What is the Main Inlet Valve?

Main inlet valve or shortly we say MIV is the spherical valve which installed before water enter into spiral casing of the hydro turbine.

Main inlet valve or MIV at hydro power plant.

Water from the dam go to the penstock and before water enter the turbine, MIV is a component in between stop the water for small maintenance purpose in the turbine hall.

Francis Turbine

Francis Turbine

Francis Turbine Blade

The Francis turbine is a type of water turbine that was developed by James B. Francis. It is an inward flow reaction turbine that combines radial and axial flow concepts.Francis turbines are the most common water turbine in use today. They operate in a head range of ten meters to several hundred meters and are primarily used for electrical power production.

Theory of Operation

The Francis turbine is a reaction turbine, which means that the working fluid changes pressure as it moves through the turbine, giving up its energy. A casement is needed to contain the water flow. The turbine is located between the high pressure water source and the low pressure water exit, usually at the base of a dam.The inlet is spiral shaped. Guide vanes direct the water tangentially to the turbine wheel, known as a runner. This radial flow acts on the runner's vanes, causing the runner to spin. The guide vanes (or wicket gate) may be adjustable to allow efficient turbine operation for a range of water flow conditions.As the water moves through the runner its spinning radius decreases, further acting on the runner. For an analogy, imagine swinging a ball on a string around in a circle; if the string is pulled short, the ball spins faster due to the conservation of angular momentum. This property, in addition to the water's pressure, helps Francis and other inward-flow turbines harness water energy efficiently.

Application

Francis turbines may be designed for a wide range of heads and flows. This, along with their high efficiency, has made them the most widely used turbine in the world. Francis type units cover a head range from 20 meters to 700 meters, and their output power varies from just a few kilowatts up to one gigawatt. Large Francis turbines are individually designed for each site to operate at the highest possible efficiency, typically over 90%. In addition to electrical production, they may also be used for pumped storage; where a reservoir is filled by the turbine (acting as a pump) during low power demand, and then reversed and used to generate power during peak demand.

Turbine Runner Type in Hydroelectricity Power Plant

Turbine Runner Type in Hydroelectricity
Various types of water turbine runners.
From left to right: Pelton Wheel, two types of Francis Turbine and Kaplan Turbine

Type of water turbines in hydro are as below:

1) Reaction turbines
1.1 Francis
1.2 Kaplan, propeller, bulb, tube, straflo
1.3 Tyson, Gorlov (Freeflow types)
1.4 Water wheel
1.5 Archimedean screw turbine

2) Impulse turbines
2.1 Pelto
2.2 Turgo
2.3 Michell-Banki (crossflow/ ossberger turbine)