Nominal T model of a medium transmission line has two components- series impedance and shunt admittance. In this post, we shall discuss the nominal T model of a medium transmission line. In a nominal T model of a transmission line;

- The series impedance is divided into two equal parts.
- The shunt admittance is concentrated at the center of the line.

**Nominal-T Representation:**

The nominal T model of a medium transmission line is as shown below.

Where,

Series impedance of the line Z = R + jX

Shunt admittance of the line Y = jwc

Receiving end voltage = V_{r}

Receiving end current = I_{r}

Current in the capacitor = I_{ab}

Sending end voltage = V_{s}

Sending end current = I_{s}

By KCL and KVL rules, We can calculate the sending end voltage and current. The voltage across the capacitors is ;

The current flowing through capacitor is

From above equations, we can calculate the sending end voltage and current.

The sending end voltage is ;

**Sending end voltage and current **is as written in matrix form;

**The A,B,C and D constant of medium transmission line is.**

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Classification of Transmission Line |

The phasor diagram of the nominal T-circuit for a lagging power factor is as shown below.

**Abbreviation in Phasor Diagram**

OA = V_{r} – receiving end voltage to neutral, as reference voltage

OB = I_{r} – load current lagging V_{r} by an angle ∅. Where, cos∅ is the power factor of the load.

AC = I_{r}R/2 – Voltage drop in the reactance of the right-hand half of the line. It is 90 degree to OB, i.e., Ir.

OD_{1} = V_{ab }– voltage at the midpoint of the line across the capacitance C.

BE = I_{ab} – current in the capacitor. It leads the voltage V_{ab} by 90.

OE = I_{s} -sending-end current, the phasor sum of load current and capacitor current.

D_{1}C_{1} = I_{s}R/2 – voltage drop in the resistance on the left-hand side of the lines.It is perpendicular to Is.

C_{1}D = I_{s} X/2 – voltage drop in the reactance in the left half of the line. It is perpendicular to Is

OD = V_{s} – sending end voltage. It is the phasor sum of the of V_{ab} and the impedance voltage drop in the left-hand half of the line.

∅_{s} – phase angle at the sending end. cos∅_{s} is the power factor at the sending end of the line.

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