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Electrical Engineering Objective Questions { Alternators }

36. The Potier's triangle separates the
A. iron losses and copper losses
B. field mmf and armature mmf
C. stator voltage and rotor voltage
D. armature leakage reactance armature reaction mmf.
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37. In a slip test on a salient-pole machine, the emf induced in the field winding is
A. zero for Xd
B. maximum positive for Xd
C. zero for Xq
D. maximum positive for zero for Xq.
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38. If in a 3-4) alternator, a field current of 50 A produces a full-load armature current of 200 A on short-circuit and 1730 V on open circuit, then its synchronous impedance is
A. 8.66 ohm
B. 4 ohm
C. 5 ohm
D. 34.6 ohm
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39. For a P-pole machine, the relation between electrical and mechanical degrees is given by
A. Oelec ?3 Ornech
B. ?eiec =p emech
C. emech = ?2 eelecn ? 1
D. 0elec = ?2 0mech
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40. El, E3, E5 are the fundamental, third harmonic and fifth harmonic per phase voltage generated in a starconnected alternator. Its line voltage is
A. 3VE12 + E32 + E52
B.JE E12 ^ E32 E52
C.+ E32
D.I VE12 ^ E52
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41. An alternator has rated field current of 2A. This alternator is developing 200 V at a field current of 1 A at rated speed. If its field current is made 2A at rated speed, then the generated voltage would be
A. 400 V
B. 380 V
C. less than 400 V
D. more than 400
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42. An alternator running at 1500 r.p.m. delivers rated current of 30A to a purely inductive load. With the filed current remaining constant, If the speed is reduced to 1000 rpm, the load current becomes
A. 20 A
B. 30 A
C. a little less than 20 A
D. a little more than 20 A.
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