Creepage distance of mains transformers AS 3108

[Geoff C]

Does anyone know off hand the isolation distance between primary and
secondary on a EI tranny? i thought it was something like 6mm?

Domestic or light industrial, low to average pollution degree.

 

[Phil Allison]

"Geoff C"

Does anyone know off hand the isolation distance between primary and
secondary on a EI tranny? i thought it was something like 6mm?

** Your question is far too vague.

AS3108 gives " Distances through insulation between input and output
circuits." ( which applies to a transformer ) as being a little as 0.1mm
( ie 4 thou) for a 250 volt AC supply.

The VA rating of the transformer come into the figure as does the type of
insulation used.

How about you ask for the info you are really after?




........ Phil

 

[Geoff C]

"Geoff C"


** Your question is far too vague.

AS3108 gives " Distances through insulation between input and output
circuits." ( which applies to a transformer ) as being a little as
0.1mm ( ie 4 thou) for a 250 volt AC supply.

The VA rating of the transformer come into the figure as does the type
of insulation used.

How about you ask for the info you are really after?




....... Phil

OK. I do not have access to the standard but will attempt to describe.

Transformer is mains and approx 300VA peak, 150VA average with multiple
secondaries, elecrostatic screen and 120/120 primary for international
voltages. Max secondary winding is 285 volt.

Centre leg 40x73mm, stack height 53 mm. Inter winding insulation is mylar
tape, (the yellow stuff) with elephantide type wrap. I am evaluating a
new supplier of this tranny and would like to give the go ahead to the
manufacturer for an initial run if it is OK. I will do hi-pot testing
after I unwrap and check construction. I would like to know the legal
requirement for the creepage distance from primary to secondary winding.

 

[Phil Allison]

"Geoff C"

OK. I do not have access to the standard but will attempt to describe.

Transformer is mains and approx 300VA peak, 150VA average with multiple
secondaries, elecrostatic screen and 120/120 primary for international
voltages. Max secondary winding is 285 volt.

** For a valve amp ??

Centre leg 40x73mm, stack height 53 mm. Inter winding insulation is mylar
tape, (the yellow stuff) with elephantide type wrap. I am evaluating a
new supplier of this tranny and would like to give the go ahead to the
manufacturer for an initial run if it is OK. I will do hi-pot testing
after I unwrap and check construction. I would like to know the legal
requirement for the creepage distance from primary to secondary winding.

** Still far to vague.

1. Is the tranny of "overwound" construction ?

2. Is there a plastic bobbin ?

3. Is it intended to meet class 2 requirements ?

4. Is the mylar layered ?

5. Is the paper wrap between primary and secondary?


BTW

You seem to think that "creepage" and "clearance " are the SAME as
"distance through insulation...."

They are not.




........ Phil

 

[Geoff C]

"Geoff C"


** For a valve amp ??

No, measuring equipment.

** Still far to vague.

1. Is the tranny of "overwound" construction ?

Yes, overwound, it is not a split bobbin.

2. Is there a plastic bobbin ?
Yes


3. Is it intended to meet class 2 requirements ?

No, earthed equipment

4. Is the mylar layered ?

It varies, 2 layers or more mostly. Have not yet measured the thickness.

5. Is the paper wrap between primary and secondary?

Yes, 2 wraps.

BTW

You seem to think that "creepage" and "clearance " are the SAME as
"distance through insulation...."

They are not.

I am aware of the distinction, and it is creepage I am wanting to know
about. ie the distance between pri and sec around the insulators.

 

[Phil Allison]

"Geoff C"


** That ES screen complicates the situation.

Normal creepage and clearance rules go out the window.

Describe it .





......... Phil

 

[Geoff C]

"Geoff C"



** That ES screen complicates the situation.

Normal creepage and clearance rules go out the window.

Describe it .





........ Phil

Yes, I see where you're coming from. Sheet copper, between pri and sec,
2l ayers of mylar tape and a single paper on each side. 40 mm width and
centred in bobbin. Layer of paper and mylar tape underneath the end to
prevent shorted-turn.

 

[Phil Allison]

"Geoff C"

"Phil Allison"

Yes, I see where you're coming from. Sheet copper, between pri and sec,
2l ayers of mylar tape and a single paper on each side. 40 mm width and
centred in bobbin. Layer of paper and mylar tape underneath the end to
prevent shorted-turn.

** Long as that sheet of copper is the same width as the primary winding you
have complied.

Often, tranny makers will just wind a singe layer and use that as a ES
shield - being careful not to join the ends !



........ Phil

 

[Geoff C]

"Geoff C"


** Long as that sheet of copper is the same width as the primary
winding you have complied.

Often, tranny makers will just wind a singe layer and use that as a
ES shield - being careful not to join the ends !



....... Phil

Thanks.

Yep, I've seen the ES as a winding before too.

 

[Joe G \(Home\)]

Here
http://www.saiglobal.com/shop/Script/Details.asp?DocN=stds000011541

Buy the standard and all your questions will be answered!

JG

 

[Phil Allison]

"Joe G (Home)"

Here
http://www.saiglobal.com/shop/Script/Details.asp?DocN=stds000011541

Buy the standard and all your questions will be answered!

** That would be the optimist's point of view.

The reality is, you wind up $130 poorer and likely more confused that you
ever imagined.





......... Phil

 

[Geoff C]

Here
http://www.saiglobal.com/shop/Script/Details.asp?DocN=stds000011541

Buy the standard and all your questions will be answered!

JG

I have lots of standards here, but we dont make transformers and have no
wish to be experts in the safety requirements, it is not our business.
Better to ask of experts sometimes. It takes me a few days to digest a
technical standard and I'd rather spend my time elsewhere. (EN61010 is
enough for now) Also, it may be years before I need to an autopsy on
another tranny. The manufacturer has been told the specs anyway.

 

[Alf Katz]

The reality is, you wind up $130 poorer and likely more confused that you
ever imagined.

$130 would be lovely. If it's like most other standards these days, it
won't actually give you the information that you need, but will reference 15
other standards, each of which you'll have to buy to painfully extract the
few titbits you're after. The standards industry is all about the money
these days. Get a bunch of academics and inustry experts to volunteer their
time to define the standards, mandate compliance, change it as often as
possible, then sell it to all, including the experts who defined it.

Cheers,
Alf

 

[Joe G \(Home\)]

Sorry - that was ment to be a sarcastic statement!

You will have more questions after you read the std!


It's understanding the "intent" of the requirement clauses - gives real
meaning to the std.... unfortunately std's
are like a legal statements - and real meaning is deduced by to those who
live and beath the stds applied to their field of expertise.


There are quite a few cases where lab's can have different interpretation of
the same std....

JG