The Craftmans Shop > New from Old
Resurrection of a CFEI 100 KVA Induction Furnace
awemawson:
Yes it's all very odd Matthew :scratch:
I measure the transformer output as 26 volts AC. By using the emergency stop button (which is in the chain in question) I can power up / down the 'no volts solenoid' and the relay K1 which has a 500 mSec delay built in and it is apparent that the delay is working.
Quite possible that the circuit has been drawn wrong and that the coils are in parallel, or maybe the coil and contact of K1 are interchanged in the drawing. It wouldn't be the first error I've found in the drawings!
I strongly suspect that I'm going to have to pull the big contactor out and try it on the bench - I really don't waant to as it's far from simple and I suspect that it's a red herring as far as the original fault is concerned.
At least the transformer, fuses and relay K1 are all close together on one panel for fault finding but the 'no volt coil' isn't really accessible without pulling the entire contactor.
awemawson:
So nothing for it - pull that huge isolator out for examination !
First ABSOLUTELY ensure no main can be connected. Then it's just a case of unbolting the three phase input lines, three phase busbar output lines, disconnecting the trip coil connections, and removing four M6 bolts securing the beast to the chassis.
OK isolator removed :thumbup:
awemawson:
Now at last I can see where the trip coil is located - round the back !
The trip coil unit clips in with it's two wire threaded though a channel to the front terminals. Pulling it out it is all rather sad - obviously suffered water damage and from it's terminals is open circuit. However scratching about, the actual coil is OK (2K ohms) and the solenoid pulls in nicely from 20v DC (bench supply) so I'm confident that I can clean it up to serviceable condition.
With the trip coil removed I can physically latch the mechanism 'ON' and trip it to 'OFF' by holding the lever that the solenoid presses on in the appropriate position - ah good I (ERRONEOUSLY) think.
When latched 'ON' there is no electrical connection between input and output on any of the three phases, and indeed the 'double break' contact arrangement that I assume should slide to the left to impale the contacts onto a bridge piece hasn't moved. This is VERY odd - I must be missing something here
As far as I can tell the entire plastic assembly that holds the three sets of 'double break' contacts should slide to the left onto the bridge pieces but it doesn't - this has me greatly confused :scratch:
Time to sit and cogitate I think :coffee:
hermetic:
Hi Andrew, very often in this type of breaker there is an interlink mechanism which stops the isolator operating unless the trip mechanism is in place, thus preventing nuisance tripping being cured by merely removing the coil. Is there anything that the trip coil depresses as it is pushed into position? Does the act of resetting the trip push the solenoid core along and actuate the switch at the same time? Baffling!
phil
awemawson:
Phil, I've looked for such cunningnesses but not found anything. I reinstalled the trip for precisely this reason, using the external lever to put it in the 'volts present' position (rather than 24v activated' and it's still the same.
I'm off back to the workshop for more experiments now though so watch this space !
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