Tan delta measurement of paper insulated laminates using capacitance method from 300kHz to 50MHz

Tan delta measurement of oil impregnated kraft paper extracted from paper insulated lead covered cables (PILC) has been performed using a parallel plate capacitor and a vector network analyzer (VNA) from 30 kHz to 50 MHz. The material under test (MUT) is flat and thin sample clamped between the capacitor plates and connected to the VNA to obtain its two port S parameters. The S parameter is converted into impedance to calculate the complex permittivity using Matlab program. Techniques used to overcome the air gap and stray capacitance was described. Measurement obtained using the proposed method was compared with the free space method to validate its accuracy. The percent difference is less than 5%.

I. Introduction

At present, the measure of Tan delta for oil impregnated kraft paper in PILC cables is only gross measurement by using very low frequency (VLF) and power frequency in which the MUT is usually several to tens of meters long of medium voltage (MV) power cables. These measurements have no way to determine the localized aging of the insulation material as the paper is in a form of strip with width and thickness of about 2.8 cm and tenth of a millimeter only. In order to make localized measurement in the laboratory, a new sample holder is needed for the samples. As the dimensions of the samples are very small hence the high frequency technique to determine the complex permittivity is more suited as available equipment such as the network analyzer can be employed for the measurement at a much lower cost.