155. A 400V, 50 kVA, 0.8 pf leading A-connected, 50 Hz synchronous machine has a synchronous reactance of 2S1 and negligible armature resistance. The friction and windage losses are 2 kW and the core loss is 0.8 kW. Teh shaft is supplying 9kW load at a power factor os 0.8 leading. The line current drawn is '

A. 12.29 A

B. 16.24A

C. 21.29 A .

D. 36.8 A

156. 3-phase Y-connected synchronous generator has a rated voltage of 21.5 kV at 0.85 pf. The line current when operating at full load rated

A. 13.43 kA

B. 15.79 kA

C. 23.25 kA

D. 27.36 kA

157. In relation to the synchronous machines, which one of the following statements is false?

A.In salient pole machines, the direct-axis synchronous reactance is greater than the ? quadrature-axis synchronous reactance

B.The damper bars help the synchronous motor self start

C.Short circuit ratio is the ratio of the field current required to produce the rated voltage on open circuit to the rated armature current

D.The V-curve of a synchronous motor represents the variation in the armature

158. The voltage across the open-circuited field terminals of a synchronous machine under slip test is

A. dc

B. ac of slip frequency

C. a modulated supply frequency ac voltage with slip frequency envelope

D. ac of supply frequency

159. In a synchronous generator operating at zero pf !aging, the effect of armature reaction is

A. magnetizing

B. demagnetizing

C. cross-magnetizing

D. both magnetizing and cross-magnetizing

160. Following a sudden short-circuit at the terminals of a 3-phase unloaded synchronous generator, the initial effect of the pole-face damper winding, is to

A. establish the armature flux through the direct-axis magnetic circuit of the machine

B. allow only partial linkage of the armature flux with the main field winding

C. confine the armature flux to completely link the damper winding

D. repel the armature flux and confine it to the leakage flux path in the air-gap.

161. Short-circuit ratio of a synchronous machine is the ratio of the

A. open-cirucit voltage to the short-circuit current at a given excitation

B. short-circuit current to the open-circuit voltage at a given excitation

C. excitation current required for the rated voltage on open-circuit to the excitation current required for the rated armature current under short-circuit

D. excitation current required for the rated armature current under short-circuit to the excitation current required for rated voltage on open-circuit

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