Alternating Current Circuits

For an AC generator, the current (/) and emf (e) will vary with time (t) sinusoidally as follows  

The effective value of current (IJ responsible for power loss is the root mean square value for a half cycle (cut = 0 to r) 

The quantity cos 6 is called the power factor. For high efficiency, it is desirable that the power factor be as large as possible. In most industrial situations, the power factor is negative (/ lags v), but it may be improved (raised) by use of a bank of capacitors in parallel with the load. 

While analysis of AC circuits is mathematically more complex than analysis of DC circuits, the basic principles are the same involving corresponding applications of Kirchoff s two laws. 

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High voliage alternating current circuit breakers 13118/1991 BS 5311/1996... 

In 1874 Heaviside established the ordinary symbolic method of analyzing alternating current circuits in common use today. It was a technique developed about fifteen years before AC came into commercial use. He emphasized the role of metallic circuits as guides, rather than conductors of AC currents. He discussed in detail causes of line distortion and suggested ways of alleviating it. 

BS 5311, High voltage alternating current circuit breaker BS 6867, Code of Practice for maintenance of electrical switchgear for voltages above 36 kV BS 158, Insulating oil for transformers and switchgear BS 5622, Insulation co-ordination... 

Power factor in an alternating current circuit is defined as the ratio of actual circuit power in watts (W) to the apparent power in voltage amperes (VA). The need for correction arises from fact that the majority of A.C. electrical loads take from the supply a lagging quadruple current (voltage amperes reactive, var) and thus operates at a lagging power factor due to the reactive (rather than capacitive) nature of their construction. 

The parameter impedance in electrical alternating-current circuits is the equivalent of resistance in direct-current circuits. If a linear and time-invariant system, L, is considered, then it can be said that ... 

In addition to the electric controls that control the grid connection and the conversion between direct and alternating current circuits, a massive... 

The dielectric constant is ordinarily measured in an alternating current circuit. The direction of the field across the capacitor changes back and forth with the frequency of the applied potential. If we imagine a single polar molecule between the plates of a capacitor, then if the frequency is not too high, this single molecule will flip back and f orth as the field oscillates, always adjusting its orientation to match the direction of the field. 

Part 2 Special requirements for ampere-meters and voltmeters. High-voltage alternating-current circuit breakers. 

BS5311 High-voltage alternating current circuit breakers. 

A number of instructive applications of differential equations concern alternating-current circuits containing resistance, inductance, capacitance, and an oscillating voltage source, as represented in Fig. 8.1. In the simplest case, in a circuit with resistance R and voltage (or emf) E, the current / is determined by Ohm s law. 

APPARENT WATTS - The product of volts times amperes, in an alternating current circuit. 

Alternate usage. Beware of not restricting, even in electrodynamics, the notions of impedance/admittance to the sole domain of alternative current circuits Too often these notions are defined in the frame of periodically varying currents or potentials when in fact they are much more general operators working with any signal shape. 

Automatic circuit recloser. A self-controlled device for automatically interrupting and reclosing an alternating-current circuit, with a predetermined sequence of opening and reclosing followed by resetting, hold closed, or lockout. 

Apparent power The product of the root-mean-square values of the voltage and current in an alternating-current circuit without a correction for the phase difference between the voltage and current. 

Two-phase A source of alternating current circuit with two sinusoidal voltages that are 90° apart. 

Phaser diagram of voltage through inductance (VL), capacitance (VC), and resistance (VK) for alternating current circuit. Source Halliday, D., R. Resnick, and J. Walker. 2008. Fundamentals of Physics, 8th ed. New York John Wiley Sons, pp. 600-900. With permission.)... 

These components have relevance only in alternating current circuits. At dc a capacitance appears to be an open circuit (apart from a small leakage current through the resistance of the dielectric), and an inductor appears to be a small resistance (that of the coil conductor). However, on connection or removal of the dc snpply, the effects of capacitance and indnctance are apparent due to the change in the energy stored in the device. 

LePage, W. R. Analysis of Alternating-Current Circuits, McGraw-Hill, New York, 1952. 

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