ABT Rectifier

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loyd Associate Join Date: Mar 2011 Posts: 48	ABT Rectifier 01/28/2012 11:58 AM
	Dear Engineers, May be the question I am asking is looks silly,but i am confused about it so please give clarification. In 3 phase rectifier we are using 6 thyristor and if we give 415v ac it will come around 560v dc at output when we measure with our voltmeter. Now if one of this 6 thyristor was not getting firing signal or it was bad (not conducting) then output voltage when we measure with voltmeter will show 560 v dc only? Is this right, or is there any changes in o/p voltage? As our voltmeter measures peak value. How we can find out there is problem in 1 thyristor? Thank you
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MUKULMAHANT Guru Join Date: Dec 2006 Location: Long.92E,Lat.26N Posts: 1336 Good Answers: 14	#1 Re: ABT Rectifier 01/29/2012 12:18 AM
	Simple way will be thus: Filter the harmonics out of a "DC Volt-Out " measuring circuit--branching from Rectified output-- which is loaded with a constant heavy resistive load RL . You are suspecting that 1 of the 6 -not working: Take the reading=V11.RL is the load. Now disconnect any one thyristor. Load as before .Take the reading=V12.RL is the load Likewise 4 more times --take readings V13>>V16-all tested. RL is the load each time . Now see which being disconnected made no difference. That is the FAULTY one .
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Haajee Guru Join Date: Feb 2006 Posts: 1758 Good Answers: 6	#2 Re: ABT Rectifier 01/29/2012 8:29 AM
	In that case only 2 Φs are conducting in full wave. It will give as much output but ripple may increase on full load. If you have a CRO try to measure ripple on both conditions [disconnect filter] See Rectifier
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kwcharlie Power-User Join Date: Jan 2010 Location: Houston off/on-shore @ Oil Patch Posts: 223 Good Answers: 2	#3 Re: ABT Rectifier 01/30/2012 6:55 PM
	You won't see much voltage output difference at all when one diode opens, you will see whatever the rectifier is powering get VERY hot, then you need a scope to find which is bad/not-firing. Now if you have a blown fuse DON'T replace it until you check if one of the diodes/SCR's are still shorted, then you won't have to use a scope to find the open/not-firing one. in the real world the voltage drop isn't useful for troubleshooting 6 diode circuits __________________ Why do they make manhole covers round? so they won't fall in [before asking "Who is John Galt?"]
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Haajee (1); kwcharlie (1); MUKULMAHANT (1)

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