# Electrical Engineering

3
What is connection between impedance and power for discrete port in CST MW&RF?

What is connection between impedance and power for discrete port in CST MW&RF? Which power corresponds to the value of impedance of 50ohm?

Thanks Hans-Walter and Marcelo!

5
How we imagine/say frequency in Discrete time signals?

Let say x(n) is the discrete time signal, which have N number of samples..How to say the frequency of the signal...can anybody explain this in graphical way?

Note: I can understand frequency in continuous time signals.

If the discrete time signal is obtained by sampling a analog signal with the sampling rate fs samples/sec, you can observe the frequency content of the signal by taking N point DFT of the sequence. The equivalent analog frequency corresponding to kth bin is equal to (k/N) *fs.

5
How do parallel operation of alternators take phase shift into consideration?

A dark lamp or bright lamp or synchroscope will check point at which the maximum brightness and darkness is found, it is going to check out the instantaneous peak voltage. frequency and voltage matching can be done, phase matching can be done that is R,Y,B but if a phase shift is present in the generator suppose R of generator A leads R of generator B by 30 degrees then all the phases of generator A lead by 30 degrees. how synchronisation is possible with a mismatch in phase angle?

Dear

with variation in  speed  of the alternator not only  frequency  but phase shift too will happen that's how dark or bright period is achieved.

with regrds

vasanth

4
Why current control scheme of inverter is difficult in standalone PV system?

voltage  control scheme of inverter is followed in standalone PV system and why not the current control scheme like in grid connected PV system

Thank you  prof.Abdelhalim Zekry

2
PSIM - multisine signal generation ?

How to generate multisine perturbation by means of a dependant voltage source driven by a look-up table in PSIM.

9
What is the critical velocity for aquaplanning of rolls under load at nearly smooth surfaces?

Has anyone an idea at which velocity a wide roll made of solid rubber under a certain load F lifts off a wet surface with a determined roughness of about 1 µm by aquaplanning?

The roll itself has got a smooth surface.

Please also consider the influence of the fluids viscosity.

Go to Google Scholar https://scholar.google.com/ and type in "elastohydrodynamic lubrication" or "hydroplaning". Also see the classic treatise by Pinkus and Sternlicht "Hydrodynamic Lubrication" for background on the former. You will need access to a library with comprehensive journal subscriptions or else a friend who has access.

2
Extensiometer intercomparison - does anybody know about quality tests and intercomparrisons within extensiometers - length measurements?

Does any laboratory arrange tests for intercomparison of extensiometers - or arrange cources with extensiometers?

Kind regards,

Jan/Metrology/FORCE Technology, Denmark.

The following articles and mentioned references explain how to test with extensometer? If you have special questions I can explain.

Plastic Deformation Influence on Material Properties of Autofrettaged Tubes Used in Diesel Engines Injection System. DOI: 10.1115/1.4026452.

7
Is it necessary to test CONVEXITY of an MILP/MINLP problem?

As we know that any MILP/MINLP problem is feasible only on some points in its search space. Consequently, it is not possible get its JACOBIAN as well as HESSIAN matrices, as I think. As a result, for MILP/MINLP problems it is not important to know its convexity. Further, as MILP/MINLP problems are having their feasible search space in form of a set of some discrete points so these problems are NON-CONVEX.

How can you justify my observations? Am I right? or Am I missing something very important?

With sincere regards,

M. N. Alam

Thanks a lot Dr. Alberto Costa.

3
Triphasic motor speed regulation art status?

i want to know the diferent kind of develops that this topic has had

Hello, Rolando!

Nowadays, the efficiency increasing of electric drives is getting more and more relevant. There are a lot of techniques to control speed and torque of an induction motor but the most prospective technique is to employ frequency converter to adjust both magnitude and frequency of stator voltage. Some state-of-art issues are highlighted by the next references.

Best wishes!

+ 1 more attachment

12
How can we remove artifacts of EEG signal?

I want to remove an artifacts from EEG signal such Eog , ECG and EMG etc

Look at their frequencu and amplitude characteristics and apply analog or digital filtering, you might need processor for postprocessing as well.
• Mahdi Kordi asked a question:
New
Is there a material with the refractive index between 3 and 4 ?

thanks a lot

4
Can I expand log(x) by an convergent infinite series?

something like log(x)=a0+a1x+a2x^2+---------

Not looking at your example but at "... by a convergent infinite series": YES

You may want to check for "CORDIC" (e.g. at wikipedia), which is not the fastest algorithm. But it is reliable and well understood, a lot of "material" being available "out there".

4
Why isochronous operation of two (or more) generator-sets without some kinds of load-sharing will result in unstable frequency?

If two machines are synchronized together in isochronous speed control and the load changes after a while, the frequency will start to change and the governors will sense the change and immediately want to counter the speed change. When all machines do that at the same time, their output start swinging back and forth wildly, until the under- or over-frequency relays or the reverse power relay of one of the machines actuates and trips that machine, and if the total load is higher than one machine can sustain, well, that machine is going to trip very soon (probably on overload or under-frequency, depending on the governor and generator protections being used on the machines).

