# Questions tagged [power-engineering]

Power electrical engineering. Includes industrial electrical engineering (i.e. motors, switchboards), transmission and distribution (poles, wires, transformers, grids) and generation.

305 questions
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### What will be Resistance for maximum Power transfer from network A to network B?

simulate this circuit – Schematic created using CircuitLab Can we apply Maximum Power transfer theorem if we are given two networks both with voltage sources. In solution it was said that for ...
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### The critical clearing time (CCT) of a fault in DIgSILENT

How can I determine the critical clearing time (CCT) of a fault in DIgSILENT? How can I use DPL to determine the critical clearing time (CCT) of a fault in DIgSILENT?
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### Does using HVDC for distance transmission make theft of electricity easier to detect?

In particular, if you were going to try to steal power from HDVC transmission lines you'd need one cable attached to current going in 1 direction and the other attached to current flowing in the ...
113 views

### can someone help with this question with capacitors

Please I need help solving this one, the book is Thomas Floyd 3rd edition Electric circuit fundamentals. The final answer is supposed to be $\text{0.0052 } \mu F$ The ac source frequency \\$f=...
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### Harmonics in power system

I have seen in some text books that power converters produce harmonics in power systems. How do power converters inject harmonics in a power system?
9k views

### Why do utility companies supply at a frequency of either 50/60 Hz?

It just struck me that Utility Companies world-wide supply domestic users at either 50/60Hz. It could have been selected to be 10 Hz, or 100 Hz ... whatever Was 50/60 chosen at random? Is there some ...
225 views

### How to predict the output of a solar panel depending upon weather conditions for real time hardware simulation?

I want to build a system for smart grid which can optimize the grid power, load and battery charging to reduce my costs for grid power. For the optimization problem, I must know the current date to ...
130 views

### Off grid LED solar lighting without batteries

I have 2 COB LEDs (12-14V DC, 50W, I think with 3,75 A in data sheet). I need to run them with a solar panel, it should only run when there is sunlight no batteries needed. Using a 270W panel (open ...
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### Instantaneous power

A sinusoidal voltage source v =10V sin(ωt) is connected across a 1k resistor. Make a sketch of p(t), the instantaneous power supplied by the source. Determine the average power supplied by the ...
15k views

### How big current I can commutate using D-sub connectors?

The question Did someone knows what are the current capabilities of the standard D-sub (aka Cannon) connector. I want to use it for power source connection together with the signal. I need pretty ...
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I came across the terms 'Rectifier Loading Effect' and 'Rectifier Loading Factor' when reading IEEE Std 421.5-2005 Recommended Model for Power Stability Studies, mentioned in those ACxA models. What ...
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### How to have Wye-connected Potential Transformers(PTs) and Neutral Ground Resistor short circuit detection at my ground fault protection relay?

Detecting if the Neutral Ground Resistor (NGR) is shorted is something that must be checked at the Ground Fault Protecting Relay. The typical way to do this is to inject a DC component and to measure ...
12k views

### Can a bird, previously at earth potential, get electrocuted by landing on a powerline at high-enough voltage due to the initial “equalization charge”?

At the voltage levels of typical overhead transmission lines in the US, a bird can land on one and be just fine (as long as it doesn't do something like spread its wings and touch a tree or something ...
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### What is the direction of negative reactive power

In a R+1/(jwC) load (AC)voltage lags current with θ degrees. Reactive power Q is negative because sin(θ) is negative. My question is how can a capacitive load deliver power to the source wich is ...
4k views

### When a wind turbine does not produce enough electricity how does the power company compensate for the loss?

I heard once that when a wind turbine power plant doesn't produce enough electricity the power company's are sometimes forced to turn on a couple of jet engines in order to compensate for the loss, is ...
223 views

### How is Line and Phase Voltage the same for a Delta connected system?

I am having a little bit of confusion for some reason understanding how the phase and line voltage can be the same for a delta connected system, i understand why the current is different for the phase ...
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### What determines the phase difference between two voltages at an AC bus?

At an AC bus, the power flow is given by the following equation : In normal operation, the voltages (V1, V2), as well as the inductive resistance (x), are constants. So the parameter δ defines the ...
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### Shorten the mini Christmas light strand

I need to shorten a 100 light strand of mini lights to just 18 lights. Based on the wiring, I believe the strand is engineered as two 50 light strands in parallel. The strand is rated for 120 V and ...
93 views

### Trapezoidal Rule of Complex RLC Circuit using MATLAB

I am having difficulty trying to figure out how to solve this circuit using the trapezoidal rule. I know how to do so in a first and second order RLC circuit however this particular circuit is giving ...
206 views

### Why is parking not allowed under some overhead power lines? [closed]

At work, among others, we have overhead power lines for the main grid connection (400 kV, about 1600 MW). The power lines cross a parking lot, and the positions directly under the power lines are ...
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### Convert kW generated per minute to kWh

I have the data of power generated by a solar panel per minute in kW. I need to calculate the total number of kWh generated per day. How do I do this? So far, I divided each value of kW by 60 and ...
49 views

### Frequency of AC for electronic devices

I was wondering why using different AC frequency makes some devises not working. I found that I do not need to adjust frequency for using electric heat or electromagnetic wave such as ・rice cooker ・...
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### How much power can transit through a power line linking generation and load?

