Electrical conductance time constants for freely decaying arcs

Electrical conductance time constants for the early stages of free decay after current modulation have been calculated from experimental measurements on a 5 mm diameter cascade arc at atmospheric pressure. The time constants were found by measuring the electric field response of the asymptotic portion of the arc column immediately after a sudden step decrease of arc current. The electric field strength was monitored by means of the copper cooling disks of the cascade, whose probe characteristics were studied thoroughly. The initial high current was supplied by a capacitor discharge circuit which was inductively compensated to produce a square wave pulse of ∼ 2 msec duration. Time constants for initial decay were measured in both argon and nitrogen for initial currents ranging from 100 to 400 amperes. The initial free decay time constants of nitrogen were found to increase weakly from approximately 25 to 35 usec over the initial current range considered. The time constants of argon decreased from approximately 100 to 60 Μsec over the same initial current range.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45820/1/10050_2005_Article_BF01392412.pd

Thermal interruption performance of ultrahigh-pressure free-burning nitrogen arc

In this paper, an experimental investigation of the thermal interruption performance of free-burning nitrogen arcs at 1 bar, 20 bar, and 40 bar filling pressures is reported. This work contributes to the fundamental understanding of arc characteristics at very high gas filling pressures. A resonant circuit is used to generate an arc peak current of 130 A at a frequency of 190 Hz. An ignition copper wire initiates the arc between a 4 mm diameter pin electrode and a ring electrode. The arc burns freely at a fixed inter-electrode gap of 50 mm without any forced gas flow. A resistive-capacitive branch parallel to the arc controls the initial rate of rise of recovery voltage. By changing the parallel resistance, the rate of rise of recovery voltage is varied from 9.8 V/μs to 84.8 V/μs. Time to reignition and the corresponding re-ignition voltages are considered as the primary parameters to characterize the thermal interruption performance. It is observed that the re-ignition time rises with the decrease of rate of rise of recovery voltage at all pressure levels, which is expected. However, in the absence of a forced gas flow, high gas filling pressure results in a reduction of the time to re-ignition and the re-ignition voltage in contrast to atmospheric pressure nitrogen arc.acceptedVersio

Theory of the non-stationary arc column

The equations that describe the behaviour of a time-unsteady plasma column have been simplified by neglecting energy transfer by radiation and convection. Furthermore, the thermal diffusivity of the plasma was assumed to be constant and a simplified expression for the electrical conductivity was adopted. Thus the energy equation was cast into a universal form, requiring the specification of only two parameters to obtain solutions. Although some approximate closed form solutions were obtained it was necessary to solve the general a.c. arc problem on a digital computer. In view of the good agreement between the theoretically derived voltage waveforms and those found from a specially designed a.c. cascade it is concluded that the behaviour of the low current a.c. arc can be described by the solution of a complicated heat conduction problem. These solutions have the advantage over older theories that they can be directly related to measurable or calculable quantities that characterize a particular gas.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/48861/2/bjv18i1p65.pd