That was our situation in the Artic. Without load sharing the generator with the shortest cables to switchgear ran the majority of the load and the load was different on each generator. We had dozens of blackouts from the closest generator over-current tripping and the system would cascade out. This was on a drilling rig that 10-12 MW load swings. Without load sharing the generator cabling would all have to be cut the exact length for all generators. Then bringing a generator online caused major problems with the HRG until it reached operating temp. We also had similar problems with turbines.

We started load banking the generators for 2-3 hours before placing them in sync with other gen sets.

We finally added a load sharing system to the facility and ended most of the problems from the generators. We still had fuel problems that would shut the system down because of heavy hydrocarbons getting into the engines.

1
How to model PWM generator for sinusoidal muticarrier PWM technique used for multilevel inverter?

Kindly suggest some technique that I should use in multilevel inverter as STATCOM..

use n-1 triangular carriers. Compare the reference voltage with this set simultaneously.

The n-1 carriers divides the total space to n regions. Each region is mapped to a level voltage. the region below the lowest carrier corresponds to 0V and the region above the top most one corresponds to Vdc.

3
Have any universal pwm technique for multilevel inverter topology?

in cascade reduced switched multilevel inverter topology. i am searching for universal pwm technique that can be generated by switching table and apply to MLI.

There are many generalised pwm techniques. The simplest one is generated by comparing reference voltage with  n-1 triangular carriers , for an n level inverter. The generalised technqiues for spacevector pwm are also available in literature.

2
Does anybody know the use of PQ meter In PSCAD?

The file attached is a test system which I have configured for my PhD work. Here I need to capture the Power and Change of power wave forms for my work. So, I used PQ meter to capture it, but during simulation it showed run time error. Can anyone help me to eliminate those errors and successfully run the simulation?

+ 1 more attachment

P is active power and Q is reactive power.

Ok .I will check in Master Library of PSCAD if it is available .

8
What special consideration should we give to choose a transformer for an inverter?

which kind of core material, wiring (delat-wye, delta-zigzag, ...) is appropriate for a 3-phase inveter according to the harmonic problems, acoustic noise, neutral overload supplying nonlinear loads, etc?

(I'm looking for a transformer to be connected to an inverter and transmit 3-phase 50Hz 3-wire system to 4-wire with galvanic isolation and increasing voltage level)

May I suggest asking the customer/client/end user what is their main requirement.

If the main requirement is conversion efficiency, then this may narrow down the list of possible trafo core materials.

The customer may need to compromise on some of the other requirements, if they want their main requirement of energy conversion efficiency to be met.

3
Can any one let me know the zero sequence current flow for all connections of transformers?

zero sequence current flow with derivation for these transformer connections

YnyN , Yd orDy , ZNyN , YNyNd, YNdd, YautoN , YautoNd

please let me know or let me know which book i am supposed to refer

As zero sequence currents are in phase, thus they will flow in the star connection if there is a 4th wire or if the neutral point is grounded. Also, they will flow in the delta connected winding as circulating currents.

4
How can we calculate the size of a substation?

In a thermal power plant i saw a substation of 220Kv and in the other one 132Kv. one was producing 1050MW and other one was 800MW. So, i want to know how we decide the size of substation on KV and what major parameter considered in this calculation.

That was not what I said. On the contrary, I said that it does depend on the demand MegaWatt); current and forecast.

On the original posting you said....."decide the size of substation on KV". Kilo Volt which is voltage not power.  That was the reason why I mentioned copper losses being reduced as transmission voltage increases.

Please, let me know if this misunderstanding has been resolved, otherewise I will give it one more shot.

Thank you.

• Gurmohan Singh asked a question:
New
Related to RF simulations in EM solver tool HFSS?

How we define ground signal in HFSS? Suppose we have two cylindrical conductors. I want to give signal to one of conductor and ground to the other conductor. what will be different port configurations used for four ports of two conductors?

3
Could fractals be used in designing surface coils in the MRI?

I am supposing that this kind of coils could have a better performance in different frequency.

In principle, Fractal Analysis can be used in the design of MRI coils.  The examples provided above are not relevant to MRI scans as these are e-field antennas.  MRI antennas detect the B-field of the EM vector.  The use of a fractal based design with B-fields is possible but in principle the arrays of b-field antennas are more concerned with anatomical coverage and the flux of the field detected with a depth of penetration.

4
How can economic analysis or what is called Cost-Benefit Analysis for electric distribution substation be done ?

I'm doing Energy Audit study for a distribution utility, and there are two studies one for energy efficiency improvement and the second focuses on the economic analysis, I have searched and found that mainly the energy audit is done for building or any energy dependent place, but for an electric distribution substation, the economic study is not clear for me, if anyone can help understand it briefly or if there are articles supporting the study, please do share them.

