Charles Le. G. Fortescue

The Measurement of Power in Polyphase Circuits

The object of this paper is to point out that the existing methods of measuring power when applied to unbalanced three-phase systems are not equitable for symmetrical polyphase machinery. On the other hand, unsymmetrical loads on polyphase systems are not sufficiently penalized for the trouble which they create in the system. It is first of all shown that a symmetrical generator cannot deliver power except through the balanced components of current. The unbalanced currents are capable of resolution into two balanced systems of currents, one of which is of the same phase sequence as the generator e. m. f., and the other component is of reversed or negative phase sequence. The generator cannot deliver power through the medium of this latter component of the currents, because the instantaneous product of the generated voltage and these currents in the three phases is always zero. However, the volt-ampere product per phase is of great significance, because it is a measure of the effect of the current unbalance on the system. The generator therefore delivers power only through the medium of the positive phase sequence currents. Any power that appears in the system through the negative phase sequence currents is positive phase sequence power which has been supplied by the generator and degraded through unbalanced loads and fed back to the system in the form of negative phase sequence power.

Counterpoises for Transmission Lines

Counterpoises are recommended for protecting electric power transmission lines against damage from lightning surges where other methods do not reduce the tower footing surge impedance to the desired level. In this paper a physical explanation of the theory or counterpoises is given together with an analytical solution of parallel counterpoise problems. Or the 2 types studied, the parallel counterpoise is shown to be the more effective.

Power, power factor, and reactive volt-amperes

As part of the symposium on reactive power to be conducted at the Institutes Schenectady, N. Y., meeting, May 10–12, 1933, the following article discusses the relations between power, reactive volt-amperes, and power factor for sinusoidal and non-sinusoidal electromotive forces and currents. Vector equations for these relations are derived, and polyphase power and reactive volt-amperes are defined. Non-linear circuits are discussed. The method of symmetrical components is used for the analysis.