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Field Thyristor Failure at Power Up

1/17/2012 5:05 AM	Rate (0)
sanjaywani7 Posts: 11 Rating: (0)	Dear DK; Do you have any guidelines for how select the surge arrestor for thyristor? regards
sanjaywani7 Posts: 11 Rating: (0)
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1/17/2012 5:13 AM	Rate (0)
PISCEAN 2010 Posts: 8092 Rating: (884)	sanjaywani7 Dear Deep; 2) Motor Field current is 6.3A and Resistance is 25.6 Ohms. 3) Field to Armature and with respect to ground is 200 M.ohms regards How much is the DC field voltage?
PISCEAN 2010 Posts: 8092 Rating: (884)
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1/17/2012 6:04 AM	Rate (0)
sanjaywani7 Posts: 11 Rating: (0)	Dear DK; What should be the rating of Surge Suppressor for this thyristor?
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1/17/2012 6:09 AM	Rate (0)
sanjaywani7 Posts: 11 Rating: (0)	Dear Deep; DC Voltage is 180V.
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1/17/2012 6:46 AM	Rate (0)
PISCEAN 2010 Posts: 8092 Rating: (884)	Hello, Are those thyristers, which fails are from the same drive/motor or every time when they fail are fromdifferent drive/motor? If those are from the same motor, then depending upon motor inside field winding connection, there might be some dry or loose connection insidefield winding pole connection. Thisis why during power failure or switch on time, field isdrawing more current. Since there is no protection to limit for inrush field current, which is very high, thyristers must be failing. If possible please replace the motor from equivalent & check the motor field winding. *Moreover it is always recommended to provide semiconductor fuse link in line to protect power devices from line polution.* As far asvoltage surgesare concerned, I think, if that would have been the cause then all drives would have faced the same problem. Secondly though the surge voltage value is high it would damaged electronic component & not power device (In this case PIV of thyrister is 1600 volt) Please check & revert back. Best luck. DEEP.
PISCEAN 2010 Posts: 8092 Rating: (884)
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1/17/2012 7:14 AM	Rate (0)
sanjaywani7 Posts: 11 Rating: (0)	Dear deep; The failure occurs randomly. It is not repeated with the same drive. In my opinion surge can damage the power device also. That is why we use the surge suppressor R-C unit across the Thyristor. We will put Semiconductor fuse definately but the real cause is still unknown.
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3/16/2012 9:02 AM	Rate (0)
MyoThant.Aung Posts: 10 Rating: (0)	Hi, I was reading your post of "Field Thyristor Failure at Power Up". It is a very interesting topic and I would like to know what the root cause is. How is the saturation now? alread solve the problems? With best regards.
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