Yoitsu Sekiguchi

Methods of discriminating partial discharge and noise for power cable lines

This paper describes a new multiple means of discriminating partial discharge (PD) and noise for power cable lines, which is applied in some newly developed PD auto-measuring systems, not only for the PD measurement in laboratory, but also for the after-laying testing of power cable line on-site. Discrimination of PD and noise can be divided into two kinds of PD judgment. First, the judgment is executed automatically based on multiple logic gates: f-gate for frequency, n-gate for pulse count rate, q-gate for pulse magnitude, /spl phi/-gate for PD phase position, t-gate for continuous time, set logically in serial or in parallel. Second, the signals can be recognized by their pattern distributions: neural network recognition is based on the /spl phi/-q-n pattern; multiple frequency recognition is based on f-q-t pattern; and statistical source location pattern is based on x-q-t pattern. Satisfactory discrimination of high accuracy has been obtained through applying the measuring systems using the method in several PD measurements on-site.

Deterioration diagnosis of epoxy resin evaluated by current integration meter

In our life space, several kinds of electrical equipments are applied and they sustained our daily lives. As kinds of insulation materials are used in the equipments, it is important to collect information of deterioration in the materials for their maintenance. In this study, to understand the 1st step of the deterioration, current distribution of the plaque sample made of epoxy resin was investigated under nonuniform electric field by using direct current integrated method. The phenomenon in which current centered on the electrical tree according to the growth of the tree was captured by the method.

A study on electric charge behaviors in polymeric materials using “direct current integrated charge method”

The space charge accumulation in polymeric materials is one of the important behaviors of pre-ageing phenomena in electrical insulations. The Pulsed electro-acoustic (PEA) method is an appropriate method to understand the space charge behavior, but some kind of charges such as charges with high speed are hardly detected by the method. To understand the whole information of charges, that is Q(t) behaviors, we have been trying the direct current integrated charge (DCIC-Q(t)) method, which is using a measuring capacitor directly connected to a sample, and measuring from the starting point of applying voltage to the end point of grounding. The basic technologies of the method and some investigation results of generally used polymers, low- and high-density polyethylene (LDPE and HDPE), and polyethylene terephthalate (PET) are described in this article. Even concluded in same category of polyethylene, LDPE and HDPE show a different behavior, and PET which contains aromatic groups in the molecular chain shows excellent ability to control charges.

Current distribution measurement in insulating polymer cross section by current integration meter

In a space charge measurement, a threedimensional (3D) measurement technique has been developed by using the PEA method. As a result, space charge distribution and electric field distribution of insulating polymer can be measured even under non-uniform electric field. On the other hand, a current distribution measurement in an insulating polymer cross section has not been realized yet. We have assembled a two-dimensional (2D) current integration meter (CIM) by using the DCIC-Q(t) method experimentally. And a current distribution of insulating polymer under a nonuniform electric field was measured. In this paper, the experimental results of current distribution in an insulating polymer cross section are reported by using 2D-CIM. The assembled 2D-CIM consists of 10 electrodes with 2 mm diameter placed at intervals of 3 mm and a current integrating meter circuit connected to each electrode. The 2D current distribution in a 30-pm LDPE and an 18-pm PP film have been measured under a dc electric field.

Electrical charges and currents distribution analysis in plaque samples by the DCIC-Q(t) method

Both the space charges and the currents in the solid dielectrics are important properties to describe the insulating and dielectric behaviors of insulation materials. Usually, they are measured by the individual appropriate method, such as PEA method for space charges and pico-ammeter for leakage currents, however, as weak signals should be treated with, the information obtained from the measurements is that of bulk samples in general, and thus it is difficult to find the properties in a small area. We have been investigating “direct current integrated charge (DCIC-Q(t)) method” which the charges can be estimated as a time integration of the whole current in. As the current is integrated in the method, compared to the pico-ammeter, the measuring accuracy of a small current is expected to be improved. From the view points, applying DCIC-Q(t) method, we have tried to decrease the dimensions of measuring electrodes, and have arranged the electrodes in the square area, and then have made Q(t) meter with “the multiple electrodes”. Some of plaque samples of oil-impregnated papers are measured by the method, and space charges and currents distributions were evaluated.

Evaluation of insulating materials during DC voltage charging by DCIC method

We have developed a new method “direct current integrated charge (DCIC) method” for evaluating a deterioration of insulating materials in power equipments. The three important dielectric parameters, that is, conductivity, relative permittivity, and accumulated charge amounts are evaluated simultaneously by a relatively simple treatment of the method. Since the total amount of charges is found as an integration of currents, charging voltage of a measuring capacitor which capacitance is known and which is connected in series to the sample under dc voltage, the time dependence of charges Q(t) can be estimated as an integration of currents I(t) in the method. For understanding of the dielectric properties, we should investigate a current flowing behavior of the materials. Capacitance and permittivity are estimated from the momentary charging current, conductivity from the leakage current and a charge accumulation behavior from the absorption current respectively. The influences of the absorption current to charge accumulation can be estimated to calculate the ratio of the integrated charge at a certain time, which is 300 sec here, and that of initial state of charging as Q300/Q0. When the value Q300/Q0 is 1, there is no charge accumulation in the bulk of the sample. However when the ratio is increasing from 1, some charges may accumulate in the bulk. Investigating the electric stress dependence of the ratio, if the charge accumulation occurs under lower dc stress than in the previous measurement, we can assume the sample has deteriorated something else. As a first step of studies, we have tried to measure some generally used polymers, polystyrene (PS), polypropylene (PP), low-density and high-density polyethylene (LDPE and HDPE) by the method, and have compared the obtained results to the space charge distributions by PEA (pulsed electro-acoustic) method here. As a result, the good correspondence between both measurements was recognized.