Tuesday, January 5, 2016
DC Generator Working Principle
Generator is a machine which produces EMF dynamically from a mechanical input.In other words it is a machine which converts mechanical energy to electrical energy.DC generator is nothing but which gives DC output voltage.Working principle DC generator is very simple.
DC generator works on the principle of faraday's laws.It states that,
Whenever conductors cuts the magnetic flux (φ) EMF induces,the amount of EMF is directly proportional to rate of change of flux linkages.
E=-dφ/dt
[-ve sign given by lenz's law]
The above equation of faraday's law is the fundamental working principle of generator,Synchronous generator..etc.A DC generator produces direct power,AC generator produces alternating power.
To get better idea on working of generator you need to know about simple loop generator.Let us consider a simple loop DC generator as shown in the figure with one turn coil and one pair of magnet to produce magnetic flux.
| Read: Construction of DC Generator |
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Simple Loop DC Generator Working
So to get rate of change in flux (φ) linkages either conductors or magnetic field should be in motion.So for our convenience assume magnets are stationary and coil is rotating with the help of any mechanical input.now consider the arrangement as below without any input it is in stationary position.
ABCD is the rectangular loop of conductor[coil] which is placed in magnetic field.working of simple loop generator can be explained in 3 steps,
Note:Current & Voltages have same direction because voltage is cause of current.we cant find direction of voltage simply by applying any rule so we take current direction as reference in DC generator working
Step-1
Rotate the coil ABCD in the clockwise direction with help of mechanical input say prime-mover,and it is moved to right angled position,
As during this movement AB and CD sides of the coil cut the flux lines there will be an EMF induced in these both of the sides (AB & BC) of the loop by faraday's law,Maximum flux is linked in this position because AB and CD are parallel to magnetic filed direction.field strength at AB & CD are not same so dφ exist.As the closed path exists in the coil current flows in the coil.Current direction can be found by flemming's right hand rule.
By flemming's right hand rule current flow we find current direction as from A to B ,C to D.
Step-2
Now coil is rotated to next right angled position, AB and CD are perpendicular to magnetic filed direction.Magnetic field strength at AB & CD are same.So difference between the field strength is zero i.e., dφ almost zero.hence induced emf,current also zero.
Step-3
Now coil is rotated to next right angled position, AB and CD are parallel to magnetic filed direction.So maximum amount of EMF will induce[Like Step-1].But the current direction reverses.By flemming's right hand rule current flow from B to A ,D to C.
This is the working principle of any generator,but from step-1 & step-2 we can observe that,current getting reversed that we don't want in DC generator to eliminate alternating current we use commutator.Commutator is an arrangement which converts AC to DC, in this way DC generator works produces DC voltages.In practical DC generator there will no.of conducts and poles[magnets] to produce required amount of EMF.
DC generator Working with Commutator
DC generator Output Wave
After completion of half rotation, the direction of current in the particular conductor will be reversed.Hence, the direction of current in every armature conductor will be alternating after a half rotation. With a split ring commutator, connections of the armature conductors also gets reversed when the current reversal occurs. And therefore, we get unidirectional current at the terminals.
| Must Read: Commutation in DC Machine |
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