Comparison between AC and DC supply system

Difference between ac and dc transmission & explain its advantage and disadvantage | Comparison between AC and DC supply system | Differentiate between ac and dc system

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Key points	AC	DC
Definition	In this alternating current is transmitted through the conductor.	In this direct current is transmitted through the conductor.
No. of conductor	Generally 3 conductors are used.	Generally 2 conductors are used.
Inductance, Capacitance, Phase displacement and surge problems.	It has inductance, capacitance, phase displacement and surge problems.	It does not have inductance, capacitance, phase displacement and surge problems.
Voltage Drop at same load and voltage	High voltage drop at same load and same voltage.	Low voltage drop at same load and same voltage.
Voltage regulation	Low voltage regulation	High voltage regulation
Skin effect	It is present in this system	No skin effect
Conductor utilization	A Small cross-section of conductor is utilized in transmission due to skin effect.	Entire cross-section of  conductor is utilized in transmission.
Stress on insulation	The potential stress on insulation is high	The potential stress on insulation is low at same working voltage
Corona loss	High corona loss	Low corona loss
Communication interference	High interference with communication line.	Low interference with communication line.
Dielectric loss	High dielectric loss	Free from dielectric loss
Stability	High stability problems	No stability problems
Synchronization	High synchronizing difficulties	No synchronizing difficulties
High voltage generation	AC can be generated at high voltage.	DC can not be generated at high voltage due to commutation problem.
Construction of line	More complicated	Easy
Overall cost	Low	High

 

HVDC and HVAC transmission cost comparison

A.C. vs D.C. power pros and cons :

The electric power can be transmitted either by means of  d.c or a.c. Each system has its own advantages and disadvantages. 

1. A.C transmission : Nowadays, electrical energy is almost entirely generated, transmitted and distributed in the form of alternating current(A.C).

Advantages :-

(i) The A.C power can be generated at high voltages.

(ii) The maintenance of a.c. sub-stations is easy and cheaper.

(iii) The a.c. (alternating current) voltage can be stepped up or stepped down by step-up or step-down transformers with ease and efficiency. 

Disadvantages :-

(i) An a.c. transmission line requires more copper than a d.c. line.

(ii) The construction of a.c. transmission line is more complex than the d.c. transmission line.

(iii) Due to the presence of skin effect in the a.c. system, the effective resistance of the transmission line is increased.

(iv) An a.c. line has capacitance. Therefore, there is a continuous loss of power due to charging current even  when the line is open.

2. D.C. transmission : From past some years, the transmission of electric power by d.c. has been receiving the active considerations by power industry due to its many advantages.

Advantages :-

(i) D.C. transmission requires only 2 conductors as compared to 3 for a.c. transmission.

(ii) There is no inductance, capacitance, displacement in phase and voltage surge problems in d.c. transmission.

(iii) As there is no inductance in dc line, the voltage drop in a d.c transmission line is less than the a.c line for the same load.

(iv) D.C transmission line has better voltage regulation.

(v) There is no skin effect present in d.c. system.

(vi) In d.c. transmission, there are no stability problems.

(v) No synchronizing difficulties.  

Disadvantages :-

(i) Electric power of d.c. can not be generated at high d.c. voltage due to commutation problems.

(ii) The d.c. voltage can not be stepped up for transmission of power at high voltages.

(iii) The d.c. switches and circuit breakers have their own restrictions.

• Compare ac and dc power transmission system.
• Comparison of transmission lines.
• Is dc transmission better than ac ?