WHAT IS AN ALTERNATOR?
ALTERNATOR IS AN ELECTRIC MACHINE THAT CONVERTS MECHANICAL ENERGY INTO ELECTRICAL ENERGY. THE MECHANICAL ENERGY CAN BE PROVIDED BY MEANS OF PRIME MOVERS.

PRINCIPLE OF ALTERNATOR?

ALTERNATOR WORKS ON THE PRINCIPLE OF FARADAY'S LAW OF ELECTROMAGNETIC INDUCTION, "WHENEVER A CONDUCTOR IS ROTATED BETWEEN A MAGNETIC FIELD, THE CURRENT GETS INDUCED IN THAT CONDUCTOR DUE TO RELATIVE MOTION BETWEEN CONDUCTOR AND MAGNETIC FIELD".

THERE IS ANOTHER RULE IMPLEMENTED FOR ALTERNATORS/GENERATORS WHICH FLEMING'S RIGHT HAND RULE, THIS RULE SHOWS THE DIRECTION OF CURRENT, FORCE, MAGNETIC FIELD. THIS RULE ONLY SHOWS THE DIRECTION OF EITHER ONE IF OTHER TWO DIRECTIONS ARE KNOWN. HOWEVER, IT DOES NOT SPECIFIES THE MAGNITUDE OF THESE PARAMETERS.

TO APPLY FLEMING'S RIGHT HAND RULE WE WILL USE 3 FINGERS OF RIGHT HAND AND HELD THEM PERPENDICULAR TO EACH OTHER SUCH THAT, THE THUMB WILL SHOW DIRECTION OF FORCE/MOTION OF CONDUCTOR, FOREFINGER WILL SHOW THE DIRECTION OF MAGNETIC FIELD, MIDDLE FINGER WILL SHOW DIRECTION OF CURRENT.

UNDERSTANDING WORKING OF ALTERNATOR -

LET US TAKE TWO OPPOSITE MAGNETIC POLES N-POLE AND S-POLE. WE WILL PLACE A COIL/CONDUCTOR IN BETWEEN THE TWO MAGNETIC POLES. WE WILL DIVIDE THE COIL/CONDUCTOR IN TWO PARTS, CONDUCTOR A-B AND THE CONDUCTOR C-D. THE MAGNETIC FIELD OR LINES IS MOVING FROM N-POLE TO S-POLE.

NEGLIGIBLE CURRENT FLOW 0°

NOW, AS PER THE PRINCIPLE, CONDUCTOR NEEDS TO BE ROTATED IN THE MAGNETIC FIELD. FOR THE FIRST ROTATION CONDUCTOR A-B WILL ROTATED CLOCKWISE FOR 90°.NOW THE CONDUCTOR A-B WILL MOVE NEAR S-POLE AND CONDUCTOR C-D WILL MOVE NEAR N-POLE IN HORIZONTAL POSITION.

NOW IF WE APPLY FLEMING'S RIGHT HAND RULE RULE WE CAN SEE THAT THE CONDUCTOR IS NOW PERPENDICULAR TO THE MAGNETIC FILED. THUS, IT WILL PROVIDE MAXIMUM INDUCED CURRENT BECAUSE CONDUCTOR WILL CUT MORE AMOUNT OF MAGNETIC FIELD.AS WE KNOW THE DIRECTIONS OF MOTION OF CONDUCTOR AND THE MAGNETIC FIELD WE CAN USE THE FLEMING'S RIGHT HAND RULE AND CHECK THE DIRECTION OF CURRENT, WE CAN SAY THAT THE CURRENT IS NOW MOVING THROUGH CONDUCTOR A-B FROM POINT A TO B. AND SIMILARLY, THE CONDUCTOR C-D WILL HAVE CURRENT FLOWING FROM POINT C TO D.

MAXIMUM CURRENT FLOW 90°

SO, FOR THE NEXT 90° ROTATION THE CONDUCTORS A-B AND C-D ARE NOW COME IN VERTICAL POSITION. AT THIS POSITION THE CONDUCTOR WILL CUT NEGLIGIBLE AMOUNT OF FLUX AND ALMOST ZERO CURRENT WILL BE INDUCED IN THE CONDUCTOR.

NEGLIGIBLE CURRENT FLOW 180°

ONCE AGAIN, FOR NEXT 90° OF ROTATION THE CONDUCTOR A-B IS NOW COME IN THE VICINITY OF N-POLE AND CONDUCTOR C-D WILL MOVE NEAR S-POLE HOWEVER, THE DIRECT OF CURRENT THROUGH THE CONDUCTOR A-B IS NOW FROM POINT B TO A, AND FOR CONDUCTOR C-D THE DIRECTION OF CURRENT FROM POINT D TO C.

MAXIMUM CURRENT FLOW 270°

THUS, AS PER THE ROTATION THE CONDUCTOR WILL KEEP ON ROTATING AND CURRENT DIRECTION WILL BE KEEP ON CHANGING ACCORDINGLY. THE CIRCULATING CURRENT WHEN THE CONDUCTOR COMES IS HORIZONTAL POSITION FROM VERTICAL POSITION IS B->A->D->C.

