Single Phase AC Circuits:



A single-phase electric power is the distribution of AC electric power using a system in which all the voltages of the supply vary simultaneously. Single-phase distribution is used when loads are mostly lighting and heating, with few large electric motors. A single-phase supply connected to an AC electric motor does not produce a revolving magnetic field; single-phase motors need additional circuits for starting and such motors are uncommon above 10 kW in rating. Because the voltage of a single phase system reaches a peak value twice in each cycle, the instantaneous power is not constant.



A single-phase load may be powered from a three-phase distribution transformer in two ways:



• By connection between one phase and neutral
• By connection between two phases

Electric circuits supplied by an alternating current sources(ac) are called ac circuits. An alternating quantity , voltage or current, is one that varies periodically both in magnitude and direction. The shape of curve is obtained by plotting its magnitude versus time or angle and is called waveform.



The periodic waveform has definiate cycle of change . Each cycle consists of two half cycles, during which the AC quantity acts in one direction around the circuit and during other half cycle in opposite direction.


Generation of Sinusoidal Voltage:


The voltage is induced in a conductor according to Faraday’s laws of electromagnetic induction. For this it is necessary to have field, conductor and mechanism to get the relative motion between the field and conductor for flux to link to the coil. By principle of electromagnetic induction, voltage may be generated by,


1. Rotating field and stationary conductor.
2. Rotating conductor and stationary field.

a) Basic AC Circuits:


1.AC voltage applied to Resistance:

when resistance applied to AC voltage, the circuit behaves similar to the DC circuit. For more details click the link


2.AC voltage applied to Inductance:

When inductance applied to AC voltage, it will draw current lagging the voltage by 90 degrees and consumes no power.Click the link


3.AC voltage applied to Capacitance:

The capacitor is excited with AC voltage drwas an AC current that leads the voltage across the capacitor by 90 degrees and consumes no power.Click the link



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