# TRANSMISSION LINE MODEL

May 27 • General • 2033 Views • 2 Comments on TRANSMISSION LINE MODEL

TRANSMISSION LINE MODEL

For transmission line model first of all we have to know about transmisssion line.

TRANSMISSION LINE:

Transmission line is defined as a short length line having length less than 80km.In balanced condition the line is represented by the equivalent circuit of a single phase with resistance.

FACTOR AFFECTING TRANSMISSION LINE PARAMETERS:

Some of themain factors are as follow:

• Line length
• Voltage leval
• Number of conductors
• Types of conductor
• Spacing of conductors

The leval of loading at which an operating criterion or thermal rating of a line from which whichever is more constraining limit to  the load carrying capacity of the line is called as line loadablity.To access the power carrying capacity of the transmission system it is very necessary to know the capability of specific load of transmission line. Mostly the capability of the transmission line is limited to thermal rating of the conductor or with associated thermal equipment.

TRANSMISSION LINE MODEL:

An electric transmission line models are the models which can be modeled using series resistance,inductance,shunt capacitance,and shunt conductors.Genrally line resistance and inductive reactance are important.

LINE RESISTANCE:

The most important cause of power loss in a power line is the resistance offered by the conductors.And direct currentresistance is given by:

Rdc=þl/A

Where þ is resistivity of conductor,l is the length,A is the cross sectional area.

LINE INDUCTANCE:

The inductive reactance is considered as the most dominating impedence element.It depends  upon :

• Size of conductors
• Spacing between conductors
• Transposition
• Arrangement and material of each conductors

Some of the conductors arrangement is given below

Line inductance is calculated by formula:

L1=2×10-7ln(D/r1)

L2=2×10-7ln(D/r2)

There are three types of transmission line model:

• Short transmission line model
• Medium transmission line model
• Long transmission line model

SHORT TRANSMISSION LINE MODEL:

If the transmission line is less than 80km than it is called as transmission line model .The circuit diagram of short transmission line model id given below:

MEDIUM TRANSMISSION LINE MODEL:

If the transmission line is between 80km to 240km than it is called medium transmission line model.There are two models of it that is pi model and T model.Figures of both the models is given below

Pi model

T model where Z=R+jx,Y=jwC

LONG TRANSMISSION LINE MODEL:

If the transmission line is more than 240km than it is called as long transmission line model:

IMPORTANT QUESTION:

1-What is transmission lines?

Ans- Transmission line is defined as a short length line having length less than 80km.In balanced condition the line is represented by the equivalent circuit of a single phase with resistance.

2-What are the factors affecting transmission line parameter?

Ans- Some of themain factors are as follow:

• Line length
• Voltage leval
• Number of conductors
• Types of conductor
• Spacing of conductors

3-Define transmission line model?

Ans- An electric transmission line models are the models which can be modeled using series resistance, inductance,shunt capacitance,and shunt conductors.Genrally line resistance and inductive reactance are important.

4-Describe line resistance?

Ans- The most important cause of power loss in a power line is the resistance offered by the conductors.And direct currentresistance is given by:

Rdc=þl/A

Where þ is resistivity of conductor,l is the length,A is the cross sectional area.

5-Describe line inductance?

Ans- The inductive reactance is considered as the most dominating impedence element.It depends  upon :

• Size of conductors
• Spacing between conductors
• Transposition
• Arrangement and material of each conductors
• Line inductance is calculated by formula:
• L1=2×10-7ln(D/r1)
• L2=2×10-7ln(D/r2)

6 How many types of transmission line model are there according to their length?

Ans- There are three types of transmission line model:

• Short transmission line model
• Medium transmission line model
• Long transmission line model