Earthing Materials And Layout Of Substations

Earthing Calculation

Give Any Earthing Materials?

Give The Intoduction To The Layout Of Substation?

What Are The Different Layouts For A Substation?

What Are The Components Of A Substation?

What Are The Substation Transients And Hazards Towards Human Body?

Kersting, (1984) a sub-station is a set of equipments connected together to reduce the original high voltage to low voltage that will be used by consumers also called a subordinate station. For this to be done effectively the sub-station is made in its own layout. Sub-stations work by stepping up voltage for transmission purposes or stepping down for consumption.  If there is a situation where there can be no substation there can be a lot of hazards due to the effect of high voltage. The sub-station is always powered by the main power grid.

Yoshida, et al (1986) the first part in designing a sub-station is developing the bonding earthing System. The work of the bonding earthing system is to provide an earth connection to which the neutrals of the transformer are connected in order to deliver excess fault current to avoid mechanical worn out and also minimum thermal destructions. This damage is seen mostly on the facilities within the substation. This design helps in providing safety to all operations and also personnel. The earthing and bonding system helps in creating eqipotential bonding so that there can be no dangerous potential gradients in the substation.

1. Touch voltage: The potential difference between the surface potential and the earthed equipment potential when a person is touching the earth surface.
2. Mesh voltage: The over average touch voltage that is always developed in the mesh of the earthing grid.
3. Step voltage: It is defined as the potential difference in a situation where a man gaps a distance of one meter while not in touch with any earthed equipment.

In earthing we have the earthing calculation methodology. They mostly consider site measurements of the level of sensitivity of the ground and the fault levels of the system. Then the layout of the grid with specific conductors is scientifically studied  to see the  earthing resistance of the substation and the voltage of the earthing is calculated from there. There are some probe tests that are taken to measure the earth resistivity. These tests are taken during the dry weather period so that the resistivity readings are obtained.

Fellin, Kusstatscher, and Rostagni, (1995) clearly explains several earthing materials that are very efficient in such a station.

Conductors: Bare copper is the one that is usually used in the substation earthing grid. To add to the buried  earth grid, a different and separate earthing ring is usually provided that is always above the ground to which all metallic substation plant are joined in this area,

Connections: They should not be joined together because the heat generated during fault conditions could cause the joints to fail functioning. The joints are fixed using bolts and they are also tinned.

Earthing Materials

Earthing Rods: The rods are used to supplement the grid to assist in the disposal of earth fault currents hence reducing the substation earthing resistance. The rods are made up of copper clad steel or solid copper.

Switchyard Fence Earthing: They are used for different utilities. These are:

The substation earthing grid is extended further over the fence circumfrence and then connected to the grid at regular intervals.

The fence is placed beyond the perimeter of the switchyard earthing grid and the fence and it’s earthing rod system are bonded. This rod system isn’t joined to the big substation earthing grid.

Dutta, and Overbye, (2011) argues that it is very important because there should be a security concerning the  supply. In a well equipped substation all the circuits would be produced as many copies so that in case of a fault,  connections remains available. The cost of implementation of the design is high hence there is a method to compromise between security and cost. Substations are divided into two categories according to securities of the supply.

Category 1: No failure is necessary within the substations for maintaining or fault conditions.

Category 2: Short failure is needed to transfer the load to an another circuit for fault conditions or maintenance.

Category 3: Loss of a section of the substation resulted by fault condition or maintenance.

Category 4: Loss of the whole substation because of fault condition or maintenance.

Sumic, and Pistorese, (1994) and Ochoa, and Hirt, (1998) considers the following layouts for a substation;

Single Busbar:

Each socket is protected by its own circuit breaker and due to this there may be no loss in its supply.

A fault on the transformer circuit breaker causes loss of the transformer and can be amended after isolating the faulty circuit breaker.

Maintenance of a feeder circuit breaker is due to loss of the circuit.

A busbar fault causes loss of one feeder and one transformer.

These are some of its characteristics.

Mesh Substation:

Its characteristics are:

Two different circuit breakers are required to disconnect or connect a circuit while the disconnection process is the opening of the mesh.

