Substation Equipments

1. Power Transformers
2. Current Transformers
3. Voltage Transformers
4. Busbars 
5. Circuit breaker
6. Isolator
7. Earthing Switch
8. Shunt Capacitor
9. Shunt Reactor
10. Surge Arrestor (Lightning Arrestor)
11. Line Trap
12. Line
13. Power Cables
14. Control Cables
15. Series Capacitor
16. Metering, Control and Relay Panel
17. Insulators
18. Coupling Capacitor

Corona

During cloudy, rainy weather the high voltage gradient at the surface of conductor may cause ionization of air surrounding the surface of conductor giving audible, violent visible, intermittent discharge corona. Corona losses are high on a new transmission line and n rainy season. Corona is accompanied by hissing sound, vibration, power loss and radio interference (R.I.). The phenomena of corona is accompanied by predominant third harmonic currents which cause radio interference in the adjacent communication circuits.

Properties of Electric Current

Electric Current posses some properties which make it as most useful form of energy.

1. Heating Property: Whenever current flows through any conducting material it heats the material.
2. Magnetic Property: When current flows through a conductor produces magnetic field.
3. Electro-Chemical Property: Whenever current passes through electrolyte it produces chemical reaction.

Advantages of Electrical Energy over other types of energy

 Its most common form of energy used in houses and industry. And some reasons for its popularity are listed below:-

1. Its called  "Clean and Green energy" . Clean because it does't have any byproducts and green because it doesn't cause any kind of pollution neither any of the resources of mother earth are exhausted when we use this form of energy.
2. It can be easily converted to other form of energy.
3. It is much cheaper than other forms of energy.
4. It can be easily transmitted to various location very conveniently and efficiently.
5. This form of energy can be controlled and monitored easily.

Methods to Decrease earth resistance

Clean the surface of the electrode, mix the soil in the earthing pit with charcoal, salt and soft soil. Pour sufficient water in the earthing pit.  Connect the earthing rod with the equipment by low resistance copper strip. Use  more number of electrodes, larger mesh.

Gas Insulated Switchgear

SF6 Gas Insulated Switchgear (GIS) are preferred for voltage rating of 36 kV, 72.5 kV, 145 kV, 245 kV, 420 kV and above. In such a substation, the various equipments like Circuit Breakers, Busbars, Isolators, Load Break Switches, Current Transformers, Voltage Transformers, Earthing Switches, etc are housed in metal enclosed modules filled with SF6 gas. The SF6 gas provides the phase to ground insulation and phase to phase insulation. As the dielectric strength of SF6 gas is higher than air, the clearance required are smaller. The overall size of each equipment and the complete substation is reduced to about 10% of convention air-insulated substation. GIS are installed indoor.

The various modules of GIS are factory assembled and are filled with SF6 gas at a pressure of about 3kgf/cm2 .  Thereafter, thy are taken to site for final assembly. Such substations are compact and can be installed conveniently on any floor of a multistoried building or in an underground substation. The installation time s substantially reduced. Such installation are preferred in cosmopolitan cities , industrial townships, hilly terrains etc., where cost of land is very high and higher cost of  gas insulated switchgear is justified by saving due to reduction in floor area requirement. They are also preferred in heavily pollutes areas where dust, chemical fumes and salt layers cause frequent flashovers in conventional outdoor air-insulated switchgear.

The SF6 Gas Insulated Switchgear (GIS) contain the same component as the conventional outdoor substations. All live parts are enclosed in metal housings filled with SF6 gas. The live parts are enclosed in metal housings filled with SF6 gas. The live parts are supported on cast resin insulators. Some of the insulators are designed as barriers between neighboring modules such that gas do not pass through them. The entire installation is sub-divided into compartments which are gas tight with respect to each other. Thereby the gas monitoring system of each compartment can be independent and simpler.

The enclosures are non-magnetic material such as aluminum or stainless steel and are earthed. The gas tightness si provided by static ‘O’ seals placed between machined flanges. The ‘O’ rings are placed in the grooves such that after assembly, the O ring get squeezed by about 20%. Quality of material and dimension of grooves and O-seals are important to ensure gas tight performance.

The GIS has gas monitoring system. The gas density in each compartment is monitored. If pressure drops slightly, the gas is automatically tapped up. With further gas leakage, the lo pressure alarm is sounded or automatic tripping or lock out occurs.

Creep in Hydro Turbines

Creep is the situation in which there is slow rotataion (below 20 rpm) due to leakage of water through wicket gates which is always there. Creep situation is totally unwanted and undesirable for the m/c life. To know its presence we usually apply an instrument known as Creep Indicator. This assembly consists of solenoid and brushes. In ususal case when unit is not runing brush has contact with shaft and for any movement of shaft, brush tilts actuating a micro switch which give an alarm signal. Creep inidcator is designed such that it remains insensitive during Start Up, Running and Stopping. During this period solenoid get energised and removes the brush contact from the shaft.