Question

A 3 phase system, 33 kv with the conductor suspended by
insulating string three insulators. The capacitance of each
insulator disc is ten times the capacitance to ground.
calculate:

a) the voltage across each insulator

b) string efficiency

Answer #1

Each line of a 3-phase system is suspended by a string of 3
similar insulators. If the voltage across the
line unit is 17·5 kV, calculate the line to neutral voltage and
string efficiency. Assume that shunt capacitance
between each insulator and earthed metalwork of tower to be 1/10th
of the capacitance of the
insulator.

A 33 kV, three-phase, 50 Hz line of resistance 2 Ω/ph and
reactance j9 Ω/ph supplies a 33 kV/440 V transformer having
negligible resistance and reactance of j2 Ω/ph referred to 33 kV.
The transformer supplies a 440 V feeder of resistance 0.01 Ω/ph and
reactance j0.007 Ω/ph. If VR, the receiving-end voltage,
is 440 V, calculate VS, the sending-end voltage, when
the three-phase load delivered is 440 kW at unity power
factor.

1- A 69-kV, three-phase short transmission
line is 16 km long. The line has a per
phase series impedance of 0.125 +
j0.4375 ohm per km. Determine the sending
end voltage, voltage regulation, the
sending end power, and the transmission
efficiency when the line delivers
a. 70 MVA, 0.8 lagging power factor at 64 kV
b. 120 MW, unity power factor at 64 kV
2-three-phase, completely transposed 345-kV, 200 km
line has two 795,000-
cmil 26/2 ACSR conductor per bundle...

A 132 KV, 50 HZ, 3 phase, 3 core metal sheathed cable gave the
following resutls in testing for capacitance:
(a) capacitance between shorted conductors and sheath is 0.8 micro
farad.
(b) capacitance between two conductors shorted with sheath and the
third conductor is 0.6 micro farad.
Draw the test arrangment in each case and determine:
(i) the capacitance between any two conductors.
(ii) the conductor self capacitance and the capacitance between any
two shorted conductors and the third conductor....

A 100 MVA, 13.2 kV three phase generator (G) having a
synchronous reactance of 10% is connected to a three phase Y-Y
transformer T1 which feeds a 132 kV 10 miles transmission line
having an impedance per phase of 2 + j5 ?/mile. At the receiving
end of the transmission line is a Y-Y step down transformer T2.
Three loads are connected to the secondary side of the transformer
T2. Loads are as follows:
Load#1 40 MVA at 0.8 pf...

1- 30-kV, three-phase transmission line has a per
phase series impedance of z = 0.05+j0.45 ohm per Km and a per phase
shunt admittance of y = j3.4x10-6
siemens per km. The line is 80 km long.
Using the nominal π
model, determine
a The transmission line ABCD constants.
b Find the sending end voltage and current,
voltage regulation, the sending end power
and the transmission efficiency when the line
delivers
1. 200 MVA, 0.8 lagging power factor at 220...

Problem 2. A three phase transformer rated at 5 MVA, 115/13.2 kV
has a per phase series impedance of 0.007 + j0.075 per unit (shunt
parameters are ignored). The low voltage side is connected to a
short distribution line which modeled by a series per phase
impedance of 0.02 +j0.1 per unit on the base of 10 MVA. The line
supplies a balanced three phase constant impedance load at 4 MVA,
13.2 kV with power factor of 0.85 lagging
•...

The capacitances per Km of 3 core cable are 0.9 micro
farad between the three bunched conductor and the sheath, and 0.4
micro farad between one conductor and the other two connected to
the sheath. Draw the arrangement in each case and find:
a) the line to ground capacitance of a 20 Km cable length.
b) charging current if the cable operates at 11 KV line voltage at
50 HZ.
c) the power loss and loss angle if the power...

Plate values of a three-phase transformer are given
below:
1600 kVA, 15 kV / 400 V, 50 Hz, io = 1.2%; ukN = 6%, idle losses
2450 W, rated
copper losses of power 14500 W; Dy5.
a) Calculate primary and secondary line and phase currents.
b) Secondary at 75% load in power factor with 0.85 inductance and
0.85 capacity
calculate the voltage separately. Compare and interpret the
results. capacity
at what time of day can the upload be seen? To...

Plate values of a three-phase transformer are given
below:
1600 kVA, 15 kV / 400 V, 50 Hz, io = 1.2%; ukN = 6%, idle losses
2450 W, rated
copper losses of power 14500 W; Dy5.
a) Calculate primary and secondary line and phase currents.
b) Secondary at 75% load in power factor with 0.85 inductance and
0.85 capacity
calculate the voltage separately. Compare and interpret the
results. capacity
at what time of day can the upload be seen? To...

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