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Questions tagged [power-engineering]

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

32
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5answers
20k views

Why don't we use neutral wire for to ground devices and earth wire for closing the circuit?

I know that the neutral point of a distribution transformer is connected to the grounding (earthing) wire, so I think they are the same. Can I use the neutral wire for protecting metal-cased electric ...
13
votes
14answers
24k views

Why are the power transmission/distribution systems AC and not DC?

Is there a good reason why we are not in the process of completely converting our electrical transmission system to DC? The main reason for using AC on the grid (no offense Tesla, I love you man) was ...
7
votes
2answers
46k views

Why does a delta/wye transformer make 30 degrees phase shift ?

I'v heard that a delta/delta or Wye/Wye transformers do not make any phase shift. In delta/wye or wye/delta transformers, There is a 30 degrees phase shift between the primary and secondary coils. So, ...
71
votes
8answers
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 ...
11
votes
7answers
2k views

Power grids : AC vs DC

We know that we have now 50/60Hz in our walls due to mainly historical reasons - back 100 years ago there were no ways to up/down scale DC voltage. These days we just have problems due to that - ...
37
votes
8answers
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 ...
7
votes
3answers
15k views

How to synchronize a generator on the electrical grid?

I've read many articles about paralleling two portable generators or synchronizing a power generator on the electrical grid. I have the theoretical background about that topic and I know the four ...
44
votes
11answers
18k views

Why three-phase power? Why not a higher number of phases?

Is there a reason, beyond historical reasons, that three phases has become the dominant number of phases? I am aware of the advantages against one phase and two phase, namely the reduced amount of ...
30
votes
3answers
9k views

Why 3 phase and not 1 phase power transmission?

Why does power transmission use three lines with three different phases? Why not three lines all in the same phase? Does it have to do with the alternators used for generating the power, or is there ...
6
votes
3answers
2k views

Why is the earth a viable return path for power distribution?

I'm having trouble understanding why the earth is a viable fault path for electricity brought into my home. Isn't there really high resistance? I mean, it's dirt? Also, let's say I connect the hot ...
5
votes
1answer
5k views

What is the percent impedance of a typical residential power line transformer?

Power transformers are rated by percent impedance. A 5% transformer, when loaded to full spec secondary current, will show a ~5% deviation from nominal output voltage. What is the percent impedance ...
3
votes
2answers
2k views

Why does frequency splitting happen when two resonant circuits are magnetically coupled in wireless power transfer?

When two circuits are tuned to a self resonant frequency and are then magnetically coupled, the resonance happens at multiple frequencies if they are near. How and why does this happen?
10
votes
3answers
12k views

How is transition from three-phase distribution without neutral to three-phase consumption with neutral achieved?

A typical distribution grid supplies 6 or 10 kilovolts AC to a substation near the consumers. This is typically done with a three-phase line without neutral - just three wires going in parallel. Then ...
32
votes
4answers
15k views

How do transposition towers in transmission lines work?

There're such things as transposition towers in power distribution powerlines. The idea is that for example you have three conductors running in parallel at the same height and the leftmost of them is ...
9
votes
2answers
440 views

mains frequency accuracy worldwide

I like to build a device that needs long term time stability. In germany, one of the best simple clocks use the mains power frequency to obtain a time measure. While the frequency is allowed to change ...
2
votes
3answers
442 views

Isolation provided by transformers

I have a few questions about transformers and isolation. I will describe my understanding (maybe wrong) and questions about them. Transformers provide safe isolation by disconnecting two circuits ...
2
votes
1answer
6k views

What is the zero-sequence equivalent of a YNy0 transformer?

The zero sequence equivalent network of a YNy0 transformer with grounded primary is shown below (source). It looks like there is no connection between the primary and secondary side of the ...
10
votes
3answers
13k views

What is the purpose of the thin wire at the top of power transmission lines?

I know a power transmission line carries usually two sets of 3 phase conductors. But I have noticed a relatively thin wire at the center-top of the power transmission line. What is the purpose of this ...
10
votes
3answers
10k views

Why would a power cable need copper wire shielding?

Today I witnessed burying 10 kilovolt power cable in the ground. I noted the cable mark and Googled it. The description is rather interesting. It's a single conductor cable - it takes three such ...
5
votes
4answers
5k views

How does DC transmission require several times less wire than AC?

In this YouTube video (scrolled to 5:55) there's a claim that replacing an AC high voltage transmission line with a high voltage DC transmission line allows for having seven times fewer powerlines (...
2
votes
3answers
456 views

Electrical System Harmonics

I'm a mechanical engineer so I don't know much about electric circuits and power generation to begin with. Can somebody explain what a harmonic is in the power grid and what is the reason why it is ...
1
vote
1answer
1k views

Why are the ground and neutral bonded in my panel?

