with at a given confidence level.  We published a paper on how to estimate these percentiles for the 2-parameter Weibull distribution.  It is available for download at ResearchGate.
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Using ONAF (oil natural air force) cooling conditions, calculate the H. V(high voltage) and L.V(low voltage) side current of the power transformer having following ratings; 31.5/40 MVA, 132/11.5kV ? 
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Dear Waqas,
Your problem is not clear for me. I have not seen a transformer with two base apparent powers (40 and 31.5MVA)! Furthermore, the voltage values must be presented based on 40MVA or 31.5MVA.
However, this is my solution:
S_base=min{40 , 31.5} = 31.5 MVA
As you know, in the ideal Transformer equations we have:
a (Turns ratio ) = V1/V2 = I2/I1
And By law of Conservation of Energy, apparent, real and reactive power are each conserved in the input and output :
S_base = V1 * I1 = V2 * I2
As a result, we can find the values of primary and secondary currents as follows:
31.5 MVA = 132 KV * I1  -->   I1 = 238.636 A
and
31.5 MVA = 11.5 KV * I2 --> I2 = 2.739 KA !
Regards,
Morteza Shabanzadeh
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What is the minimum and maximum voltage that it could be? Please respond with a valid source. Thank you.
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In Europe there was 220V in the continent and 240V in the UK.
To unify the value they set a new standard of 230 V +- 10% which covers 220 and 240 V networks without changing physically anythig. So now in Europe the rated voltage is 230V. All new devices are rated 230V.
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I would like a to build a low cost HV DC power supply.
Specifications would be 3-7KV, low amperage (maybe 2mA at best).
I have seen many examples from old CRT televisions/monitors.
The purpose would be for electrospraying. Fluctuations in power supply are okay, I know that instabilities will occur within the electrospray regime
Does anyone have experience?
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For these high voltages and low power, I found that a transformer (or the inductor, if you use a non isolated boost) was too expensive so I used a converter with an output voltge which could cope with standard wire and transformer insulation, say 400 V, and then a diode-capacitor multiplier network. I added a 10Mohm resistor in parallel with every diode, so the output voltage is shared with the same value for every diode, regardeless of the leakage current.  If you use controlled avalance diodes you may omit this resistor. As a converter I used a small full bridge.
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I am using electronica leader-1 znc.
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Hi Gangadhar, I actually thought about this question several answers come, but unfortunately not. I am assuming that you do not spark breakdowns in transformers look like, but the electrical discharge machining of conductive materials. Since the gap width and the breakdown voltage are mutually dependent, it must be decided which parameter I need, eg for process control.
The gap width can actually measure only the average gap voltage during processing. One has to be clear that this is a fictitious quantity, because the surface roughness of the electrodes produce locally different distances.
The breakdown voltage can be determined by recording the voltage and the current curve. Due to the roughness peaks and the uneven distribution of the contamination, the breakdown voltages for the individual pulses of the processing are very fluctuate, ie for scientific analysis must be used with a mean and the deviations determined or the distribution of breakdown voltages.
It must also be considered that breakdown voltages of electric arcs, as well as their current rise times and RF superposition of the burning voltage are very different from those of a desired spark discharge.
Best regrds
Hans-Peter
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I am working on insulation condition monitoring of low voltage network. I would like to know if there is any method or technique for instantaneous detection of insulation fault or leakage current in low voltage network offline. I can not use high voltage as it may harm the insulation of the network.
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Thank You very much for your answer and guidance.
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We would like to know if there are some standardized overloads authorized by TSOs if, for example, any failure takes place in other lines. In addition to this, we would like to know if there is any lifetime reduction assessment available for the power cables under these circumstances.
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XLPE is sensitive to over-temperature. There is a risk of permanent degradation of the insulation structure if the rated temperature rise is exceeded.
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Since recovery time of a spark gap can be useful in high power pulse applications.
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You could do it in Matlab. Knowing the distance between the sparkgap, temperature, pressure and humidity, the dielectric recovery could be mathematically modeled and the same could be adapted to MATLAB. I have seen people using Matlab to calculate the recovery time of SF6 gas during the switching operation of HV breakers. For the physics involved, you could use Ansys Maxwell or comsol
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A part of my thesis is to examine different fault events in MVDC architectures for shipboard power systems. A recent thought was to include a fault caused by a lightning strike in order to observe the behavior of my grid and circuit breaker. I found the circuit of the lightning impulse that has been introduced in the literature but I cannot find out how to simulate the sphere gap.
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I am pretty much sure that you are done with your thesis work. I had a similar problem while building an impulse circuit on orCAD Pspice. I could not find the sphere gap, but there is a possibility of doing this with a TCLOSE switch on spice. You may rummage through the library of simulink and I am sure u could find something like this. You may find the screenshot of my LI circuit. All the best
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We are aware of partial discharges in AC systems, but the same effect at HVDC level can cause serious damage to system, can anyone provide relevant information, test results on this sector.
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@Despoina Pitsa .... actually am unable to view the article as access to the jounal is not available .. can you share a printable version ?
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We have the maximum rating of 6.5kV with 3kA switch this rating is not enough for high power conversion. So we are connecting discrete switches in series to achieve maximum rating high voltage switch.
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Dear Mr. Imayavaramban,
as currently 6.5kV is the highest blocking voltage for industrial IGBT-modules and series connection is very rarely the best option, could you please add information about the apllication?
Wouldn't a multilevel approach be a more viable solution?
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I came across this term in the context of flash overs on the surface of insulators in vacuum.
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SSEE occurs for dielectric surface flashover in vacuum. As the flashover develops some of the electrons will strike the dielectric surface between the two high voltage electrodes. These so called primary electrons will knock electrons from the dielectric with a certain probability, causing secondary electron emission. Hence, the number of electrons is amplified as long as the energy of the primary electrons is large enough (tens of eV) to have a secondary electron emission coefficient larger than one.
Since the emitted secondary electrons leave a positive surface charge behind, the trajectories of the electrons moving from cathode and anode will change, so will their kinetic energy. In the saturated case, the impact energy is such that just one secondary electron will be emitted for each primary electron and the motion becomes a hopping motion as the trajectory of the electron is determined by the field tangential to the surface (from the HV electrodes) and the field normal to the surface (due to positive surface charge electrons are pulled towards surface). In this saturated condition, the number of electrons doesn't multiply anymore until other mechanisms take over such as electron impact induced gas desorption from the surface.
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When a traveling wave meets a short circuit, it is totally reflected
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Open to correction. hope this is of some use...I think you are looking for a physical explanation..Consider
the voltage wave as a packet of positive charges traveling along the conductor.
When this packet encounters the ground (short) a good amount of electrons
are drawn up from the earth to neutralize this instantaneously (that is zero voltage).
This would I suppose be akin to the concept of p holes traveling in semiconductors
and we imagine a negative wave mathematically to simulate this effect.
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In order to develop dynamic model of arc propagation over insulator polluted surface, I’m looking for ideas concerning the use of FEMM at each time step simulation in Matlab to get the whole system electrical parameters.
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