Insulating Oil Testing
Insulating oil in electrical power apparatus serves two primary roles, as an insulator and a coolant. As an insulating liquid, oil’s most important property is a high dielectric strength and as a cooling liquid, a low viscosity is paramount.
The principal nemeses of insulating oil are oxidation, contamination (particularly moisture, which tends to lower the dielectric properties of insulating oil), and excessive temperature. These enemies are managed through design, regimented installation processes and prudent operation of the oil-filled power apparatus. At all stages of a power asset’s life, testing must be conducted to evaluate the condition of the insulating oil. In fact, for some assets, it can be argued that the oil is tested more frequently than any other component.
Tests that are concerned with the immediate condition and acceptability of the insulating oil include dielectric breakdown tests, moisture measurement by the Karl Fischer (KF) method, and dielectric dissipation factor. Megger provides laboratory grade oil test equipment, backed by experience reaching back to the early 20th century, to test these fundamental characteristics of insulating oil.
The Oil Tan Delta (OTD) is a laboratory instrument, which measures the Tan Delta, Resistivity and Relative Permittivity of insulating liquids. These tests give a wider picture of the overall quality of the insulating oil, and will indicate if there is any contamination. Megger has developed features of the OTD to ensure that productivity levels within laboratories are maximised.
The microprocessor controlled inductive heater means that there is uniformity of temperature throughout the cell, in compliance with IEC 60247, and for cooling a fan effectively speeds up the cell cooling time. The instrument has a temperature measuring range of 10 to 110 ºC, with an accuracy of ± 1 ºC. It can be set to preheat before testing takes place. The automated oil drain facility negates the need to move the oil vessel.
Portable Oil Test sets - Weighing in at only 16 kg the OTS60PB is the lightest, most portable oil test set available. Meanwhile the OTS80PB is the most flexible test set because it offers more power in a test set which weighs less than 21 kg. Featuring the same easy-empty vessel and quick-drain chamber design as the laboratory models, the large, bright, colour screens are easy to read in sun light. Features like the electrode precision lock and ultra fast HV switch off time are particularly important for instruments that may not be used in the ideal environment. The OTSPBs can be configured to match the users needs. 60 kV manual oil test set.
Designed for Laboratory use, these instruments measure the dielectric strength of mineral, ester and silicon insulating oils. With re-thought out ergonomics, the vessels and chambers are particularly easy to drain and clean out. The screw adjusted electrodes have a unique mechanism to lock precisely the electrode gap. The detection circuit offers direct measurement of both voltage and current and the system has an ultra fast HV switch off time of less than 10 μs to reduce oil deterioration. Each instrument has a large, bright, coloured screen to make user interface intuitive. To assist with the labelling of results files and recording of comments there is a phone-like 12 key alphanumeric pad. The products can be configured to meet the testing requirements of the laboratory.
Over 20 years’ experience has led to the development of the Megger KF875 and KF-LAB MkII Coulometric Karl Fischer Test Sets designed to determine moisture in oil, to provide highly accurate results on-site. The KF875 and KF-LAB MkII are highly portable instruments, complete with integral printer and carrying case, are easy to use and provide highly accurate results.
Optimized for testing insulating oils with a specific gravity of 0.875, the Megger KF875 simply requires the operator to press one button and inject a 1ml sample into the test cell. The simple ‘one touch’ operation makes the KF875 so easy to use that it requires no specialist knowledge or training to use it effectively. Results are presented on the instrument display and on the integral printer in both micrograms of water and in milligrams per kilogram (parts per million, ppm).
The KF-LAB MkII allows the titration of samples with a range of specific gravities from 0.60 to 1.40 and also permits the use of different sample sizes. The KF-LAB MkII also has a default setting optimized for analyzing insulating oils with an SG of 0.875. This means it can be used to measure water content in a variety of different materials but is also easy to set up for transformer insulating oils.