What is the potting compound?
The potting compound is the solid fill inside the transformer case. It leaves no air around the core and windings, keeps moisture out, holds everything still and helps carry heat away.
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Complete fill. The compound fills the case right around the core and windings, with no air gaps. It insulates between conductors, seals out moisture and dirt, holds the windings firm against vibration and temperature swings, and carries heat from the windings to the case.
The potting compound is the resin that fills the housing of a series isolation transformer around the core and windings and sets solid. It does four jobs: it insulates by leaving no air gaps between conductors, it seals the windings against moisture and dirt, it holds the core and windings firm against vibration and temperature swings, and it carries heat from the windings to the case.
A good fill has no voids and stays bonded to the housing and leads. Air pockets can become hot spots and weak points, and a crack or lifted seal, often at a lead entry, lets moisture reach the windings, which shows up as falling insulation resistance and in time an earth fault. The fill is sealed inside the unit and cannot be repaired or topped up in the field, so a transformer with suspected potting or housing damage is tested and replaced. Isolate and prove the circuit dead under site procedures before touching any lead.
Frequently Asked Questions
Q1What is potting compound in an AGL isolation transformer?
A resin, commonly an epoxy or polyurethane, that fills the housing around the core and windings and sets solid. It leaves no air gaps, seals the windings against moisture, holds the parts firm and carries heat to the case. The exact material varies by manufacturer.
Q2Why is the transformer potted instead of left as an air-filled case?
Isolation transformers sit in pits, base cans or the ground, where they can be damp or even flooded, and they take vibration and temperature swings. A solid fill keeps moisture and dirt out, stops the windings moving, removes air gaps in the insulation and helps heat leave the windings.
Q3What goes wrong with potting?
Air voids or shrinkage gaps left from the fill, cracks, a fill that lifts away from the housing or leads, and heat damage from overload. A damaged housing or lead entry can also let moisture past the fill. Each weakens the insulation system and can lead to an earth fault.
Q4How would you know the potting has failed?
Usually indirectly: a cracked case or damaged lead entry found on inspection, a transformer that runs hot, or insulation-resistance readings that fall from test to test. The fill itself cannot be seen, since it is sealed inside the housing.
Q5Can potting be repaired or topped up in the field?
No. Potting is done under factory conditions and the unit is sealed. A transformer with suspected potting or housing damage is tested and replaced under site procedures. Isolate and prove the circuit dead before touching any lead.
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