Components of Hydroelectric Power Plants:

 Components of Hydroelectric Power Plants:

Different references has been taken from devighat hydropower plant -nuwakot, Nepal

Dam

The dam is the most important component of a hydroelectric power plant. The dam is built on a large river that has an abundant quantity of water throughout the year. It should be built at a location where the height of the river is sufficient to get the maximum possible potential energy from water. Dams are individually unique structures, and dam construction represents the biggest structures in basic infrastructure in all countries.

 

Water Reservoir

The water reservoir is the place behind the dam where water is stored. The water in the reservoir is located higher than the rest of the dam structure. The height of water in the reservoir decides how much potential energy the water possesses. The higher the height of water, the more its potential energy. The high position of water in the reservoir also enables it to move downwards effortlessly. The height of water in the reservoir is higher than the natural height of water flowing in the river, so it is considered to have an altered equilibrium. This also helps to increase the overall potential energy of water, which helps ultimately produce more electricity in the power generation unit.

forebay

A forebay or head pond is the temporary water storage, regulating reservoir provided at downstream end of canal just at upstream of penstock. When the turbine rejects the load forebay acts as a storage reservoir whereas it supplies water a a sort of regulating reservoir when load increases.

 In Devighat HPS there is forebay just at upstream of penstock where water from downstream of trishuli is collected. A spillway has also been provided at side of forebay for the purpose of spilling the excess water. The water spilled is mixed into the river by dissipating its energy at stilling basin. For the purpose of flushing the sediments of fore-bay, three flushing gates are also provide

 

Intake or Control Gates

These are the gates built on the inside of the dam. The water from the reservoir is released and controlled through these gates. These are called inlet gates because water enters the power generation unit through these gates. When the control gates are opened the water flows due to gravity through the penstock and towards the turbines. The water flowing through the gates possesses potential as well as kinetic energy.

 

The Penstock

The penstock is the long pipe or the shaft that carries the water flowing from the reservoir towards the power generation unit, composed of the turbines and generator. The water in the penstock possesses kinetic energy due to its motion and potential energy due to its height. The total amount of power generated in the hydroelectric power plant depends on the height of the water reservoir and the amount of water flowing through the penstock. The amount of water flowing through the penstock is controlled by the control gates.

Penstock in Devighat HPS is steel penstock which is partially buried and open in some locations. Length of penstock pipe is 510 m.

No. of penstock pipes= 3 (one for each unit)

 

 

Water Turbines

Water flowing from the penstock is allowed to enter the power generation unit, which houses the turbine and the generator. When water falls on the blades of the turbine the kinetic and potential energy of water is converted into the rotational motion of the blades of the turbine. The rotating blades cause the shaft of the turbine to also rotate. The turbine shaft is enclosed inside the generator. In most hydroelectric power plants there is more than one power generation unit. There is a large difference in height between the level of the turbine and level of water in the reservoir. This difference in height, also known as the head of water, decides the total amount of power that can be generated in the hydroelectric power plant. There are various types of water turbines such as Kaplan turbine, Francis turbine, Pelton wheels etc. The type of turbine used in the hydroelectric power plant depends on the height of the reservoir, quantity of water and the total power generation capacity.

Used Water turbine:  Vertical – axis Francis Turbine

Speed of turbine: 333 rpm

 

Francis turbines are the most prominent reaction turbines, and they are best fit to the medium head and flow conditions. The water enters these turbines radially, which means it enters perpendicular to the rotational axis. The water always flows inwards, towards the center, once it enters the turbine. The water exits the turbine axially, parallel to the rotating axis, after passing through the turbine. The flow is controlled in these turbines by wicket gates or guide vanes located upstream of the runner. The guiding vanes are oriented to provide the inlet angle in the runner that is required for a specified flow. This opening angle is changed to maintain the turbine's consistent speed under variable load conditions. A significant amount of hydraulic energy is converted into kinetic energy inside guide vanes. When the flow reaches the inlet of the runner, a part of the total pressure energy is converted into kinetic energy and the rest of the energy is converted inside the runner blades and the runner is connected to a shaft, which rotates the generator at a constant rpm to generate electricity.

Generators

It is in the generator where the electricity is produced. The shaft of the water turbine rotates in the generator, which produces alternating current in the coils of the generator. It is the rotation of the shaft inside the generator that produces a magnetic field which is converted into electricity by electromagnetic field induction. Hence the rotation of the shaft of the turbine is crucial for the production of electricity and this is achieved by the kinetic and potential energy of water. Thus in hydroelectric power plants potential energy of water is converted into electricity.

 

 

 

 

 

General layout of hydropower plant

 

Figure 2 General Lay-out of hydropower

Powerhouse components

·         Cooling system,

·         Ventilation system,

·         Lubrication system,

·         Drainage and dewatering system,

·         OHT crane, HVAC,

·         Air compressor system,

·         Lighting system, emergency supply system,

·         Station earthing, lightening protection,

·         Fire detection, fire-fighting and hydrant system, and

·         Safety tagging and safety interlocks.

Cooling system

The cooling is realized by a closed system that circulates the cooling medium (water or oil) over the components and a heat exchanger where it releases the heat to secondary cooling water. The secondary cooling water is the same surface water that drives the turbines and it causes problems with fouling/scaling of those heat exchangers. As a result of this, the turbines need to be shut down regularly for heat exchangers to be cleaned. The economic impact due to loss of income for each day of turbine downtime is enormous, in addition to the budget that needs to be set aside for the workload of this.