**Phasor diagram**

A figure or **diagram** which gives the information (i.e. magnitude and phase angle) about **alternating quantities** known as **phasor diagram or vector diagram**.

**Phasor Algebra**

Any alternating voltage or current can be represented by vector , e.g.

A vector can be represented by two methods

### (i) **Rectangular representation**

Vector can be represented in terms of X and Y components. As shown in the figure given below, vector E` angle 0`

can be represented by two components

‘j’ is used to indicate that Y component is perpendicular to X component. The value of

The representation A + j B is known as rectangular **representation**.

### (ii) **Polar representation**

A vector E angle 0 is the polar representation. E is the magnitude and is the angle with X-axis, clockwise for (—) ve value of and counter clockwise for (+) ve value of **Polar representation** can be converted to rectangular representation or vice-versa.

Addition and subtraction arc done in rectangular form.

e.g. (A +j B) + (C +j D) = (A + C) +j (B + D)

or (A +j B) – (C +j D) = (A + C) + j (B + D)

Multiplication and division is simpler in polar form

**Leading and Lagging ac quantities**

Leading ac quantities arc those which cover or attain its maximum value earlier or before as compared to other **ac quantities** on the time axis, whereas lagging ac quantities arc those which cover or attain its maximum value after or later as compared to other ac quantities.

As shown in above figure i.e. wave diagram and phasor diagram (i) v3 is leading with V1 by 60^{0} and is leading with v2 by 90^{0} .

(ii) V1 is lagging with v3 by 60^{0} and is leading with v2 by 30^{0} (iii) v2 is lagging with V1 by 30^{0} and is lagging with v3 by 90^{0}.

## A.C. CIRCUITS TOPIC

- Introduction Of AC Circuits In Electrical Engineering
- How emf is induced in single phase system ? single phase generation .
- Explain what is ac quantity : and Advantages of AC over DC in circuits
- What is waveform, amplitude, cycle, time-period, phase & phase difference
- Define RMS & average value as applied to A.C. voltage & current
- What is form factor? crest factor? peak factor? & power factor? in ac circuits
- what is phasor diagram, phasor algebra, leading & lagging ac quantities
- Phasor representation of alternating quantities – resistive, inductive, capacitive
- What is R-L-C series connection for A.C. circuit ? Explanation
- What is series combination of R-L circuit ? Explanation
- Define what is active power, reactive power, apparent power & power factor
- Explain what is series combination of R-C circuit in electrical engineering
- What is simple parallel AC circuits ? Explanation -electrical engineering
- Resonance as applicable to simple RLC series circuit? effect on circuit performance
- Explain three phase generation of voltage ? electrical engineering
- Explain in detail about what is star and delta three phase system ?
- Relation between phase voltage & line voltage in case of balanced star connected load
- relationship between line current & phase current for delta connected 3 load
- Relation between power consumed in a balanced star & delta connection

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