Insulation materials
Diamond Dotted Paper (DDP) for Transformer Windings
Diamond Dotted Paper is insulating paper with a diamond-pattern epoxy resin coating that bonds the winding layers of a transformer together during curing.
In oil-filled transformers, insulating paper sits between the layers of each winding. In a short circuit, strong forces act on the winding and can displace individual turns. Diamond Dotted Paper, DDP for short, prevents this: the paper is printed with small epoxy diamonds that melt, cross-link and firmly bond adjacent layers while the winding is dried and cured. The result is a mechanically stable winding without an extra process step.
Between the diamonds the paper stays uncoated. Through these areas the transformer oil can penetrate the winding freely and saturate it completely. This combination of spot bonding and free oil uptake makes DDP the standard layer insulation in distribution transformers.
DDP and DDP TU
Besides standard DDP we supply DDP TU. TU stands for thermally upgraded: the base paper is thermally stabilised and ages considerably more slowly at higher operating temperatures. DDP TU is used when the transformer runs at higher load or a longer service life is required.
For applications that need a film instead of paper as the carrier, for example instrument transformers, the same principle is available as Diamond Printed Film.
Delivery formats
We supply DDP as slit rolls in the width of your winding layer or as sheets. On our slitting lines we convert web material from 4 mm strip width, see cutting. We also stock pressboard, pressboard sheets and other printed insulating papers for transformer construction.
Request grade, thickness, width and quantity via our contact form.
Product view
Diamond-pattern epoxy resin coating on insulating paper
Frequently asked questions
What is Diamond Dotted Paper?
DDP is insulating paper printed with epoxy resin in a diamond pattern. When the winding is cured, the resin bonds the layers and makes the winding mechanically stable.
Why is the resin applied only in diamonds?
So that transformer oil can penetrate the winding between the diamonds. A full-surface coating would block oil uptake.
What does DDP TU mean?
TU stands for thermally upgraded. The base paper is thermally stabilised and suits higher operating temperatures and longer service life.
Where is DDP used?
As layer insulation in oil-filled transformers, above all in distribution transformers.
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Talk to us. We will find the right insulation solution.