Delayed Transition
When the delay transition is activated, the switch will stay in an open circuit (main contact will stay in off position for a period of time. It is applicable for 2 poles, 3 poles, and 4 poles). This delay allows the residual voltage of the load to decay within the allowable range.
Condition of Delayed Transition
The delayed transition is recommended when motors are located on the load side. Indeed, in the case of voltage loss on motors, the following may happen:
-
When the inductive load loses power, it will generate self excitation voltage due to inertia.
-
The self excitation voltage needs a certain time constant to attenuate.
-
When the self-excited voltage is 180° different from the voltage of another power supply and superimposed, it will cause about twice the voltage impact.
-
When the resistance of the motor is fixed, the current will also be increased to 2 times. In addition, the starting current of the motor is large (6-8 times rated current), so the current shock of 12-16 times may occur.
The setting time of the delay shall ensure that the time length of the motor disconnected from the power supply is equal to or greater than 1.5 open circuit AC time constants of the motor; generally 0.5-1 s.