Design Guide for Underground Transmission Line

Design Guide for Electrical Energy Transmission in Underground Cable Network

Voltage level of transmission line network is the key considering design guide factor for bouth overhead transmission system and underground cable transmission system.

Schematic line diagram in below , the specific voltage level guide are used for conventional overhead transmission and new concept underground transmission network system for-

1. Power Generation;
2. Bulk Transmission;
3. Sub-Transmission; &
4. Distribution System.

What The Distribution Voltage Level Is?

In electrical power transmission and distribution system, voltage levels are divided into different category considering the equipment operating capability, such as-

1. Low Voltage (LV)              - up to 1000Volt;
2. normalVoltage (MV)       - 1000 Volt ~ 35 kilo Volt;
3. High Voltage (HV)            - 35kilo Volt ~ 230 kilo Volt;
4. Extra High Voltage (EHV)  - above 230 kilo Volt; &
5. Ultra High Voltage (UHV)  - above 800 kilo Volt.

Also, very safe low voltage like less than 70 Volt is known as extra low voltage (ELV).

What The common Transmission & Distribution Voltage Level Is?

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In the above line diagram from power generation station to end user consumer, passing through different level of transmission voltage system shows the most common transmission and distribution voltage level. Very common Low Voltage (LV) is 120V, 230V,385V,420V, 625V etc; normalVoltage (MV) is 11kV, 19kV, 33kV etc; High Voltage (HV) is 110kV,132kV, 220kV, 230kV etc: Extra High Voltage (EHV) is 230 kV, 400kV, 500kV, 765kV etc. It is differ from country to country.

The selection of transmission voltage level depends on load flow distance. If energy necessary to travels a long distance or comparatively short distance but energy is bulk amount then voltage level needs higher.

During energy transmission, a certain percentage of energy losses, to minimize or reduce this losses voltage needs to increase.

“A voltage of (nominally) 230 V and a frequency of 50 Hz is used in Europe, most of Africa, most of Asia, much of South America and Australia. In North America, the most common combination is 120 V and a frequency of 60 Hz. Other voltages exist, and some countries may have, for example, 230 V but 60 Hz. This is a concern to travelers, since portable appliances designed for one voltage and frequency combination may not operate with or may be destroyed by another”.

Why Underground Transmission Network Is Necessary?

Underground Energy Transmission is costly compare to conventional overhead transmission. It’s need less maintenance, but takes more time to find out some cable fault.

Though initial cost is high for underground cable energy transmission, then it is the first priority to energy transmission network administrator to change the network into underground.

Advantages are less maintenance, less environmental trouble like storm or cyclone, easy monitoring and ensure reliable power supply.

Now XLPE insulated copper or alluminium core power cable is widely using for large scale of advantages on reliable power supply”.

Read about: High Voltage Power Line and Health Risk

Underground network requires less land uses, destroy less forest/vegetation, keeps the city clean electrical accident free, trouble free power supply, etc.

What Is The Main Equipment Used In Underground Energy Transmission?

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The main equipment’s for underground electrical energy transmission networks are as below-

1. Power Cable;
2. Insulated & Straight Through Cable Joint;
3. Gas Insulated Cable Termination;
4. Indoor or Outdoor Cable Termination;
5. Cable Sheath Earthing Link Box;
6. Fiber Optic Cable for Communication & Monitoring System, etc.

The Design Guide for both underground and overhead electrical energy transmission line system is not a limited span, it’s need divert rules considering the site situation and international and local standard codes.