Question

Three single phase transformers having a 15:1 ratio are wye-connected to a 2400 V three phase line as a step-down transformer. What is the line voltage of each transformer? What is the secondary voltage of each transformer if they are delta connected to the same line?

Answer #1

A Wye-Delta transformer is connected to a 66 kV input
three-phase transmission line. Each transformer is rated at 1000
kVA and has a step-down ratio of 8:1. The bank supplies a balance
load having a power factor of 0.8 lag with a load current of 70 A.
Assume ideal transformer, determine.
The primary line and phase voltages
The secondary line and phase voltages
The secondary line and phase currents
The apparent and active power at the load
Total kVA capacity...

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...

A wye connected three-phase source is delivering a line voltage
of 480 V at a line current of 25 amperes.
Find
a) the phase voltage
b) the phase current
c) the line voltage
d) the line current
e) the total power delivered.

A balanced wye-connected three-phase source has line-to-neutral
voltages of 400 V rms.
- Find the rms line-to-line voltage magnitude.
- If this source is applied to a wye-connected load composed of
three 33 Ω resistances, find the rms line-current magnitude.
- If this source is applied to a wye-connected load composed of
three 33 Ω resistances, find the total power delivered.

The transformer is protected by a differential relay. The relay
is connected to three phase transformer, 50 MVA, 22 kV/33 kV delta
– star connection. The relay is connected in delta. The current
transformer ratio is 1500/5 Amp at the lower voltage and 1000/5 Amp
at the high voltage. Calculate the primary and secondary current of
the relay and it’s the primary turns. State any assumption.

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...

Three 1-φ, 100 kVA, 1730/208 V, 60 Hz transformer are connected
to form a 3-φ1730/480 V transformer bank. The equivalent impedance
of each transformer referred to the high voltage side is 0.3 + j0.4
ohms. The transformer delivers 40 kW to the load at 0.8 p.f.
leading.
a) Determine the phase and the line currents at the primary and
the secondary sides.
b) Draw the equivalent per-phase circuit refereed to the primary
side and determine the primary volt

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
minimize the line current.

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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