Synchronous Machines Practice Questions

A hydraulic turbine having rated speed of 250 rpm is connected to a synchronous generator. In order to produce power at 50 Hz, the number of poles required in the generator are

Two 3-phase, Y-connected alternators are to be paralleled to a set of common bus bars. The armature has a per phase synchronous reactance of 1.7 $\Omega$ and negligible armature resistance. The line voltage of the first machine is adjusted to 3300 V and that of the second machine is adjusted to 3200 V. The machine voltages are in phase at the instant they are paralleled. Under this condition, the synchronizing current per phase will be

A 400 V, 50 kVA, 0.8 p.f. leading $\triangle$ -connected, 50 Hz synchronous machine has a synchronous reactance of 2 $\Omega$ and negligible armature resistance. The friction and windage losses are 2 kW and the core loss is 0.8 kW. The shaft is supplying 9 kW load at a power factor of 0.8 leading. The line current drawn is

A 500 MW, 3-phase, Y-connected synchronous generator has a rated voltage of 21.5 kV at 0.85 p.f. The line current when operating at full load rated conditions will be

Curves X and Y in figure denote open circuit and full-load zero power factor(zpf) characteristics of a synchronous generator. Q is a point on the zpf characteristics at 1.0 p.u. voltage. The vertical distance PQ in figure gives the voltage drop across

When stator and rotor windings of a 2-pole rotating electrical machine are excited, each would produce a sinusoidal mmf distribution in the airgap with peal values $F_s$ and $F_r$ respectively. The rotor mmf lags stator mmf by a space angle $\delta$ at any instant as shown in figure. Thus, half of stator and rotor surfaces will form one pole with the other half forming the second pole. Further, the direction of torque acting on the rotor can be clockwise or counter-clockwise. The following table gives four set of statement as regards poles and torque. Select the correct set corresponding to the mmf axes as shown in figure.

A stand alone engine driven synchronous generator is feeding a partly inductive load. A capacitor is now connected across the load to completely nullify the inductive current. For this operating condition.

A 4-pole, 3-phase, double-layer winding is housed in a 36-slot stator for an ac machine with 60c phase spread. Coil span is 7 short pitches. Number of slots in which top and bottom layers belong to different phases is

A round rotor generator with internal voltage $E_{1}$ = 2.0 p.u. and X = 1.1 p.u. is connected to a round rotor synchronous motor with internal voltage $E_{2}$ = 1.3 p.u. and X = 1.2 p.u. The reactance of the line connecting the generator to the motor is 0.5 p.u. When the generator supplies 0.5 p.u. power, the rotor angle difference between the machines will be

The flux per pole in a synchronous motor with the field circuit ON and the stator disconnected from the supply is found to be 25 mWb. When the stator is connected to the rated supply with the field excitation unchanged, the flux per pole in the machine is found to be 20 mWb while the motor is running on no load. Assuming no load losses to be zero, the no load current down by the motor from the supply

Figure shows the magnetization curves of an alternator at rated armature current, unity power factor and also at no load. The magnetization curve for rated armature current, 0.8 power factor leading is given by

It is desirable to eliminate 5th harmonic voltage from the phase voltage of an alternator. The coils should be short-pitched by an electrical angle of

A power system has two synchronous generators. The Governor-turbine characteristics corresponding to the generators are $P_1 = 50(50-f)$ , $P_2 = 100(51-f)$ Where f denotes the system frequency in Hz, and $P_1$ and $P_2$ are, respectively, the power outputs (in MW) of turbines 1 and 2. Assuming the generators and transmission network to be lossless, the system frequency for a total load of 400 MW is

A star-connected 440 V, 50 Hz alternators has per phase synchronous reactance of 10 $\Omega$ . It supplies a balanced capacitive load current of 20 A, as shown in the per phase equivalent circuit of figure. It is desirable to have zero voltage regulation. The load power factor should be

$X_{d}$ , ${X}'_{d}$ and ${X}''_{d}$ are steady state d-axis synchronous reactance, transient d-axis reactance and sub-transient d-axis reactance of a synchronous machine respectively. Which of the following statements is true?