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Unformatted text preview: ELECTRICAL ENGINEERJNG DEPARTMENT
CALIFORNIA POLYTECHNIC STATE UNIVERSITY BB 255 Assignment #3
Problem 1:
A 3 KVA, 480:240V, 60Hz singlephase ideal transformer is supplying .a load
impedance of 15 + j20 Q at 240 V. Determine the load current, source current and the
impedance seen by the sourCe. Problem 2: ‘ A 2200/220—V, 60Hz, singlephase ideal transformer is supplying a load through a line
impedance of 9 + j12 Q. The load is a heating load with a resistance of 180 Q. The line is
in series with the load and is connected to the 220 V side. Determine the power supplied
to the load and the power supplied by the source. What is the efﬁciency of the system? Problem3: A 115/5 V, 60 Hz, singlephase ideal transformer is delivering a power of 15 W to a pure
resistive load at the 5 V side. Determine the resistance of the load, secondary current, the
primary current, and the power supplied by the source. Problem4: ‘ An ideal transformer is delivering power to a 6 + j8 9 load impedance. The power
supplied to the load is measured to be 150 W. Determine the primary and secondary
voltages, primary and secondary currents if the primary current is half the secondary
current. Problem 5:  
A 140KVA, ll,000:2,200—V, 60Hz singlephase transformer has the following circuit
parameters:  Primary (HVS) Secondary (LVS)
R1=6.IQ R2=0.3§2
X1=31.29 ' X2=1.2§2
Xm=124,000 9 R6 = 57,300 g The transformer is supplying at the 2200—V the rated load at a power factor of 0.7
lagging. Using the exact equivalent circuit, determine: ‘
(a) The voltage regulation of the transformer, ' (b) The efficiency of the transformer. Problem A singlephase, SOKVA, 400/2000V transformer has the following parameters:
R1= 002 Q R2 = 0.5 Q
X1=0.06Q X2=l.5§2
Xm = 166.7 Q Xm is a Low Voltage Side parameter. The transformer supplies a load of 40 KVA at 2000 V and 0.8 pf lagging. Calculate the
efﬁciency and the voltage regulation of the transformer for the given load. Use the
approximate circuit with the excitation circuit across the supply. Problem 7:
A 25KVA, 4200/480V, (SOHz single—phase transformer has the following circuit
parameters: '  Primary (HVS) Secondary (LVS)
R1 = 6 £2 ' R2 = 0. 19) X1 = 459 X2 = 0.69 RC = 44 K9 Xm=14 KS2 The transformer is supplying at 480V full load at a power factor of 0.8 leading.
Determine: ' . .
(c) The voltage regulation of the transformer,
(d) The efﬁciency of the transformer.
(e) The allday efﬁciency for the following load cycle:
10 hours at full load and 0.8 power factor leading
14 hours at noload. Problem 8: A singlephase, 60KVA, 2200/460V transformer has the following parameters:
R1=2£2 R2=O.OSQ
X1=8£2 X2=0.32§2
Xm = 4.2 KQ
RC = 6 Kg ’ Km and Re are High Voltage Side parameters. The transformer Supplies a rated load at 460 V and unity pf. Calculate the efﬁciency and
the voltage regulation of the transformer for the given load. Use the exact equivalent circuit.  ' Problem 9: _
A 7.16KV generator supplies power to a load through a transmission line. The load impedance is Z, d 22894363212; and the transmission line impedance is 00 Z a 34.64160o Q. line
1. If the generator is directly connected to the load, what is the ratio of the load
voltage to the generator voltage? What are the transmission losses of the system?
2. If a 1:10 stepup transformer is placed at the generator side of the transmission
line and a 10:1 stepdown transformer is place at the load side of the transmission
line, what is the ratio of the load voltage to the generator voltage? What are the
transmission losses of the system? (Assume ideal transformers.) No. 937 8115 A Esmenmsw Engineer‘s Computalion Pad ’ . Engineer's Computation Pad . No. 937 811E "E
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 Fall '05
 Shaban
 Transmission line, Impedance matching, Impedance bridging, singlephase ideal transformer, transformer Supplies

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