Chapter 41, Problem 1SQ

What assurance is there that the rotor will lock into step at the synchronous speed with the use of a timing relay?

To determine

What is the assurance of the synchronization with the use of a timing relay to lock the rotor of a motor at the synchronous speed.

Answer to Problem 1SQ

The only assurance is that if the timing period of the relay is adjusted for the rotor’s maximum acceleration, then the rotor will be near the synchronizing speed.

Explanation of Solution

A motor can be operated at the synchronous speed by exciting the DC field using the definite time-delay relay in a timed, semiautomatic synchronizing installation process. In the starting cycle, the delay-in-closing contact TR of the timing relay is closed to accelerate the rotor until it reaches the synchronizing point. Timing relay has the timer setting; it can be adjusted to the maximum time required to accelerate the rotor to reach the synchronous point, and after completing the synchronizing process of the motor, the attempt may not be successful, or the rotor may reach the maximum near to the synchronous speed.

The time relay based push-button control and timed semiautomatic control of a synchronizing installation process of the rotor are not guaranteed in achieving the synchronization on every attempt; while it fails, it is necessary to repeat the starting cycle by adjusting the timer setting of the timing relay. In every attempt, the only assurance is that if the timing period of the relay is adjusted for the rotor’s maximum acceleration, then the rotor will be near the synchronizing speed.

Conclusion:

Thus, the only assurance is that if the timing period of the relay is adjusted for the rotor’s maximum acceleration, then the rotor will be near the synchronizing speed.