Скачать или смотреть How to measure relative permittivity of insulation material ( PVC & Teflon )

In this video I show how to measure relative permittivity of insulation material of a typical wire used in electrical installation.
here i only measure real part of the relative permittivity. In general relative permittivity is a complex number which is frequency dependent. The imaginary part of relative permittivity gives information about the dielectric loss (polarization and conduction) of the material, while the real part gives information about capacitance of the sample. Measurement of real part is simple as it is shown in this video, while measurement of imaginary part requires accurate measurement equipment together with mathematical manipulation using Fourier transform to extract phase shift between voltage and current and hence calculation the imaginary part of the complex permittivity. I may do it in another video.
I have measured the relative permittivity of PVC used in electrical installation (code of the wire h07v2-k 6mm2). According to this measurement the relative permittivity of this PVC is epsilon_r=3.85.
the values typically found in literature suggest numbers of 2.7, 2.79, 4, and also 3-7, which is most likely because each reference refer to different type of PVC.
I have also measured the relative permittivity of Teflon (PTFE) and my measurement showed a value of 2.04, but from literature i see numbers like 2.1.
Some of the measurement errors are: fringing effect, air gaps introduced between the electrodes and the sample, misalignment of the two electrodes (in case of parallel plate capacitor measurement), thickness of the glue attached to the aluminum tape, and length and capacitance measurements.

IN laboratory, usually we use metallic electrodes, and the measure electrode is usually has smaller diameter than the voltage electrode. also there is always a guard ring around the measure electrode to ensure measurement is done only for the area of the measure electrode and leakage current does not disturb the accuracy of the measurement.