Unformatted text preview: 3. A 20 KVA: 440/220V, 60 Hz., singlephase transformer has iron loss of 324 watts. A
. A 3phase, 300 KVA, 12,470/208 V, 60 Hz., WyeWye connected transformer ﬂ I .. cl The line breaker capacities on the HV and LV side of the transformer.’ 5/
I v“. ﬂi— .f\ [am Monday, February 26, 2001 EE 381 . ' Spring 2001 Test 1 . An iron ring has a crosssectional area of 4 square centimeters. An airgap of length 0.4 millimeters is cut across its section. The mean length of the iron is 100
centimeters. The ring is wound with a coil of 500 turns and carries a current of 1.2
amperes. If the total magnetic ﬂux is 0.3 milliwebers, ﬁnd the relative permeability
of the iron and the energy stored in the air gap. Neglect fringing and leakage.
uo=41t 10'7. , . A singlephase, 600 KVA, 11000/550 V,>6O Hz. transformer has an equivalent impedance referred to the HV side given as Zch = I. 8 + j ’i 4 ohm Determine the
percent regulation of the transformer when the transformer is supplying an inductive
load with 450 KW and 262.5 KVAR at 550 volts. k” _ (put.9 #4421): Vi . w \JA ,the copper loss is found to be 100 watts when delivering half full load current.
Determine the efﬁciency when delivering full load current at 0.8 power factor '
leading. Find also the KVA for maximum efﬁciency and the efﬁciency at this KVA
if the power factor is 0.6 lagging.  4. A small 2winding transformer has its voltage and current ratings as shown. This translurmer is to be connected as a 120 V to 132.6 V Stepup autotransformer, a) Show the connection diagram indicating all dot terminals. . 125*:
b) What is the tull load VA or the autotransformer? c) What are the winding currents and V'Amdmm and V’Amducﬁyc. Lu:
“W 3M5. ‘2'“
I lll i supplies a department store. .The department store 3phase load is 250 KVA at 0.8 . ' T—
lagging and connected in delta. If the transformer is assumed ideal show the '_ (qr...
following: if a) The diagram of connections  showing the primary, secondary and the load.  L_.i l\ TL .—— —L_ ‘_ J 1.. A an
U) Lite Pm. yuan» Luau uupCuaﬂuu. 9!. 9/ [1" _ I. L‘L‘\) M 4 _ ‘I gug 435,13 ; I i I ﬂan_ '
' ”’2 :' ...
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 Spring '08
 Rahman

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