- High voltage DC electrical transmission system.
- High AC electrical transmission system.
There are some advantages in using DC transmission system-
- Only two conductor are required for DC transmission system. It is further possible to use only one conductor of DC transmission system if earth is utilized as return path of the system.
- The potential stress on the insulator of DC transmission system is about 70 % of same voltage AC transmission system. Hence, less insulation cost is involved in DC transmission system.
- Inductance, capacitance, phase displacement and surge problems can be eliminated in DC system.
Even having these advantages in DC system, generally electrical energy is transmitted by three(3) phase AC transmission system.
- The alternating voltages can easily be stepped up and down, which is not possible in DC transmission system.
- Maintenance of AC substation is quite easy and economical compared to DC.
- The transforming of power in AC electrical sub station is much easier than motor-generator sets in DC system.
But AC transmission system also has some disadvantages like,
- The volume of conductor used in AC system is much higher than that of DC.
- The reactance of the line, affects the voltage regulation of electrical power transmission system.
- Problems of skin effects and proximity effects only found in AC system.
- AC transmission system is more likely to be affected by corona effect than DC system.
- Construction of AC electrical power transmission network is more completed than DC system.
- Proper synchronizing is required before inter connecting two or more transmission lines together, synchronizing can totally be omitted in DC transmission system.