Cooling system architecture in Hydropower

The main function of cooling system is to cool Generating lubricating oil and turbine shaft seal. So, basically, two main consumer of cooling system in Power house are

a)     Generating lubricating oil cooler:   Generator bearing is cooled by Lubrication oil and Lubrication oil is cooled by the water, circulated by cooling system..

      Fig: Heat Flow Diagram

b) Turbine shaft seal: Water also used to cool/seal turbine shaft seal.

Water from draft tube/tailrace is used as coolant .Cooling system can be open loop or closed loop. In open loop cooling water system water is finally discharged to tail race level or MIV pit. However, in closed loop cooling the same water is recirculate back.

The major components of cooling system are as follows:

1)      Pump: An appropriate pump is used to circulate the water. Normally, there are two centrifugal pumps in parallel per unit. One will be the main pump and other will be stand-by pump. Standby pump will operate main pump fails thereby increasing reliability of the system.

2)      Filter/Strainer: Water is filtered by duplex/simplex filter to remove silt and abrasive material from it before reaching to consumer. Two or more filters of different capacity can be used in series connection based on the size of the particles to be filtered.

3)      Water Tank: Pumped water is stored in a tank. The Tank will acts as buffer

4)      Fitting and Arrangement: It consists of valves, Pressure switch, piping and pressure gauge.

5)      Heat exchanger: An appropriate heat exchanger is used to extract heat to water from the consumer.

                                  

Heat Treatment

There are different heat treatment method.Heat treatment change the crystalline structure and hence change the property of material.Hardness, Strength and ductility can be controlled by heat treatment process.

1. Annealing: It is the process of heating the material above re crystallization temperature followed by very slow cooling at the furnace. Annealing is done to increase the toughness.However, hardness is reduced in the process.Following are the significance of annealing
   It increases the ductility of the material
   It improves the grain size of crystal structure
   It helps to relieves internal stress
   
2. Quenching: It is the process of heating the material above re crystallization temperature (to red hot) followed by immediate cooling at brine solution. Quenching increase hardness of the material.However, the material becomes brittle after quenching
   
3. Tempering: Tempering is usually done after quenching(hardening) to reduce the brittleness.In tempering, the metal is heated below the critical point for some time and then allowing it to cool in still air.
   
4. Normalizing: Normalization is the process of heating the metal to upper critical temperature and then cooling in still air.Tempering provides a way to carefully decrease the hardness of steel, thereby increasing the toughness to more desirable point. Normalizing increases the ductility and help to relieve the internal stress.
   
   
   If you find difficult to visualize these processes the following video might be useful
   
   https://www.youtube.com/watch?v=fLvZkZxiXnE&list=LLaXo5zVPTkRjLHl4CHv9Vbw&index=2