Question

**Use MATLAB:**

A three-phase Y-A transformer is rated 225-kV:24-kV, 400 MVA and has a series reactance of 6.08 Ohms as referred to its high-voltage terminals. The transformer is supplying a load of 375 MVA, with 0.89 power factor lagging at a voltage of 24 kV (line-to-line) on its low-voltage side. It is supplied from a feeder whose impedance is 0.17 + j 2.2 Ohms connected to its high-voltage terminals. The total load in the system remains constant at 375 MVA.

**A)** Plot the line-to-line voltage which must be
applied to the sending end of the feeder to maintain the load
voltage at 24 kV line-to-line for load power factors in range from
0.3 lagging to unity to 0.3 leading.

**B)** Plot the sending-end voltage as a function
of power factor angle.

Answer #1

a) A three phase transformer rated at 30 MVA 10 kV(Δ)/1 kV(Y) is
supplying a load at the low voltage side. The load absorbs 5 MVA,
0.7 power factor lagging at line to line voltage 0.9 kV. The
transformer has an equivalent reactance 0.05 Ω/phase. Assuming 10
MVA and 1 kV as base value, draw the per unit diagram for the
system. Find the Line to Line voltage at the primary side of the
transformer.
b) A three-phase synchronous generator...

Problem 2. A three phase transformer rated at 5 MVA, 115/13.2 kV
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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
•...

A 100 MVA, 13.2 kV three phase generator (G) having a
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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...

A 33 kV, three-phase, 50 Hz line of resistance 2 Ω/ph and
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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
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A 125 MVA 11 kV three phase 50 Hz synchronous generator has a
synchronous reactance of 1.33 p.u. The generator achieves rated
open circuit voltage at a field current of 325 A. The generator is
connected to a network with an equivalent line-line voltage of 11
kV and an equivalent impedance of 0.17 pu on the generator base.
The generator is loaded to a real power of 110 MW.
a- Find the generated voltage Eaf in p.u. such that the...

A three-phase transformer has a nameplate rating of 20 MVA,
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base of 20 MVA and 345 kV on the high-voltage side. Please
determine the following:
(a) Turn ratio of windings
(b) Transformer reactance referred to low-voltage side in ohms
(c) Transformer reactance referred to low-voltage side in per
units

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...

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-
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0.11 per unit). Take into account the transformer’s phase shift and
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(a) Find the per-unit load currents (IA, IB, and IC).
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at the output terminals of the generator if the load is suddenly
disconnected. Assume the speed and the excitation current is to
remain unchanged.

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