Difficult electrical questions (well for me, anyway:-)

[bothyhead]

Does RMS mean that if I integrate the area of the sine wave (I know the total is zero) but where it is positive and divide by the time limit then I get 230V.

Root-mean-square can be calculated as follows:

1) Square all the values
2) Get the average of the squares
3) Get the square root of the average

The above works fine if you have a number of discrete values. To apply this to a sine wave, such as AC voltage you can integrate as follows:

1) Sum the squares: Integrate between 0 and 2PI ... ASin^2
Where A is the maximum voltage (the wave amplitude)

2) Divide this by 2PI to get the average of the squares

3) Finally get the square root of step 2 to give you the RMS

 

[ban-all-sheds]

Does RMS mean that if I integrate the area of the sine wave (I know the total is zero) but where it is positive and divide by the time limit then I get 230V.

That's why it's squared first, to make it positive.

However you do the integration, you are calculating the square Root of the Mean of the Square.

And Andrew - it is 0.7071 1/(SQRT 2)

http://en.wikipedia.org/wiki/Alternating_current

 

[plugwash]

That's why it's squared first, to make it positive.

thats one reason for using squares but the same could be accomplished by just taking a half cycle average

the main reason for using root mean square is because power is proportional to the square of voltage or current. Therefore mean power is proportional to the square of RMS voltage or current.