Page 60 - Energize June 2022
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TECHNICAL



        nitrogen system, a nitrogen tank or generator, or a conservator
        tank equipped with a rubber diaphragm (bladder). Using inhibited
        oils under these circumstances is not required, although it might
        add additional protection against oil oxidation if the preservation
        system were to fail.   2

        Passivator content: Passivators, also known as metal deactivators,
        react with reactive metal surfaces and dissolved metals such
        as copper and silver and reduce their rate of reaction with
        compounds in the oil. This includes oxidation reactions with
        organic compounds and reactions with corrosive sulphur.
        Passivators are composed of two basic types, sulphur-based   a direct correlation between interfacial tension and neutralisation
        and nitrogen-based. The first suggested use of passivators in   number. Therefore, the interfacial tension becomes a quality
        transformer oil, of which the author is aware, was in 1967 by J.J.   criterion: the oil must be changed below a predefined limit.
                                            3
        Melchiore and I.W. Mills of the Sun Oil Company.  As the oil ages,   •  If results are good, continue the regular sampling interval.
        the passivator might deplete more rapidly; this depletion might   •  If results are fair, decrease the sampling interval.
        accelerate when the oil is uninhibited.                •  If results are poor, check the oil for sediment and/or sludge.
        •  With good results, regular sample intervals can be maintained.
        •  With fair results, maintain regular monitoring.     Corrosive sulphur: This is not a routine test. Oil is either
        •  When poor, it is advised to remove the oil or remove the   corrosive or non-corrosive. The presence of corrosive sulphur
          source of corrosivity from the oil via special oil treatment.   in transformer oil and its effect on the transformer system can
                                                               be significant. The extent of the corrosion damage caused by
                                                               the sulphur can be so severe that it might cause failure of the
                                                               equipment if not checked. The addition of a copper passivator can
                                                               reduce the impact of this compound on the transformer system.
                                                                  In a study by Doble, it was found that rubber products used
                                                               in transformers might add to the corrosivity of the oil. Nitrile
                                                               rubber gaskets and hoses not approved for oil filtration might
                                                               contaminate the oil with corrosive sulphur.
        Sediment and sludge: This is not a routine test. It is advised that   CIGRE Brochure no 378, 2009, stipulates the necessity of
        this test is performed when the oil results indicate a high acid   corrective actions based on this institute’s risk assessment
        value, and the dissipation factor is near the unacceptable limit.   study.   4
        The results need to be less than 0,02% by mass to be negligible.
        If the results return a value of more than 0,02% by mass, it
        is suggested that it be reclaimed; otherwise, an oil change is
        recommended.























        Interfacial tension: This is not a routine test. The interfacial   Particle counting and sizing Table 3, particles Table B.1:
        tension between transformer oil and water reduces during the   Typical contamination levels (particles) encountered in power
        ageing process. What this means in practical terms is there is   transformer insulating oil as measured using IEC 60970  Particles:
                                                                                                        5
        more polar compound present in the oil, decreasing the ability of   Typical contamination levels (particles) encountered in power
        an oil to serve as an insulator in the transformer system. There is   transformer insulating oil as measured using IEC 60970



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