Short circuit | EPFL Graph Search

A short circuit (sometimes abbreviated to short or s/c) is an electrical circuit that allows a current to travel along an unintended path with no or very low electrical impedance. This results in an excessive current flowing through the circuit. The opposite of a short circuit is an open circuit, which is an infinite resistance (or very high impedance) between two nodes. Definition A short circuit is an abnormal connection between two nodes of an electric circuit intended to be at different voltages. This results in an electric current limited only by the Thévenin equivalent resistance of the rest of the network which can cause circuit damage, overheating, fire or explosion. Although usually the result of a fault, there are cases where short circuits are caused intentionally, for example, for the purpose of voltage-sensing crowbar circuit protectors. In circuit analysis, a short circuit is defined as a connection between two nodes that forces them to be at the same volta

Development of a system for part quality prediction and process parameters adjustment in wire electrical discharge machining

Olcay Akten

In the past decades, wire electric discharge machining (W-EDM) has undergone a number of techno-logical developments aimed at improving its process performance. Still the current practice of W-EDM is not defect-free and results in a number of surface related defects on the machined parts. The main defects related to surface quality of parts produced by the W-EDM process include the occurrence of surface lines, surface roughness and the occurrence of recast layer on the machined surface. The experimental evidence suggests that surface defects in W-EDM occur mainly due to short-circuiting or abnormal sparks. If the W-EDM process is controlled to minimize the duration of short circuit or abnormal sparks, the occurrence of surface defects can be minimized. Furthermore, online monitoring of the spark quality can help minimize the occurrence of surface lines by first predicting the possible occurrence of surface lines in W-EDM as a function of certain critical process variables, namely, discharge gap and spark frequency, and then proactively implementing the corrective action in the form of adjustment of vital process parameters, like pulse-off time, before the sequence of abnormal sparks could develop into a visible surface line. Two systems are proposed to achieve the objectives mentioned above: an offline multiple-input multiple-output (MIMO) fuzzy-nets prediction system and a multi-objective optimization system for process parameters adjustment and an online prediction and adjustment system based on the short circuit duration. For the offline prediction system, the two part quality characteristics considered in this thesis are surface roughness and recast layer thickness. A fuzzy logic based approach called fuzzy-nets approach for the prediction of these part quality characteristics on the basis of the initial conditions is proposed. A hybrid multi-objective optimization method combining fuzzy-nets prediction technique and genetic algorithm is applied to find best setting of process parameters based on desired surface roughness and minimium recast layer thickness. The online prediction and adjustment system comprises: (i) a procedure for the online prediction of the occurrence of surface lines in W-EDM based on the short circuit duration, and (ii) a procedure for online adjustment pulse-off time (electrical process parameter) to prevent the occurrence of surface lines if and when their occurrence is predicted. Both systems required intensive experiments based on carefully designed experiment plans to collect and assess the training data for the different fuzzy rule bases. A case study from GF Machining Solutions Ltd. illustrating the different issues related to the proposed approaches is described. The experimental results validate the proposed approach for both online and offline systems.

EPFL2015

VHDL-AMS Virtual Prototyping of a Generator Circuit Breaker Ablation Monitoring System

Qianqian Ha, Yannick Maret, Juan Sebastian Rodriguez Estupinan, Alain Vachoux

Generator Circuit Breakers (GCBs) are commonly used in electrical power generation systems to protect key equipment such as transformers and generators from damage due to overload or short-circuit. However the interruption and feeding of high currents lead to the ablation of the electrical contact system of the breaker. This deterioration process needs to be monitored in order to guarantee the healthy condition of the breaker. In this paper, we propose a virtual prototype of a GCB fitted with an ablation monitoring system. This is an early model of the complete system, which is highly desired before the physical implementation, since it facilitates the study of detection methods and the exploration of system limitations. The virtual prototype is implemented in VHDL-AMS with certain low-level models described in SPICE. The virtual prototype has been validated by measurements performed on the real system. It is therefore adequate for performing design optimization and to obtain useful observations for further usage of the monitoring system.

IEEE Conference Press2015

Potential Induced Degradation Mechanism in Rear-Emitter Bifacial Silicon Heterojunction Solar Cells Encapsulated in Different Module Structures

Olatz Arriaga Arruti, Christophe Ballif, Luca Gnocchi, Quentin Thomas Jeangros, Alessandro Francesco Aldo Virtuani

Recent studies showed that silicon heterojunction (SHJ) solar cells can be prone to potential induced degradation (PID) when encapsulated with ethylene vinyl acetate (EVA). Here, to gain understanding in the role of EVA, we perform PID test in humid conditions (85 degrees C/85% RH) under a negative bias (-1000V). We study the effect of moisture ingress and cover materials by using different module structures. We focus on studying both sides of the cell for modules packaged in a glass/glass scheme after 500 hours of test (corresponding to similar to 5 times the duration foreseen by the corresponding IEC standard). The front-side degradation is dominated by a reduction in short-circuit current (J(SC)), whereas the rear-side degradation is driven by a loss in fill factor (FF). EQE measurements show that increased front-surface recombination is largely responsible for the observed degradation of the front-side. From TEM and EDX measurements, it seems that the degradation at the cell level is predominantly caused by diffusion of sodium into the cell, which is triggered by humidity and low encapsulant resistivity. Assuming that the Na is also accumulated at the rear-side of the cell, this would create defects at the p-n junction, leading to the loss of FF observed.

IEEE2021

Development of a system for part quality prediction and process parameters adjustment in wire electrical discharge machining

Olcay Akten

EPFL2015