Changes of Molded Transformers

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Recommendation of Upgrade


Easily diagnose the degree of deterioration of the resin in molded transformers

Optical deterioration diagnosis service for molded transformers MOLMOS

Moltra Multi-optical Diagnostic System

Deterioration diagnosis by MOLMOS

  • MOLMOS diagnoses the degree of deterioration (mass reduction rate) by measuring the optical reflectance in the dark surface color of the epoxy resin.

Introduction effects

  • Evaluation of the remaining service life for optimal upgrade planning.

  • Evaluation of the degree of deterioration for optimal maintenance planning.

  • Evaluation of the quantitative degree of deterioration degree based on numerical data.

Resin deterioration process and insulation breakdown

The service life of a molded transformer is greatly affected by the deterioration of its insulating epoxy resin. Epoxy resins become brittle and easily break down due to darkening and a decrease in mass caused by thermal deterioration.

Resin deterioration diagnosis method

Diagnosis examples

Diagnostic conditions

Equipment type:

Fuji Electric extra-high or high voltage molded transformers.


No significant discoloration, dirt, or repainting.


Capability to power down the transformer during measurement.

Diagnosis flow

Diagnosis cases

As of the end of March 2023, we have performed diagnosis on 1,111 molded transformers.
Although day-to-day visual observations and insulation resistance measurements taken at periodic inspections were unable to find abnormalities, we will propose economical maintenance and upgrade plans based on quantitative diagnostic indicators such as the degree of deterioration and remaining service life by using optical diagnosis of deterioration.

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