What is the most practical method of...

What is the most practical method of...

Question 1 of 270705eccefa4bacbc34ba4d481f5

What is the most practical method of controlling the RPM of a multi-speed AC motor operating at a constant frequency?

Question 1 of 27070

Q

What is the most practical method of controlling the RPM of a multi-speed AC motor operating at a constant frequency?

🔍 Key Concepts

• Synchronous speed of an AC motor and how it depends on supply frequency and the number of poles • What happens to torque and slip when you vary voltage versus when you vary poles • Which parts (poles, brushes, power factor) are actually present and adjustable in a typical multi-speed AC induction motor

💭 Think About

• Start by recalling the formula for the synchronous speed of an AC motor and identify which variables it contains and which ones are fixed in this question • Think about what changing the input voltage mainly affects in an induction motor: speed, torque, or losses? • Ask yourself which of the listed options is normally used in practice to design a motor that can run at two or more distinct fixed speeds from the same constant-frequency supply

✅ Before You Answer

• Write down the relationship between motor speed, frequency, and number of poles and see which parameter can be changed here • Eliminate any option that refers to components not normally used to set speed in a multi-speed AC induction motor • Check which option represents a standard design feature of multi-speed squirrel‑cage motors rather than an operating adjustment like voltage or power factor