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When should a transformer core be potted? Should it be potted at all? For this type of job, you would pot the transformer when you can't obtain the necessary creepage and clearance between the...
Answer
#2: Post edited
by
Andy aka
·
2024-01-22T11:30:46Z (4 months ago)
- > _When should a transformer core be potted? Should it be potted at all?_
- For this type of job, you would pot the transformer when you can't obtain the necessary creepage and clearance between the secondary (raised externally to 10 kV) and the low-voltage parts of the transformer (including the ferrite core).
A typical dielectric strength for 1 mm of potting resin is 20 kV but, you need to verify this and, you need to ensure that your potting process does not allow bubbles or air-locks to form. The bubbles/air-locks can expose high-voltages to low-voltages via a less-than-adequate creepage path (a much lower breakdown voltage than through solid resin because it is a "surface path").- > _Can I place the high voltage conductors of the secondary coil on the inner layers considering the high dielectric strength of the PCB_
- It makes no difference; you should regard all your secondary layers and windings as one block of metal raised to 10 kV.
- > _IPC 2221 specifies a much higher clearance requirement for the same. Is this to ensure reliability in various environmental conditions?_
- It certainly is.
- > _"The core is at a floating potential that could be anywhere between 0 and 10 kV" - Is this correct?_
- This is your call. If you say it is then, that's what it is.
- > _When should a transformer core be potted? Should it be potted at all?_
- For this type of job, you would pot the transformer when you can't obtain the necessary creepage and clearance between the secondary (raised externally to 10 kV) and the low-voltage parts of the transformer (including the ferrite core).
- <sub>$$$$</sub>
- The "typical" dielectric strength for 1 mm thickness of potting resin is 20 kV but, you need to verify this with the materials you want to use and, you need to ensure that your potting process does not produce internal bubbles or air-locks when setting. The bubbles/air-locks can expose high-voltage circuits to low-voltage circuits via a less-than-adequate creepage path. A "creepage" path is a much lower breakdown voltage (compared to the solid resin) because, it **is** a "surface path".
- <sub>$$$$</sub>
- > _Can I place the high voltage conductors of the secondary coil on the inner layers considering the high dielectric strength of the PCB_
- It makes no difference; you should regard all your secondary layers and windings as one block of metal raised to 10 kV.
- <sub>$$$$</sub>
- > _IPC 2221 specifies a much higher clearance requirement for the same. Is this to ensure reliability in various environmental conditions?_
- It certainly is.
- <sub>$$$$</sub>
- > _"The core is at a floating potential that could be anywhere between 0 and 10 kV" - Is this correct?_
- This is your call. If you say it is then, that's what it is.
#1: Initial revision
by
Andy aka
·
2024-01-21T11:53:47Z (4 months ago)
> _When should a transformer core be potted? Should it be potted at all?_ For this type of job, you would pot the transformer when you can't obtain the necessary creepage and clearance between the secondary (raised externally to 10 kV) and the low-voltage parts of the transformer (including the ferrite core). A typical dielectric strength for 1 mm of potting resin is 20 kV but, you need to verify this and, you need to ensure that your potting process does not allow bubbles or air-locks to form. The bubbles/air-locks can expose high-voltages to low-voltages via a less-than-adequate creepage path (a much lower breakdown voltage than through solid resin because it is a "surface path"). > _Can I place the high voltage conductors of the secondary coil on the inner layers considering the high dielectric strength of the PCB_ It makes no difference; you should regard all your secondary layers and windings as one block of metal raised to 10 kV. > _IPC 2221 specifies a much higher clearance requirement for the same. Is this to ensure reliability in various environmental conditions?_ It certainly is. > _"The core is at a floating potential that could be anywhere between 0 and 10 kV" - Is this correct?_ This is your call. If you say it is then, that's what it is.