In: Electrical Engineering

A three phase transformer of 400kVA, 10kV/400V, Dy11 is connected to its nominal load with cosφ = 1.

a) Calculate the nominal primary and secondary line
current.

b) Calculate the corresponding currents in the primary and
secondary winding.

At an open circuit test, the primary line current is 0,52A with
cosφ = 0,05 at nominal line voltage.

The short circuit test (at nominal current) shows 214V primary line
voltage and P=1,333kW per phase.

c) Calculate the total iron losses and total copper losses of this transformer.

d) Calculate the efficiency η of this transformer.

Now the transformer will be loaded with 210kW with cosφ = 0,83 (lagging).

e) Give both the iron losses and the copper losses as a percentage of what they are nominally.

**Please show process and computations with
comments.**

A balanced three-phase delta-connected load is connected to a
balanced three-phase delta-connected source via a transmission
line. The line-line voltage for the source is 100∟0° V/phase and
the impedance of load is (27 + j18) Ω/phase. The transmission line
has an impedance of (1 + j4) Ω/line.
a) Draw the complete schematic of the power system showing the
location of wattmeters. (Two-Wattmeter system is considered for
this problem). Phase “a” could be considered as a reference
phase.
b) What must...

b) The load connected to a three-phase supply comprises three
similar coils connected in star. If the phase currents are 10A and
the total active power and power factor absorb by the loads are 3kW
and 0.8 lagging, respectively. Find:
i. The magnitude of phase and line voltages
ii. Total apparent power (1 mark)
iii. The impedance of each coil.
c) If the coil in Q3(b) are now connected in delta to the same
three-phase supply, calculate the magnitude of...

Three balanced 3-phase loads are connected in parallel. Load 1
is Y-connected with an impedance of 400 + j300 ? per phase, load 2
is ?-connected with an impedance of 2400 – j1800 ? per phase, and
load 3 is absorbing 172.8 + j2203.2 kVA. The loads are fed from a
set of distribution lines with an impedance of 2 + j16 ? per line.
The magnitude of the line-to-neutral voltage at the load end of the
line is 24?3...

A three phase transformer of 200MVA, 33kV/380kV, Yd11 is
delivering nominal power at cosφ = 1.
Calculate the nominal primary and secondary line
current.
Calculate the winding ratio n of this
transformer.
The primary line current is 15,9A during an open circuit test.
The measured power per phase is then 53kW. During a short circuit
test (at nominal current), 271V primary line voltage is measured at
cosφ = 0,225.
Calculate the total iron losses and total copper losses of
this...

A balanced three-phase generator delivers 6.3 kW to a
delta-connected load with impedance 13 - j23.4 Ω per phase. The
magnitude of the line current ILis:

A three phase 10kW, 1700rpm, 60Hz, four poles, Y connected
induction motor has a no-load speed of 1750rpm. The rotational
mechanical losses are constant and equal to 500W. The core losses
are constant and equal to 300W. The copper losses in the stator
equal to the copper losses in the rotor at full load. If the rotor
resistance per phase is 0.25?, calculate the following:
a.The frequency of the induced current in the rotor circuit at full
load.
b.The percentage...

A balanced three-phase delta-connected source has a line veltage
of 120 V. It is connected to a load via a three-wire transmission
line. The per-phase impedance of the delta-connected load is 30 +
120j (2. The impedance of each wire of the transmission line is 2 +
4j 2. How much power is dissipated by the load? By the transmission
line? What is the power factor of the load? What is the overall
power factor?

Plate values of a three-phase transformer are given below:
1600 kVA, 15 kV / 0,4 kV, 50 Hz, i0 = 1.2%;
ukN= 6%, idle losses 2450 W, rated power copper losses
14500 W; Dy5 connected..
III) If there is 75% load in the power factor with 0.85
inductance and 0.85 capacity. At what times of the day can capacity
loading be seen? What solution should be applied to prevent voltage
change?
IV) Draw the fastening group. How can this transformer...

Plate values of a three-phase transformer are given below:
1600 kVA, 15 kV / 0,4 kV, 50 Hz, i0 = 1.2%; ukN= 6%, idle losses
2450 W, rated power copper losses 14500 W; Dy5 connected..
Calculate the secondary VOLTAGE separately at 75% load in the power
factor with 0.85 inductance and 0.85 capacity. Compare and
interpret the results. At what times of the day can capacity
loading be seen? What solution should be applied to prevent voltage
change?

A company plans to purchase a transformer that will be used 12
hours at full load and 12 hours with no load but still connected to
the power supply at all times. The transformer has copper losses of
5 kW and core losses of 3.5 kW. Electricity costs $0.07/kW-hr. What
is the total cost of transformer losses over a period of 1
year?

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