Table of Contents

## Alternating Current

A.C. means alternating current -The following voltage which alternates its direction and magnitude every time. Nowadays 95% of the total energy is produced, transmitted, and distributed in A.C. supply.

Nowadays, owing to multiple systems of transmission and distribution, we come across parallel circuits such as impedance joined in parallel more often.

Practically all lighting and power circuits are constant voltage circuits which are circuits with the loads connected in parallel. In a parallel A.C. circuit like a parallel D.C. circuit, the voltage is the same across each branch. And a series circuit the current is the same across each branch also the voltage is divided.

## The reason is following

- More voltage can be generated up to 33000 volts. than D.C. 650 volt only.
- AC voltage can be increased and decreased with the help of a static mechanic called the transformer.
- AC transmission and distribution is more economical as line materials say copper can be saved by transmitting power at a higher voltage.
- AC motors for the same horsepower as DC motors are cheaper, lighter in weight, require less space, and require lesser attention in operation and maintenance.
- A.C. can be converted to D.C. meaning direct current easily when required but D.C. can not be converted to A.C. so easily and it will not be economical.

- However, D.C. entails the following merits and hence finds wide application.

D.C. series motors are most suitable for traction purpose in tramway, railway, crains and lifts. For electroplating, electrolytic and electrochemical processes battery charging etc. DC is required. Arc lamps for search light and cinema projectors work on D.C. Arc welding is better than on AC.

Relay and operating time switches, etc. and circuit-breakers, D.C. works more efficiently. In rolling mills, paper mills, colliery winding, etc. where fine speed control of speeds in both directions is required, D.C. motors are required.

Alternating voltage may be generated in the following two ways.1.By rotating a coil in a stationary magnetic field.

2.By rotating a magnetic field within a stationary coil.

**A.C. series circuit**

Under this heading, we shall discuss R-L and L-R series circuits.

__R-L circuit__

Resistance and inductance in series a pure resistance R and a pure inductive coil inductance L connected in series. Such a circuit is known as an R-L circuit.

In the circuit,

Let V is the R.M.S. value of the applied voltage,

I am the R.M.S. value of the resultant current,

Vr is IR equal to the voltage drop across the L coil, ahead of I by 90 degrees.

The voltage drop voltage resistance and voltage inductance are taken as the reference vector.

**R-L-C circuit**

R-L-C connected in series

In simple, An R-L-C circuit is an electrical circuit consist resistor, inductor, and capacitor are connected in series or parallel connection is generally called an R-L-C circuit.

R-resistance of the resistor, L- inductance of the conductor, C- capacitance of a capacitor is shown in fig as known as R-L-C and this three are connected in series across the voltage applied.

The resonant frequency of R-L-C circuit where L is inductance and C is capacitance.

**R-L-C circuit in Parallel **

R-L-C parallel connection the same of r is the resistance of resistor and L ii inductance of conductor and c is the capacitance of capacitor are connected in parallel connection as shown in the figure above. The frequency of voltage that gives the maximum value of the current in the circuit is called resistance frequency, and the circuit is said to be **resonant.**