Skogsgurra
Electrical
- Mar 31, 2003
- 11,815
I did my first measurements on machines like these 15-20 years ago.
The exciter shorts out the excitation winding during start (high induced voltage due to high slip makes the control unit gate the thyristors on) and when near synchronous speed, the induced voltage is reduced so the thyristors (SCR:s) stay off and the rectifier just rectifies. All fine and dandy.
Now, there was a spare rotor that a winder shop wanted to test before returning it to the plant. They have done this test many times before, but this time - the control unit let out some smoke. It still worked as intended. But the smoke was not pleasant and I think that life of the unit may be reduced by this. Pictures below:
The waveforms show how the ctrl unit trigs the SCR:s at around 400 V - which is OK and works well in this application. This picture is from around 2004.
The "Smokey" had been set to a higher trigger voltage. Instead of 400 V peaks, we had 800 - 820 V. The original Smokey had burned a hole where you could see the smoke exit. The second unit didn't smoke. But got quite hot in the same place. We switched off before there was any severe damage to it.
The funny thing is that both units behaved well and showed the same characteristics.
The units that we have seen before (from 2000 - 2010, cirka) could all be tested without any problem. The new ones can't tolerate AC voltage for more than ten or twenty seconds.
We do not need speculations. But if someone has had this problem and can say if there are any differences between the older units and the newer ones (from 2014 and onwards) we would be very grateful.
For political and business reasons, I do not disclose supplier or type. But anyone who has had this kind of problem will know what it is about.
Gunnar Englund
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
The exciter shorts out the excitation winding during start (high induced voltage due to high slip makes the control unit gate the thyristors on) and when near synchronous speed, the induced voltage is reduced so the thyristors (SCR:s) stay off and the rectifier just rectifies. All fine and dandy.
Now, there was a spare rotor that a winder shop wanted to test before returning it to the plant. They have done this test many times before, but this time - the control unit let out some smoke. It still worked as intended. But the smoke was not pleasant and I think that life of the unit may be reduced by this. Pictures below:
The waveforms show how the ctrl unit trigs the SCR:s at around 400 V - which is OK and works well in this application. This picture is from around 2004.
The "Smokey" had been set to a higher trigger voltage. Instead of 400 V peaks, we had 800 - 820 V. The original Smokey had burned a hole where you could see the smoke exit. The second unit didn't smoke. But got quite hot in the same place. We switched off before there was any severe damage to it.
The funny thing is that both units behaved well and showed the same characteristics.
The units that we have seen before (from 2000 - 2010, cirka) could all be tested without any problem. The new ones can't tolerate AC voltage for more than ten or twenty seconds.
We do not need speculations. But if someone has had this problem and can say if there are any differences between the older units and the newer ones (from 2014 and onwards) we would be very grateful.
For political and business reasons, I do not disclose supplier or type. But anyone who has had this kind of problem will know what it is about.
Gunnar Englund
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.