rectifier block, and surge supressor
rectifier block, and surge supressor
(OP)
how do I test a rectifier block of a genset? How about the surge supressor?
How do I know if they are deffective or not?
How do I know if they are deffective or not?






RE: rectifier block, and surge supressor
Transient suppression is trickier. If you try to supply a voltage to check breakdown, you will probably overheat it (rated for very short pulses). But, you can connect it to an inductor and apply current to the inductor. Then remove current and catch the transient on a scope.
Other way is to charge a capacitor to double protection voltage and connect via resistor to MOV. Again, catch with scope to see limiting voltage.
I would replace the MOVs if in any doubt. It costs a lot less than having marginal testing leading to problems later.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: rectifier block, and surge supressor
What happens if the suppressor is damaged or defective? Decent size inductor + a couple of amps = bye-bye 'scope?
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Sometimes I only open my mouth to swap feet...
RE: rectifier block, and surge supressor
You know better than that. Always use a 100:1 probe when measuring high voltages. You may (very unlikely) damage the probe. But the scope will survive.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: rectifier block, and surge supressor
Try this link to a very good manual for field troubleshooting generators
http:
RE: rectifier block, and surge supressor
One more lps.
*Nothing exists except atoms and empty space; everything else is just an opinion*
RE: rectifier block, and surge supressor
Page 8, Polarization Index is given as (1 min value / 10 min value). It should be (10 min value / 1 min value)
*Nothing exists except atoms and empty space; everything else is just an opinion*
RE: rectifier block, and surge supressor
The resistance measurement method on p.6 is also something that shouldn't be done. Doing this, you include DMM series resistance plus test lead resistance and contact resistance in your result. Not recommended when you measure .5 - 5 ohms. Error will be considerable.
The varistor testing with an ohm-meter in Megohm range is not recommended: "A good Surge Suppressor should have a very high resistance,(more than 100 Megohms in either direction)." See p.11.
This is pure non-sense. Varistors shall be tested at rated current - usually 1 mA - and with short pulses. If that is not possible, see if the varistor limits inductive kick-back as described earlier. It does not have to be a large set-up. Use a bench PSU and a coil of any kind (transformer primary works well), connect varistor parallel to coil, apply and break DC, measure resulting peak with scope. Simple, easy, safe.
It is possible that the Stamford book is good for some, but I see it as a source of confusion. You have to know what you are doing and Stamford does not encourage that. It just gives tips that are mostly difficult to follow or even downright wrong.
Feeling quite grumpy now, I cannot resist asking if negative polarity diodes have left-hand threads? P.7.
Also, the resistance numbers for diodes are worthless if you do not specify at what voltage and current they are taken. That is why DMMs have diode test ranges, where diode fwd drop is measured. That measurement makes a lot more sense. But I still wouldn't use that on power diodes.
I could go on forever pointing out things that confuse the unexperienced technician, but I will stop with this observation: Polarity is different on DMMs and analogue meters. So the pictures on p.7 will confuse those who use DMMs.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: rectifier block, and surge supressor
All this sounds like a lot of work, but it is better than putting dead diodes back in the rectifier and having to shut down a unit, dismantle it a second time to repair a fault that was missed, and explain to the management why it was missed! The above test works well with big capsule thyristors too: trigger the gate using a pulse of at least a few hundred mA.
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Sometimes I only open my mouth to swap feet...
RE: rectifier block, and surge supressor
*Nothing exists except atoms and empty space; everything else is just an opinion*
RE: rectifier block, and surge supressor
Go do a web search on "AC Generators" and see how much really recent info you find on 100 to 2000 kVA size generators. Lots of pretty good info out there on utility size stuff, but with the changes in how newer generators are manufactured, applied, and worked on, there sure isn't much out there to really help a guy just trying to fix his machine.
In 20+ years doing generators in the field, using a DMM and doing the "simple" tests have found the problems about 99.99% of the time. And yes, there has been times when they didn't find the problem, but the boss is happy with the trend, and at least it gives us a starting point.
If someone was going to publish an up to date field troubleshooting guide for "small" synchronous generators, with repeatable tests using readily available test equipment, I'd be one of the first in line to buy it. Without that, forums like this at least are helping get info into the hands of people who need it, and the info I have picked up here has been invaluable.
RE: rectifier block, and surge supressor
"In 20+ years doing generators in the field, using a DMM and doing the "simple" tests have found the problems about 99.99% of the time."
Yep, it worked for me too for over 2 decades.
*Nothing exists except atoms and empty space; everything else is just an opinion*
RE: rectifier block, and surge supressor
Most of my work is on 'big' machines where the imperfections of just about everything take on greater significance than on normal sized equipment. Tests that work just fine on small components go straight to hell on big ones. I appreciate the link to that Cummins document - it might give me a clue when one of smaller sets which we sometimes hire in for primary injection tests breaks down at the most inopportune moment. Does our supplier knowingly send us sick machines because they know we abuse them with massive single phase loads?
I thought it was worth pointing out some of the potential shortcomings of some of the tests if they are taken as gospel. I take little at face value these days - I have been lied to by too many normally trustworthy test instruments when I have been testing big semiconductors and accepted the reading at face value. The diode test example is one which has bitten me on the ass rather hard a couple of times: in both instances we had to dismantle virtually all of a rotating rectifier to find a failed diode that the simple test had passed.
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Sometimes I only open my mouth to swap feet...
RE: rectifier block, and surge supressor
I don't work for a Cummins dist, but have found their field manual, even with it's faults, to be one of the best overall generator troubleshooting manuals I have found. Wish the other manufacturers would think the same way, and make this kind of info more "open".
And as for instruments, we are starting to dictate to our field staff brands and models top use, since even with regular calibration intervals, some of what is on the market today just ins't reliable.
I hope the fellow who started this thread is getting to the bottom of his problem.