Electrical Design Analysis

SITUATION A nominal 69-kiloVolt short transmission line has a length of 16 kilometers, with an impedance of (0.25 + j0.4375) ohm per kilometer. It supplies a 70MVA 3-phase load, with 80% lagging power factor, at 64 kiloVolts only. What is the line's transmission efficiency? ANALYSIS 1.) One line diagram: o|---V,src---Z,line---Z,load---|> V,src-> = i,line-> (Z,line-> + Z,load->) V,load-> = i,line-> Z,load-> V,src-> = i,line-> Z,line-> + V,load-> 2.) Line impedance: Z,line-> = (0.25 + j0.4375) * 16km Z,line-> = (4 + j7) ohms Z,line-> = 8.0623ohms < 60.2551deg 3.) Load voltage, line-line, as reference: V,load,LL-> = 64kV < 0deg 4.) Load voltage, line-neutral: V,load,LN-> = V,load,LL-> / sqrt(3) V,load,LN-> = (64kV < 0) / sqrt(3) V,load,LN-> = 36.95kV < 0 5.) Power factor angle: S<a = P + j Q S<a = S cos(a) + j S sin(a) P = S cos(a) cos(a) = P/S = pf = 0.8 a = (+)arcco...

This post is inspired by Problem 21, Chapter 18 (Transmission Lines) of "Textbook-Reviewer in Electrical Engineering, 1st Edition" by Professional Electrical Engr. (PEE) Marcialito M. Valenzona. SITUATION A manufacturing plant is supplied by a 3-phase transmission line 10 km long. The plant receives 2.5MVA at 6kV with power factor 0.8 lagging. With a phase impedance of (0.30 + j0.40) ohm per kilometer, what is the sending voltage between the lines? ANALYSIS 1.) One line diagram: o|---V,src---Z,line---Z,load---|> V,src-> = i,line-> (Z,line-> + Z,load->) V,load-> = i,line-> Z,load-> V,src-> = i,line-> Z,line-> + V,load-> 2.) Line impedance: Z,line-> = (0.30 + j0.40) * 10km = (3 + j4) ohms |Z,line| = sqrt(3^2 + 4^2) = 5 ohms angle (b) = arctan(X/R) = arctan(4/2) = 53.13deg Z,line-> = |Z,line|<b = 5 ohms < 53.13deg 3.) Load voltage, line-line, as reference: V,load,LL-> = 6kV < 0deg 4.) Load volta...