How to avoid star delta Timer failure in star delta starter

How to avoid star delta Timer failure in star delta starter:

In star delta starter timer is doing most important function. Due to starter delta timer failure we have face lot of problem like stoppages, downtime etc. Basically star delta timer failures due to continue running. Each machines are having some life time limitation. Ok then you will ask what is the solution for the same. Some wiring tricks avoid this problem permanently. By this, we can extend star delta starter timer life time.

What is star delta timer?

Star delta timer is an electronic timer which counts the time of its coil energize and trip the circuit when the time exceed presetting time. The timer is doing normal NO and NC operation. Here star operation need NC and Delta needs NO. To reset the time again you have to start.

Types of timers are available in the market:

  1. Star delta timer
  2. On delay timer
  3. Off delay timer

How to avoid star delta timer failure?

By stopping the supply where is going to the timer coil. Remaining circuit will operate through NO and NC logic. See the circuit diagram,



Here when you press On push button, supply is going to the star contactor, main contactor and timer coil. The star delta timer starts count time. The motor start rotates in star mode. After preset time reaches in timer the timer Tnc become Tno then the starter star contactor released, due to this star contactor releasing the Star NC will be activated, then at the same time delta contactor holds. Then the motor continues in operation with main contactor and delta contactor without timer.

This is real case study. I have suffered before installing this circuit. Monthly I have changed minimum 3 timers per 10 motors, after installing this circuit I got ‘0’ failure. Timer maintenance cost per year reduced from Rs 35,000 to zero rupees.

 

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