Pi Type Modeling of Medium Transmission Line:

Medium Transmission Line:

A transmission line of length 80 km to 240 km is called medium transmission line.

Its voltage is 21 kv to 100 kv. The transmission can be done by two ways of models.

1.Nominal PI model

2.Nominal T model

Both models have their own advantages and disadvantages as well,but more effective

is T model because its nodes ( i.e ABCD) calculation is very easy becase T model has

less nodes as compare to PI model.But we have to discuss about PI model here.

EXPLANATION

In a transmission line, the resistance, inductance, and capacitance are uniformly distributed along the line. An approximate model of the distributed parameter line is obtained by joining several identical PI sections, as shown in the following figure.

The Three-Phase PI Section Line block implements a balanced three-phase transmission line model with parameters lumped in a PI section.

Contrary to the Distributed Parameter Line model where the resistance, inductance, and capacitance are uniformly distributed along the line.

The line parameters R, L, and C are specified as positive- and zero-sequence parameters that take into account the inductive and capacitive couplings between the three phase conductors, as well as the ground parameters. This method of specifying line parameters assumes that the three phases are balanced.

The PI section linear model has a finite number of states that permit you to compute a linear state-space model. The number of sections to be used depends on the frequency range to be represented.

Frequency used for this model:

The over al rated frequency is 60 Hz but as for Pakistan we use 50 Hz in this PI model

Resistance per unit length

The resistance per unit length of the line, in ohms/km (Ω/km). which is 50 in this nominal PI model.

Inductance per unit length

The inductance per unit length of the line, in henries/km (H/km). This parameter can not be zero, because it would result in an invalid propagation speed computation.

Capacitance per unit length

The capacitance per unit length of the line, in farads/km (F/km). This parameter can not e zero, because it would result in an invalid propagation speed computation.

Measurements

Select Input and output voltages to measure the sending end (input port) and receiving end (output port) voltages of the line model.

The user can connect multiple pi section in series to form an equivalent for a long transmission line.

Tools Used in Model: Resistor Capacitor Voltage Measurement Current Measurement Scope RL Load Ac voltage source

POWERGUI: Graphical user interface for the analysis of circuits and systems

Library:Powerlib ( in Simulink)

Procedure: First we pen the mat lab software. Then we the simmulink in matlab.

Now we have to chose required parameters from simmulink voltage measurement, current measurement, ac voltage source, RLC load, resistor, capacitor inductor. Now double click on each parameters to arrange the following value. Now measure the sending end voltage, receiving end voltage.

The output graphs are shown infollowing.

Required values:

Capacitor= 10e-6 Frequency=50 Nominal voltage = 500 Inductance= 10e3 Resistance=60

BLOCK REPRESENTATION:

GRAPHICAL REPRESENTATION:

Steady state:-