These circuit breakers can be maintained without supply loss or protection while in the same case there is no bypass facility needed.

Busbar faults cause just one circuit breaker loss while breaker faults causes loss of two circuits at maximum.

One and a half Circuit Breaker layout:

Substation Design Categories

It is known as the 1 1/2 circuit breaker because of the fact that in its design, there are nine circuit breakers that are used for the protection of the six feeders. Some of the characteristics are:

• Very high security against supply loss.
• Can control any one pair of circuits or in groups.
• It has complex arrangements and there are additional costs of the circuit breakers.Circuit breaker:

Dead tank: circuit breaker is located at earthly potential.

Live tank:  it’s circuit breaker is located at its line potential.

These can be done by increasing creep age length, insulation greasing among others.

Power Transformers

It is  the largest  item which is single in a substation. Precautions are highly taken due to large quantity of oil that can lead to fire. There are auto transformers that are smaller and have reduced loss.

Overhead line termination

There are two methods namely

Tensioning conductors to substation structures.

Tensioning conductors to ground winches.

The choice is determined considering the height of towers and also substation proximity.

Dutta, and Overbye, (2012) explains that a transient event is the instantaneous change in the state leading to a burst of energy for a short period of time. Transients are further divided into impulsive and oscillatory transients. In consideration of their response, impulsive would elevate in a period of 0.1ms and hold till 1ms. Oscillatory could have a frequency surge up to 5 KHz.

The hazards of these substations are very dangerous to human body. Lumbreras, and Ramos, (2013) the electric magnetic field which has a phase of 90 deg and oscillating at angle of 180 degrees traverses the air and starts revolving inside the human body causing human cells to heat up. These will damage the body tissues. These magnetic fields also results to an electric current in human tissues and cells and because the skin is in contact it can be remorsefully damage. Those people living within 300 meters of a substation have an increased rate of getting some type of cancer.

To wind up, Adams, and Laughton,  (1974) suggests that the best design of a substation is one that has minimum loss of supply and still its maintenance cost is not high although it’s hard to find one. In its design all process must be followed and properly structured. The cost of expenditure is very high taking to consideration the number of equipment used to set up this station and also their individual value. These substations should be located in their own strategic positions away from human residences. The reason for this is to provide safety to human body which is mostly affected by the electric magnetic field created.

References

Adams, R. N., & Laughton, M. A. (1974, February). Optimal planning of power networks using mixed-integer programming. part 1: Static and time-phased network synthesis. In Proceedings of the Institution of Electrical Engineers (Vol. 121, No. 2, pp. 139-147). IET.

Dutta, S., & Overbye, T. J. (2011, February). A clustering based wind farm collector system cable layout design. In Power and Energy Conference at Illinois (PECI), 2011 IEEE (pp. 1-6). IEEE.

Dutta, S., & Overbye, T. J. (2012). Optimal wind farm collector system topology design considering total trenching length. IEEE Transactions on Sustainable Energy, 3(3), 339-348.

Fellin, L., Kusstatscher, P., & Rostagni, G. (1995). Overall plant design, layout and commissioning. Fusion engineering and design, 25(4), 315-333.

Kersting, W. H. (1984). A method to teach the design and operation of a distribution system. IEEE Transactions on Power apparatus and Systems, (7), 1945-1952.

Lumbreras, S., & Ramos, A. (2013). Optimal design of the electrical layout of an offshore wind farm applying decomposition strategies. IEEE Transactions on Power Systems, 28(2), 1434-1441.

Ochoa, J. R., & Hirt, R. L. (1998). U.S. Patent No. 5,798,939. Washington, DC: U.S. Patent and Trademark Office.

Sumic, Z., & Pistorese, T. A. (1994). U.S. Patent No. 5,329,464. Washington, DC: U.S. Patent and Trademark Office.

Yoshida, K., Kobayashi, Y., Ueda, Y., Tanaka, H., Muto, S., & Yoshizawa, J. (1986, November). Knowledge-based layout design system for industrial plants. In Proceedings of 1986 ACM Fall joint computer conference (pp. 216-222). IEEE Computer Society Press.