Electrical Engineering XYZ MCQs
The sequence of induction motor is RYB, then the direction of induction motor can be changed by which of the following sequence:
- BRY
- BYR
- RBY
- All of the above
Correct answer: 3. RBY
Explanation:
The direction of rotation in a three-phase motor is determined by the order in which the phases are connected, creating the rotating magnetic field.
For a standard connection sequence RYB (Red, Yellow, Blue), the motor rotates in a specific direction. To reverse this direction, we indeed need to swap any two phases of the motor:
- Original sequence: RYB
- Normal direction of rotation
Changing each sequence accordingly:
- BRY: Here, the original RYB becomes BRY. This switches the positions of Red and Blue while Yellow remains in the middle. This sequence will not simply reverse the motor’s direction because it’s more than just a two-phase swap; it alters the overall sequence significantly.
- BYR: This switches Red and Yellow, placing Yellow in the second position and Red in the third. Like BRY, this is not a straightforward two-phase swap; it alters the overall sequence significantly.
- RBY: This involves swapping Yellow and Blue, while keeping Red in the first position. This sequence does accurately represent the swapping of two phases without changing their relative positioning to Red.
Upon reviewing these sequence swaps, RBY is the correct choice because it directly swaps just two of the phases (Yellow and Blue), which is the typical method used to reverse the rotation direction of an induction motor. In contrast, BRY and BYR do more than just swap two phases; they change the position of all three phases relative to each other.
Correct Answer: RBY is the sequence that will reverse the direction of the induction motor by swapping only two of the phases, maintaining the correct method to achieve a reversal in rotation direction.