Loss tangent meter in dielectric oil TAND220A

TAND220A Dielectric Oil Delta Tangent Meter

The measuring instrument type TAND220A complies with the international standard IEC 61620.

The instrument is based on the so-called "low-amplitude, low-frequency alternating current square wave method" and allows accurate measurements of conductivity and relative permittivity. Conductivity measurement in the range of 0.01 pS/m to 20,000 pS/m allows the use of this instrument for quality control of high resistivity liquids even at room temperature.

The TAND220A works with a low test voltage and also with a low test current so that it does not represent a danger for the operators.

Measurement method

The liquid in the test vessel is excited with a low amplitude (30 V), low frequency (0.5 Hz) and square alternating wave without a continuous component (see figure 1).

By measuring the current flowing through the liquid, the capacity C and conductance G can be determined and the values of relative permittivity εr and conductivity σ are provided according to the following equations

εr = C/Co

σ = εo.G/Co

The dissipation factor derived tanδ for a given frequency f can be determined by the following equation:

tanδ = G/C-2

For the determination of conductivity or tanδ, the alternating square wave method is far more sensitive than the bridge method. It allows the determination of conductivity down to values as low as 0.01 pS/m and values from tanδ as low as 10-6 (at 50 Hz). This high sensitivity allows conductivity and tanδ measurements at low temperatures and therefore the characterization of liquids at room temperature can be performed safely.

Test vessel

The application of the square-shaped excitation voltage with a low amplitude of only ±30 V allows the development of a test vessel with a simple, easy to use and clean design. The test vessel of the LCM-8716 consists of only two parts, a container and an active part. Two coaxial electrodes (stainless steel) are installed in one vessel (also stainless steel). This beaker also holds two BNC connectors attached to the two electrodes. The electrodes have a clean and polished surface. The vessel and the active part can be cleaned according to procedures described in appendix A. It is not possible or necessary to disassemble the active part for cleaning.

The required amount of liquid for the test is 210 ml. To reach this amount fill up to 23 mm from the end of the vessel with liquid.

The temperature of the liquid can be determined by inserting an electronic thermometer into the vessel through the hole in the lid.

Application

A typical application of TAND220A is the quality control of mineral oil used as a dielectric fluid in high-voltage switchgear such as power or measurement transformers, capacitors, terminals, etc.

Several studies have shown that the conductivity of the oil is influenced by impurities and ionic components, which were introduced into the oil or were produced in the oil. Therefore the conductivity of the oil characterizes well the quality of the oil. On the other hand it has been proven that moisture dissolved in oil does not significantly influence the conductivity. The following conductivity values at room temperature are typical depending on use:

• New oil (laboratory quality) ≤ 0.05 pS/m
• New oil (industrial quality) 0.05...0.1 pS/m
• Oil with little use in good condition 0.1...1.0 pS/m
• Oil with average use in acceptable condition 1.0...5.0 pS/m
• Heavily used oil in bad conditions > 5.0 pS/m

Specifications

Optional equipment