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Material Type: Assignment; Class: El/CP En For Nonmajors; Subject: Electrical & Computer Engg; University: University of Utah; Term: Unknown 1989;
Typology: Assignments
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Note: In the following problems, you may assume voltages and currents are RMS unless stated otherwise
or given as a function of time. Transformers are ideal unless stated otherwise.
. A capacitance is hooked in parallel with the load
and the power factor is corrected to
, lagging.
a) Find the reactive power (
) of the capacitor. Draw a phasor diagram as part of the solution.
b) Find the value of the capacitor assuming f = 60Hz .
The resistor and capacitor together make up the load.
i( t)
v
s
155.6 V cos( )
377 t
a) Find the load impedance of the circuit.
Load
b) Compute the average power dissipated by the load.
800 μF
load (
L
and
L
taken together).
b) Compute the power dissipated by the
internal source resistance (
S ) in this
circuit.
100 μF
rms
ω
rad
s
Load
turns on the primary winding and
turns on the secondary. If the primary is
connected across a
(rms) generator, what is the rms output voltage?
1
turns and
2
= 1000 turns
. If the input voltage is v(t) = (255 V)cos(ωt) , what rms voltage
is developed across the secondary coil?
(rms) when the primary is connected
across a
(rms) source.
a) If there are
turns on the primary winding, how many turns are required on the secondary?
b) If a load resistor across the secondary draws a current of
, what is the current in the primary, assuming
ideal conditions?
and the primary voltage is
is delivered to a load
resistor connected to the secondary. Calculate the voltage across the secondary.
1
2
) of
. It is desired to operate a
resistive load at
(rms).
a) Find the secondary and primary currents.
b) Find the source voltage ( V 1
c) Find the power dissipated in the load resistor and the power delivered to the primary from the source.
d) Find the impedance the source sees looking into the primary winding by calculating Z eq
2 Z L
and again by
calculating V 1
1
find v o
(t) if v s
(t) is 320Vcos(377t) .
Find the following:
a) I 1
s
b) V 2
transformer's voltage rating times its current rating.) Find the allowable primary and secondary currents at a supply
voltage of 12,000 V at 100% power factor. Repeat for a power factor of 50%.
The source voltage applied to the primary winding is 440 V (rms). Find:
a) the load voltage
b) the load current
c) the kVA delivered to load
d) the power delivered to load
e) the primary current
f) the power factor of primary
g) the impedance the source sees looking into primary.
a) How much current can the transformer supply to the customer?
b) If the customer's load is purely resistive (i.e. if the pf = 1), what is the maximum power the customer can receive?
c) If the customer's power factor is 0.8 (lagging), what is the maximum usable power the customer can receive?
d) What is the maximum power if the power factor is 0.7 (lagging)?
e) If the customer requires 300 kW to operate, what is the minimum allowable power factor given the rating of this
transformer?
Answers
2.55 kVA b)
29.4 μF
5.67 Ω e
.. j 35.8 deg
b) P
av
1.73 kW
av
364 W b)
0.4 A b) 24V
o Ω
870 A b)
400 kW c)
320 kW d)
280 kW e) 0.