Electrical Mach...

A 4-pole DC generator with wave wound armature has 50 slots containing 18 conductors in each slot. The induced emf is 357 V and the speed is 9000 rpm. The flux per pole in mWb is _______

The inter-pole winding consists of:

A 6600/440 V, single-phase transformer has an equivalent resistance of 0.02 pu and an equivalent reactance of 0.05 pu. If the primary voltage is 6600 V, the secondary terminal voltage at full load is ______ (in V) (Assume that power factor is 0.8 lag)

A three phase 460 V, 60 Hz, six-pole wound rotor induction motor drives a constant load of 100 N-m at a speed of 1140 rpm when the rotor terminals are short-circuited. It is required to reduce the speed of the motor to 1000 rpm by inserting resistances in the rotor circuit. The rotor winding resistance per phase is 0.2 ohms. Neglect rotational losses. The stator to rotor turns ratio is unity.

The value of the resistance inserted is ________ (in Ω/phase)

A 3-phase, 6-pole, 50 Hz induction motor has a full load speed of 960 rpm with its slip rings short-circuited the motor drives a constant torque load. If the rotor speed is reduced to 400 rpm by inserting external resistance in the rotor circuit. The ratio of the rotor ohmic loss at reduced speed to full load speed is

The torque at the load of a 3 ϕ, 50 Hz 6 pole inductance motor is 200 Nm. The frequency of the emf induced in the rotor 2Hz. Mechanical losses are 600 W. Calculate the total power available to the rotor form the stator. (in kW)

A single-phase resistor split induction motor draws θ_m = 60° lagging main winding current at starting. If the resistance and the reactance of the auxiliary winding are 1 Ω and 1.16 Ω respectively, the external resistance to be added to the auxiliary winding to get the maximum starting torque is _______ (in Ω)

A 400 V, 50 kVA, 0.8 pf leading delta connected, 50 Hz synchronous machine has a synchronous reactance of 2 ohm and negligible armature resistance. The friction and windings losses are 2 kW and the core loss is 0.8 kW. The shaft is supplying 9 kW load a power factor of 0.8 leading. The line current drawn is ______ [in Amperes, up to 2 decimals]

A 3-ϕ cylindrical rotor synchronous generator with its armature resistance and leakage reactance being neglected, is synchronized to an infinite bus and its field excitation is kept constant thereafter. Now the machine is loaded by supplying mechanical input to the shaft so that the load angle δ reaches a value of 60°. Under this condition, the operating power factor would be _______

A permanent magnet DC motor has a no-load speed of 4000 rpm when connected to 110 V supply. The armature resistance is 1.5 Ω. By assuming other losses to be negligible, the speed of the motor in rpm, if the voltage is reduced to 55 V and the load torque is 0.6 Nm is _______

A 220 shunt motor has armature resistance of 0.5 ohm and takes a full load current of 40 A. By what percentage should the main field flux be reduced to raise the speed by 50%, if the developed torque remains constant?

The rotor current at start of a three-phase, 460 V, 1710 rpm, 60 Hz, four pole, squirrel cage induction motor is six times the rotor current at full load.

The maximum torque developed by the motor is _________ times the full load torque.

A 3-phase induction motor has an efficiency of 0.9 when the load is 37 kW. At this load, the stator copper and rotor copper loss each equals the iron loss. The mechanical losses are one third of no-load losses. The slip is

The resistance and reactance of the main winding of a 50 Hz single phase induction motor are 1 Ω and √3 Ω, respectively. The motor is capacitor start motor. If the resistance and the reactance of the auxiliary winding are 1 Ω and 1.2 Ω respectively, then the external capacitance (in mF) to be added to the auxiliary winding to get the maximum starting torque is ________

A 3-ϕ, 5 kVA, 208 V, four pole, 60 Hz, star connected synchronous machine has negligible stator winding resistance and a synchronous reactance of 8 ohms per phase at rated terminal voltage.

The machine is operated as a synchronous motor from the 3ϕ, 208 V, 60 Hz, power supply. The field excitation is adjusted so that the power factor is unity when the machine draws 3 kW from the supply.

If the field excitation is held constant and shaft load is slowly increased, the maximum torque (pull-out torque) that the motor can deliver is __________ (N-m)

A synchronous motor operating at rated voltage draws 1.0 pu current at 1.0 power factor. The machine parameters are: synchronous reactance 1.0 pu; armature resistance, negligible. Apart from supplying this rated power, if the motor has to supply an additional leading reactive power of 0.8 pu, then the field current has to be increased by _______%

A 480,3ϕ star connected, salient-pole, synchronous motor is drawing 50 A current at full-load unity power factor. The per phase d-axis and q-axis reactances are 3.5 Ω and 2.5 Ω respectively. The armature winding resistance is assumed to be negligible.

The power angle in degrees is _______

In order to minimize both fifth and seventh harmonics, the coil span in three phase AC machines must be