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In what ways can a transformer fail....?

R

royalmp2001

Jan 1, 1970
0
Hi everyone,

I am looking at safety issues concerning transformers.

Basic question, I know, but other than an open circuit due to a
winding burnout, or maybe a shorted turn, how else can a transformer
fail?

Is it likely/possible that the primary voltage of a mains step-down
transformer can appear on the secondary due to some fault?

I have a transformer that has an oval core encapsulated in plasic with
the primary on one side of the core and the secondary on the opposite
side. Other than a simple open or shorted turn, the possibility of
mains voltage getting to the secondary must be impossible due to the
physical separation, right?

Comments gratefully received with thanks.
 
P

Phil Allison

Jan 1, 1970
0
** Groper wanker alert

I am looking at safety issues concerning transformers.

Basic question, I know, but other than an open circuit due to a
winding burnout, or maybe a shorted turn, how else can a transformer
fail?

Is it likely/possible that the primary voltage of a mains step-down
transformer can appear on the secondary due to some fault?


** Of course.

Insulation can burn or just fail.


I have a transformer that has an oval core encapsulated in plasic with
the primary on one side of the core and the secondary on the opposite
side.


** Well, that ain't no mains transformer.

You sure the two sides are not interconnected ?

Other than a simple open or shorted turn, the possibility of
mains voltage getting to the secondary must be impossible due to the
physical separation, right?


** Not quite impossible.

A secondary short might cause both windings to burn right down to the metal
core.




........ Phil
 
H

Homer J Simpson

Jan 1, 1970
0
Is it likely/possible that the primary voltage of a mains step-down
transformer can appear on the secondary due to some fault?

Yes, and either winding can short to the core.
 
D

Don Bruder

Jan 1, 1970
0
royalmp2001 said:
Hi everyone,

I am looking at safety issues concerning transformers.

Basic question, I know, but other than an open circuit due to a
winding burnout, or maybe a shorted turn, how else can a transformer
fail?

Is it likely/possible that the primary voltage of a mains step-down
transformer can appear on the secondary due to some fault?

I have a transformer that has an oval core encapsulated in plasic with
the primary on one side of the core and the secondary on the opposite
side. Other than a simple open or shorted turn, the possibility of
mains voltage getting to the secondary must be impossible due to the
physical separation, right?

Maybe.

Ferinstance, what happens if primary shorts to the core, and secondary
is ALSO shorted to the core? without actually trying it, it seems fairly
intuitive that the primary voltage *COULD* appear on the secondary. Not
"will", but "could"...
 
R

Ross Herbert

Jan 1, 1970
0
Hi everyone,

I am looking at safety issues concerning transformers.

Basic question, I know, but other than an open circuit due to a
winding burnout, or maybe a shorted turn, how else can a transformer
fail?

Is it likely/possible that the primary voltage of a mains step-down
transformer can appear on the secondary due to some fault?

I have a transformer that has an oval core encapsulated in plasic with
the primary on one side of the core and the secondary on the opposite
side. Other than a simple open or shorted turn, the possibility of
mains voltage getting to the secondary must be impossible due to the
physical separation, right?

Comments gratefully received with thanks.


Is this the type you mean?
http://www.custommag.com/products/r-core.shtml

I have seen mains transformers of this type in only a few items of
equipment. Usually more expensive than other more common types but P -
S isolation is absolute and makes them very safe for medical
equipment.
 
C

Christian Treldal

Jan 1, 1970
0
Den Thu, 15 Feb 2007 21:23:50 -0800 skrev Don Bruder:
Ferinstance, what happens if primary shorts to the core, and secondary
is ALSO shorted to the core? without actually trying it, it seems fairly
intuitive that the primary voltage *COULD* appear on the secondary. Not
"will", but "could"...

I think it's easier to win in lotto, than to be in that scenario.
 
P

Phil Allison

Jan 1, 1970
0
"Christian Treldal"

I think it's easier to win in lotto, than to be in that scenario.



** Just love to have the same odds on lotto.

Short the secondary winding and both it and the primary will heat to
combustion temperatures - as they have very similar heat dissipations.

Ordinary plastic or paper insulation used to separate them from the core
fails when burned.

Carbon soot conducts electricity.

Humans die with as little as 35 mA flow between hands.

Nothing a dumb kraut ham would comprehend.





........ Phil
 
P

Phil Allison

Jan 1, 1970
0
"Ross Herbert" >>
Is this the type you mean?
http://www.custommag.com/products/r-core.shtml

I have seen mains transformers of this type in only a few items of
equipment. Usually more expensive than other more common types but P -
S isolation is absolute and makes them very safe for medical
equipment.


** But *no way* are the primaries and secondaries on opposite sides of the
R core !!!

There are two of each, wound side by side & interconnected.




