[amp_mcq option1=”the direction of rotation is not fixed” option2=”the direction of instantaneous torque reverses after half cycle” option3=”startes cannot be used on these machines” option4=”starting winding is not provided on the machines” correct=”option2″]<\/p>\n
The correct answer is: B. the direction of instantaneous torque reverses after half cycle.<\/p>\n
Synchronous motors are not self-starting because the direction of instantaneous torque reverses after half cycle. This is because the torque produced by a synchronous motor is proportional to the sine of the angle between the rotor and stator magnetic fields. When the rotor is aligned with the stator field, the torque is zero. As the rotor rotates, the torque increases until it reaches a maximum when the rotor is 90 degrees out of phase with the stator field. After this point, the torque decreases and reverses direction. This means that the synchronous motor will not start by itself, and must be started by some other means, such as a starting winding or a capacitor.<\/p>\n
Option A is incorrect because the direction of rotation of a synchronous motor is fixed. The rotor of a synchronous motor will always rotate at the same speed as the stator field, which is determined by the frequency of the power supply.<\/p>\n
Option C is incorrect because starters can be used on synchronous motors. In fact, starting windings are often used on synchronous motors to help them start.<\/p>\n
Option D is incorrect because starting windings are often provided on synchronous motors.<\/p>\n","protected":false},"excerpt":{"rendered":"
[amp_mcq option1=”the direction of rotation is not fixed” option2=”the direction of instantaneous torque reverses after half cycle” option3=”startes cannot be used on these machines” option4=”starting winding is not provided on the machines” correct=”option2″]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[965],"tags":[],"class_list":["post-44919","post","type-post","status-publish","format-standard","hentry","category-synchronous-motors","no-featured-image-padding"],"yoast_head":"\n