Question

A three-phase wye-connected (Y) synchronous generator is operating at Ea = 8.OLO° kV (lineneutral) and has synchronous reactance of X~ = 1.0 fl . The generator is connected to a threephase delta-wye connected step-down transformer that is constructed from three individual single-phase transformers. Each the single-phase transformers has rated power of 200 kVA has a turns ratio of 4:1 where the rated primary voltage of 8.0 kV and a rated secondary of 2.0 kV and a per-unit series reactance of 5% (neglect series resistances, core loss resistance and magnetizing reactance). The three-phase transformer supplies power to a three-phase 4-pole induction motor. The induction motor has the following parameters (all values referred to the stator circuit).

R1= 0.500 0 ohms, R2= 0.5000 ohms X1= 1.00 ohms, X2= 1.00 ohm and Xm =10.00 ohm

A)Determine the magnitude of the generator line current when the motor is started from a zero-speed condition

B) What is the line-line (magnitude) of the motor’s stator voltage under the conditions in part ‘a’?

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...

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...

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negligible resistance. The generator is connected to an infinite
bus at 6.6 KV and 60 Hz.
a)Determine the excitation voltage (Ea) when the machine is
delivering rated power at o.8 PF lagging.
b)The field excitation current is increased by 10% without
changing the power input from the prime mover. Find the stator
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A three-phase, 9,375 kVA, 13.8 kV, 4-pole, 60 Hz, Y-connected
synchronous generator has a synchronous reactance, Xs = 17.9, and
is connected to an infinite bus at rated voltage. If the rotational
and electrical losses are negligivle, what is Ia, Ef, delta, theta,
Tdrive, Phasor diagram, and power flow diagram (label completely
with numerical values for,
A) the machine as a generator; the prime-throttle is opened and
If is adjusted so that the machine delivers rated kVA, 0.8 pf
lagging,...

A three phase Y connected synchronous motor has negligible
armature resistance and a synchronous reactance of 12 ohm/phase.
The motor takes 12,000kW at a line voltage of 13,200V. If the line
current is adjusted so that the excitation voltage is
9000V/phase:
a. What is the torque angle?
b. At what power factor is the motor operating?
c. What is its armature current?

A 42 kVA three-phase synchronous generator with line voltage
4.16 kV at a frequency of 60 Hz, is connected in star
configuration. The generator has a winding whose armature
resistance is 0.8 Ω and a synchronous reactance of 7.4 Ω, both per
phase. Determine the voltage regulation when the power factor is
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A 300MVA, 20KV three-phase generator has a sub-transient
reactance of 20%. The generator supplies two parallel synchronous
motors (M1 and M2) over a 100km transmission
line. The line has two transformers T1 and T2 at the beginning and
at the end of the line respectively. Both motors are rated at
13.0KV with X"=20%. Motor M1 has a rated input of 100MVA and M2 has
a rated input of 50MVA. The transformer T1 is rated 350MVA,
20/230KV and T2 is rated...

A three phase, 200 kW, 2300 V, 50 Hz star (wye) connected
non-salient rotor synchronous
motor has a synchronous reactance of 11 Ohms per phase. When it
draws 175 kW the power
angle is 10 electrical degrees. Neglect the ohmic losses.
a. Determine the excitation voltage per phase.
b. Calculate the supply line current.
c. Determine the supply power factor.
d. Draw the phasor diagram.
e. By what percentage should the field current be changed to
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Please be clear in concept and handwriting.
A 20HP, three-phase, Wye-connected synchronous motor is
connected to a 277VAC, 60Hz
power supply. At rated conditions, the motor runs at 3600 rpm and
presents a 0.85 lagging
power factor to the power supply. The per-phase armature reactance
is 350m?. Armature
resistance is negligible, as are all other sources of power
loss.
Considering rated conditions,
a. draw a single-phase equivalent circuit showing V?, Ea and IA,
with values.
b. draw a phasor diagram...

A three-phase Wye-connected synchronous generator is rated 3600
rpm, 200kVA, 480V, 60 Hz. The generator’s armature winding
resistance is RA = 0.03Ω and the synchronous reactance
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at rated voltage. Taking the phase voltage at the output as a
reference, answer the following questions.
How many poles...

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