Frequency Arc Research Articles

The Ignition of Commercial Frequency Arc by High Frequency Voltage

The Ignition of Commercial Frequency Arc by High Frequency Voltage

A high frequency arc welding generator

A high frequency arc welding generator

Abridgment of arcing grounds and effect of neutral grounding impedance

This paper was written to review and extend the theory of overvoltages due to the arcing grounds because of the increasing tendency to use impedances between the neutral point and the ground, thereby losing the advantage of the solidly grounded neutral. The “third-class conductor” theory of Steinmetz is touched upon very briefly and is considered as not applying to transmission line conditions. The theory when the phenomenon is controlled by normal frequency arc extinction, as presented by Peters and Slepian, is reviewed, and the maximum voltage for this analysis is found to be <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$3{1\over 2}$</tex> E, where E is the normal line to neutral voltage. The theory when the phenomenon is controlled by oscillatory frequency arc extinction as originated by Doctor Petersen is given in detail but in a modified and extended form. The maximum voltage for a single-phase circuit when no damping is considered is found to be 6 E. The analysis for the three-phase circuit is newly developed for the case in which there is an impedance between the neutral and ground and the maximum voltage is found to be 7.5 E when the effect of the damping factors and capacitance between lines is neglected. The method of determining the various reductions or damping factors is outlined. The effect of a neutral grounding resistor is discussed and it is pointed out that a surprisingly high value of resistance can be used without incurring the possibility of dangerous overvoltages. It is shown that the use of reactance is more liable to result in overvoltages than resistance but that relatively large values of reactance can be used in conjunction with resistance. The Petersen Coil is usually considered as causing the arc to go out by giving a balance of lagging and leading currents in the arc. It is brought out in this paper that there will be no voltages built up when the Petersen Coil is used, whether or not the arc goes out. The relation of the overvoltages on a non-grounded and an effectively grounded system is outlined, and a criterion for determining whether or not a system is effectively grounded is proposed.

Arcing Grounds and Effect of Neutral Grounding Impedance

This paper was written to review and extend the theory of overvoltages due to arcing grounds because of the increasing tendency to use impedances between the neutral point and the ground, thereby losing the advantage of the solidly grounded neutral. The ``third class conductor'' theory of Steinmetz is touched upon very briefly and is considered as not applying to transmission line conditions. The theory when the phenomenon is controlled by normal frequency arc extinction, as presented by Peters and Slepian, is reviewed and the maximum voltage for this analysis is found to be 3 ? E, where E is the normal line to neutral voltage. The theory when the phenomenon is controlled by oscillatory frequency arc extinction as originated by Dr. Petersen is given in detail but in a modified and extended form. The maximum voltage for a single-phase circuit when no damping is considered is found to be 6 E. The analysis for the three-phase circuit is newly developed for the case in which there is an impedance between the neutral and ground and the maximum voltage is found to be 7 ? E when the effect of the damping factors and capacitance between lines is neglected. The method of determining the various reductions or damping factors is outlined. The effect of a neutral grounding resistor is discussed and it is pointed out that a suprisingly high value of resistance can be used without incurring the possibility of dangerous overvoltages.

The Theory of Linear-Sinoidal Oscillations

Constant frequency arc discharges; theory assuming direct current supply and arc potential drop to remain constant.---A vacuum arc is shunted with inductance, capacitance and resistance in series which constitutes a discharge circuit. The arc is supplied with direct current through a large inductance. The arc vapor is ionized and de-ionized at a constant frequency. The variations of potential and current in the discharge circuit are termed linear-sinoidal oscillations. Mathematical expressions are derived for the following quantities in terms of the priming angle and damping angle, viz., the logarithmic decrement, ratio of natural frequency to discharge frequency, impedance factor and ratio of the effective discharge circuit current to the direct current. These quantities are expressed in terms of transcendental functions of the angles, hence relations between them are determined by means of a chart and a table. Expressions for potentials at the instants of priming (critical ionization) and unpriming are given. The relation between the values of the direct current and effective currents through the arc and in the discharge circuit is established. The actual fluctuation of the direct current supply is approximately determined. The counter E.M.F. of an oscillator having a coupled secondary oscillatory circuit varies in a manner similar to the counter E.M.F. of a motor.De-ionization of arc vapor; experimental determination of the rate.---An arc is extinguished by means of initiating a series of linear-sinoidal oscillations of decreasing frequency. The values of the priming angle, ratio of frequencies, discharge frequency, unprimed interval, re-ignition potential and other quantities are approximately determined for the initial oscillations. An expression for the numerical value of the rate of de-ionization is given.Stability of an arc oscillator.---The values of series resistance to produce stability depends upon discharge circuit resistance, rate of de-ionization and rate of change of the rate of de-ionization. Auxiliary means to produce a constant discharge frequency are required to stabilize an efficient arc oscillator for radio signalling.