voltage drop question

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Re: voltage drop question

tawfiq and other interested parties
The equations for calculating line impedances are summarized in Westinghouse's Transmission and Distribution Reference Book Chapter 3, Characteristics of Overhead Lines.
I have a summary of those equations, applicable at distribution voltages, on one page. If you will PM me with a fax # I will try to send it.
Jim T
 
Re: voltage drop question

hi good morning, i hope i can help you.
for the area that you have the cable is 4/0 but the name for ACSR cable is "penguin" (107.20 mm2)this cable has 6 aluminum wires and 1 steel wire
the Geometric Mean Radius for this cable is
r'=(2.30385)(r), where:
r = 0.00715 m (radius of aluminum wire)
r = 0.016472 m
the Geometric Mean Distances is:
D' = cubic root of[(Dab)(Dac)(Dbc)]in meters, where:
Dab = distance between phases A y B
Dac = distance between phases A y C
Dbc = distance between phases B y C
note: you have to know the real distance between the phases.
then we calculate the inductance:
L = (2)(10^-7)[LN(D'/r') in Henrys/m
then we calculate the inductive reactance:
Xa = (2)(3.1416)(f)(L)(1000) in ohms/Km
Xa = (Xa)(35Km) in ohms
let's calculate the resistance
for 20?C R=[(rho)(l)]/A
for aluminum (rho=resistivity=17 [(ohms)(circularmils)]/feet
R=(17)(114829.39)]/(211559.2)= 9.227 ohms
35000 m = 114829.39 feet
107.20 mm2 = 211559.2 circular mils
if your ambient temperature is other than 20?C, you have to use the follow formule:
R1 = [(9.227)(228?C + ambient temp.)]/[(228?C+20?C)].
35 Km is a short transmission line, then:
Ve=Vr+(Ir)(Z)
the voltages have to be consider from phase to neutral.
Ve= voltage at the start of the line
Vr= voltage at the end of the line
Ir=100 amp
Z=R+Xa
you have to consider power factor, and make math with complex numbers
 
Re: voltage drop question

Alberto
Your thoughts seem correct if you are dealing with a delta system. If the system is wye or grounded wye, you have zero sequence impedances to calculate also.
Jim T
 
Re: voltage drop question

ok jtester tell me how can i calculate zero sequence impedance?, because i don't know, when i took that subject, i used zero sequence circuit for short circuit calculations.
 
Re: voltage drop question

Charlie B.

I was thinking it forms an arc and calculating the percentage to add. I would expect it to matter.

It's interesting to watch some of the factors that are considered.
 
Re: voltage drop question

Alberto
Your comment about fault current calculations has made me stop and think for a minute. I still believe that the impedance to ground of a 3 phase line will be (Z1+Z2+Z0)/3 whether you are doing fault current calcs or voltage drop calcs.
For 3ph 3w z0=ra+j(xa+xe-2xd)
xd=[xd(ab)+xd(bc)+xd(ac)]/3

For 3ph 4w z0=z0(a)-[z0(ag)**2/z0(g)]
z0(a)=ra+re+j(xe+xa-2xd)
Z0(g)=3r'a+re+j(xe+3x'a)
Z0(ag)=re+j(xe-3x'd)
3x'd=xd(ag)+xd(bg)+xd(cg)
Primed quantities are neutral values
re=.286 xe-2.888ohms/mile
I will think some more about zero sequence applicability to regulation, in this case grounded wye systems.
Jim T
 
Re: voltage drop question

Physis
Speaking of learning Charlie, if you're calculating for some number of miles, do you consider the sag in the lines?
Click to expand...
The formula uses the distance of the conductor which should include the sag. The utility doing the design would have that information since they must account for sag to maintain the proper ground
clearance.
 
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