Pulsed Electroacoustic Measurement System Research Articles

Effects of electric field and temperature on space charge characteristics in double-layered polytetrafluoroethylene films

As the core component of composite insulation for dry-type high-voltage equipment, polytetrafluoroethylene (PTFE) films are subjected to high temperatures and complex electric fields. Therefore, this study explores the effects of electric field and temperature on the space charge characteristics of double-layered PTFE films based on the measurement of space charge distribution in double-layered PTFE films under different DC voltages and temperatures using the pulsed electro-acoustic measurement system. Results show that more charges accumulated in the PTFE sample subjected to a positive electric field during polarization and the space charges dissipated more rapidly during depolarization compared with those subjected to a negative electric field. The existence of a PTFE/PTFE interface increased the density of trap and deepened the trap. The positive charges that accumulated at the PTFE/PTFE interface during polarization gradually held a dominant position with the increase of temperature. Finally, the formation of charge in the PTFE/PTFE interface mainly depended on two factors. When the applied DC voltage was not large, the charge formation was mainly dominated by the Maxwell-Wagner polarization effect. When the voltage increased to a certain threshold, the charge formation was mainly caused by the charge injection and migration characteristics.

エナメル線の被覆用絶縁材料中に蓄積する空間電荷の分布測定

Space charge distribution in a thin insulating layer of an enameled wire for motor windings was carried out using an improved PEA (pulsed electro-acoustic) measurement system under a dc and a square shape voltage. When a high voltage is applied to the windings of motor, a PD (partial discharge) sometimes occurs. Since the PD gives a physical damage to the insulating layer, many researchers have investigated the mechanism of PD generation. From their results, some researchers have pointed out the effect of space charge accumulation. Therefore, measurements of the space charge distribution in the insulating layer of the winding are required. The space charge accumulation in the insulating material is usually carried out using the PEA method. In this method, we observed the space charge distribution in film shape samples. However, the properties of specially-made film samples are different from those of the insulating layer with the actual configuration of the winding wire, and it is difficult to evaluate the actual influence of the space charge to the motor windings. In this research, we have improved the PEA system which is enable to measure the space charge distribution in the actual insulating layer of the winding wire.

Portable space charge measurement system using the pulsed electrostatic method

The pulsed electroacoustic (PEA) method is used to measure space charge distributions in insulating materials. A high-resolution PEA measurement system and signal procedure has been discussed in previous papers. Since the signal procedure is necessary for high-resolution measurement, the system must include a computer. In this paper, a new PEA system without signal processing is introduced. In order to eliminate the inevitable signal distortion of the conventional PEA method, the new system employs a new voltage waveform generator, one that is different from the very narrow pulse generator used in conventional PEA systems. Using the new waveform, designed based on the impulse response of the measurement system; the output signal can show the space charge distribution directly, without the need to conduct deconvolution. Thus, space charge distributions can be measured on site, such as in a factory, with a portable oscilloscope. The spatial resolution of the space charge measurement of the system is 10 /spl mu/m, which is the same as that of conventional PEA systems. Such a portable PEA system can contribute to various industrial applications.

Three-dimensional PEA charge measurement system

The pulsed electroacoustic (PEA) method already has been used widely to measure the space charge distribution in the pulsed electric field direction of sheet specimens. We have developed a new PEA measurement system which can observe the space charge distribution in three dimensions. Since the PEA system is not damaged if the specimen breaks down, the new PEA system can measure the space charge distribution of dielectric materials safely and nondestructively within a short time.

High-resolution PEA charge distribution measurement system

The pulsed electroacoustic (PEA) method is widely known to be an excellent method for measuring the space charge distribution that accumulates in thick dielectric materials (1 to 5 mm). We have refined the PEA measurement system for use on thin dielectric materials. With FFT deconvolution to compensate for the frequency characteristics of the piezoelectric sensor, the resolution in the depth direction is improved to /spl sim/3 /spl mu/m. This improved system is thus expected to be useful for the quantitative and nondestructive measurement of the space charge distribution in dielectric films.