univotec assignment

1. Page 1 of 2
UNIVOTEC
(Q1)
a) Describe the properties of an ideal transformer.
b) Draw the equivalent circuit diagram for ideal transformer and practical transformer.
c) State the basic differences between single phase and three phase transformers.
d) A three-phase transformer has 500 primary turns and 50 secondary turns. If the supply voltage is
2.4kV find the secondary line voltage on no-load when the windings are connected;
i. Star-delta
ii. Delta-star
(Q2)
a) A transformer has 600 primary turns and 150 secondary turns. The primary and secondary
resistances are 0.25Ω and 0.01Ω respectively and the corresponding leakage reactance are 1Ω
and 0.04Ω respectively. Determine,
i. The equivalent resistance referred to the primary winding.
ii. The equivalent reactance referred to the primary winding.
iii. The equivalent impedance referred to the primary winding.
iv. The phase angle of the impedance.
INSTRUCTIONS:
 This Assignment#1 is based on given lecture notes. You may require referring additional
resources for more information.
 Answer all questions.
 Submission of Assignment#1 can be done by personally handing it over to the respective
Coordinator (Mr. Pasan Maduranga).
 Deadline for submission: 30th May 2019. Please note that late submissions will not be
entertained.
UNIVERSITY OF VOCATIONAL TECHNOLOGY
FACULTY OF INDUSTRIAL & VOCATIONAL TECHNOLOGY
BACHELOR OF TECHNOLOGY IN MECHATRONICS TECHNOLOGY
EE30405 – ELECTRICAL MACHINES
ASSIGNMENT#1

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b) A 200kVA rated transformer has a full-load copper loss of 1.5kW and an iron loss of 1kW.
Determine,
i. The transformer efficiency at full-load and 0.85 power factor.
ii. The transformer efficiency at half full-load and 0.85 power factor.
(Q3)
a) Describe the basic principle an operation of DC motor and DC generator.
b) Sketch the important characteristics (no load and load characteristics) of different types of
generators.
c) Identify the various factors responsible for internal voltage drop.
d) “The generated emf in motor called the back emf”. Explain.
(Q4)
a) An 8-pole, lap-wound armature has 1200 conductors and a flux per pole of 0.03Wb. determine,
i. The emf generated when running at 500rev/min.
ii. The generated emf if the armature is wave-wound.
b) A separately-excited generator develops a no-load emf of 150V at an armature speed of 20rev/s
and a flux per pole of 0.1Wb. Determine the generated emf when,
i. The speed increases to 25rev/s and the pole flux remains unchanged.
ii. The speed remains at 20rev/s and the pole flux is decreased to 0.08Wb.
iii. The speed increases to 24rev/s and the pole flux is decreased to 0.07Wb.
END