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Electric Predictive and Preventive Maintenance


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Life of transformer

Residual Life Assessment

According to IS 10028 Part III Transformer more than 5 years old should be assessed for residual life and steps should be taken for life extension.


Dissolved Gas Analysis

Insulating materials within transformers and electrical equipment break down to liberate gases within the unit. The distribution of these gases can be related to the type of electrical fault, and the rate of gas generation can indicate the severity of the fault. The identity of the gases being generated by a particular unit can be very useful information in any preventative maintenance program.


Furan Analysis (Remaining Life of Transformer)

The decomposition of paper is caused by the processes of hydrolysis, pyrolysis and oxidation. The degree of polymerization (DP-value) of paper was defined by IEC 60450 and it counts the number of polymerized glucose rings. During the paper decomposition, the DP-value is reduced and the tensile strength decreases. New cellulose has a DP-value of 1000-1100, aged cellulose on the other hand has a value of only 150-200, which means the end of the transformer’s lifespan.

As it is not possible to take paper samples during running operation, the condition of the solid insulation is estimated based on the cellulose decomposition products (2- Furfural). For this purpose a regular trend analysis is necessary.


Type test of Transformer as follows:

  1. Transformer winding resistance measurement
  2. Transformer ratio test.
  3. Transformer vector group test.
  4. Measurement of impedance voltage/short circuit impedance (principal tap) and load loss (Short circuit test).
  5. Measurement of no load loss and current (Open circuit test).
  6. Measurement of insulation resistance.
  7. Dielectric tests of transformer.
  8. Temperature rise test of transformer.
  9. Tests on on-load tap-changer.
  10. Vacuum tests on tank and radiator.



Life Extension Program

Lifting of coil with sludge removal from coil and tank

Sludge forms from the degradation of the oil and paper insulation due to stressors such as oxygen and temperature and catalysts such as copper. Excessive sludge deposition reduces life of transformer and poses various safety hazards. The presence of solid particles reduces electric strength of the oil and in addition deposit may hinder heat transfer, thus promoting further deterioration of insulation. The process of lifting the coil is for sludge removal from coil and tank which is not possible with Transformer oil filtration and dehydration


Use of Ester Based transformer oil to increase the life of transformers.