I need to drive a 3-phase motor such that in one cycle the motor will turn in one direction for 2-4 seconds and then for 1 second in the opposite direction. The set-up is expected to do 5000 cycles daily.

What is the better option to select, Relays or Triacs? Of course, contractors will also be used.

 

What power is the motor?
what do the contractors switch?

 

You are very likely to break something, ( like a gear-box ),
unless You use a proper VFD to control your Motor.
3-Phase Motors have brutal start-up Torque.
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I second the VFD , otherwise the repeated inrush is going to heat the motor drastically.
What HP?

BTW, You don't need a 'contractor' if you do it your self.

 

this would be a poor choice for an induction motor, unless the motor ran continuously and some transmission created the desired motion. A stepper / servo might be better.

 

Also application details would help??

 

The motor is 1HP, 700rpm.
The contractors are used to change the phases to turn it in the opposite direction. The relays or traics are to be used to activate the contactor coils.

The motor is used for installing screws in worm clamps. The motor drives a shaft (with chain) which has an adapter to hold the head of the screw.

 

Are you sure you could not adapt a pneumatic motor to do the job?
For much repetitive short operation and reversing, could cause excessive heating.
Alternatively, the AC motor + VFD may be the best choice.

 

certainly you want torque control to set the clamp pressure. A vote for VFD. Hydraulics are very handy for clamping, as are air over oil circuits.