Voltage may drop to 70% during starting and at 95% during running.Ĥ.2 Check the motor starting and running current.ĥ. This may result to the Star contactor burning.Ĥ.1 Check the (three-phase mains voltage) during starting and running. Star is insufficient to overcome the load torque. If the starting current failed to drop within say approx 8s, the motor could be under-sized or the motor torque produced in ģ.1 Check the (control transformer), if there is one.Ĥ. Check that the (contactor coil voltage) which shall be minimum 80% of rated. Refrain from using contactors of different manufactures.ģ. Check the (contactors sizes) are based on, see IEC for definition of AC-3.Ģ.1 Check that the three contactors are based on the manufacturer's recommendation for AC-3 operation. The fuse or the breaker shall trip, should any of the Star or Delta contactor is welded.Ģ. This may explain why the Main does not burn out. A SD starter assembly, the (Main contactor) is (usually) sized than the Star = Delta. My humble opinion for your consideration:ġ. RE: Star Delta Contactors Got Burnt When Starting the Motor but The Main Contactor Did Not RRaghunath (Electrical) 18 Jan 21 10:00 The timer for the star contactor in the close position is 4 seconds. Does anyone know what seems to be the problem that causes the star and delta contactors to get burnt but the main contactor doe not? Thank You However, it got burnt again.Īnd then I realized that because the current that flows through the star and delta contactor also flows through the main contactor, thus, if the star and delta contactors got welded, then there should be three contactors that got burnt, not just 2. Hence, I added 1.6 seconds after the star contactor opened for the delta contactor to close. I figured that it was probably caused by the star and delta contactors being closed at the same time during the transition. The FLA is 93 A, and the contactors have a rating current of 105 A, breaking current of 930 A, and making current of 1050 A. However, I haven't figured out why the contactors got burnt. The star and delta contactors of the motor have been for several occasions got burnt.
I have a 45 kw induction motor with starting method using star delta method.
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