Fast and secure breaker failure detection algorithms

In a power system, every apparatus is equipped with a primary protection to detect faults and isolate the equipment by opening the circuit breaker. Breaker failure (BF) protection is employed as a means of local backup protection to detect failure of a circuit breaker. In this research work, a critical challenge facing numerical BF relays namely longer reset time of current based BF algorithms is examined by means of simulations and realistic experiments. Two new fast resetting algorithms for BF protection with reset time of less than half a power system cycle are proposed as means of enhancing BF protection. Simulations and experiments reflecting realistic conditions were used for performance evaluation of the enhanced BF algorithms. The proposed algorithms have a reset time of around half a cycle compared to 2?3 cycles in the case of a commercial numerical BF relay selected. Results indicate that the new algorithms significantly enhance the numerical BF protection.     

潜水电泵失效检测技术与方法

 按照潜水电泵80%～90%的失效或故障是由其机械密封和轴承的失效引起的实际情况,及潜水电泵其他故障的产生一般会引起电机电流增大的原理,提出通过检测机械密封和轴承是否失效、电流变化是否超标,来判断小型潜水电泵是否失效的检测方法。根据水泵机械密封主要是因端面过量磨损而产生泄漏,轴承则因润滑不良导致早期磨损而引起泵体振动的失效机理和特征,提出通过检测水泵密封腔的含水量和泵体振动加速度的大小来判别机械密封和轴承是否失效的方法和技术。研制开发了小型潜水电泵的失效检测系统,通过试验确定并验证了相应的失效判据。     

in situ failure detection in thick film multilayer systems

By means of in situ e.m.f.-measurements, leakage current measurements and impedance spectroscopy, it has been possible for the first time to detect spontaneous and forced blistering in thick film multilayers during formation at high temperatures. Also the occurrence of high temperature shorts in Ag-dielectric-Ag multilayers under DC-bias was detectable.     

Discrete failure mode detection in a woven SiC cloth reinforced glass composite

Single layer silicon carbide cloth reinforced glass composites were fabricated and subjected to three-point bending in order to develop better models of failure mechanisms. Acoustic emission (AE) monitoring was also performed during the bend tests to help isolate these mechanisms. During the basic flexural tests, discrete failure modes, which were often not visible from specimen surfaces, displayed their existence through characteristic load-deflection curve unloading regions and abrupt changes in acoustic activity. Microscopic three-point bend tests were then performed to elaborate on the results of the conventional bend tests. Observations made during the microscopic bend tests provided a one-to-one correlation with load-deflection curve anomalies and acoustic emission activity. As a result of the different mechanical, optical and acoustical techniques used, discrete failure mechanisms for the cloth reinforced ceramic matrix composite (CMC) were conclusively established.     

Multi-scale detection of failure in planar masonry thin shells using computational homogenisation

This paper presents a computational homogenisation-based technique for localisation detection in planar masonry shells. A computational homogenisation procedure is used for the in-plane and the out-of-plane behaviour of masonry walls taking the periodicity of the material into account. The quasi-brittle nature of the masonry constituents results in initial and damage-induced (evolving) anisotropy properties with localisation of damage at both the structural and fine scales. Using a closed-form damage model at the mesoscopic scale, it is shown that a structural scale localisation criterion based on the acoustic tensor adapted to shell kinematics allows to detect the structural scale localisation. This detection identifies average preferential cracking orientations consistent with the stacking mode of masonry for both in-plane and out-of-plane failure. This approach is illustrated by examples of bed joint and stair-case failure, and its subsequent integration in multi-scale nested computational schemes is discussed.     

A study on the failure detection of composite materials using an acoustic emission

Fiber reinforced composite materials have been increasingly used as structural material in airplanes, in space applications, and in robot arms because of their high specific stiffness and strength. Structural design and nondestructive test techniques have evolved as increased emphasis has been placed on the durability and damage tolerance of these materials. There are several methods used to detect damaged regions of composite materials. Acoustic emission is one of these. It is a suitable technique for detection of a wide range of micro-structural failures in composite materials.

In this paper, an AE signal analyzer was designed and fabricated with a resonance circuit to extract the specified frequency of an acoustic emission signal. From the tests that were completed, the disturbance noise levels, such as impact or mechanical vibration, of the fabricated AE signal analyzer had a very small value in comparison to those of the conventional AE signal analyzer. Also, the fabricated AE signal analyzer was proven to have generally the same crack detection capabilities as a conventional AE signal analyzer, under static and dynamic tensile tests of the composite materials.