Megger Dielectric Oil Testing
Physical properties of insulating oils are important to monitor. Various laboratory test instruments are available to meet the different test methods.
Oil dielectric strength test set is one such test. Excerpt from ASTM D1816 Test Method:
The dielectric breakdown voltage of an insulating liquid is of importance as a measure of the liquid's ability to withstand electric stress without failure. The dielectric breakdown voltage serves to indicate the presence of contaminating agents such as water, dirt, cellulosic fibers, or conducting particles in the liquid, one or more of which may be present in significant concentrations when low breakdown voltages are obtained. However, a high dielectric breakdown voltage does not necessarily indicate the absence of all contaminants; it may merely indicate that the concentrations of contaminants that are present in the liquid between the electrodes are not large enough to deleteriously affect the average breakdown voltage of the liquid when tested by this test method.
The oil dielectric strength test instrument carried by TEquipment is suitable for field use and can be powered from a range of mains supplies. The maximum 60 kV output allows tests to be performed on oil from a wide variety of electrical installations including transformers, circuit breakers and other equipment. The operation of the test set is extremely simple and the results are displayed on a bright LED display. A selection of vessels allows the instrument to be configured for a variety of test standards.
The microprocessor controlled, semi-automatic operation allows the user to select a choice of voltage rise rates as specified in many national standards. The start button will then initiate the test. If oil breakdown occurs the instrument will remove the test voltage and display the breakdown value. Alternatively the user can pause the test voltage at any time to carry out a withstand test. The voltage will be maintained at this level for one minute or until breakdown. After one minute the voltage will automatically continue to rise until breakdown occurs or to the maximum output of the instrument.
Over the years various U.S. and International Standards have been developed for oil dielectric strength. While the instrument may perform multiple tests, test procedure and accessory glassware varies by test. With any order specify the test method(s), so proper glassware can be recommended.
List of Domestic and International Oil Dielectric Strength Test Methods
|
Test Method |
Title |
|
ASTM D877 |
Standard Test Method for Dielectric Breakdown Voltage of Insulating Liquids Using Disk Electrodes |
|
ASTM D1816 |
Standard Test Method for Dielectric Breakdown Voltage of Insulating Liquids Using VDE Electrodes |
|
IEC 156 |
Test Method for Dielectric Breakdown Voltage of Insulating Oils |
|
VDE 370 (German) |
Test Method for Dielectric Breakdown Voltage of Insulating Oils |
Excerpt from ASTM D877
This test method describes two procedures, A and B, for determining the electrical breakdown voltage of insulating liquid specimens. The breakdown test uses ac voltage in the power-frequency range from 45 to 65 Hz. This test method is used to judge if the disk electrode breakdown voltage requirements are met for insulating liquids, as delivered from the manufacturer, that have never been filtered or dried.
Excerpt from ASTM D1816
This test method covers the determination of the dielectric breakdown voltage of insulating liquids (oils of petroleum origin, silicone fluids, high fire-point mineral electrical insulating oils, synthetic ester fluids and natural ester fluids). This test method is applicable to insulating liquids commonly used in cables, transformers, oil circuit breakers, and similar apparatus as an insulating and cooling medium.