Direct current :- Definition, Sources and Difference between A.C. and D.C.

 1.Introduction to Direct current :- Direct current always flows in one direction from positive terminal to negative terminal.In a given circuit the direction of current is from ABCDA.Main source of Direct current is cell/battery and D.C. generator but today we use a.c. in our house and offices more.

2.History of Direct current (Historical Development) :-  The development of direct current was done by Italian physicist Alessandro  Volta In 1800. Alessandro Volta developed a voltaic pile  which is also known as the first electric battery. 

H.V. D.C.(High voltage Direct current) transmission system developed in 1950s which is used in long distance transmission nowadays.Because it is economical for long distance transmission. 

 

American scientist Thomas Alva Edison developed low voltage direct current incandescent lamp(bulb) for home and offices 

in 1882.  

3. Basic concepts of Direct current :- 

When d.c. Voltage is applied across any conductor cross section area then electrons start to flow in the direction of higher potential to lower potential. The direction of flow if Direct current is opposite of electron flow direction.thus the direction of Direct current is from higher potential to lower potential. 

There are two type of Direct current 

• Constant Direct current: - The source of constant Direct current is Battery and d.c. generator. The magnitude of constant d.c. remain the same with the time or not fluctuate with time.

• Variable Direct current: - The source of variable Direct current is rectifier (full wave rectifier, half wave rectifier and bridge rectifier) .The magnitude of variable direct current changes with time or does not remain the same with time. 

4.Alternating current vs Direct current :-

Alternating current	Direct current
Direction of flow of electric current changed with time	Direction of flow of electric current not change with time
It is generated by a synchronous generator and power plant on high volts .	It is generated by different types of d.c. Generation and electric battery.
It is used for transmission and distribution for both purposes.	It is used mainly for long distance transmission purposes.
We can generate it from  high voltage.	We can't generate it from above 650 volt  easily.

5.Generation of Direct current :Direct current generated through  batteries,photovoltaic cells and it is also generated from d.c. generator for industrial uses.For other uses(smartphone,computer and electronics gadgets)  d.c. Current generated mainly from rectifiers circuits  and adopters .  

6.Conversion of A.C. into D.C.:- Mainly we convert A.C. into D.C. by using rectifier circuits. There are two rectifier circuits by which we can convert A.C. into D.C.

1. Half wave rectifier circuit: - In this type of rectifier circuit only positive half cycle of input a.c. supply rectifiers conduct current. In the negative half cycle no current is conducted in the circuit. So this type of  rectifiers maximum efficiency is 40.6℅. 

2.Full wave rectifier circuit: - In this type of rectifier circuit current flows always in the same directions for both input a.c. supply is on positive half cycle or negative half cycle.in this type of rectifier circuit maximum efficiency is 81.2℅.there are two type of full wave rectifier circuit is used - 

• Centre -tap Full wave rectifier circuit:-In this type of rectifier circuit a centre tapped transformer, two diodes and some connecting wire is used for making the circuit. In this type of rectifier circuit when one diode is forward biassed then the other is in its reverse biases. So a centre tapped full wave rectifier can convert both positive half cycle and negative half cycle of a.c. current into d.c. current .

• Bridge rectifier circuit: -For eliminate the need of centre tapped transformer we can use bridge rectifier circuit . Such a type of circuit consists of 4 diodes ,a  transform and some connecting leads.This type of circuits are mainly used in many electronic devices like adapters, television and other devices which convert a.c. to d.c..

7.Application of Direct current in Everyday life :- Direct current is used for low voltage and low current application. In our everyday life we use direct current mainly electronics devices like- Laptop,smartphone charging, battery charging and computer or other electronic devices. 

D.C. mainly used in industries where speed control is required because d.c. motor is better than a.c. motor for speed control application. 

D.C. is also used in relay circuits which are used in power plants and electric sub-station. 

Sometimes it is also used in robot circuits and automation. Although d.c. has its own application but nowadays we prefer a.c.

8.Advantage and Disadvantage of Direct current :- Advantage of direct current: -There are many advantages of direct current. 

• In D.C. we required less conductor as compared to A.C.. 

• In D.C. transmission only resistance exists not conductance nor inductance.

• A D.C. transmission circuit is not complicated as an A.C. transmission circuit. 

• D.C. is used for long transmission circuits. 

• D.C. transmission has no skin effect. 

• There are less corona losses occurring in d.c. transmission circuit as compared to a.c. transmission circuit. 

• Voltage regulation is good in d.c. transmission circuit.

• Efficiency is also good in d.c. transmission because losses are low as compared to a.c. transmission circuits.

• There is no dielectric loss occurring in d.c. transmission. 

Disadvantages of Direct current: - There are some disadvantages are Direct current -

• Direct current is not step up and step down like Alternating current. 

• For step up and step down first we convert Direct current into Alternating current then we step up or step down which increases the cost of d.c. transmission.

• D.C. can not be generated at high voltage. It is generated generally at 650 V.

• The switch gear of d.c. is expensive.

• The energy generation cost of d.c. is higher than the a.c..

9.Direct current in renewable energy:- Some renewable energy sources like solar energy and other produce d.c. current. Solar panel consists of many photovoltaic cells which are connected in series and parallel order. Photovoltaic cells produce d.c. Voltage. In our home where we generate energy through solar panels we use an inverter for convert d.c. to a.c..

10.Safety considerations when working with Direct current:- When anyone works on d.c. circuit first we have to insure that the d.c.  circuit has no potential or all electrical energy  source  in circuit is shut off.Because if any energy source is connected  to the circuit then it can be dangerous.And wear all Safety equipment like gloves  and shoes and other Safety equipment.

11. Conclusion:- Direct current is produced from many renewable energy sources so it is the current that is generated by solar and batteries. Using direct current can improve efficiency,voltage regulation and also reduce the losses in electrical systems.