Question

The generalized circuit constants (ABCD) of a 345 kV transmission line are given as:

A = D = 0.82 + j0.019

B = 40 +j150 ohm

C = (-1.35 + j193.3) x 10^-6 S

Do this problem using the per unit system. Hint: The sending end power and voltage will make good base values.

a) At the sending end, the transmission line is delivering 400 MVA at 0.8 pf at the rated voltage. Find the receiving end voltage and current phasors.

b) What kind of load is being served at the receiving? What is the efficiency of the line?

c) Find the receiving end no-load voltage, the sending end no-load current and the voltage regulation.

d) You are asked to compensate and reduce the high value of no-load voltage. How are you going to accomplish this? Implement your solution such that there is no more than 10% variation between the full-load and no-load voltage at the load end.

Answer 1

Given

Transmission line parameters are

(a)

Sending end parameters are

power

source power factor  

Sending end Voltage

Relation for ABCD parameters are

From above Matrix relation

Sending end power

Hence we need to convert those actual to PU system of equations

Base Impedence

Hence equations 1 and 2 can be modified as

by solving above two equations

(b)

From above two recieving end paramaters

Hence the Phasor Angles defines that Load is a LEADING POWER FACTOR (CAPACITIVE)LOAD

Efficiency of above transmission system is

(c)

Under NOload Ir=0

Voltage regulation

(d)

By placing Voltage regulators(Capacitive Banks) we can reduce the Voltage regulation(i.e the difference of the No load and Full Load Voltages)