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Unformatted text preview: eff/7t BE 4420 Name; MATTHEw Banana. MIDSEMESTER TEST
NO. 1 Answer 3 out of 5 theoretical questions (#1  #5) and solve numerical problem (question
#6). Check the chosen questions. Question #1 (2 points)
1)‘ Draw the equivalent circuit of singlephase transformer with all parameters and write the appropriate voltage equations for primary and secondary side.
2) Draw the phasor diagram for an inductive load (lagging power factor) with all currents (II, 1;, IFS, and I”) 3) Specify the power losses in a transformer core and write how they relate to the
magnetic flux density and frequency. Deﬁne (by equation) the efficiency (in terms
of output power and power losses) of the transformer. When it reaches the maximum value? Question #2 (2 points) 1) Draw the V2 — I; characteristics of transformer at constant voltage and frequency
supply for inductive, capacitive and resistive loads. 2) Deﬁne by equation the voltage regulation. When the voltage regulation is higher: at
pure resistive or at pure inductive load? When it takes the negative value? 3) Draw the circuit diagram of an autotransformer. Show how the power is transmitted
from primary to the secondary side (write the equations for apparent power of two
components or draw the circuit diagrams illustrating the power transfer from the primary to secondary side). PM 1 / N 2/2 Question #3 (2 points) 1) Draw phasor diagrams for positive, negative and zero sequence voltage
components. Write the equations that allow calculating unsymmetrical voltages
from known symmetrical components. 2) Draw schematically the 3phase transformer windings connected in AYN to a 3
phase line. Will zero sequence phase voltage components be induced in the
windings if there are unbalanced currents in a secondary winding? Explain why. it”
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1) Draw the circuit diagram of twowinding singlephase transformer for transient current analysis and write the voltage equations for primary and secondary side in
terms of resistances, selfinductances and mutual inductances.
2) Draw the block diagram for singlephase transformer with the supply voltage as an input and currents as an output signals. [2: Ni'N1 [la 37, 1‘
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1) Draw the circuit diagrams of instrumentation voltage and current transformers connected to 3phase lines,
2) Explain using the equivalent circuit why the current transformer with open secondary Circuit cannot be connected to the line. C7 K
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Question #6 (4 points) A shortcircuit test is performed on a singlephase transformer of 10 kVA, 2200/220 V, 6OH2, and the following results are obtained: V1 = 150 V, I,c = 4.55 A, PSC = 215 W.
Determine: 1. The parameters of simpliﬁed equivalent circuit, 2. The voltage, which supplies the primary at shortcircuited secondary side, to get the rated primary current.
3. Voltage regulation at 70 % full load, 0.7 PF lagging, .
4. Efﬁciency at 70 % ﬁill load, 0.7 PF lagging, if the power losses in the core at rated voltage are AP}:e = 100 W, ‘igr. ‘ELN 4C _ —  ———  k/ f \I DARTD 2““ 135:: 4.55;»: ‘ $S§L \JSL: ‘60 '
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