6,311 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 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
Evaluation of the volumetric erosion of spherical electrical contacts using the defect removal method
No full textVolumetric erosion is regarded as a significant index for studying the erosion process of electrical switching contacts. Three-dimensional (3-D) surface measurement techniques provide an approach to investigate the geometric characteristics and volumetric erosion of electrical contacts. This paper presents a concrete data-processing procedure for evaluating volumetric erosion of spherical electrical contacts from 3-D surface measurement data using the defect removal method (DRM). The DRM outlined by McBride is an algorithm for evaluating the underlying form (prior to erosion) parameters of the surfaces with localized erosion and allowing the erosion characteristics themselves to be isolated. In this paper, a number of spherical electrical contacts that had undergone various electrical operations were measured using a 3-D surface profiler, the underlying form parameters of the eroded contacts were evaluated using the DRM, and then the volumetric erosions were isolated and calculated. The analysis of the correlations between the volumetric erosion and the number of switching cycles of electrical operation that the contacts had undergone showed a more accurate and reliable volumetric erosion evaluation using the DRM than that without using the DRM
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 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
Displacement measurements at a connector contact interface employing a novel thick film sensor
No full textOne of the key failure mechanisms for wiring and connector
systems used in the automotive industry, is fretting and fretting
corrosion at the contact interface of connectors. For many
years, procedures have been carried out under laboratory controlled
conditions to investigate both thermal and vibration fretting
effects using environmental chambers and fretting tests. Both
optical and visual inspections have also been adopted to observe
the movement at the contact interface. However, these methods can
be considerably inconvenient and costly. Furthermore, their suitability
for field applications is limited. In order to study the fretting
degradation at the actual interface for in-situ measurement effectively,
a novel position sensor is designed to monitor the relative
displacement. Thick film techniques are employed to fabricate
miniaturized and cost effective resistive devices. The sensor is assembled
into a connector sample by taking the place of the male
component. When the interface experiences movement, the relative
displacement of the contact point would cause a corresponding
linear change of resistance measured across the male and female
connection. The sensors are validated by a series of experiments
and subsequently used in a field test to establish the relationships
between the fretting effects with temperature, humidity and differential
pressure, which is associated with temperature variation
The volumetric erosion of electrical contacts
No full textIn this paper a method for measuring the volume of eroded electrical contacts is presented. The main emphasis is on the measurement of volume relative to a contact support surface, allowing severely eroded contacts to be measured. A noncontact system is described, which allows contacts to be evaluated for volume change without the contact being removed from contact supports. The accuracy of the measurement method is discussed and results show how the volume measurement can be used to evaluate contact performance. Results are presented on the erosion characteristics of Ag/SnO2 contacts used in automotive relays. A new measurement methodology is presented which will allow for the evaluation of the performance of relay contacts in devices
Improving the contact resistance at low force using gold coated carbon nanotube surfaces
No full textInvestigations to determine the electrical contact performance
under repeated load cycles at low force conditions for carbonnanotube
(CNT) coated surfaces were performed. The surfaces
under investigation consisted of multi-walled CNT synthesized
on a silicon substrate and coated with a gold film. These planar
surfaces were mounted on the tip of a PZT cantilever and
contacted with a hemispherical Au plated probe. The dynamic
applied force used was 1mN. The contact resistance (Rc) of
these surfaces was investigated with the applied force and with
repeated loading cycles performed for stability testing. The
surfaces were compared with a reference Au-Au contact under
the same experimental conditions. This initial study shows the
potential for the application of gold coated CNT surfaces as an
interface in low force electrical contact applications
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
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