Voltage at load of distribution network

Click For Summary
SUMMARY

The discussion focuses on calculating the load voltage levels for a distribution network, specifically at points B and C, using complex power and current calculations. The user initially struggled with the volt drop calculations due to discrepancies between estimated and calculated currents. Key equations used include complex power representations and current calculations based on the given loads. After identifying errors in their voltage loop equation and rounding issues, the user successfully resolved the problem and submitted their homework.

PREREQUISITES
  • Understanding of complex power in AC circuits
  • Proficiency in phasor representation of current and voltage
  • Familiarity with voltage drop calculations in distribution networks
  • Knowledge of electrical engineering principles related to load analysis
NEXT STEPS
  • Study the principles of complex power and its applications in AC circuit analysis
  • Learn about voltage drop calculations in three-phase systems
  • Explore advanced techniques for solving AC circuit problems using phasors
  • Investigate common errors in electrical calculations and how to avoid them
USEFUL FOR

Electrical engineering students, professionals involved in power distribution, and anyone looking to enhance their understanding of load voltage calculations in AC systems.

ClimberTom
Messages
2
Reaction score
0
Please bare with me, this is my first post here (although I've read a lot on here over the past few months)
Hopefully I've used the correct formatting etc.
I've got to a sticking point on the final point of the question below (2iii) I'm pretty happy with my answers to 2i and 2ii so I've not shown them so as to not confuse the situation, the only parts carried over are the total current drawn (It) and the total load (S).
In case the attachment isn't very clear, the load at 'C' is 0.6pf lead.

I have omitted the volt drop part of the calculations as I cannot get the calculated current at the end to be close to the estimated current at the beginning. I am happy with the volt drop part once the currents make sense.

Details below and attached.

1. Homework Statement

Determine the load voltage levels for the following distribution feeder systems.
(see image attached for the sketches)

Homework Equations


## B=3.2 ∠-36.9° \text {MVA}\ ##
## B= 2.56-j1.92 \text {MVA}\ ##
## C=1.8 ∠53.1° \text {MVA}\ ##
## C=1.08+j1.44 \text {MVA}\ ##
## S=3.67 ∠-7.5° \text {MVA}\ ##
## S=3.64-j0.48 \text {MVA}\ ##
##I_t≈192.63∠-7.5° \text {A}\ ##
##I_t ≈ 192.78-j2.23 \text {A}\ ##

(I_t and S are both calculated from question 2i as shown on the attached sheet.

The Attempt at a Solution



Estimating Current drawn at points B and C:

##I_{BE} = {\frac{3.2*10^6}{\sqrt{3}*11*10^3}} ##
##I_{BE}=167.96∠-36.9° \text {A}\ ##
##I_{BE}=134.37-j100.85 \text {A}\ ##

##I_{CE} = {\frac{1.8*10^6}{\sqrt{3}*11*10^3}} ##
##I_{CE}=94.48∠53.1° \text {A}\ ##
##I_{CE}=56.69+j75.55 \text {A}\ ##

Assuming the lowest voltage will be at load 'B' (drawing the most current) therefore, 'B' should be fed from both sides as current will flow from highest potential to lowest potential.

Volt drop around ACBA = 0
Therefore:

## 0=-2.7I_{z2}-5.4(I_{z2}-94.48∠53.1°)+4.6(192.63∠-7.5°-I_{z2}) ##
##=-2.7I_{z2}-5.4I_{z2}+306.126-j407.97+886.788-j10.258-4.6I_{z2}##
##=-12.7I_{z2}+1192.914-j418.228##
##12.7I_{z2}=1192.914-j418.228##
##=1264.10∠-19.3°##
##I_{z2}=99.54∠-19.3° \text {A}\ ##
##I_{z2}=93.95-j32.9 \text {A}\ ##

##I_{z1}= I_t-I_{z2}##
##=192.78-j2.23-93.95-j32.9##
##I_{z1}=98.83-j35.13 \text {A}\ ##
##I_{z1}=104.89∠-19.6° \text {A}\ ##

##I_{z3}=I_{z2}-I_ce##
##=93.95-j32.9-56.69+j75.55##
##I_{z3}=37.26+j42.65 \text {A}\ ##
##I_{z3}=56.63∠48.9° \text {A}\ ##

##I_b=I_{z1}+I_{z3}##
##=98.83-j35.13+37.26+j42.65##
##I_b=136.09+j7.52\text {A}\ ####
##I_b=136.3∠3.16° \text {A}\ ##I feel sure that I have overlooked something simple here. I'm pretty confident that I'm correct in assuming B to be the lower voltage. That said, I have tried working the volt drop around the loop as ABCA = 0 and still not got the correct answer.

Can anyone offer any pointers on where I am going wrong?

Many thanks
 

Attachments

  • Screenshot from 2016-01-18 18:19:04.png
    Screenshot from 2016-01-18 18:19:04.png
    30.5 KB · Views: 449
Physics news on Phys.org
Ignore the above, After lots of tea and scrap paper, I realized that my equation for the voltage around the loop was wrong and also due to some rounding and conversion errors, other values were also incorrect.

I've now sussed it out and submitted it so just waiting for it to be marked.
 

Similar threads

  • · Replies 3 ·
Replies
3
Views
3K
  • · Replies 15 ·
Replies
15
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 7 ·
Replies
7
Views
2K
  • · Replies 1 ·
Replies
1
Views
2K