Thanks,

Thanks alot

1
How does thermal noise of an electromagnetic mode appear on a square law detector?

I have a signal which is thermally occupied. The signal is filtered with an cavity, therefore the noise spectrum is simply a Lorentzian function. I was wondering what would be the resulting noise floor on a square law detector (V ~ P2). Will the signal to noise ratio just be the square of signal power / integrated noise spectrum? I am asking this since I think there should be a beating between different frequency components of the noise. Shouldn't that increase the noise floor? If so, how can it be derived? Can anyone provide literature on that?

In my opinion, to observe noise beats the “frequency components” of the noise should be phase-locked. However, it is usually assumed that noise phases are random.

On the other side a frequency modulation can arise because of parametric amplification of an unwanted signal, which can be called noise as well. Both problems have been faced from a classical viewpoint at radio frequencies, for instance:

http://www.pa.msu.edu/~edmunds/Parametric_Amplifier/parametric_amplifier_some_notes_on_history.pdf

2
What I want to know is how to calculate the dielectric constant of Binary mixtures theoretically ?

I am working on binary solvent mixtures. What I want to know is how to calculate the dielectric constant of Binary mixtures theoretically and the variation of dielectric constant with temperature?

Just google "dielectric constant binary solvent mixtures" and you will get enough hits to start off. Note that this calculation is always just a more or less working bulk approximation. It totally fails when there are intermolecular interactions like hydrogen bonding, pi-stacking, large dipoles, quadrupoles, etc.

3
How can I distiguish anisotropy from bianisotropy in measurements?

Hello colleage,

I would like to know if there is some way to see if the metamaterial that I am measuring has a bianisotropic or an anisotropic behavior. I know that measuring the cross polarization behavior we can say that the material is not isotropic if the level I get is greater than the one without the material (only contributions to the polarization of the antennas and noise are measured). However, I cannot find a way to determine if it is anisotropic or bianisotropic.

Thanks to all of you for the quick responds.

I was just trying to figure the problem out. I haven't got an specific problem right now

1
How can I calculate ripple on output voltage of grid side LC filter for Solar Inverter?

Hello,

I have 833 kW solar inverter whose output voltage is 560 V. MPPT range of this inverter is 800-1270 V DC. I have designed LC filter based on theoratical calculation and resonance freq, as 30% of switching freq. (4000 Hz). The simulation of the system shows satisfactory results in terms of THD. Now, I am looking for the optimization of the analytically calculated value.

However, I am not sure, how the DC input voltage will affect on my AC output voltage of inverter. The voltage ripple will surely increase with increase in input DC voltage from 800 V to 1270 V. I am also aware that the shunt capacitor will have effect on voltage refinement and L will have an effect on current refinement. The question is under:

1. How can I calculate ripple voltage on generated output voltage waveform by capacitor. Can I do it by merely putting a summation block with inputs before and after filter and watching its value as I increase input DC voltage from 800-1270 V?

2. How can I optimize C value such that, my LC filter can operate satisfactorily between 800 V- 1270 V DC input? Is there any analytical method or do I have to do it merely by simulation? Is drawing frequency response (bode plot) of LC filter be the solution as an answer of this quesition?

Thanks and Regards,

Aalok

7
Is there any book available regarding close loop control of electical machine?

is there any book available regarding close loop control of electical machine(dc m/c, PMSM, BLDC, IM, SM etc) which includes machine modelling along with control system design like we have erickson maksimovic'in Converter control area???

Many books available with the concepts from different popular publishers.

13
Vehicle to grid (V2G) active power discharge practically implemented?

Hi,

As we know new fast charging stations are booming up around the world which will certainly enhance the EV penetration in distribution grids.  But did any one of you have seen a system operator/utility implemented a infrastructure utilizing the battery charge (so called Vehicle to grid V2G).

Thank you somesh. The reactive power capability input from you to this discussion is indeed a new topic. We were also thinking about exploring the same.

One thing that I noted is each and every researcher is more concerned about battery life. Once we can make an advancement in battery life this will be a great hope in future power systems.

2
What is the reason behind choosing minimum pickup current as double of steady state load current?

In over current relay, minimum pickup current is taken as double of steady state load current not 1.5 times why?

Hello Debasree,

In this website linked with this answer, the force used to keep the contact in its normal position, either normally opened or closed, is called the controlling force.  The force used to move the contact from its normal position is called the deflecting force.

In a relay, a coil is used as the mechanism to create the deflecting force.  The pickup current is the current that passes through the coil in creation of the deflecting force.  The contact will move once the deflecting force is greater than the controlling force.

In this website, it states that the current setting is usually set at 50% to 200% (1.50 to 2.00).  As a designer, you don't have to make the minimum pickup current as double steady state current, it could be 1.50.  The parameters of the design will dictate your minimum pickup current; for example, may be your current source can't provide 200% of the steady state current but it could provide 175%.  Therefore, the minimum pickup current will be 1.75 of steady state current.

You want the minimum pickup current to be as much as possible because the controlling force could actually overcome the deflecting force and pull the contact back to its normal position even though the relay has been actuated.

I hope this helps.

james