........ Phil
 
P

Paul E. Schoen

Jan 1, 1970
0
Phil Allison said:
"Ross Herbert" >>



** But *no way* are the primaries and secondaries on opposite sides of
the R core !!!

There are two of each, wound side by side & interconnected.

These appear to be C-cores, which are similar to toroids, having a
tape-wound construction that is more efficient than E-I laminations. Unlike
toroids, however, C-cores are generally cut so the winding bobbins can be
installed, and then held back together, but this causes gaps in the
laminations which cause higher impedance. Some high voltage transformers
are made this way, with primary and secondary on opposite sides of the
core.

The safest transformer design I have seen is that used by Signal
Transformer 241 series, Stancor SWC series, and and Triad F4-F8 series, as
well as PC mounted styles like Tamura 3FS series. They are standard EI
cores, but the bobbins are molded plastic with a divider, so the primary
and secondary windings are physically isolated from each other.

Usually a transformer winding will fail open in the hot spot deepest in the
windings, or else where it is connected to the leads. I have seen most fail
in the primary, where the insulation breaks down between two or more
windings, causing a high current in that small area, which melts the wire.

Some smaller transformers are impedance protected, or power limited, so
they will not fail catastrophically with an overload or shorted secondary.
I think this is how most wall-warts are designed. It is always good
practice to ground the core of power transformers, so any primary to core
short will not cause dangerous currents in the secondary. Larger
transformers should be protected with fuses or circuit breakers rated
according to normal current draw.

Paul
 
J

john jardine

Jan 1, 1970
0
Phil Allison said:
"Ross Herbert" >>



** But *no way* are the primaries and secondaries on opposite sides of the
R core !!!

There are two of each, wound side by side & interconnected.




....... Phil

Just looked at the one I have. Yes, wound as you mention. The plastic cores
are half shells that clip together and the whole thing looks much more
effort to make than a normal toroid.
Got mine (20Vac) from a cheapo mass produced hifi. Somehow just didn't seem
right that it was in there. Couldn't bear to throw it away as the shaped
tape core is a work of art.
 
P

Phil Allison

Jan 1, 1970
0
"john jardine"
"Phil Allison"

Just looked at the one I have. Yes, wound as you mention. The plastic
cores
are half shells that clip together and the whole thing looks much more
effort to make than a normal toroid.


** It is actually FAR less effort to make an R-Core transformer than a
toroidal.

Note how the bobbins have teeth around the perimeter so that can be spun in
a winding machine.

Note how the core itself can be easily clamped to a chassis.

Note how it is easy to make class 2 ( double insulated ) examples.

Got mine (20Vac) from a cheapo mass produced hifi. Somehow just didn't
seem
right that it was in there. Couldn't bear to throw it away as the shaped
tape core is a work of art.


** Agreed.



....... Phil
 
J

jasen

Jan 1, 1970
0
Ferinstance, what happens if primary shorts to the core, and secondary
is ALSO shorted to the core? without actually trying it, it seems fairly
intuitive that the primary voltage *COULD* appear on the secondary. Not
"will", but "could"...

I can't immagine a scenario in which that is more likely than the primary
shorting to the secondary. (or vice versa)

Bye.
Jasen
 
R

Ross Herbert

Jan 1, 1970
0
"Ross Herbert" >>



** But *no way* are the primaries and secondaries on opposite sides of the
R core !!!


Did you not see this paragraph on the link I gave.

"The other unique feature is the use of Bobbins in two parts. The
primary winding and secondary winding are done on separate bobbins
thus ensuring complete isolation between the two windings. This allows
meeting of any safety standards requirement."
 
R

Ross Herbert

Jan 1, 1970
0
Did you not see this paragraph on the link I gave.

"The other unique feature is the use of Bobbins in two parts. The
primary winding and secondary winding are done on separate bobbins
thus ensuring complete isolation between the two windings. This allows
meeting of any safety standards requirement."

I think I get what you are referring to Phil.

You are correct in that the windings are distributed over both
bobbins. The windings on an individual bobbin are separated by an
interleaving barrier of the same material as the main bobbin.

This page gives a cross-section of the winding pattern.
http://www.kitamura-kiden.co.jp/english/products_e.html
 
P

Phil Allison

Jan 1, 1970
0
"Ross Herbert"
I think I get what you are referring to Phil.


** The why the HECK snip the crucial line out of site ???

" There are two of each, wound side by side & interconnected. "

You are correct in that the windings are distributed over both
bobbins. The windings on an individual bobbin are separated by an
interleaving barrier of the same material as the main bobbin.


** From the same site you gave:

http://www.custommag.com/products/r-core_compare.shtml

Under " Insulation " it says:

" Double structure bobbins are used .... "

This page gives a cross-section of the winding pattern.
http://www.kitamura-kiden.co.jp/english/products_e.html


** Not all R- cores are like that example, which does not claim to be class
2 compliant.

The insulation material separating the primary and secondary must be very
high temp and fireproof - eg Kapton - to meet the class 2 requirement.
Easier if they use side by side - ie " split " bobbins.



