What are the Different Generator Cooling System in Power Plants

 

The generator in the power plant are designed for continuous operation. Thus, the cooling system plays an important role in order to keep it's reliability. Generators used in power generation applications can be placed in three major design classifications based on the cooling medium used:

• Air
• hydrogen
• Water

The table below shows the different characteristics of the cooling medium: 

This table provide us with information about the relative heat removal capability of different medium of cooling. For example, the air has lesser removal capability compare with water. The hydrogen on the other hand is dependent on it's pressure. Thus, the higher the pressure, the higher is the heat removal capability of the hydrogen. 

Air Cooling

Air cooled generators are produced in two basic configurations: 

• Open ventilated (OV) - In the OV design, outside air is drawn directly from outside the unit through filters, passes through the generator and is discharged outside the generator. 
• Totally enclosed water to air cooled (TEWAC)-  In the TEWAC design, air is circulated within the generator, passing through frame-mounted air to water heat exchangers. In this process, the water is circulating and enters the heat exchanger that cools down the air which directly penetrate the internal part of the generator. 

TEWAC Cooling System

Hydrogen Cooling

Hydrogen-cooled generator construction except for the frame is very similar to that of air cooled generators. Most designs use direct radial flow cooling similar to that shown in Figure below. 

Hydrogen Cooling System

The stator frame, on the other hand, because of the need to contain 30 psig to 75 psig hydrogen, uses thick plate cylindrical construction. End shields are more rugged and contain a hydrogen seal system to minimize leakage. Conventional hydrogen cooling, while available for generators rated below 100 MVA, is most often applied to gas and steam turbine driven units above 100 MVA.

The armature voltage and current of a hydrogen/water-cooled generator is significantly higher than those of air cooled units. As a result, the insulation voltage stress and forces on the armature windings can be several orders of magnitude larger than those experienced on lower rated units can. 

Direct Water Cooling

Water-cooling adds manufacturing complexity, as well as, requires the need for auxiliary water-cooling and deionizing skid, and associated piping, control and protection features. Even more compact generator designs are achievable through the use of direct water cooling of the  generator armature winding. 

Direct Water Cooling System

This design uses hollow copper strands through which deionizer water flows. A closed loop auxiliary base- mounted skid supplies the cooling water. The cool water enters the winding through a distribution header on the connection end of the generator. The warm water is discharged in a similar manner on the turbine end of the generator.

Water cooling is expensive to use since it needs auxiliary plant to cool the return water. Also, it needs complex and sophisticated piping system inside the generator in order to avoid leaks that could lead to the damage of the generator unit.