First things first I am not an electrical engineer at all so please bear that in mind when you reply/comment. I am looking at the following problem, I have a power line which connects a windfarm to a ...
384 views

### Power System Faults Problem

A sustained three-phase fault occurs in the power system shown in the figure (See Link). The current and voltage phasors during the fault (on a common reference), after the natural transients have ...
2k views

### How to power grid suppliers control the voltage and frequency?

Can anyone give me some pointers on the ways used by electricity suppliers to control voltage levels and frequency in power networks?
635 views

### Can we use 125VAC 20A switch in place of 12VDC 20A switch?

Can we use 125VAC 20A switch in place of 12VDC 20A switch? I have searched my local market and found 125VAC 20A switch. Can i use this AC switch in place of 12V 20A switch as it is not available in ...
61 views

### Assemble Peltier Cooler to Li-poly Rc Battery

I have procured a thermoelectric cooler (TEC, this one) and my purpose of the TEC is to produce current for the Li-poly RC battery to increase its battery life. The Li-poly RC battery has 7.4V stated ...
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### Startup and auxiliary/station transformer power parallel to bus

This question is in regard to switchyard/electrical distribution operations in a utility power plant. During a startup, the electric distribution system is lined up so that the startup transformers ...
214 views

### dq0 Transformation Interpretation

What is the physical interpretation of dq0 axis transformation in electrical machines and power systems? How does this transformation helps? Thanks
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### What are the practical differences between AC and DC transmission?

I have a long (2m) but thick wire between transformer-based power supply and low frequency power amplifier. Know your best advice ahead, but no, I cant get rid of it. I can put it in two ...
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### What is the effect of very small AC frequency deviations from the grid on invertors and transformers for normal comsumer objects?

What additional wear or inefficiencies are there from inverting a AC signal to DC from say, 59.99 hertz instead of 60.00 hertz? And is there additional wear on transformers? How do small deviations ...
36k views

### Guessing power line voltage from the number of disc insulator

Is there a good way to guess the power line voltage based on the number of insulator discs that attach the line to the transmission tower? Wikipedia seems to suggest that there is a "Typical number ...
46 views

### Capacitance of short length transmission lines

I would like to simulate a short length transmission line in MATLAB/Simulink. In the library, there is a block that simulates a transmission line. The parameters that are required are the resistance R,...
71 views

### How do you close a switch on a high-voltage network?

This is something I've been curious about for a long time. Let's say you're a utility trying to connect two segments of a distribution grid. Both segments will have about the same frequency, because ...
275 views

### Why maximum power transfer condition is suitable for communication system but not for transmission of electricity?

A fundamental concept that i have learned from basic electrical circuit study is to receive maximum power by a load of resistance RL from a source the necessary ...
197 views

### DC-DC step down 12V to 5V source versus straight 5V source

Here is the scenario: I have a project needing 3 supply powers: 3.3V to run the microcontroller (max 100mA) 5V to run a bunch of adressable LEDs (max 8A, the most current intensive) 12V to supply op ...
112 views

### How fast do power plants need to respond to demand?

I've heard the layman's description of electrical grid response time before - it usually contains the word "instant" or "real-time". But I'm interested in the actual response times of the various ...
95 views

### Chimp climbing wires not electrocuted? [closed]

Reference video: https://www.youtube.com/watch?v=U5-Fy4ULdPg The chimp is climbing both wires out of phase (i would have to assume, it is in Japan), do the power lines have to be closed for the chimp ...
256 views

### How many horsepower does an alternator take from an engine at different speeds? [closed]

I want to know how much horsepower the engine deliver to the alternator at idle rpm,normal rpm and maximum rpm
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### How much power do power stations in parallel supply?

In modern power systems, the power is supplied by effectively connecting multiple generators in parallel. However, not all these generators are equal, some stations supply more power than others (I ...
2k views

### Understanding ground current

I am trying to understand ground current in a power distribution system. The basics, of course, are simple: in the power grid, the "hot" wires carry high voltage, while the return path (the neutral ...
8k views

### When can I use the formula P=V^2/R?

I'm currently learning about the transportation of electrical energy through power lines. I now know that transporting current at a very high voltage cause minimal power loss compared to transporting ...
118 views

### How to plot input reflection coefficient in dB scale using Matlab

So I have a problem that asks to plot the input reflection coefficient of a transformer in dB scale between 0.5 GHz and 4 GHz using Matlab. Here is the code I have thus far, it is plotting in ...
100 views

### How is power out one side of 220 only - Problem is with incoming 3-phase. But how?

[EDIT] Can someone who understands what I wrote explain this? [EDIT 2] Sorry I didn't say I'm in the USA, the power is 110/220vac 60Hz. The input to the main power transformer is 3-phase, underground,...
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### What is the typical voltage of power distribution in rural North America?

I mean the electrical utility power that connects to the transformer outside of the home or other buildings. i.e. what is the primary winding voltage of the transformer having 220 VAC center-tap ...
103 views

### Use of 3 phase transformers which are ∆-Y connected and Y-∆ connected

Different literatures say different things regarding ∆-Y and Y-∆ 3 phase transformer connection... Some say that ∆-Y is used for step down and Y-∆ is used for step up while others say just the ...
5k views

### Why does power dip during a lightning storm?

If lightning were to strike power lines, wouldn't you expect it to increase the power, and hence your room lights get brighter? Why do they go dim for 1 second at a time?
503 views

### Why is a short circuit in the secondary winding of a transformer reflected on the primary side?

I was reading this answer and I would like to understand why if the secondary is short circuited the primary winding will also reflect the short circuit despite the fact that they are isolated. Would ...