A three-phase motor can be made to run backwards by A. connecting a resistor in series with the armature. B. reversing the control voltage connections. C. reversing three of its power leads. D. reversing two of its power leads.

Electrical engineering subject of electrical machines/ I need a correct and accurate solution

7. A 4-pole, 500V shunt motor has 720 wave connected conductors on its armature. The full-los armature current is 60A and flux per pole is 0.03 Wb. The armature resistance is 0.020 and th contact drop per brush is 1V. then the full-load speed of the motor is -- a) 675 r.p.m. b) 690 r.p.m. c) 705 r.p.m. d) none of the previous,

A motor operates on a periodic duty cycle consisting of a loaded period of 40 min and no load period of 22 min. The maximum temperature rise is 90֩ C. Heating and cooling time constants are 55 and 77 min respectively. When operating continuously on no load the temperature rise is 13֩ C. Determine: a- Minimum temperature during the duty cycle. b- Temperature when the motor is loaded continuously.

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H1. A motor _________shunt has the better speed regulation of the cumulatively connected DC compound motor.a) long b) short c) both "a" and "b" have the same speed regulation H2. You "bump" a DC motor when you are......a) trying to move it b) checking if it is mounted properly c) checking its direction of rotation d) none of the above H3. When a DC compound motor is cumulatively connected its series and shunt windings are wired te create magnetic fields which are______ polarity. a) opposite b) the same c) either "a" or "b" d) neither "a" nor "b"

An increase in the torque angle a results in: O A. No change in the induced torque O B. Decreasing the induced torque O C. Decreasing the load on the synchronous motor D. None of the other choices are correct O E. Increasing the induced totque

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K-1)The speed of a 3-phase wound-rotor induction motor can be changed by varying the amount of resistance in the rotor circuit. a) true b) false K-2). Which of the following statements are true about a 3-phase synchronous motor? a) It is a constant speed motor even under varying loads. b) It runs at the same speed the magnetic field rotates on the stator. c) It can correct its own, and the supply line's power factor d) all of the above K-3. A) What determines the speed of a 3-phase synchronous motor? a) the number of poles b) the frequency of the supply c) both "a" and "b" d) neither "a" nor "b" K-3)B) From a technician's standpoint, which of the following is the most practical method of providing a wide range of speed control for a 3-phase synchronous motor? a) by changing the frequency b) by changing the number of poles c) both "a" and "b" d) neither "a" nor "b"

A DC series motor will _______if operated without a load. a. Operate a rated speed b. Operate slower than rated speed c. Operate slightly higher than rated speed d. Run away