Problems of Varistor Quality Assessment During Exploitation

Abstract

Varistors are commonly used elements which protect power supply networks against high-voltage surges or lightning. Therefore, quality and endurance of these elements is important to avoid losses when an expensive laboratory equipment would not be protected from random overvoltages. Additionally, excessive leakage currents generate serious costs due to high energy consumption. The paper presents shortly properties of varistors that comprized different ZnO grain types and can have various quality which changes continuously during exploitation (due to exposition to overheating and overvoltage pulses). Therefore, it is important to monitor varistors during their ageing (causing changes within their microstructures). A few methods of varistor property diagnosis were considered and compared with the methods currently applied in laboratory or industry applications. A new measurement (diagnostic) system that can monitor varistors during ageing and can be widely applied in power networks is presented. The proposed system fulfills requirements of the industrial customers which demand various methods for power line protection. The proposed system can be simply developed into a more advanced wireless diagnostic system of long power supply lines.

Microstructure and Defects Evaluation of Varistors by Ultrasonic Waves in Low Frequency Range

“…It is known that large grains of ZnO can be characterized by highly non-linear contacts between them. When grains are smaller, the contacts are weakly non-linear or even ohmic only [1]. Each set of varistors was prepared with different size of grains.…”

“…Varistors are commonly tested at the final stage of production by measuring their current leakage at sufficiently high voltage. It is an expensive measurement and takes a long time [1]. New methods for testing varistors are needed.…”

“…Noise measurements, quality assessment by third harmonic index, and resonant ultrasonic spectroscopy are non-destructive testing methods (NDT) auspicious for testing of varistors. These methods are performed at Gdansk University of Technology [1][2][3][4][5]. The electro-ultrasonic spectroscopy (EUS) is also the method of NDT type [6][7][8][9][10].…”

Analysis of Noise and Non-Linearity of I-V Characteristics of Positive Temperature Coefficient Chip Thermistors

“…Analyses of electron transport parameters are the most promising methods which provide non-destructive evaluation. Experiments are based on the measurements of device I-V characteristics [7], I-V characteristic nonlinearity using the non-linearity index (NLI) [8,9], electronic noise spectroscopy [10 -12], and electro-ultrasonic spectroscopy [13].…”