Unit 2: AC Circuits Overview
BEEE Unit 2 covers Single Phase and Three Phase AC Circuits. This unit is important for RGPV exams because questions are commonly asked from RMS value, average value, power factor, impedance, RLC circuits and three phase systems.
Students should focus on formulas, phasor diagrams, power triangle, star-delta relationships and repeated numerical problems.
Unit 2 Syllabus
- Generation of Sinusoidal AC Voltage
- Average Value
- RMS Value
- Form Factor
- Peak Factor
- Phasor Representation
- Power Factor
- Impedance and Admittance
- Active, Reactive and Apparent Power
- R-L Series Circuit
- R-C Series Circuit
- R-L-C Series Circuit
- R-L-C Parallel Circuit
- Three Phase AC System
- Necessity and Advantages of Three Phase Supply
- Phase Sequence
- Balanced and Unbalanced Supply
- Star Connection
- Delta Connection
- Line and Phase Relationship
- Power Measurement in Three Phase Circuits
Most Important Topics for Exam
RMS Value
Very important formula-based and numerical topic.
Power Factor
Frequently asked theory and numerical question.
Impedance & Admittance
Important for AC circuit calculations.
RLC Circuits
Common topic for theory and numericals.
Three Phase System
High weightage long-answer topic.
Star & Delta Connection
Important for line and phase relationship questions.
Short Notes for Quick Revision
1. Generation of Sinusoidal AC Voltage
Alternating voltage is generated when a coil rotates in a magnetic field. It works on Faraday’s Law of Electromagnetic Induction. The AC voltage equation is e = Em sinωt.
2. RMS Value
RMS value is the equivalent DC value that produces the same heating effect. For sine wave, Vrms = Vm / √2 = 0.707 Vm.
3. Average Value
Average value is the average of instantaneous values over half cycle. For sine wave, Vavg = 2Vm / π = 0.637 Vm.
4. Form Factor
Form factor is the ratio of RMS value to average value. For sine wave, its value is 1.11.
5. Peak Factor
Peak factor is the ratio of maximum value to RMS value. For sine wave, its value is 1.414.
6. Power Factor
Power factor is the cosine of angle between voltage and current. Formula: Power Factor = cosφ.
7. Impedance
Impedance is the total opposition offered by an AC circuit. Formula: Z = R + jX. Its unit is Ohm.
8. Admittance
Admittance is the reciprocal of impedance. Formula: Y = 1/Z. Its unit is Siemens.
9. Active, Reactive and Apparent Power
Active power is useful power, reactive power is stored and returned power, and apparent power is total supplied power.
10. R-L Series Circuit
In R-L series circuit, current lags behind voltage and power factor is lagging. Impedance is Z = √(R² + XL²).
11. R-C Series Circuit
In R-C series circuit, current leads voltage and power factor is leading. Impedance is Z = √(R² + XC²).
12. R-L-C Series Circuit
R-L-C circuit contains resistance, inductance and capacitance. Its impedance is Z = √(R² + (XL − XC)²). At resonance, XL = XC.
13. Three Phase AC System
A three phase system contains three AC voltages separated by 120°. It is efficient, economical and widely used in power transmission and industries.
14. Star Connection
In star connection, one end of each phase is connected to form a common neutral point.
15. Delta Connection
In delta connection, the end of one phase is connected to the starting point of the next phase, forming a closed loop.
Formula Sheet
| Topic | Formula / Key Point |
|---|---|
| AC Voltage | e = Em sinωt |
| RMS Value | Vrms = Vm / √2 = 0.707 Vm |
| Average Value | Vavg = 2Vm / π = 0.637 Vm |
| Form Factor | Form Factor = Vrms / Vavg |
| Peak Factor | Peak Factor = Vm / Vrms |
| Power Factor | Power Factor = cosφ |
| Impedance | Z = R + jX |
| Admittance | Y = 1 / Z |
| Active Power | P = VI cosφ |
| Reactive Power | Q = VI sinφ |
| Apparent Power | S = VI |
| Power Triangle | S² = P² + Q² |
| R-L Circuit Impedance | Z = √(R² + XL²) |
| R-C Circuit Impedance | Z = √(R² + XC²) |
| R-L-C Circuit Impedance | Z = √(R² + (XL − XC)²) |
| Resonance Condition | XL = XC |
Important Questions
- Explain generation of sinusoidal AC voltage.
- Define RMS value, average value, form factor and peak factor.
- Explain power factor and its importance.
- Explain impedance and admittance.
- Explain active, reactive and apparent power.
- Explain R-L series circuit with phasor diagram.
- Explain R-C series circuit with phasor diagram.
- Explain R-L-C series circuit.
- Explain three phase AC system.
- Differentiate balanced and unbalanced system.
- Explain star connection.
- Explain delta connection.
- Derive relationship between line and phase quantities.
- Solve numerical problems based on RMS value.
- Solve numerical problems based on power factor.
- Solve numerical problems based on three phase power.
PYQ Analysis Table
| Topic | Repeated Pattern | Importance |
|---|---|---|
| Generation of Sinusoidal AC Voltage | Theory question | Important |
| RMS, Average, Form Factor, Peak Factor | Definition + formula + numerical | Very Important |
| Power Factor | Theory + importance + numerical | Very Important |
| Impedance and Admittance | Definition + numerical | Very Important |
| Active, Reactive and Apparent Power | Power triangle + formula | Very Important |
| R-L, R-C and R-L-C Circuits | Formula + phasor diagram + numerical | Very Important |
| Three Phase AC System | Long answer | Very Important |
| Balanced and Unbalanced System | Difference table | Important |
| Star and Delta Connection | Derivation + relationship | Very Important |
Sample Numericals
RMS Value Numerical
Question: Find RMS value if maximum voltage is 200V.
Formula: Vrms = Vm / √2
Solution: Vrms = 200 / 1.414 = 141.4V
Final Answer: RMS Value = 141.4V
Power Factor Numerical
Question: If phase angle between voltage and current is 60°, find power factor.
Formula: Power Factor = cosφ
Solution: Power Factor = cos60° = 0.5
Final Answer: Power Factor = 0.5
Download BEEE Unit 2 PDFs
Download complete Unit 2 notes, important questions and PYQ analysis for RGPV BEEE exam preparation.
Download Notes PDFHow to Prepare Unit 2
- First revise RMS value, average value, form factor and peak factor formulas.
- Practice power factor and impedance numericals.
- Prepare R-L, R-C and R-L-C circuit formulas with phasor diagrams.
- Revise active, reactive and apparent power with power triangle.
- Learn star and delta connection relationships.
- Solve repeated PYQ numericals before exam.
Frequently Asked Questions
Is BEEE Unit 2 important for RGPV exams?
Yes, Unit 2 is important because RMS value, power factor, RLC circuits and three phase systems are repeatedly asked.
Which topic is most important in BEEE Unit 2?
RMS value, power factor, impedance, RLC circuits and star-delta connection are the most important topics.
Are numericals asked from Unit 2?
Yes, numerical questions are commonly asked from RMS value, power factor, impedance, RLC circuits and three phase power.
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