18 research outputs found
The energetics of gas flow and contact erosion during short circuit arcing
No full textThe processes governing the movement of short circuit arcs in circuit breakers are complex and variable and the detailed understanding of these processes is incomplete. This paper presents a new approach to our understanding of the short circuit arcing process by concentrating on the bulk thermal behavior and energetics of the arcing and gas flow during contact opening. It is shown how considerations of the arc power and the heating and vaporization of the contact material can be used to examine the flow of gas through the arc chamber and the erosion of contact material. Experimental data from a flexible test apparatus and arc imaging system along with measurements of pressure and arc current and voltage are used as the basis of the analysis. It is demonstrated how the air initially present in the arc chamber will be rapidly expelled from the arc chamber to leave an arc burning in the products of contact volatilization. Data on mass and volume flow rates are presented as well as estimates of the gas velocity in the contact region. These data provide information on the nature of the gas flow in the arc chamber as well as contact erosion during the arcing process. Arcing conditions of interest are short circuit faults (103-104 A) in low voltage (220-380 VAC) circuit breakers
Arc root mobility on piezoelectrically actuated contacts in miniature circuit breakers
No full textA novel contact opening mechanism has been developed using a piezoelectric actuator to open the contacts in a low contact opening velocity circuit breaker. The arc control on the contacts is critical for successful current interruption (103 - 104 A) in low voltage (<250V) devices. Previous work has shown how arc root commutation from the contact region into the arc chamber is affected by arc chamber materials, contact materials and the gap behind the moving contact for contact velocities between 1ms-1 and 10 ms-1. This work is extended using a commercially available piezoelectric actuator to open the contacts. Contact opening speeds are assessed and the arc root mobility is characterized under this operating regime. A flexible test apparatus and solid-state high-speed arc imaging system are used to gather data on the arc root during the opening of the contacts. New experimental results are presented on the anode and cathode root velocity and arc root motion in an arc chamber with piezoelectrically actuated contact opening. These results can be used to improve the design of high current low voltage circuit breakers suitable for piezoelectric actuation
Arc root commutation from the contact region in low contact velocity circuit breakers
No full textCircuit breakers are widely used in commercial and industrial installations for automatically switching off a short circuit current. Arc motion in low voltage (240VAC) high current (103-104 A.) circuit breakers is dominated by arc root mobility. This study provides a vital step in the development of a consistent arc structure and motion in circuit breakers operating at low contact opening velocity.The experimental investigations focus on the influence of the contact material, arc chamber material, contact velocity, power supply polarity, the gap behind the moving contact and the peak short circuit current level on the arc motion. The gas flows and gas composition effects are inspected. This thesis concentrates on the arc commutation at reduced contact opening velocity down to 1 m/s from a moving contact and in particular the point at which the arc root moves off from the contact regionTo investigate the arc root motion, the Flexible Test Apparatus (FTA) is used to simulate circuit breaker operation. The Arc Imaging System (AIS) is used to record series of the arc motion. New pressure transducers and a spectrometer are used to observe the gas flow and gas composition in the contact region. This data combination provides a new insight into the arc motion. The studies have observed that the gas flow in the region of the moving contact has been shown to affect the arc root mobility. The spectral emission from the arc gases confirms the presence of electronegative species. Experimental results are presented which include the measurements of pressures in the arc chamber, arc spectrum, and arc root motion.The interrelation of gas dynamic and magnetic forces is investigated further by developing relationships between electromagnetic forces and high temperature gas dynamic flows. New semi-empirical modelling is presented in terms of electrical and thermal energy transfer between the arc and the gas flow
Arc root commutation from moving contacts in low voltage devices
No full textThis paper focus on the arc commutation from a moving contact and in particular on the anode motion of a high current arc in low voltage current limiting circuit breakers. Recent investigations have observed that the anode arc root motion is affected by arc chamber geometry. It was previously assumed that cathode root motion was the dominant process. The study uses a flexible test apparatus with a solid state high speed imaging system. The experimental results presented show the influence of arc chamber venting, current level, current polarity and contact velocity on arc motion, Particular emphasis is made on the anode motion. The physical processes occurring in the anode root are discussed and related to the observed motion. The results show that the anode root is retarded at the tip of the moving contact and that this is primarily related to the venting process in the arc chamber
Gas flow and composition effects on arc motion in current limiting circuit breakers
