Electrical Machines Drives and Power Systems 6th. Edition by Théodore Wildi | 9781292024585 | 1292024585 | Holooly

Electrical Machines Drives and Power Systems [EXP-57633]

221 SOLVED PROBLEMS

Question: 13.2

A 0.5 hp, 6-pole induction motor is excited by a 3-phase, 60 Hz source. If the full-load speed is 1140 r/min, calculate the slip.

Verified Answer:

The synchronous speed of the motor is [late...

Question: 10.11

A 100 kVA transformer is connected in parallel with an existing 250 kVA transformer to supply a load of 330 kVA. The transformers are rated 7200 V/240 V, but the 100 kVA unit has an impedance of 4 percent while the 250 kVA transformer has an impedance of 6 percent (Fig. 36a).

Verified Answer:

a. Nominal primary current of the 250 kVA transfor...

Question: 14.4

A 100 kW, 60 Hz, 1175 r/min motor is coupled to a flywheel by means of a gearbox. The kinetic energy of all the revolving parts is 300 kJ when the motor runs at rated speed. The motor is plugged to a stop and allowed to run up to 1175 r/min in the reverse direction

Verified Answer:

During the plugging period, the motor speed drops ...

Question: 5.5

A 15 hp, 240 V, 1780 r/min dc series motor has a full-load rated current of 54 A. Its operating characteristics are given by the per-unit curves of Fig. 11. Calculate a. The current and speed when the load torque is 24 N·m b. The efficiency under these conditions

Verified Answer:

a. We first establish the base power, base speed, ...

Question: 20.2

A 150 kW (200 hp), 460 V, 3-phase, 3520 r/min, 60 Hz induction motor has a locked-rotor torque of 600 Nm and a locked-rotor current of 1400 A. Three resistors are connected in series with the line so as to reduce the voltage across the motor to 0.65 pu.

Verified Answer:

a. At full voltage the locked-rotor apparent power...

Question: 3.7

A 150 kW electric motor has an efficiency of 92 percent when it operates at full-load. Calculate the losses in the machine.

Verified Answer:

The 150 kW rating always refers to the mechanical ...

Question: 17.3

A 150 kW, 1200 r/min, 460 V, 3-phase synchronous motor has a synchronous reactance of 0.8 , per phase. If the excitation voltage Eo is fixed at 300 V, per phase, determine the following: a. The power versus curve b. The torque versus curve c. The pull-out torque of the motor

Verified Answer:

a. The line-to-neutral voltage is

\b...

Question: 17.6

A 1500 kW, 4600 V, 600 r/min, 60 Hz synchronous motor possesses a synchronous reactance of 16 and a stator resistance of 0.2 , per phase. The excitation voltage Eo is 2400 V, and the moment of inertia of the motor and its load is 275 kgm2. We wish to stop the motor by shortcircuiting

Verified Answer:

a. In Fig. 22a the motor has just been disconnecte...

Question: 21.9

A 16 kV dc source having an internal resistance of 1 Ω supplies 900 A to a 12 kV, 3-phase, 6-pulse, 60 Hz inverter (Fig. 48). Calculate a. The dc current carried by each SCR b. The dc voltage generated by the inverter c. The required firing angle α

Verified Answer:

a. Each SCR carries the load current for one-third...

Question: 12.5

A 2-phase, 7.5 kW (10 hp), 240 V, 60 Hz motor has an efficiency of 0.83 and a power factor of 0.80. It is to be fed from a 600 V, 3-phase line using a Scottconnected transformer bank (Fig. 16c). Calculate a. The apparent power drawn by the motor b. The current in each 2-phase line

Verified Answer:

a. The active power drawn by the motor is [...

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