Underground System:
The underground system uses the insulated cable for transmission or distribution purpose. The insulated cable are buried inside the earth. The underground system are very costly. The underground system mostly used for distribution of power. The underground system is not used for transmission purposed more because underground cables are costly for higher voltage.
Advantages of overhead system
1. The Underground system ensures the non-continuity of the supply
2. The maintenance cost of the underground system is very less.
3. The underground system has long life.
4. The appearance of the underground system is very good.
Overhead system:
The overhead system uses bare conductor supported at electric poles. Overhead system also used for transmission and distribution purpose. The overhead system mostly used for transmission purpose because overhead system is less costly for higher voltages.
Advantages of overhead system.
1. The overhead system is easy to repair and maintain.
2. The overhead system has lower installation cost.
3. The higher voltage power transmission will be possible with the overhead system.
4. The long distance power transmission will be possible with the overhead system.
| Underground System | Overhead System |
|---|---|
| The public safety are more in Underground system. | The Public safety are less in overhead system. |
| The Underground system are more expensive. | The Overhead system are less expensive. |
| The Underground system are less flexible because load expansion are possible in underground system. | The overhead system are more flexible because load expansion are possible. |
| The underground system working voltage limited to 66KV because of insulation problem. | The overhead system working voltage is 400KV or more. |
| The Underground system uses insulated cable for power transmission and distribution purpose. The underground cable are buried inside the earth. | The Overhead system uses bare conductor which is supported on electrical pole or tower for transmission and distribution of electrical power from long distances. |
| The Underground system uses insulated cable and size of the cable is larger. | The overhead system uses bare conductor and size of the conductor is smaller. |
| The current carrying capacity of underground system is smaller because more insulation required for higher current. | The current carrying capacity of the overhead transmission is very higher because there is no any insulation requirement. |
| The maintenance cost of the underground system is smaller. | The maintenance cost of the overhead system is higher. |
| The frequency of the faults or failure are less in unground cable because underground cable buried inside the earth and having stronger insulation. | The frequency of the fault or failure is more in overhead system because overhead system are remain in open atmosphere. |
| The chances of accidents are less in underground system. | The chances of accidents are more in overhead system. |
| The fault detection and clearance are difficult in the case of underground system. | The fault detection and clearance are easy in overhead system. |
| In Underground system voltage drop is less due to the less spacing between the conductor and inductance of the cable is low. | In overhead system voltage drop is more due to the more spacing between the conductor and inductance of the conductor is more. |
| The appearance of the underground system is good because wiring are not visible. | The appearance of the overhead system is not good because wiring and poles are visible. |
| Due to less spacing between the conductor, capacitance is more in unground system and charging current are more in underground system. | Due to more spacing between conductors in overhead system, capacitance is less and hence the charging current are less in overhead system. |
| In underground system, cable jointing are difficult so tapping for load and service mains are not convenient in underground system. | In overhead system, conductor jointing are easy so tapping for loads and service mains are quit convenient. |
| The underground system are free from interruption due to thunderstorm, lightning and objects falling across the conductors. | The overhead system are not free from interruption due to thunderstorm, lightning and objects falling across the conductors. |
| In underground system, surge effect is very small because all the surge energy absorbed by the cable sheath. | In overhead system, surge effect is very high because overhead conductor is not having any sheath. |
| The underground system does not cause any interference with communications lines. | The overhead system can cause interference with the communication lines. |
| In underground system, insulated cable reduce the risk of the fire or explosions. | In overhead system, risk of fire or explosions are higher. |
| In underground system, the proximity effect is more. | In overhead system, proximity effect is less. |
| In underground system, the corona discharge does not occurs. | In overhead systems, the corona discharge will be occur. |
| The underground system are used for transmission and distribution of the power at shorter distance. | The overhead system are used for transmission and distribution of electrical power at longer distances. |
| The layout flexibility of the underground system is very less. | The layout flexibility of the overhead system is very high. |
| The underground system are more reliable. | The overhead system are less reliable. |