摘要:

The continuous-wave breakdown of air and an air/carbon-tetrachloride mixture in uniform electric fields is examined, at frequencies between 3.5 and 30 Mc/s.The observations in air indicate that, if the pressure is reduced below atmospheric, the high-frequency breakdown voltage does not fall below the 50 c/s value until the amplitude of positive-ion oscillation has become much smaller than the gap width. This result is explained by a breakdown mechanism which depends both on positive-ion accumulation and on the variation of electron-ionization coefficient with electric field strength. Measurements by an air-stream method of a quantity related to pre-breakdown ionization in the gap appear to be consistent with the suggested breakdown mechanism. The h.f. measurements also exhibit the electron-diffusion type of breakdown, where a simple theoretical relationship must be satisfied for discharge initiation.A description is given of the effect of a small admixture of carbon tetrachloride vapour on the h.f. breakdown of air at reduced pressure. The vapour concentration was insufficient to affect 50 c/s breakdown. Where the electron-diffusion type of breakdown is normally operative, the h.f. breakdown strength increases by up to 50% when the vapour is present. The increase appears to be caused by electron attachment to vapour molecules.

DOI:10.1049/pi-c.1957.0058

出版商:IEE    

年代:1957

数据来源: IET

摘要:

The present Part continues the study of ion movements in an oxide matrix enclosed between two heated core pieces. Ions are divided into two classes—residual gas ions (probably carbon monoxide) resulting from imperfections of processing technique, and oxygen ions resulting from electrolysis of the oxide matrix. The different influences of the two classes of gas on matrix conductivity are distinguished by characteristic reactions, which are examined in both d.c. and a.c. fields. The effect of electrolytic oxygen on matrix resistance may be profound, and the action is probably a fundamental aspect of cathode operation.

DOI:10.1049/pi-c.1957.0059

出版商:IEE    

年代:1957

数据来源: IET

摘要:

The need is stated for a more accurate means of admittance or impedance measurement in order that a general improvement can be made in the accuracy of measurement of other electrical quantities at radio frequencies. A description is given of a precision twin-T dual bridge having a range of admittance measurement associated with coaxial systems between 3 Mc/s and 300 Mc/s. The inaccuracy of measurement does not exceed 0.2% on either component of a complex admittance at a frequency of 200 Mc/s. The calibration of the bridge is based on a range of coaxial susceptance standards whose parameters are calculated from length and time measurements. The dual feature of the bridge enables the true r.f. conductance of its internal standard resistor to be established in terms of these standards; the uncertainty of this determination is not greater than 0.1% for frequencies up to 250 Mc/s.The importance to be attached to the design of coaxial terminations for measuring instruments and standards at these frequencies is emphasized. A practical design is detailed for a coaxial terminal for precision admittance and impedance measuring instruments, and mention is made of a proposed universal coaxial connector system for precision radio-frequency measuring instruments of all types.

DOI:10.1049/pi-c.1957.0060

出版商:IEE    

年代:1957

数据来源: IET

摘要:

The paper describes matrix methods whereby the transient voltages and currents produced during switching operations in 3-phase power systems may be evaluated, taking into account appreciable mutual impedances existing between phases of the various items of plant. Operational voltage and impedance matrices are derived which define the transient performance of a network during the clearance of a shunt fault, the individual phases of the circuit-breaker being considered to clear sequentially. The successive constraints imposed upon the network currents are defined by transformation matrices using methods based on the work of Kron. The influence of phase mutual impedances upon the transient over-voltages produced during the isolation of single-phase arcing faults on double-circuit overhead lines is also considered. A simplified mathematical treatment of the effect of circuitbreaker arc restrikes upon the transient response of a power system is described in a concluding Section dealing with resistance switching of overhead-line charging current.

DOI:10.1049/pi-c.1957.0061

出版商:IEE    

年代:1957

数据来源: IET