Time relays are divided into power-on delay and power-off delay, and the working process and principle of the two are different.
1, The most commonly used in the field of industrial control is the power delay time relay, its working principle is that when the time relay coil is powered to reach the set time, the delayed break starts the broken contact, the delayed close the dynamic contact, respectively at the same time, and the reset after the loss of power.
2, For a simple example, in the star triangle buck start need to use the power delay relay, to let the star start first, set the time to arrive after the triangle start and disconnect the star start, so as to achieve the buck start.

3, The working process of the power delay relay is that after the time relay coil is powered, the delayed closing and breaking contact is delayed, the delayed breaking and closing contact is started, and the work is immediate, until the coil is powered off, and the delay time is reset after the time is set.
4, The same simple case, suppose we control a motor, requiring a delay after pressing the stop button for a period of time, the motor to restart work, in this case, it is necessary to use the power delay relay to achieve.