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127.
The circuit diagram shows a two winding, lossless transformer with no leakage flux, excited from a current source, i(t), whose waveform is also shown. The transformer has a magnetizing inductance of (400/π) mH.
[1] The peak voltage across A and B, with S open is [2 marks]
(A) 400/πV
(B) 800V
(C) 4000/πV
(D) 800/πV[2] If the waveform of i(t) is changed to i(t)=10sin(100 πt) A, the peak voltage across A and B with S closed is [2 marks]
(A) 400V
(B) 240V
(C) 320V
(D) 160Vasked in Electrical Engineering, 2009
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128.
The star-delta transformer shown above is excited on the star side with a balanced, 4-wire, 3-phase, sinusoidal voltage supply of rated magnitude. The transformer is under no load condition.
[1] With both S1 and S2 open, the core flux waveform will be [2 marks]
(A) a sinusoid at fundamental frequency
(B) flat- topped with third harmonic
(C) peaky with third- harmonic
(D) none of these[2] With S2 closed and S1 open, the current waveform in the delta winding will be [2 marks]
(A) a sinusoid at fundamental frequency
(B) flat- topped with third harmonic
(C) only third harmonic
(D) none of theseasked in Electrical Engineering, 2009
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