BE3252 BASIC ELECTRICAL, ELECTRONICS AND INSTRUMENTATION ENGINEERING UNIT 1 PART 2.pptx

BEEIE

1. BASIC ELECTRICAL, ELECTRONICS AND INSTRUMENTATION ENGINEERING   Dr P THARCIS, ASP/ECE

2. UNIT I ELECTRICAL CIRCUITS DC Circuits: Circuit Components Conductor, Resistor, Inductor, Capacitor – Ohm’s Law - Kirchhoff’s Laws – Simple problems- Nodal Analysis, Mesh analysis with Independent sources only (Steady state) Introduction to AC Circuits and Parameters Waveforms, Average value, RMS Value, Instantaneous power, real power, reactive power and apparent power, power factor – Steady state analysis of RLC circuits (Simple problems only), Three phase supply – star and delta connection – power in three-phase systems

3. An AC circuit refers to an electrical circuit where the current periodically changes direction. " AC " stands for alternating current , which means the flow of electric charge periodically reverses direction. This is in contrast to a DC (direct current ) circuit, where the current flows in one direction continuously. AC circuits are commonly used in homes, industries, and power distribution systems because they allow for the efficient transmission of electricity over long distances. The voltage and current in an AC circuit typically vary sinusoidally with time.

4. Waveforms

5. Average value The average or mean value of a continuous DC voltage will always be equal to its maximum peak value as a DC voltage is constant. This average value will only change if the duty cycle of the DC voltage changes. In a pure sine wave if the average value is calculated over the full cycle, the average value would be equal to zero as the positive and negative halves will cancel each other out. So the average or mean value of an AC waveform is calculated or measured over a half cycle only and this is shown below.

6. RMS Value of an AC Waveform The effective value of a sine wave produces the same I 2 *R heating effect in a load as we would expect to see if the same load was fed by a constant DC supply. The effective value of a sine wave is more commonly known as the  Root Mean Squared  or simply  RMS  value as it is calculated as the square root of the mean (average) of the square of the voltage or current. That is V rms  or I rms  is given as the square root of the average of the sum of all the squared mid-ordinate values of the sine wave. The RMS value for any AC waveform can be found from the following modified average value formula as shown.

7. In an RLC circuit , the most fundamental elements of a resistor , inductor , and capacitor are connected across a voltage supply. All of these elements are linear and passive in nature. Passive components are ones that consume energy rather than producing it; linear elements are those which have a linear relationship between voltage and current . There are number of ways of connecting these elements across voltage supply, but the most common method is to connect these elements either in series or in parallel. The RLC circuit exhibits the property of resonance in same way as LC circuit exhibits, but in this circuit the oscillation dies out quickly as compared to LC circuit due to the presence of resistor in the circuit.

8. When a resistor, inductor and capacitor are connected in series with the voltage supply, the circuit so formed is called series RLC circuit .

9. The total voltage in the RLC circuit is not equal to the algebraic sum of voltages across the resistor, the inductor, and the capacitor; but it is a vector sum because, in the case of the resistor the voltage is in-phase with the current, for inductor the voltage leads the current by 90 o and for capacitor, the voltage lags behind the current by 90 o

10. Introduction to Three Phase A.C. Circuit A phase is carried out to the periodic modifications of a few quantities, which includes the voltage in an AC circuit. An electrical segment  is measured in degrees, with 360°  comparable to  an  entire  cycle. A sinusoidal voltage is proportional to the cosine or sine of the  section . Three-phase, abbreviated 3φ, refers to three different voltages and currents. It is a system produced by a generator that includes three sources that contain the same amplitude and frequency but out of phase from each other by 120°. The three phases should be supplied over six-wire, with two wires used for each phase. However, they are generally supplied over three wires The phase or line currents are the currents in each wire. AC Voltages and currents are expressed as RMS values

11. A phase is carried out to the periodic modifications of a few quantities, which includes the voltage in an AC circuit. An electrical segment  is measured in degrees, with 360°  comparable to  an  entire  cycle. A sinusoidal voltage is proportional to the cosine or sine of the  section . Three-phase, abbreviated 3φ, refers to three different voltages and currents. It is a system produced by a generator that includes three sources that contain the same amplitude and frequency but out of phase from each other by 120°. The three phases should be supplied over six-wire, with two wires used for each phase. However, they are generally supplied over three wires The phase or line currents are the currents in each wire. AC Voltages and currents are expressed as RMS values

12. Following requirements must be satisfied in order to be a alanced 3-phase set All 3 variables have the same amplitude All 3 variables have the same frequency All 3 variables are 120 o  in phase

13. Advantages of 3 Phase Circuits Electric power is generated and distributed in the three-phase system only. The instantaneous power in a three-phase system is always constant. The amount of wire required for a 3-phase system is lesser than that required for an equivalent 1-phase system. For Similar power, the three-phase system is more economical than the single-phase.

14. Power in three-phase systems