Tuesday, 20 September 2016

Comparison of AC and DC Transmission


Electric Power can either be transmitted by means of AC or DC. Each system has their advantages and disadvantages. Therefore it is very crucial to have a comparative study of their merit and demerits and then decide which method should be adopted to transmit power.

Advantages of DC Transmission:
1)    The high voltage DC Transmission has the following advantages over high voltage AC transmission:
2)    Power transmission by means of DC requires only two conductors as compared to three conductors required for AC.



3)  There is no inductance, capacitance, phase displacement and surge problem in DC transmission.


4)    Due to absence of inductance, the voltage drop in DC transmission is less than the AC transmission for same load and receiving end voltage. Because of this DC transmission has better voltage regulation.
5)    There is no skin effect in the DC transmission and therefore entire cross-section of the conductor is utilized.
6)    For the same voltage, the potential stress on the Insulators are less in DC system as compared to AC system (because in AC insulators had to bear peak voltage which is 1.414 times the RMS voltage.).
7)    A DC transmission line has less Corona and hence efficiency is improved.
8)    In DC transmission, there is no stability and synchronization problem.
Disadvantages of DC Transmission:
1)     DC Power generation is difficult due to commutation problem.
2)     Transformer does not work for DC and therefore voltage level of DC cannot be changed for power transmission.
3)     DC Switches and Circuit Breakers have their own limitations.
Advantages of AC Transmission:
1)      AC power can be generated at high voltage. The maximum voltage at which Electrical Power is generated in India is at 21 kV.
2)     AC voltage can be stepped up for power transmission at high voltage. The maximum voltage of Grid in India is 765 kV.
Disadvantages of DC Transmission:
1)      AC transmission requires more conductor material as compared to DC transmission.
2)  The construction of AC transmission line is more complicated as compared to DC transmission line.
3)      Due to Skin Effect in AC transmission, the effective resistance of conductor increases.


From the above comparison, we can see that DC transmission has many advantages as compared to AC transmission. Although at present, transmission of power is carried out by AC but there is an increasing trend for DC transmission because of advancement in Power Electronics. 

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