Oil conductivity (k) is highly dependent on the field strength, temperature and contamination. Conductivity values caused by the movement of ions. K measurements can indicate the level of purity of transformer oil. Impurities electrolytic decomposition produces positive and negative ions.
Ion mobility is constant only if Ohm’s law applies. If there is a certain field strength in the dielectric field, it will last a compensation mechanism that balances the various types of ion density to achieve a balance between creation, recombination and ion leakage are the electrodes.
Due to the mobility of different ions, the mechanism also applies to the different rate so that the value of k is a function of time. Therefore, in measuring the value of k is recommended to wait a while for example 1 minute until the transient mechanism is lost.
Electrode arrangement used in measuring the value of k must be equipped with a safety ring electrode to eliminate the influence of the flow field and the boundary surface is directly grounded.
Figure II.92 Composition of electrodes for direct voltage Caption:
1. The high voltage electrode
2. Electrodes measuring
3. Electrodes safety ring
Measurement of Transformer Oil dissipation factor
Figure II.93 Compose Schering bridge for measuring capacitance and dissipation factor with Schering bridge
Cx capacity and dissipation factor tan d must be measured as a function of the voltage U test using the above circuit. Voltage generated by the high voltage transformer T is measured with a capacitor CM and SM peak voltage measuring devices. Parallelized test tube with a standard capacitor with a capacitance value C2 = 28PF.
Copies of fiber bridges in insulating oil
Each liquid insulating materials containing impurities in the form of macroscopic particles and cellulose, cotton and so forth. If the particles absorb moisture so it will work styles are moving toward areas with higher field strength and pointed in the direction of E. Payload field with opposite polarity will be induced on the edges so that the lead following the field direction.
This situation creates a conductive channel into heat due to resistive losses that vaporizes moisture contained in the particle. Translucent then occur at relatively low voltages are described as local thermal breaks on defective parts.
