An Improved ANN–BPN to Radial Distribution System Load Flow - Proceedings of All India Seminar on Biomedical Engineering 2012 (AISOBE-2012) - page 186

• Compute with the most recent voltage V ð 6 Þ at node 6 the current I ðÞ ¼
S ð 6 Þ = V ð 6 Þ

: Apply the Kirchhoff's current law to determine the current,
I 5 ;ðÞ ¼ I ð 6 ; 7 Þ þ I ð 6 ; 26 Þ þ I ð 6 Þ :
• Similarly compute till the junction node.
• Using the current I (1,2) compute the voltage, V ðÞ ¼ V ð 2 Þ þ Z ð 1 ; 2 Þ I ð 1 ; 2 Þ :
At the end of the forward sweep compare the calculated magnitude of the rated
voltage at node 1 to the specified source voltage.
Voltage Difference V ðÞ¼ V jjj j V 1 jj
Stop if the VD is less than a specified tolerance i.e., if VD \ 0.001 pu
(& 12 V) else the backward sweep begins. The backward sweep begins at the
node 1 with the rated voltage V S ¼ V 1 ¼ 12660 þ j0V :
B. Backward sweep:

• Start with node 1 and V ðÞ ¼ V ð S Þ :
• Compute the voltage V ðÞ ¼ V ð 1 Þ Z ð 1 ; 2 Þ I ð 1 ; 2 Þ :
• Compute the voltage V 3 ¼ V 2 Z ð 2 ; 3 Þ I ð 2 ; 3 Þ :
• Compute the voltage V (4) to V (32) similarly.
• Compute the voltage V ð 33 Þ ¼ V ð 32 Þ Z ð 32 ; 33 Þ I 32 ; 33

Þ :

ð

After the backward sweep the first iteration is completed. At this point the
forward sweep will be repeated, only this time starting with the new voltage at end
nodes. These steps will be repeated until the error is less than the specified tol-
erance. At the substation, the voltage is mostly taken 5 % bigger than the rated
voltage.
The key to understand the forward and backward sweep method is that

• The forward sweep is simply obtaining estimates of currents in each of the
segments. In the forward sweep, voltage accuracy is not important.
• The backward sweep is concerned with accuracy of resulting voltages.

So the method is the same as previously given with the following additional
rules:
1. Begin the algorithm by assuming nominal voltages at all far-end load nodes.
2. Compute all downstream currents (those currents flowing from a junction node
toward the load) before moving upstream from the junction node.
3. Assign to the junction node a voltage computed base on the forward sweep
done on the last downstream branch emanating from that junction node.
(Note here that this is arbitrary—we could take the voltage computed base on
the forward sweep from any of the downstream branches emanating from the
junction node).
4. Use forward sweep currents in all backward sweep calculations.