Eighty Percentage 80% of thermal power plants has boiler feed pump , that takes the water from the feedwater system ( from the DA) and provide this water to the boiler system , to generate steam which is responsible for rolling the Turbine,Therefore Generate Electricity.
Normally Feed water pumped to the boiler is pumped to the Boiler’s Drum where at the top point of the boiler, so we have to provide big pump that can handle big pressure with great flow to the boiler.
That is happened by this huge pump ( Boiler Feed Pump ) , BFP is usually rotate with 5000 rpm ,150 barg and can provide about 300 T/H.
This big pump needs a prime mover with high electrical rating - Power Plants usually use Electrical Induction motor - to rotate this pump, the rating of this prime mover is usually about ( 5 MWatts , 6.6 KVolts , 1600 rpm ). It is very huge rating if you imagin , 5 MWatts can provide Electricity to a small town.
so , as you see in the picture ( left hand is the prime mover_motor) , (Right hand is the pump) and what is it at the middle of the picture??
Hydraulic Coupling is used to transmit Power in a wear-free manner from a prime mover (driving machine) to a power consumer(driven machine-pump). the power is transmitted in the following way:-
- by means of a connecting coupling between the driving machine and geared variable speed coupling.
- by means of a step-up gear unit between the input shaft and primary shaft.
- hydro-dynamically by means of the working oil between the primary wheel and the secondary wheel.
- by means of connecting coupling between the driving machine and geared variable speed coupling.
the control at the hydraulic coupling is done by the scoop tube control, it provide infinitely variable adjustment of the driven machine’s speed. the power from the driving machine is transmitted to the primary wheel to the working oil, the working oil is accelerated in the primary wheel, and the mechanical energy is converted into the energy of fluid flow. the secondary wheel picks up the flow energy and converts it into mechanical energy. this energy is transmitted to the driven machine.
the speed of the driven machine is infinitely variable. this is accomplished by varying the amount of oil in the coupling during operation with the aid of the adjustable scoope tube.
- Scoop tube advanced as far as possible into the scoop champer of the coupling (0% position):minimum oil ring , minimum speed.
- Scoop tube retracted as far as possible out of the scoop champer of the coupling (100% position): maximum oil ring, maximum output speed.