Electrical Power can be transmit and distribute in both system AC and DC. But Both system have their Advantages and Disadvantages. so, lets Discuss….
Advantages of DC for Transmission and Distribution:
- In DC system there is only two conductor required where in AC three conductor required. Hence much conductor saved.
- There is no inductance, capacitance, phase difference and surge problem for that small amount of voltage drop comparing to AC. Voltage regulation on DC system is better than AC.
- There is no skin effect in DC for that conductor has less cross section area.
- DC system requires less insulation as potential stress is 1/√2 times of that in AC system for same working voltage. for that price of cable is low.
- In DC line Corona loss is very low.
- DC line has reduce interference with communication circuits.
- Underground cable can be use because of less potential stress and dielectric loss.
- No stabilizer is required for transmission over long distance.
Disadvantages of DC for Transmission and Distribution:
- The only Difficulty is due to commutating difficulties, electrical power cannot be produce high voltage, necessary high voltage required for transmission, voltage cannot be stepped up as Transformer not worked in DC quantity.
Advantages of AC for Transmission and Distribution:
- In AC system the Main Advantage is the voltage can be stepped up at generating end using step up Transformer to the required value for transmission and at distribution end stepped down by using step down Transformer for distribution purpose.
- In this system electrical power can be generated at high voltage easily.
- The Maintenance of sub station is easier and cheaper. As, AC circuit breaker is cheaper than DC circuit breaker.
Disadvantages of AC for Transmission and Distribution:
- In Ac system more conductor required and the size of the conductor ( cross section area of the conductor) is greater than DC system. Overall more copper required. for that reason the cost of AC transmission line greater than DC.
- There is inductance, capacitance, phase difference and surge problem for that more amount of voltage drop or loss in AC.
- Due to skin effect cross section are of conductor is more.
- Corona loss occur in AC system.
- In case of overhead line spacing between the conductors is to be kept more in order to provide adequate insulation and avid corona loss.
- The alternator are to be synchronized before putting them into parallel.
- The variation in speeds of alternators are to be controlled within very low limit.
CONCLUSION: AC or DC transmission – Which is better?
Transmission of electrical power by DC system become possible after invention of MERCURY ARC rectifier and THYRATORNS (thyratron is gas-filled tube used for high-power electrical switch and controlled rectifier, in the year 1970 first HVDC use thyristors instead of mercury arc valve). Which can convert AC into DC and DC into AC efficiently and reasonable cost.
Distribution of AC system is no doubt superior to that by DC system as in AC voltage control is very easy by using of Transformer ( Not worked in DC system).
The best method is: Use AC system for generation and Distribution electrical power and use DC system for Transmission purpose.