DDP (diamond dotted paper) is an insulating material with diamond-shaped glue dots distributed on the surface of the substrate. Its unique structure can build a stable oil channel in the oil-immersed transformer, which not only ensures the insulation performance but also improves the heat dissipation efficiency. It is a key insulating component to ensure the safe operation of the transformer.
When using DDP in oil-immersed transformers, operators must strictly follow the process specifications to ensure the insulation performance and long-term reliability of the transformer. The following are the key steps and precautions for the correct use of this material:
Technicians select DDP paper with corresponding thickness and diamond density according to the voltage level of the transformer design to ensure that its dielectric strength and oil resistance meet the IEC 60641 or GB/T 5591.3 standards.
Quality inspectors carefully check the surface of the glue paper to ensure that the diamond dots are evenly distributed, without damage, impurities or glue dots falling off, and verify its moisture content.
Drying treatment: If the humidity of the paper roll is high, the operator needs to put it in an oven at 80±5℃ for 4~6 hours to avoid water migration in the insulating oil.
Cleaning the surface: The operator uses a lint-free cloth to clean the oil and metal particles on the surface of the winding wire or the insulating part to ensure that the glue point can fit tightly with the substrate.
Cutting size: The operator cuts according to the shape of the insulation area, leaving a margin of 5~10mm to prevent warping after shrinkage. The rhombus surface is usually facing the conductor side to optimize the oil gap distribution.
Directional laminating: The operator lays the DDP along the axial or radial direction of the winding, and rolls it from the center to the edge with a soft roller to remove bubbles. After the glue point melts, a uniform oil channel will be formed.
During the vacuum drying stage, the equipment control system gradually raises the temperature to 105~110℃ and keeps it warm for 24~48 hours to fully cure the glue point (refer to the adhesive TDS data).
The pressing equipment needs to apply appropriate pressure during the pressing stage to ensure that the insulation layer is dense and the rhombus structure is not squeezed.
Inspection before oil immersion: The inspector confirms that there is no loss of glue points or displacement of paper layers after curing, and oil-resistant epoxy glue can be applied to local locations.
Vacuum oil filling: The oil immersion system is first evacuated to ≤0.1mbar, and then transformer oil is injected to ensure that the oil can completely penetrate the oil channel formed by the diamond grid.
Environmental control: Workshop managers need to ensure that the humidity in the operating room is ≤60% and the temperature is maintained at 20~30℃ to prevent the material from absorbing moisture.
Glue point protection: Operators should avoid touching the glue surface with bare hands to prevent the glue surface from being contaminated by grease.
Compatibility test: Testers need to conduct compatibility tests on new batches of DDP with transformer oil.
No completely cured glue points: Operators can extend the drying time or increase the temperature appropriately (but the temperature does not exceed 120℃).
Excessive partial discharge: Maintenance personnel check whether the diamond grid oil channel is blocked, and re-roll or replace the glue paper if necessary.
Through the above steps, DDP can effectively improve the heat dissipation efficiency and partial discharge performance of oil-immersed transformers and extend the service life of transformers. In actual application, the technical team should make corresponding adjustments based on the manufacturer’s technical manual and on-site process verification.
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