....... Phil
 
R

Ross Herbert

Jan 1, 1970
0
"Ross Herbert"


** The why the HECK snip the crucial line out of site ???

" There are two of each, wound side by side & interconnected. "




** From the same site you gave:

http://www.custommag.com/products/r-core_compare.shtml

That is NOT the page I gave though. You have gone to the comparisons
page and I didn't give that reference. I also don't consider that the
term "double-structure bobbin" conveys accurately to those not
familiar with transformer winding how the separation is achieved. I
gave the main page link so that anyone wanting to read further could
do so, not to start a war on specific details.
 
P

Phil Allison

Jan 1, 1970
0
"Ross Herbert"
"Phil Allison"
That is NOT the page I gave though. You have gone to the comparisons
page and I didn't give that reference.


** What did I write just above the link - Ross?


I also don't consider that the
term "double-structure bobbin" conveys accurately to those not
familiar with transformer winding how the separation is achieved.


** It conveys the needed info on the point at issue - Ross.

( ie, the fact the P and S windings are duplicated and interconnected )

I gave the main page link so that anyone wanting to read further could
do so, not to start a war on specific details.


** Shame how the specific details of the winding arrangement IS the point
at issue.

Shame how YOU quoted a para on the main page that was ambiguous on the
point at issue.

Shame how YOU did not read the site further to resolve that ambiguity.

Shame how YOU treated an ambiguous marketing blurb as technical fact.

Shame how you did not have the sense to realise that any transformer with P
and S winding on separate limbs of a core would have very poor voltage
regulation.

Shame, shame shame,



........ Phil




 
R

Ross Herbert

Jan 1, 1970
0
"Ross Herbert"
"Phil Allison"


** What did I write just above the link - Ross?





** It conveys the needed info on the point at issue - Ross.

( ie, the fact the P and S windings are duplicated and interconnected )




** Shame how the specific details of the winding arrangement IS the point
at issue.

Shame how YOU quoted a para on the main page that was ambiguous on the
point at issue.

Shame how YOU did not read the site further to resolve that ambiguity.

Shame how YOU treated an ambiguous marketing blurb as technical fact.

Shame how you did not have the sense to realise that any transformer with P
and S winding on separate limbs of a core would have very poor voltage
regulation.

Shame, shame shame,



....... Phil

My original post was simply to ask the OP if he was in fact referring
to an R-Core transformer. Somehow you seem to want to blow the whole
thing into a discussion on the specific technicalities of how an
R-Core transformer is constructed. While the page I gave didn't give
all the details in this regard I didn't want to get into the specifics
of the issue. Manufacturers will naturally slant advertising to list
what they perceive as advantages for their products and I admit I
didn't give too much thought to the content of the page to determine
what it really said. And I admit that the ambiguity of the statement
on the page did mis-lead me to some extent. However, I don't see it as
any shame on myself for not delving into technical complexities
considering that I was mainly asking the OP if he was referring to an
R-Core in my first post.
 
P

Phil Allison

Jan 1, 1970
0
"Ross Herbert"
My original post was simply to ask the OP if he was in fact referring
to an R-Core transformer.


** Bollocks.

Your initial post contained a serious error that needed to be corrected

So I politely did so.


Somehow....


** No "somehow" about it - see above.


you seem to want to blow the whole
thing into a discussion on the specific technicalities of how an
R-Core transformer is constructed.


** Naturally - in order to correct the error YOU posted then later tried
to fallaciously prove was right.

This one:

" I have seen mains transformers of this type in only a few items of
equipment. Usually more expensive than other more common types but P -
S isolation is absolute and makes them very safe for medical
equipment."


Grow up - Ross.


While the page I gave didn't give
all the details in this regard I didn't want to get into the specifics
of the issue.


** That is a damn lie.

Grow up anytime - Ross.

Manufacturers will naturally slant advertising to list
what they perceive as advantages for their products and I admit I
didn't give too much thought to the content of the page to determine
what it really said.


** No sign of YOU thinking the matter through at all.

Grow up anytime - Ross.


And I admit that the ambiguity of the statement
on the page did mis-lead me to some extent.


** And you posted that false impression in contradiction of my earnest
attempts to correct your original error.

However, I don't see it as
any shame on myself for not delving into technical complexities


** Bollocks.

You were wrong, stubborn and rude about it too.

Grow up anytime & take responsibility for your actions.

considering that I was mainly asking the OP if he was referring to an
R-Core in my first post.


** How typically dishonest of YOU to ignore and want others to ignore
your posting of serious misinformation.

Piss off and do something useful - Ross.

Like checking out those illegal 2 core IEC leads that are in nearly every
hobby shop in Perth and reporting them to that fellow in the dept.




....... Phil
 
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