AC FUNDAMENTALS.pptx

AC Theory

1. AC FUNDAMENTALS - Roshan K. Aalshi R.R.C. Mumbai-19

2. WHAT IS AN ALTERNATING CURRENT (AC)? In alternating current, the electric charges flow changes its direction periodically.  Alternating current can be identified in waveform called a sine wave. In other words, it can be referred to as the curved line. These curved lines represent electric cycles and are measured per second. The measurement is read as Hertz or Hz.

3. AC V/S DC Alternating Current Direct Current AC is safe to transfer longer distance even between two cities, and maintain the electric power. DC cannot travel for a very long distance. It loses electric power. The rotating magnets cause the change in direction of electric flow. The steady magnetism makes DC flow in a single direction. The frequency of AC is dependent upon the country. But, generally, the frequency is 50 Hz or 60 Hz. DC has no frequency of zero frequency. In AC the flow of current changes its direction backwards periodically. It flows in a single direction steadily. Electrons in AC keep changing its directions – backward and forward Electrons only move in one direction – that is forward

4. A DVANTAGES OF AC OVER DC AC is less expensive and easy to generate than DC. The distance covered by AC is more than that of the DC. The power loss during transmission in AC is less when compared to the DC. The loss of energy during the transmission in AC voltage is less when compared with the DC voltage and this makes its installations easy when the transformers are at distance. AC voltage has the advantage of stepping up and stepping down as per the requirement.

5. NATURE OF AC

6. IMP TERMINOLOGIES OF AC WAVE

7. RMS VALUE OF AC “RMS value of an alternating current is that steady state current (dc) which when flowing through the given resistor for a given amount of time produces the same amount of heat as produced by the alternative current when flowing through the same resistance for the same time” rms voltage is: rms current is :

8. PHASE ANGLE Phase Difference is used to describe the difference in degrees or radians when two or more alternating quantities reach their maximum or zero values. The  phase difference  or phase shift as it is also called of a Sinusoidal Waveform is the angle  Φ  (Greek letter Phi), in degrees or radians that the waveform has shifted from a certain reference point along the horizontal zero axis. In other words phase shift is the lateral difference between two or more waveforms along a common axis and sinusoidal waveforms of the same frequency can have a phase difference. Phase Difference Equation: Where:    A m   –  is the amplitude of the waveform.    ωt   –  is the angular frequency of the waveform in radian/sec.    Φ  (phi)  –  is the phase angle in degrees or radians that the waveform has shifted either left or right from the reference point

9. Phase Relationship of a Sinusoidal Waveform

10. NON-SINUSOIDAL WAVEFORMS

11. 50 Hz POWER SUPPLY

12. RESISTANCE IN AC CIRCUITS Instantaneous current

13. Phasor diagram and wave form Current leads Voltage by 90 degrees Capacitance Reactance rms current i Using complex numbers and the j operator CAPACITANCE IN AC CIRCUITS 13

14. i – instantaneous current Current lags Voltage by 90 degree rms current Using complex numbers and the j operator Inductive Reactance i Phasor diagram and wave form Inductance in an AC Circuits 14

15. IMPEDANCE A measure of the overall opposition of a circuit to current. It is like resistance, but it also takes into account the effects of capacitance and inductance.  Impedance is more complex than resistance because the effects of capacitance and inductance vary with the frequency of the current passing through the circuit and this means  impedance varies with frequency . The effect of resistance is constant regardless of frequency.

16. RESONANCE (TUNED CIRCUITS) Resonance occurs whenever the phase angle of the circuit is zero, The only way that  f  = 0 is if  X L  =  X C Generally resonance is achieved by varying the angular frequency  w  the circuit until  X L  = X  C .

17. SERIES RESONANCE In the RLC series circuit, when the circuit current is in phase with the applied voltage, the circuit is said to be in Series Resonance. A series resonant circuit has the capability to draw heavy current and power from the mains; it is also called acceptor circuit.  At the resonance : X L  – X C  = 0 or X L  = X C

18. Effects of Series Resonance At resonance condition, XL = XC the impedance of the circuit is minimum and is reduced to the resistance of the circuit. i.e. Zr = R At the resonance condition, as the impedance of the circuit is minimum, the current in the circuit is maximum. i.e Ir = V/Zr = V/R As the value of resonant current Ir is maximum hence, the power drawn by the circuit is also maximized. i.e. Pr = I 2 Rr At the resonant condition, the current drawn by the circuit is very large or we can say that the maximum current is drawn. Therefore, the voltage drop across the inductance L i.e. (V L  = IX L  = I x 2π frL ) and the capacitance C i.e (V C  = IX C  = I x I/2π frC ) will also be very large.

19. Parallel Resonance Parallel Resonance means when the circuit current is in phase with the applied voltage of an AC circuit containing an inductor and a capacitor connected together in parallel.

20. CHARACTERISTICS OF PARALLEL RESONANCE Below resonant frequency, circuit is inductive and impedance is small since X L is small. Above the resonant frequency, circuit is capacitive and impedance is small because of X C is low. At Resonance, Circuit is resistive and impedance is maximum since X L  = X C It is also called as Rejector Circuit.

21. SERIES V/S PARALLEL RESONANCE

22. PROBLEMS