EENG $457$ POWER SYSTEM ANALYSIS I

EXPERIMENT $4$

POWER FLOW $1$

Objective

The objective of this experiment is to solve the power flow problem for a simple power system, which is the system in Experiment $3,$ using the PowerWorld Simulator.

$2.$ Preliminary Work

The oneline diagram of the system is shown in Fig.E$4-1.$ Bus $1$ is the slack bus and bus $4$ is the load bus. The ratings of the components in the system are

Transformers:

T$1$: $150$MVA,$20\frac{}{138}YkV,$ per phase winding resistance and leakage

T$2$: $150$MVA,$138\frac{Y}{13\mathrm{.}8}YkV,$ per phase winding resistance and leakage reactance of the high voltage side : $R=1\mathrm{.}8,x=4.$

Transmission line:

$z=0\mathrm{.}04+j0\mathrm{.}1\frac{}{k}m,y=j4{10}^{-6}\frac{S}{k}m,$ length $=100km.$

Load: $100$ MW $+$ j $40$ Mvar $($constant power load$).$

A system base of $100$MVA,$20kV$ is chosen on the low voltage side of transformer T $1.$ Use the nominal$-$ circuit model for the transmission line. Solve the power flow problem for this system and find the following

The load $($bus $4)$ voltage.

The transmission line currents at the sending and receiving ends.

The real and reactive power supplied by the generator at bus $1.$

for these cases: starting from $20\%$ of the nominal value given above, load power is increased in steps of $20\%$ up to the nominal value.

NOTE that the presence of transmission line shunt admittances complicates the problem. You may adopt one of the following two approaches:

Method $1$:

$($a$)$ Find the Thevenin equivalent of the system to the left of bus $4,$ thus eliminating buses $2$ and $3.$

$($b$)$ Write the Newton$-$Raphson equations for the unknown voltage of bus $4$ in terms of the Thevenin voltage and impedance.

Method $2$:

$($a$)$ Accept buses $2$ and $3$ as load buses with zero loads.

$($b$)$ Write the Newton$-$Raphson equations for the unknown voltages of buses $2,3$ and $4$ using $Y_{\text{b}\text{u}\text{s}}$ four the $4-$bus system.