Contactor Coil Burnt

Contactor coil can burnout due to one or more of these reasons:

• Low or High voltage
• Full closing of magnet faces prevented by something
• Shorted turns
• End-turn insulation failure
• Impulse voltage
• High ambient
• Too frequent starts
• Control transformer inadequate, resulting in contactor failing to pick up
• ...

If you give more details of your setup,it will help.

Is it open transition or closed transition?

Is there a mechanical interlock between the star and delta contactors. Their the favourite for going wrong.

Give more nameplate details perhaps we can fix the problem.

specify all contactor details, olr, mccb details, motor name plate details.......may be the contactor rating s not proper?

for a little info on star delta starters refer these links

http://cr4.globalspec.com/thread/59853/Star-Delta-Motor-Starters

http://samplecode.rockwellautomation.com/idc/groups/literature/documents/wp/150-wp004_-en-p.pdf

Dear Sir,

To the comments given by Mr.Sridhar, you can check up the shading

copper ring of the contactor for any breakage or partial obstruction while

closing.

Manroop. Chennai.

Ah yes manroop, good point. i missed that, thanks.

However, a broken shading ring would cause a godawful noise, OP you can tell us.

My own vote would be too small a control transformer, since it is 110V. Main and star contactors would pickup together usually, and the inrush current would be too high, voltage would sag, contactors may "pump" (drop off due to low voltage, pickup again with a staccato action), overheat and burn.

Anyway, in the absence of more data, nothing further seems possible.