In an Impulse Design of Steam Turbine,there is an attempt to attain no Expansion of Steam within the Moving Blades and as such its Pressure remains constant while passing over the Blades. The Expansion of Steam,however,takes place in a set of Stationary Nozzles which lower its Pressure but impart a High Velocity to it.The Velocity attained in a properly designed Nozzle depends upon the Pressure drop through it.
Impulse Turbine Design may be classified as Single Stage,Multi Pressure Stage,Multi Velocity Stage and Combination of Multi Pressure and Velocity Stage. The term Pressure Stage refers to unit of Nozzles combined with Moving Blades in which the Energy of the Steam resulting from each Pressure drop,is utilised. The Velocity Stage refers to the number of Moving Blades in which the energy of the Steam in each Pressure drop is absorbed.
In case of Reaction Turbine the Steam expands as it flows over the Blades which,therefore act as Nozzles.In fact it is this drop in Pressure that gives a Reaction and hence Motion to the Rotor.
A pure Reaction Turbine,comprises of two or more Radial Tubes rotating and communicating with another pipe or trunnion through which Steam is supplied to Nozzle which are screwed into the ends of the Radial Pipes and arranged with their Axis in the Tangential Direction.
The main difference between an impulse turbine and a reaction turbine lies in their mode of operation and arrangements. An impulse turbine consists of nozzles which expands and thus converts the thermal energy of the steam into kinetic energy for impact on the moving blades. However reaction turbine consists of an alternate row of fixed blades and moving blades where one half of the stage pressure drop of steam occurs at the fixed blades producing the impulse effect and the remaining one half occurs at the moving blades producing the reaction effect. Unlike impulse turbines, reaction turbines undergo two pressure drops leading to a considerable end thrust for this turbines.
in the impluse turbine pressure drop takes places only in
nozzle where as in the reaction turbine pressure takes
palaces both in nozzle ann blades van... so for thta reason
cross section of the tubine from inlet to outlet keep
constant in impluse turbine. and will vary in rection
impulse turbine rotates with the help of impulsive forces
and were as in reaction turbine with the help of reactive
force and another difference in impulse turbine is there is
pressure drop only in stationary blades and were as in
reaction turbine pressure drop is there both in stationary
and moving blades
1. In impulse turbine it is not essential that the wheel should run full. Moreover, there should be free access of air between the vanes and the wheel where as it is essential that the wheel should always run full and kept full of water in reaction turbine. 2. It is possible to regulate the flow of water without loss in impulse turbine but in reaction turbine it is not possible to regulate the flow without loss 3.In impulse turbine the entire water energy is first converted in kinetic energy but there is no energy conversion in reaction turbine.