Hi: If asked to find the power factor - I know the formula to use is cosθ - but sometimes the answer is requires a minus sign in the cos - like cos-θ. Is this to do with the direction of the sinusoids and/or whether one leads or lags the other. How do I know when to use the minus sign and when not to? many thanks
Note that the power factor (PF) is cosθ only for sine waves. For a general case, PF=real power/apparent power θ is the angle of the voltage minus the angle of the current. Apply this and the sign will be obvious.
You may want to review the following material: http://www.rose-hulman.edu/class/ee/HTML/NSF/CCLI_EMD_DUE_0088904/PDFS/lecture_notes_04.pdf http://www.rose-hulman.edu/class/ee/HTML/NSF/CCLI_EMD_DUE_0088904/PDFS/lecture_notes_05.pdf
I had a look at both sets of Notes, but found that the lecture 5 notes there are missing infomation on pages 2,3, & 4. They have to do with General Analysis & Worked Examples, can they be restored?. Thanks.