Efficiency of Synchronous Machines
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The open circuit voltage and open circuit core loss variation is
Correct!
Wrong!

A synchronous machine with its field winding on stator and polyphase armature winding on rotor. At steady state, its air gap field is
I. stationary w.r.t. stator
II. rotating at double the speed Ns w.r.t. rotor
III. rotating in direction opposite to rotor
I. stationary w.r.t. stator
II. rotating at double the speed Ns w.r.t. rotor
III. rotating in direction opposite to rotor
Correct!
Wrong!

A 100 KVA, 400V, 3phase, star connected alternator due to following data
Friction and windage losses = 340W
Open circuit core loss = 480W
Rf = 180ohms, ra=0.02ohms.
The voltage applied to the field winding is 220V. Efficiency at full load is
Friction and windage losses = 340W
Open circuit core loss = 480W
Rf = 180ohms, ra=0.02ohms.
The voltage applied to the field winding is 220V. Efficiency at full load is
Correct!
Wrong!

A 100 KVA, 400V, 3phase, star connected alternator due to following data
Friction and windage losses = 340W
Open circuit core loss = 480W
Rf = 180ohms, ra=0.02ohms.
The voltage applied to the field winding is 220V. The efficiency of the machine at half load is
Friction and windage losses = 340W
Open circuit core loss = 480W
Rf = 180ohms, ra=0.02ohms.
The voltage applied to the field winding is 220V. The efficiency of the machine at half load is
Correct!
Wrong!

The given variable losses are 5kW fr a 500 KVA, 11 kV, 3phase star connected alternator having armature resistance of 4 ohms. Calculate the current at which maximum efficiency occurs
Correct!
Wrong!

The reactive power output of a synchronous generator is limited by
Correct!
Wrong!

Rotational losses vary as following with respect to field current.
Correct!
Wrong!

The short circuit load losses is/are
Correct!
Wrong!

A synchronous machine with its field winding on rotor and polyphase armature winding on stator. At steady state running condition, its air gap field is
Correct!
Wrong!

Consider a 3phase cylindricalrotor alternator
A. E.m.f. generated by armature reaction lags armature current by 90°.
B. Air gap voltage leads the field flux by 90°
C. Air gap voltage lags the field flux by 90°
D. Armature reaction mmf lags the field flux by (90°+ internal p.f. angle)
A. E.m.f. generated by armature reaction lags armature current by 90°.
B. Air gap voltage leads the field flux by 90°
C. Air gap voltage lags the field flux by 90°
D. Armature reaction mmf lags the field flux by (90°+ internal p.f. angle)
Correct!
Wrong!

A 100 KVA, 400V, 3phase, star connected alternator due to following data
Friction and windage losses = 340W
Open circuit core loss = 480W
Rf = 180ohms, ra=0.02ohms.
The voltage applied to the field winding is 220V. The load losses at full load is
Friction and windage losses = 340W
Open circuit core loss = 480W
Rf = 180ohms, ra=0.02ohms.
The voltage applied to the field winding is 220V. The load losses at full load is
Correct!
Wrong!

A 100 KVA, 400V, 3phase, star connected alternator due to following data
Friction and windage losses = 340W
Open circuit core loss = 480W
Rf = 180ohms, ra=0.02ohms.
The voltage applied to the field winding is 220V. The short circuit load loss at half full load is
Friction and windage losses = 340W
Open circuit core loss = 480W
Rf = 180ohms, ra=0.02ohms.
The voltage applied to the field winding is 220V. The short circuit load loss at half full load is
Correct!
Wrong!

The given variable losses are 5kW fr a 500 KVA, 11 kV, 3phase star connected alternator having armature resistance of 4 ohms. Calculate the
full load armature current per phase
full load armature current per phase
Correct!
Wrong!

In a 3phase cylindricalrotor alternator, synchronous reactance is sum of
Correct!
Wrong!

A 100 KVA, 400V, 3phase, star connected alternator due to following data
Friction and windage losses = 340W
Open circuit core loss = 480W
Rf = 180ohms, ra=0.02ohms.
The voltage applied to the field winding is 220V. The field current loss will be
Friction and windage losses = 340W
Open circuit core loss = 480W
Rf = 180ohms, ra=0.02ohms.
The voltage applied to the field winding is 220V. The field current loss will be
Correct!
Wrong!