No full textArc motion in low voltage (240 VAC) high current (103-104 A) current limiting circuit breakers is dominated by arc root mobility. This is strongly affected by the gas flow and gas composition in the contact region, but there is little experimental data on these effects. New pressure and spectral data measurement during arc movement are presented using a flexible test apparatus and an arc imaging system. These measurements are used to investigate gas flow characteristics in the arc chamber. The chemical and physical phenomena occurring during the arc motion are discussed. The combination of optical and spectral data provides new insight into the arc motion. Also studied are the influences of arc chamber material, contact material, and contact opening speed. These data are used to improve arc control for a low contact opening velocity of 1 ms-1
The correlation of magnetic, gas dynamic and thermal effects on arc mobility in low contact velocity circuit breakers
No full textThis paper examines arc root mobility in relation to magnetic and gas dynamic forces in low contact opening velocity circuit breakers (1 m/s). Arcing conditions of interest are short circuit faults (10/sup 3/-10/sup 4/ A) in low voltage (220-380 VAC) circuit breakers. Previously published experimental results have shown how the gas flow and venting in the contact region affects the arc root mobility. In this paper the interrelation of gas dynamic and magnetic forces is investigated further by developing relationships between electromagnetic forces and high temperature gas dynamic flows. New semi-empirical modeling and experimental results are presented in terms of electrical and thermal energy transfer between the arc and the gas flow. The influences of magnetic field on the relationships between arc power, arc voltage, arc current and arc energy are discussed. The effects of heat transfer and thermal power on the gas flows in the arc chamber are explored. These effects are discussed particularly in relation to arc root motion in low contact opening velocity systems. Some features of arc root mobility, which had hitherto been anomalous, are explained. Furthermore, these are used to extend and develop models of arc root commutation. This study provides a vital step in the development of a consistent model of the arc structure and motion in miniature circuit breakers operating at low contact opening velocity
Arc motion and gas flow in current limiting circuit breakers operating with a low contact switching velocity
No full textArc motion in low voltage (240 VAC) high current (10/sup 3/-10/sup 4/A.) current limiting-circuit breakers is dominated by arc root mobility. The mobility is influenced by the gas flow and gas composition in the contact region, but there is little experimental data on these effects. New pressure and spectral data measurement during arc movement are presented using a flexible test apparatus and an arc imaging system. These measurements are used to investigate gas flow characteristics in the arc chamber. The chemical and physical phenomena occurring during the arc motion are discussed. The combination of optical and spectral data provides new insight into the arc motion. The influences of arc chamber material, contact material, and contact opening speed, are investigated to improve arc control for a low contact opening velocity
Arc root mobility on piezo-actuated contacts in miniature circuit breakers
No full textA novel contact opening mechanism has been developed using a piezo-ceramic actuator to open the contacts in a low contact opening velocity circuit breaker. The arc control on the contacts is critical for successful current interruption (103-104 A) in low voltage (<250V) devices. Previous work has shown how arc root commutation from the contact region into the arc chamber is affected by arc chamber materials, contact materials and the gap behind the moving contact for contact velocities in the range 10 ms-1 and 1 ms-1.This work is further extended by using a commercially available piezo-ceramic actuator to open the contacts. Contact opening speeds are assessed and the arc root mobility is characterised under this operating regime. A flexible test apparatus is used to vary the arc chamber geometry. A solid-state high-speed arc imaging system and pressure transducers are used to gather data on the arc mobility and the gas dynamic interactions occurring during the piezo actuated contact opening. New experimental results are presented on arc root velocity, arc root motion, arc imaging and pressure measurement in the arc chamber with the piezo actuated contact opening. Results are correlated using a semi-empirical model of the arc motion. These results can be used to improve the design of high current low voltage circuit breakers suitable for piezo-ceramic actuation
Motion studies of high current arcs using an optical fiber array based imaging system
No full textThis paper presents an integrated portable measurement system for the study of high speed and high temperature unsteady plasma flows such as those found in the vicinity of high current switching arcs. The system permits direct and non-intrusive measurement of arc light emission images with a capture rate of 1 million images per second (1MHz), and 8 bit intensity resolution. Novel software techniques are reported to measure arc trajectories. Results are presented on single high current (2kA) discharge events where the electrode and arc runner surfaces are investigated using 3D laser scanning methods; such that the position of the arc roots on the runner can be correlated to the measured trajectories. The results show evidence of the cathode arc root stepping along the arc runners, and regions of where the arc runner is eroded by a stationary arc
