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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.

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.

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

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

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

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

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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