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MOL-MEC
Partial discharge diagnosis device for preventive maintenance of molded transformers

MOL-MEC/Measuring Equipment of
Characterics for "MOLTRA"
This device is a portable on-site deterioration diagnosis device used to diagnose the deterioration of molded transformers installed in substation facilities by detecting the presence or absence of partial discharge.
During periodic inspections, this preventive maintenance diagnosis device for molded transformers enables the presence or absence of partial discharge to be easily diagnosed on-site by connecting the detection unit (PM tester) to the non-voltage tap changer terminal (PM terminal) on the molded transformer, which also serves as the partial discharge detection terminal.

Features
  • The device is portable so on-site diagnosis of partial discharge can be performed in a short period of time.
  • Use of the PM terminal minimizes the impact of various noises at the site enabling reliable detection of partial discharge.
  • The PM tester connects to the PM terminal by optical fiber to ensure safety during detection.
PM terminal
Configuration
Diagnosis procedure
The diagnosis is performed by a diagnostic technician with the following steps.
  • Turn off power so there is no voltage at the molded transformer.
  • Connect the PM tester to the PM terminal.
    Calibrate the electric charge of discharge.
    Turn on power so the molded transformer is in a receiving state.
  • Detect the partial discharge. (diagnosis)
    Turn off power so there is no voltage at the molded transformer.
  • Disconnect the PM tester.
  • Restore power so the molded transformer is in a receiving state again.
Features
  • The degree of deterioration of the resin in molded transformers can be easily measured using optical reflectance
    characteristics.
Introduction effects
  • The degree of deterioration can be assessed quantitatively from numerical data.
  • A ssessment of the degree of deterioration enables the creation of optimal maintenance plans.
  • A ssessment of the degree of deterioration enables the determination of the optimal replacements priority.
Diagnosis using optical reflectance characteristics
  • The life time of molded transformers depends on the thermal deterioration of the epoxy resin of insulation.
  • Thermal deterioration darkens the color and reduces the weight of the epoxy resin.
  • There is a correlation between the weight loss and dark coloring of the epoxy resin, so we diagnose the degree of deterioration by measuring the optical reflectance.
Deterioration diagnosis using optical reflectance characteristics
Molded transformers and deterioration process
Diagnosis Merits
Diagnosis conditions the diagnosis services

arget: 3kV to 30kV molded transformers manufactured by Fuji Electric.
External appearance: No discoloration due to ultraviolet, chemicals, corrosive gas, and No significant accumulation of dirt and dust or repainting.
Power shutdown: Power to the transformer needs to be shut off for measurement.

Diagnosis flow
Diagnosis cases

As of March 2013, we have performed diagnosis on 153 molded transformers.
Although day-to-day visual observations and insulation resistance measurements taken at periodic inspections were unable to find abnormalities, by using optical diagnosis of the resin we were able to find equipment for which the weight reduction had progressed up to the recommended replacements time.

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