ABCD parameters of Transmission Line | EREE | SOET | BGSBU

Описание: • For a transmission line, it is better to call input voltage and current as Sending end voltage and current. Similarly, output voltage as receiving end voltage and current.

Let

VR = Receiving end voltage

Vs = Sending end voltage

Is = Sending end current

IR = Receiving end current

Thus we can write,

Vs = AVR + BIR …………………..(1)

Is = CVR + DIR ……………………(2)

• Here A, B, C and D are constants and known as Generalized Circuit Constants of transmission line. The values of constants can easily be calculated from the above equations. For calculating the values of the ABCD parameters, we will consider two cases. Bold sign in the entire post means vector form of the quantity.

Case (1): When Receiving end is open.

As the receiving end is open, therefore load current through the line will be zero. Thus IR = 0.

From equation (1).

A = Vs / VR

Notice that the unit of A is unitless and hence called voltage ratio.

From equation (2),

C = Is / VR

From the above expression of constant C, it is clear that, the unit of C is Mho. This constant is known as open circuit conductance.

Case (2): When receiving end is shorted.

As the receiving end is shorted, therefore load end voltage will be zero. Thus VR = 0.

From equation (1),

B = Vs / IR

Notice that the unit of B is same as that of impedance i.e. Ohm and called short circuit resistance.

From equation (2),

D = Is / IR

Thus D is a dimension less quantity and known as current ratio.