Bentonite is a naturally occurring clay.  It is used to reduce the earth resistance in earth pits.  Bentonite has the property of absorbing water. 

Bentonite is mixed with ordinary clay and placed between the earthing conductor and the earth.  Water is poured into the mixture.  Bentonite expands to many times it size as it absorbs water.

The earth resistance is reduced due to the water absorbed by Bentonite.  Bentonite will also absorb rain water and retain it for longer than the surrounding soil.  Bentonite earth pits may require water to be poured into the pit during dry seasons.  Special funnels are usually provided in these earth pits for this purpose.

The downsides are that Bentonite has many corrosive impurities, which may corrode the earthing conductors.  This may require periodic maintenance of the earth pits.

PCC (Prestressed Concrete Poles) are poles used in the tranmission and distribution of power.

PCC poles are made by placing high tensile wires in moulds.  The wires are stressed by stretching mechanisms which pull the wires apart.  When the wires are in this stressed condition, concrete is poured into the mould.  After the concrete sets, the wires are released.

A galvanized wire is run through the metal frame to provide for earthing.  This wire is connected to the earthing network.

The concrete is thus prestressed.  This kind of concrete can withstand impact and has high tensile strength.

PCC poles are more expensive than RCC poles.  They are aesthetically pleasing.  They can be manufactured at the site itself.  This will save transportation costs.

RCC (Reinforced Concrete Poles) are widely used in distribution system.  They are made of concrete with a metal reinforcement.

RCC poles are used as their are aesthetically pleasing and blend in well in urban areas with streets with buildings.

RCC poles are cheaper.  They can also be constructed at the site itself.  This reduces the cost of transportation.

RCC poles also have a long life and require less maintenance.  Sometimes, the concrete may chip and become porous.  In such conditions, water may percolate through the concreate and reach the metal reinforcement.  This can cause corrosion.

A downside is that RCC poles tend to shatter when a vehicle collides with them.  This can be prevented with the use of PCC (Prestressed Cement Concrete) poles.

Earth mat is a method of earthing,  It is used in areas with rocky soil, where it is difficult to excavate earth pits.  The earth resistance obtained with pits will also be above the required value.

Earth mats obtain the earth resistance with a large contact area.  The earth mats consists of a number of flat strips laid in the form of a grid.  The grid is placed in a trench which is about 75 cms deep.  The flats are made of mild steel and are of 75 x 8 mm size. 

The flats are welded to one another.   The low resistance is achieved by the increased contact area this method provides.

The earth resistance should ideally be less than 1 ohm.  The resistance value should be periodically checked and recorded.

Earth pits are a very widely used method of earthing electric systems.  Earth pits provide a very low earth resistance and are very reliable.

The earth pit is constructed as follows:

Excavate a pit of approximately the following dimensions 70cms x 70 cms x 250 cms. 

Place a cast iron pipe electrode that is 2.5 metres long and of size 75 -125 mm diameter.  The pipe should be about 10 mms thick.

The pipe is placed vertically. 

A mixture of Bentonite and black cotton soil is mixed in the ratio of 1:6.  The pipe is filled with this mixture.  The space surrounding the pipe is also filled with this mixture.

The earth pit is an important part of any earthing scheme.  It should be maintained properly at regular intervals.  Earth resistance measurements should be taken periodically.

Load Forecasting is an important function in power system operation.  Load forecasting is projecting the estimated load in advance.  Load forecasting can be done for a range of time periods from a few hours to many years. 

Load forecasting is done to decide which power generating units need to be taken in line in a certain period of time.  This is done to determine the best mix of generating units which will give the lowest cost of generation. 

The maintenance activities of the various power plants are also planned based on the load forecasting.  Investments for new power plants which may be required a few years down the line are also planned based on the load forecasting.

The load forecasting is done using historical data and factors, such as seasonal variations, projected economic activity, population growth, etc

Shunt Capacitors  Series Capacitors 
 Shunt Capacitors are used to improve the power factor of the system.  They are used to offset the effect of the series reactance in the line.
 Shunt capacitors are not effective in situations where
the line reactance of the line is high.
 Series capacitors are useful in conditions of high series reactance.
 Shunt Capacitors are connected as a single bank
connected to the bus or individually near the loads.
 Series Capacitors are connected in series with the load