transformer fault?

[jim23]

been fault finding today at work and after some opinions as installations my norm.

the machine is a set of 3 phase rotators driven by motors.

its the usual set up. 2 contacters (fwd and rev), a transformer for the 24v supply, pendant and a circuit board for the speed control.

the operator was using the rolls, when he pressed stop there was a large bang in the panel.

found 2 fuses had blown. these fuses were the same phases that supplied the 415v primary for the transformer as well as the contacters.

IR test on the circuit through the contacters and up to the pcb is ok.

when fuses replaced and tested got 415v at the primary but nothing at the secondary. when i looked at the transformer primary windings they are all blown away and melted where they leave the terminals.

this led me to believe that the windings in the transformer had failed and brought the phases together. but the transformer its stated should be protected by a 6A fuse (it was actually a 32A fuse!).

this got me thinking that maybe the windings failure was maybe an affect of another fault.

what do people think? has anyone any experience of a transformer failing like this?

 

[ricicle]

jim,
The transformer sounds like it has failed.The transformer primary and secondary circuits should be protected so that any fault with the transformer itself or on the secondary circuits should be cleared rather than damage to the transfomer.Its sounds to me like someone has put in a bigger fuse than stated perhaps because of the inrush current.If it says 6A fuse then a D type 6A should carry any inrush current that can occur.
Depending on the VA rating of the transformer and the secondary circuit load will determine how big the secondary fuse is.
I think a new transfomer is needed with proper protection so that if there are any downstream faults they will be cleared by the fuse.I work on many industrial control panels and they can be very involving but I hope this helps as I havn't seen the panel myself

Ricicle

 

[ricicle]

By the way,
Be careful when IR testing in panels especially as you are aware that electronics don't like 500V up them.As an additon,if you are sure you can do it safely then control wiring to remote stop/starts or limits switches can be IR tested as they are favourite to short down in hidden areas of machinery due to vibration etc

Ricicle

 

[Lectrician]

But it banged as the stop button was pressed........

Something sounds a little dodgy with it, but with little information etc, difficult to advise.

 

[jim23]

cheers guys. got hold of a transformer from another machine.

bit unsure how to wire it up though. the secondary side is easy because its the same 12v - 0 - 12v terminals. on the origanol one the 2 phases were connected to the 0 and 415v terminals.

this transformer however has 0, 230, 400 and a +15 which i assume is to allow for an input flexibility. which terminals do i connect the 2 phases across?

never seen this before. cheers guys.

 

[breezer]

why not look at the m/c it came from?

 

[Spark123]

Is the +15 before the 0v on the rail?
I'm thinking it might be a case of using one side to the +15 instead of the 0v and the other to the 400v terminal (assuming a 415v supply). With a fluke, is the maximum resistance you can get between any two terminals between +15v and 400v?

 

[jim23]

no the 15v is after the 0 terminal. the old machine transformer is disconnected. bits have been robbed off it but apparently it still worked when took out of service so.......

 

[Adam_151]

no the 15v is after the 0 terminal. the old machine transformer is disconnected. bits have been robbed off it but apparently it still worked when took out of service so.......

Is the layout as you listed them?, ie. 0, 230, 400, +15 ? if so I'd suggest you want 0 and +15 across your two phases

 

[ricicle]

Im with Adam151,connect across 0/+15.Have you allowed for proper protectipn of this transformer now?What is its VA rating?Is the secondary circuit protected to prevent another burn-out?

Ricicle

 

[Spark123]

Got me wondering now, has a little bit of the first number of +15v been scuffed off, i.e. did it used to read 415v?
Still advise to check resistance with a fluke first.

 

[jim23]

cheers for the help guys.

im thinking that adam151 n ricicle are right because the layout is as i stated.

its a 150KA transformer ricicle.

am positive its a +15v terminal spark123, but nice thinking though

ill be correctly protecting the transformer now yes and making sure all the other protection is in order.