Atsuo Takahashi

Reignition Voltage of Arcs on Double-Break contacts

Experimental studies were made of the arc reignition voltage on double-break contacts for fine silver (Ag 1000), AgNi 90/10, AgCdO 90/10, and AgSnO 2 88/12. The experiments were carried out in an ac circuit with air-core reactors (power factor 0.4). The frequency of the transient recovery voltage oscillation ranged from 10 (or 5) to about 70 kHz. The reignition voltage after an arc having a duration of close to onehalf cycle (-~10 ms) was measured 15-25 times in a fixed-circuit condition. In the high-frequency range of the voltage oscillation, the value of the average reignition voltage does not depend upon the frequency, and at 103 A this constant value (immediate recovery voltage) is smaller than that at 57 A. The ratio of the reignition voltage ( \mu Rd ) of the double break to that ( \mu Rs ) of the single break at the same reignition time (time after current zero) has the value of 1.7-1.8 for AgNi 90/10, AgCdO 90/10, and AgSnO 2 88/12. Onlyfor Ag is the ratio ( \mu Rd / \mu Rs ) found, interestingly, to be almost two. This fact is considered to be due to the glow discharge which precedes the arc establishment.

Transition boundary from metallic to gaseous phase in Pd break arc

Metallic-phase duration and transition ratio to gaseous phase were investigated for Pd contacts under the variation of closed contact current I/sub o/, load inductance L (0.2-2.3 mH), and source voltage E (6-48 V). The results obtained were compared with results for Ag and W contacts, reported for the same circuit conditions. Experiments have revealed that the boundary closed contact current I/sub ob/, at which the transition ratio is 50%, decreases with increase of L and E in the same manner as for Ag and W contacts. The metallic phase duration t/sub m/ was found to increase rapidly with I/sub o/ in the vicinity of I/sub ob/, in a similar manner to Ag contacts. For Pd contacts, the degree of slope change of the t/sub m/-I/sub o/ curve, at the point where the transition ratio attains about 100%, tends to be larger than that for W and smaller than that for Ag.<<ETX>>

Arc Termination Current on Breaking Contacts

Studies were made of the arc termination current on the breaking contacts with an inductive load. Test contacts were 2 mm \phi cross rods of tungsten, gold, palladium, silver and platinum. The arc termination current was found to be closely related to an arc duration. The relation between the arc termination current and the arc duration was independent of the closed contact current (1-5A), the contact opening velocity (15-95 cm/s) and the slope of the arc current. When the arc duration was relatively short, the arc termination current increased linearly with the logarithm of the arc duration, and saturated at the specific value for each contact material. The saturation value was found to be nearly equal to the minimum arc current published by Holm. The arc termination current characteristics of silver-tungsten dissymmetric contacts were similar to those of the symmetric contacts of the cathode material.

Spectroscopic measurement of Ag break arc

The authors have studied the maintaining mechanism of the contact arc discharge. For this object, a spectroscopic measurement system was composed using two monochromators and a bifurcated image fiber. Arc voltage waveform, arc current waveform, Ag II (243.78 nm) spectrum intensity, and Ag I (328.07 nm) spectrum intensity are measured for an Ag break arc, under the conditions where source voltage E=6/spl sim/48 V, load inductance L=0-2.3 mH, and closed contact current I/sub 0/=0.6/spl sim/6A. The spectrum intensity of Ag II (ion line) becomes a maximum value near the gaseous phase transition point, and it gradually decreases in the gaseous phase. The spectrum intensity of Ag I (excited atom line) increases until the gaseous phase transition point. After the gaseous phase transition, Ag I becomes a constant value (40/spl sim/50) which does not depend on the circuit condition. Furthermore, in the boundary closed current at which the transition ratio is 50%, it is clarified that the average spectrum intensity of Ag II has a constant value without depending on the circuit condition. Therefore, the transition to gaseous phase is made when the mean number of Ag ions exceeds a certain value.