Mechanical power to electrical power- the complete concept.

We will discuss here of mechanical power being converted to electrical power. First we will discuss about the controlling of mechanical power then how it is converted to electrical power.

The first thing first- from mechanical power to electrical power is converted by only rotary machines like generators. A generators might be driven by engine, steam power, tidal force, air pressure turbine, water flow etc. The means or mechanical system that drives the alternator is called the prime mover.

01

Mechanical power in rotating machines

Mechanical power to a rotating machine is P.
P = ωT; ω = 2 π n. -ω is to be kept constant,ω = angular speed, rad/s and n=speed(which is should be kept constant)
This formula leaves us only one adjustable parameter to control the power of the rotating machine.
Which is T = torque.Torque is the power with which the piston(s) turns the crankshaft and so rotates the engine.

Thus P = ωT = ωFl = pAl 2 π n

F = pA , force is pressure multiplied by area
T = Fl , torque is force multiplied by the length of the arm (stroke/2)
p=Pressure, A=Area, l=length of the stroke

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Control the power in a rotary machine

So from above formula, we conclude the controlling factors of the power in a rotating machine- which are p=Pressure; A=area of combustion chamber, l=length of piston arm , n= rpm -speed of rotation.

large engine slow rpm

Large engine or turbine (Slow and large)
Slow rpm & big piston surface area. Slow and long stroke power from torque.


medium engine medium rpm

Medium engine or turbine-
Medium rpm & piston surface area . Medium stroke power from torque and medium rpm.


small engine high rpm

Fast engine or turbine-
Very high rpm & small piston surface area . Short stroke power from high rpm.


02

Generated electrical power in rotating machines

Electrical power is combination of two “ingredients” ; P = Active Power, kW, power which does the actual work,rotating, heating, lightning etc. and Q = Reactive Power, kvar, power which is needed for the
excitation of different coils, motors, transformers etc.

Thus the active power (P) is generated by the prime mover which leads us to the conclusion that it has to be controlled by the prime mover and Reactive power (Q) is really generated by the generator/ alternator in accordance of load and excitation.

To increase active power we will have to increase the power of prime mover – adding fuel, gas, more air, more steam etc. And to increase the reactive power we will have increase the flux strength of alternator rotor flux- this can be done by increasing excitation current to rotor circuit.

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