ELECTRICAL ENGINEERING DEPARTMENT
California Polytechnic State University
EE255
Practice Problems
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Problem #1
A 100KVA, 11,000:2,200V, 60Hz, singlephase transformer gave the following test
results
Voltage
current
power
Opencircuit test:
2200V
1.59 A
980 W
Shortcircuit test:
580V
9.1 A
1100 w
a)
Determine the parameters of the approximate equivalent circuit referred to
lowvoltage side.
b)
Determine the voltage regulation of the transformer when supplying rated
load at 2200 V and 0.8 power factor leading. [VR=2.1%]
c)
Determine the allday efficiency of the transformer for the following load
cycle:
8 hours at rated load and .8 pf lagging,
8 hours at 80% fullload and 0.8 pf lagging, and
8 hours at 50% fullload and 0.8 pf lagging.
The load is connected to the low voltage side.
[Efficiency=97.4%]
Problem #2
A 15hp, threephase, 8pole, 440V, 60Hz, woundrotor induction motor has its stator
and rotor windings connected in wye. The ratio of the effective stator turns to the
effective rotor turns is 2:1. The mechanical losses (friction + windage) are 220 W at
rated speed and may be assumed constant from noload to fullload. The stator and
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 Fall '11
 AliShaban
 Volt, Electric motor, Power factor, stator core loss, rotor leakage inductance, pf lagging, Stator leakage inductance

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