I took a look inside my panel today and saw a big green wire connected to the neutral bus bar. Why are these two bonded together? Why not just send the neutral back where it came from? Where does the ...
0
votes
1answer
2k views

Synchronising Power & Synchronising Coefficient

I am really confused with the concept of synchronising power and synchronising coefficient. I was taught 2 simple formulae in class. P = 3VEsin(del)/X Sp = dP/d(del) = 3VEcos(del)/X Now, I am ...
18
votes
6answers
11k views

How does earthing work when earth is dry?

Earthing is meant to provide reliable contact of an electric appliance to earth so that if there's an insulation fault current goes into earth instead of through a person's body. This requires ...
18
votes
8answers
50k views

What happens to excess energy fed into the power grid?

The closest question to this is Linear useage of excess power generation. I'm no engineer so I may not be able to phrase this correctly and would appreciate an answer which assumes minimal ...
14
votes
3answers
40k views

Why does reactive power affect voltage?

Why does reactive power influence the voltage? Suppose you have a (weak) power system with a large reactive load. If you suddenly disconnect the load, you would experience a peak in the voltage. Is ...
8
votes
3answers
10k views

How would an electric company detect wireless theft of electricity?

As legend goes it is maybe possible to steal electricity from power lines in a wireless way (also see this and this related questions). The legend continues that once someone does that he gets caught ...
16
votes
5answers
3k views

Why do generators have to rotate at a slower frequency if demand outpaces the supply?

EU residents might have noticed that some of the clocks in their house have been running out of sync with other clocks. Apparently, the cause for this is that power suppliers had to reduce the ...
8
votes
1answer
6k views

Comparison between AC and DC power flow analyses

Consider a power flow problem. Injected real and reactive power at a bus are functions of voltage magnitudes and voltage angles and are given by \begin{align*} P_i = \sum_{k=1}^N|V_i||V_k|(G_{ik}\cos(...
7
votes
1answer
2k views

What are these coils on transmission lines?

What are these coils? This was asked by doetoe in this physics.stackexchange Question Where I saw them (maybe six or eight pairs) they came in pairs, always on the same two lines, and they were at ...
2
votes
3answers
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 ...
2
votes
2answers
128 views

What is the effect of heavy loads on the electrical grid?

When our neighbors turns on a motor, a bulb in our home turns off for a very very short time and then it turns on again. It is something like a quick flash but a man eye can notice it. Would you tell ...
10
votes
5answers
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 ...
7
votes
3answers
9k views

How are multiple power sources synchronized in a grid that uses a distribution ring?

A large distribution grid can work like this. There're several power station each outputting 50 Hz AC. Each power station feeds energy into a substation next to it which raises the voltage and then ...
4
votes
0answers
2k views

Why DC is not used for long distance voltage transmission? (Tesla vs Edison 2015) [duplicate]

It seems this question has been marked duplicate but I believe the answers given here is much more in detail. Why we are still using AC voltage for long distance voltage transmission. As we know with ...
2
votes
1answer
441 views

Voltage drop-out after lightning strike

A powerful thunderstorm rolled through my area yesterday and something happened that I had never noticed before. Many times before when powerful thunderstorms with lightning rolled through, the AC ...
2
votes
0answers
2k views

How to calculate the earth fault current in a transmission system with no ground wire?

Background information, and my thought on the matter are provided in the end of the question. I need to calculate the fault current in case a fault occur for instance 10 km away from a transformer ...
1
vote
1answer
3k views

what is shunt charging in power systems?

I am currently working with Power World Simulator. When inserting transmission lines, there is a parameter called shunt charging. What is this and what effect does it have on power loss in the line?
1
vote
5answers
108 views

Transformers Construction

Seeing all the transformers around me looks like a huge piece of iron. I was wondering why transformers have such a huge mass. Consider if we need 11V/ 440V voltage transformation. Why don't we have ...
1
vote
1answer
538 views

Phasor Measurement Unit (PMU) vs Synchro-check Relay

What is the difference between a Phasor Measurement Unit (PMU) and a Synchro-check relay? I need to know if Synchro-check relay can be used as replacement for PMU in a Synchrophasor data system. We ...
1
vote
2answers
986 views

Electrical schematics component ID's

Is there a list of standard ID codes used for components on a schematic drawing that anyone can point to? e.g. K = Contactor S = Switch Y = Solenoid X = Terminal strip etc. Any list would be ...
0
votes
2answers
2k views

Hooking two (gasoline) generators together to make 220VAC

A question was posed on the Home Improvement SE... Can I buy or make an adapter to hook 2 generators together to run a 220 volt welder? Any contribution to this thread (from an electrical engineer) ...
0
votes
2answers
214 views

3 phase ac vs single phase [closed]

A single phase supply requires 2 wire one for forward and next for returning path. However a 3 phase supply only requires 3 wire why? How does the circuit complete with 3 phase supply?
-2
votes
1answer
163 views

What's the thick wide aluminum tape used for in last mile grid transformers?

This YT video (scrolled to 0:45) shows the process of fabricating a pole mount transformer. At 0:45 the following is shown: there's a wooden brick used to hold everything together, it's covered in ...