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Effects of Line Constants in a Long Transmission Line

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Effects of line constants: For long transmission lines with lengths above 150 km and transmission voltages (100 kV) above 100 kV, it is assumed during line calculations that the distributed capacitances are not concentrated at one or more points on the line, but distributed evenly throughout the line.

Resistance, inductance, shunt admittance are considered negligible during short transmission line calculations. The line where the effect of capacitance has to be caught is medium and long transmission lines.

Effects of line constant in long transmission lines

We know that the line constant of a transmission line is uniformly distributed over the entire line. However, these constants are considered negligible to obtain reasonable accuracy in short and medium-line calculations. If we do not take this into account even for long lines, the calculation of line performance will be seriously wrong. Hence for accuracy of calculation, this constant is assumed to be uniformly distributed over the entire line. Rigorous methods are used to solve these problems mathematically.

Effects of Line Constants in a Long Transmission Line

The figure above shows the equivalent circuit of a 3-phase long transmission line based on phase-neutral. The entire line length is divided into n number of sections. Each section of the entire line is treated as a line constant – frac{1}{n} th. The effect of line constant on long transmission lines is discussed below-

1. In fact the line constant of the entire line is uniformly distributed.

2. Resistance and inductive reactance are series elements.

3. Leakage susceptance (B) and leakage conductance (G) are shunt elements. Leakage susceptance is the capacitance between line and neutral. Leakage conductance is the loss of power due to leakage current flowing through insulators or the corona effect between conductors. Shunt admittance of said two elements = sqrt{G^2+B^2}

4. As leakage current flows in the line, the shunt admittance is maximum at the sending end and gradually decreases to zero at some point near the receiving end.

These were the effects of line constants in a long transmission line. Also Read, Effects of Line Constant on Medium or Intermediate Transmission Lines.

Frequently Asked Questions

What is long transmission line?

When the length of the transmission line is more than 150 km and the voltage is more than 100 kV, then the line is called a long transmission line.

What is character constant?

In transmission line (rigorous method) calculation, the root of the ratio of Z and Y is a complex constant, called character constant.

Which method is more effective in analyzing long transportation lines?

Is the rigorous method more effective in analyzing long transportation lines? .

What is the voltage of long transmission lines?

Long transmission lines should be more than 150 km in length and more than 100 KV voltage.

What type of elements are resistance and inductive reactance?

Resistance and inductive reactance is series elements.

How is the line constant of the entire line distributed?

The line constant of the entire line is uniformly distributed.

What are series and shunt elements between long transmission line constants?

Constants of long transmission lines-

(a) Series element – resistance, inductive reactance

(b) Shunt element – leakage susceptance, leakage conductance.

What are the names of the constants of long transmission lines?

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The constants of long transmission lines are-

(a) Series resistance

(b) Series inductive reactance

(c) shunt leakage susceptance and

(d) Shunt leakage conductance.

What are the advantages of constant voltage supply in power transmission system?

Advantages of constant voltage supply are given below-

1. The same voltage is available across all loads.

2. Increase in load value increases power factor value.

3. Enhanced power transport is possible.

4. Better protection is obtained by using high terminal reactance in the line.

What are the disadvantages of constant voltage supply in power transmission system?

Disadvantages of constant voltage supply in power transmission system are given below-

1. The short circuit current of the system increases.

2. The risk of supply interruption increases if the synchronous motor connected at the receiving end is unable to operate.

3. In case of faulty line the line reservation is reduced.

What measures can be taken to maintain voltage in transmission lines?

Following are the methods of maintaining voltage in transmission lines:

(i) Booster Transformers.

(ii) By Excitation Control

(iii) Moving Coil Regulators,

(iv) Auto Transformer Top Changing.

(vi) By Synchronous Condenser.

(v) Induction Regulators.

How is the effect of long transmission line constants considered?

The effects of line constants is considered as follows-

(a) Resistance

(b) Inductance as series element

(c) Leakage conductance as shunt element and

(d) Capacitive Susceptance.

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