Question

Introduction to Power system

Answer 1

I want to start the series on power system by introducing very basic (bread and butter) of power system. If you know nothing about power system , this is be a good starting point.

Answer 2

Anyone have anything constructive to add, feel free to do so. Let's stimulate discussion.

Answer 3

The power system is uses AC which is sinusoidal in voltage and current. Any sinosoidal can be(completely) represented by 3 parameter : Amplitude, frequency ,phase. Each of the three parameter will be explored much deeper in next session.

Answer 4

Frequency:
Depend on where you live , the power system is either 50Hz or 60Hz. It is very important that frequency stays very close to this frequency otherwise instability will happen. We will explored instability in the future. Frequency of the power system originate from speed of the generator and number of poles.Generator( Synchronous Machine) will be explored in future as well.

Answer 5

Phase:
Power system is polyphase. which mean there are 3 phase which is 120 degree apart from each other. Phase A is at 0 degree phase shift, Phase B is 120 degree shifted, Phase C is 240 degree shifted.

Why 3 Phase: 3 Phase motor are superior to 1 phase motor. They are more efficient . More power is supplied to load in one period in 3 phase than 1 phase.

Here is pictorial representation of three phase

http://electrical-engineering-portal.com/wp-content/uploads/three-phase-voltage-waveforms-separated-by-120-electrical-degrees.gif

Answer 6

Amplitude: There are different amplitude of voltage al throughout the power system. Our home are supplied by 120/240 supplies. The generator generate the voltage at around 30kV. The transmission line supplies at high voltage(as high as) 760kV

Answer 7

@ParthKohli

Answer 8

@iPwnBunnies

Answer 9

o-o
How does Phase 3 allow more power to a load during one period.

Answer 10

so imagine you turning a wheel. if you turn a wheel one time( analogous to one phase) in 1 period. or if you turn it three time(three phase) in one period. the power to the wheel will be greater hence it will spin faster.

Answer 11

Tru, but a phase shifted wave will still have the same frequency, therefore the same period. Right?

Answer 12

this it is shifted., it started and end at different time

Answer 13

So basically, before one period of 1st phase has ended. second and third will begin .

Answer 14

so if you integrate over that one period , you power will be greater

Answer 15

Ok, I think that makes sense.

Answer 16

I can't decide if I should make the this series mathematical intensive or intuitive

Answer 17

Mathematically intuitive pl0x. Wait, I'm losing it. If we integrated over a curve of time by amplitude, what would that give us?

Answer 18

Amplitude by time*

Answer 19

Average power is attained if you integrate and divide by period

Answer 20

Ok. Gotcha.

Answer 21

@radar

Answer 22

Nice introduction @modphysnoob .

Answer 23

then i have a question
why we mainly use 3 phase systems why not higher phases like 6 or 12 phases where more power can be obtained?

Answer 24

Hmm.. More than three phases are occasionally used whenever lots of DC is required for example in some arc furnaces. More phases can reduce the amount of smoothing required and the amount of harmonic distortion on the supply.

Generally three phase and the inverse of each phase is used giving six phase, this is nice and easy as it can be created with transformers and doesn't need special generators or fancy electronics.

Does this helps? @sidsiddhartha

Answer 25

More Understanding Ref: http://www.theiet.org/forums/forum/messageview.cfm?catid=226&threadid=22715 Post by "Freeman291082" Helps out !!

@sidsiddhartha \(Nice~To~Meet~You~!!\)

Answer 26

yeah thank u @Koikkara nice to meet u too :)
yeah 6 phases are used in rectification purpose because when the number of phases in the input increases then the output DC will be more smooth
but generally 3 phase is preferred over 6 phases why? i havent got any satisfactory reason so far :(

Answer 27

@sidsiddhartha - https://www.youtube.com/watch?v=HqZtptHnC2I

May be that answers your question ?^

Answer 28

someone gave me an explanation-------
6 phases would add twice power than three phases but 12 phases do not add power double than that of 6 phases so it will cause more constrain in grid and losses will increase and when no of phase increases then we also have to increase no of busbars and circuit breakers

Answer 29

yes @Koikkara Post by "Freeman291082" Helps :)

Answer 30

Hey you can find \(\color{red}{Answer}\) for " generally 3 phase is preferred over 6 phases why? i havent got any satisfactory reason so far :" in the \(\color{red}{link}\) provided with my response. !!

Answer 31

\(Awesome~!!~ You~Are~Genius !!\) \(Have~A~Nice~Day~!!\)

Answer 32

thanks to u :)

Answer 33

very good article @modphysnoob waiting for more :)

Answer 34

Thanks , sidsidhartha. I plan to go much deeper:graph theory for power network analysis, electromagnetics, electromechanical conversion,algorithm development ,and quite a bit of control engineering, and stability criteria and software like Comsol(which I am still learning), matlab, simulink, and possibly Solidworks.

Answer 35

wow that would be great for electrical engineering students like me :)

Answer 36

that's my goal, I want to teach what I know and learn by discussion stimulated.

Answer 37

thanks will wait for the next one :)

Answer 38

if you can , can you support these lessons here
http://openstudy.com/study#/updates/539a3d4ae4b0206eed08c74d

Answer 39

I actually would love to get more into the mathematics as well as the intuitive understanding. I think both would be good to go hand in hand. I'm really lacking when it comes to understanding AC and I think from what you've said you're really quite "grounded" in your explanation of electricity @modphysnoob .

My dad was an electrician and would talk about this kind of stuff, and he taught me a fun way to draw a graph with three phases on it. Just make a zig zag, and then connect the points. Like this: That might come in handy for drawing out nicer diagrams of 3 sine waves shifted by 120 degrees in general for anybody who might need it haha.