creepage and clearance for transformers

[Jamie Morken]

Hi,

What do creepage and clearance mean exactly as a specification for
transformers?

cheers,
Jamie

 

[D from BC]

Hi,

What do creepage and clearance mean exactly as a specification for
transformers?

cheers,
Jamie

IIRC... (There might be errors. Please check.)

Creepage is spacing on a surface that collects pollution.
Clearance is spacing in air.
This pops up because of a difference in air breakdown and the
breakdown of accumulated pollution.

Clearance applies to the transformer terminals and any internal air
spacings.
But if the terminals are on a block that collects pollution, then
creepage might be considered.

However I don't think creepage applies inside the transformer..
Transformers are often bundled up or sealed.
It's all up to the insulators and air gaps to block breakdown.

*
*
* <<pollution accumulating between conductors
()*() <creepy
----

*
() * () <clear (just air)
*


D from BC
British Columbia
Canada.

 

[Paul Mathews]

IIRC... (There might be errors. Please check.)

Creepage is spacing on a surface that collects pollution.
Clearance is spacing in air.
This pops up because of a difference in air breakdown and the
breakdown of accumulated pollution.

Clearance applies to the transformer terminals and any internal air
spacings.
But if the terminals are on a block that collects pollution, then
creepage might be considered.

However I don't think creepage applies inside the transformer..
Transformers are often bundled up or sealed.
It's all up to the insulators and air gaps to block breakdown.

*
 *
  * <<pollution accumulating between conductors
()*() <creepy
----

 *
() *  () <clear (just air)
    *

D from BC
British Columbia
Canada.

Creepage applies equally inside of a transformer and is the primary
reason for 'margins' on either side of windings and for sleeving
applied over terminations, splices, and such. 'Enamel' insulation on
windings does not count as safety insulation. Under many regulations,
you can get away without margins if you use 'triple insulated' wire,
however you still may need sleeving and/or special bobbins to provide
proper creepage and clearance near terminations.
Paul Mathews