Questions tagged [power-engineering]

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

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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 ...
52
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1answer
5k views

What is this object found on transmission lines?

What are the components, circled in red in the figure, on this transmission line ?
44
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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 ...
38
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 ...
34
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 ...
33
votes
5answers
21k 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 ...
33
votes
3answers
6k 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?
32
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2answers
1k views

If we could start our electrical grid from scratch with today's technology, which would be the most efficient choice? AC or DC?

Lately, I’ve been reading about the many advantages of HVDC transmission systems for long distance transmission, undersea links, and others. The historical reason of why AC was picked over DC was ...
30
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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 ...
24
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5answers
4k views

Why are consumers located near high-voltage lines typically not connected to those lines but instead are connected through a lower high-voltage line?

A typical grid uses 110..500 kilovolts lines to deliver electricity to substations which lower that to 6..20 kilovolts and then lines with that lower voltage get to consumers where yet other ...
22
votes
2answers
5k views

Why do condors get electrocuted by power lines?

Plenty has been said about why birds are safe to land on power lines. But condors, apparently, are not. The linked article explains that condors are electrocuted often enough and endangered enough ...
22
votes
3answers
2k views

What is this device attached to a high-voltage power line?

I noticed this white, cylindrical device on a power pole near Seattle that facilitates a 90-degree turn of the transmission line. It looks like the lightning conductor comes down the pole into a sort ...
19
votes
6answers
12k 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
52k 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 ...
16
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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 ...
14
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4answers
4k views

Why does electric arc in a switch prefer a curved path over a straight path?

Recently I found this video of a 500 kilovolts line being opened under load. When the switch contacts are pulled apart an electric arc predictably starts. While the contacts are close to each other ...
14
votes
3answers
41k 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 ...
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 ...
11
votes
2answers
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 ...
11
votes
4answers
2k views

Using DC in transformers?

I read in many websites that transformers can only be used, to step voltage up or down, with AC current (which is why AC is preferred for power transmission since they can transfer huge power in the ...
11
votes
7answers
23k views

What causes overvoltage in power grid?

In the region where I live there's a state standard that says that mains voltage deviation can be within 5 percent continuously and within 10 percent for short periods of time, so if the mains voltage ...
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 - ...
11
votes
5answers
38k 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 ...
10
votes
5answers
3k views

Why/when is AC-DC-AC conversion superior to direct AC-AC conversion?

I am currently studying wind power and the power electronics used for it. In wind power a generator is driven by wind, thus the resulting power is of widely varying frequency and amplitude. The power ...
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 ...
10
votes
3answers
13k 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 ...
10
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3answers
14k 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 ...
9
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5answers
4k views

What does this symbol indicate (line with brackets)?

I'm modelling a power system, and encountered a few symbols I have never seen before in a single line diagram. I believe the first one is a switch with three possible position. Closed, open and ...
9
votes
2answers
451 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 ...
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 ...
8
votes
2answers
927 views

Why the delay between transformer failure and power outage?

A friend witnessed the explosion of the 14th street substation. I believe these transformers, about 1 city block in extent, delivered power to most of lower Manhattan. I am guessing the flood water ...
8
votes
1answer
7k 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(...
8
votes
3answers
345 views

How does the Electrical Grid React to Large Changes in Supply or Demand?

Background I'm performing some research for a software project that monitors power generation and consumption for a large fictional spaceship. My rationale is I'd like to first understand how real-...
8
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1answer
2k views

Typical zero sequence data for 80MVA transformer

I need to model a 80MVA transformer 132/33kV built in 1973. There is very little information on this transformer but I need to populate certain values in the model. Where can I find typical zero ...
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 ...
7
votes
3answers
48k 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, ...
7
votes
3answers
1k views

Capacitor exploding in a paper plant

Two years ago I was in an internship in a paper plant in the Superintendence of Electrocontrol, in the area of maintenance of electrical equipment. Well, they had a problem regarding some capacitor ...
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 ...
7
votes
1answer
193 views

How practical would it be to field rewind a large power transformer that's suffered damage from a geomagnetic storm?

It is commonly accepted in power distribution circles that large (large substation-sized or larger -- smaller substation-class transformers are much more readily replaceable) distribution transformers ...
7
votes
1answer
3k 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 ...
6
votes
2answers
7k views

Why is it desirable to inject reactive power into a transmission system?

This website explains the basics of FACTS technologies and how they can be used to exchange active and reactive power with the transmission system, namely: SSSCs - can exchange active and reactive ...
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
7answers
1k views

Excess capacity in the power grid

My question concerns capacity in the power grid. I am an attorney trying to understand whether excess capacity runs in a power grid to avoid brown outs and how long can the excess capacity exist ...
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 (...
5
votes
4answers
388 views

Is it practically possible to transfer electrical power around the World by wires?

Assume that we installed plenty of solar cells in all continents; mainly in Asia, Africa and America. Can we transfer the electrical power harvested from them around the World through wires? So that ...
5
votes
4answers
11k views

Why are twisted pair cables used in electric power distribution systems?

I'm an Electrical Engineer, and understand how a twisted pair of wires can be used to reduce noise in the presence of magnetic fields. However, I recently noticed the power company replacing the ...
5
votes
1answer
6k views

What happens to a transformer if the supply side is shorted?

Suppose I have an industrial plant, where a switchboard is fed through a transformer. The switchboard have only "passive" loads, i.e. they don't contribute with short circuit currents. If there is a ...
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 ...
5
votes
4answers
16k 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 ...
5
votes
2answers
236 views

Identification of a part on a power line's lightning arrester

I recently spotted an arrangement of wires on a lightning arrester on top of a power line. The power line is IIRC a 110 kV, 16.7 Hz, two phase line for railway systems. The lightning arrester is of ...