FROM THIS WE CAN SAY THAT THE CURRENT WHICH IS INDUCED AT EVERY 180° OF ROTATION WILL FLOW IN OPPOSITE DIRECTION WHICH RESULT IN TOTAL 360° OF ROTATION TO GIVE 1 COMPLETE CYCLE OF AC WAVEFORM OF CURRENT.HOWEVER, ALTERNATOR PRODUCED 3 PHASE OUTPUT IN A MORE SIMILAR BUT LESS DIFFERENT WAY WHICH WE WILL DISCUSS NOW.

HOW 3-PHASE AC POWER IS PRODUCED BY ALTERNATOR?

NOW AS WE KNOW HOW THE ALTERNATOR INDUCES CURRENT IN IT, LET US KNOW HOW TO UTILIZE THIS CURRENT. SO, IF WE TAKE THIS INDUCED CURRENT OUT WITH THE HELP OF BRUSHES WE CAN UTILIZE THIS AC CURRENT.

HOWEVER, THE PRACTICAL ALTERNATOR HAS A DIFFERENT DESIGN THAN A TRADITION GENERATOR DESIGN. THE ACTUAL ALTERNATOR HAS STATIONARY ARMATURE AND ROTATING FIELD INSTEAD OF TRADITION GENERATOR DESIGN. IN ALTERNATOR ROTOR IS CONNECTED WITH TURBINE BLADES WHICH IS ROTATED WITH THE HELP OF SOME MECHANICAL FORCE. THIS WILL HELP ROTOR TO ROTATE AT SYNCHRONOUS SPEED Ns. THE ARMATURE CONDUCTORS ARE STATIONARY AND THEY ARE DISPLACED AT 120° ARRANGEMENT IN THE SLOTS. THIS WILL CAUSE THE CONDUCTORS TO CUT THE MAGNETIC FILED EVERY 120° OF TIME DELAY. RESULTING IN THE PRODUCTION OF THREE DIFFERENT PHASES INSTEAD OF ONLY SINGLE PHASE OF 360° OF AC CYCLE. THIS PRODUCED 3 PHASE AC POWER CAN NOW BE TRANSMITTED TO DISTRIBUTION STATION TO FULFILL THE DOMESTIC AND INDUSTRIAL CONSUMER NEEDS.

3-PHASE AC WAVEFORM

WHAT IS AN ELECTRICAL MACHINE?

AN ELECTRICAL MACHINE IS A DEVICE THAT CONVERTS MECHANICAL ENERGY INTO ELECTRICAL ENERGY AND VICE VERSA. FOR EX. GENERATOR AND MOTOR. HOWEVER, TRANSFORMER IS A TYPE OF MACHINE THAT DOES NOT CONVERT ONE FORM OF ENERGY INTO OTHER BUT IT DOES CONVERTS ONE AC VOLTAGE LEVEL INTO ANOTHER AC VOLTAGE LEVEL.
AN ELECTRICAL MACHINES PLAYS VITAL ROLE IN NOT ONLY INDUSTRIES BUT ALSO IN OUR DAILY LIFE. ELECTRICAL MACHINES ARE USED IN FAN, AC, HAIR DRYER, VEHICLES, TOYS, ETC WHICH WE USE IN DAILY WITHOUT THEM OUR LIFE MORE LIKELY TO BE STOPPED.

TYPES OF ELECTRICAL MACHINES:

ELECTRIC GENERATOR - 

AN ELECTRIC GENERATOR IS A MACHINE THAT CONVERTS MECHANICAL ENERGY INTO ELECTRICAL ENERGY. IT WORKS ON THE PRINCIPLE OF ELECTROMAGNETIC INDUCTION. THIS STATES THAT WHENEVER A ROTATING CONDUCTOR PLACED IN A MAGNETIC FIELD IT CUTS THE MAGNETIC FIELD WHICH INDUCED EMF(ELECTROMOTIVE FORCE) IN THE CONDUCTOR.

EMF (ELECTROMOTIVE FORCE) IS NOTHING BUT A VOLTAGE OR ELECTRIC POTENTIAL. THAT CAUSES CURRENT TO FLOW THROUGH A CONDUCTOR.

GENERATOR IS MADE UP OF A ROTOR AND A STATOR. MECHANICAL ENERGY IN THE FORM OF ROTATION IS PROVIDED TO THE ROTOR BY MEANS OF PRIME MOVERS SUCH AS, TURBINES LIKE, STEAM TURBINE, WIND TURBINE, WATER TURBINE, ETC. ALSO BY IC ENGINES, ETC.

TYPES OF ELECTRICAL GENERATOR -

• AC GENERATOR OR ALTERNATOR = THIS GENERATORS CONVERTS MECHANICAL ENERGY INTO AC CURRENT. ALTERNATORS HAVE STATIONARY ROTOR AND ROTATING FIELD OR STATOR.

• SALIENT POLE TYPE - THIS ALTERNATOR USED FOR LOW AND MEDIUM SPEED BECAUSE IT HAS LARGE NUMBER OF POLES PROJECTING OUT OF ITS PERIPHERY. THIS ALTERNATORS HAVE LARGE DIAMETER AND SHORT AXIAL LENGTH.

• NON-SALIENT OR CYLINDRICAL TYPE - THIS ALTERNATOR HAS SHORT DIAMETER AND LARGE AXIAL LENGTH OF ROTOR, WHERE THE FILED WINDING IS PLACED INSIDE THE TOOTHED TYPE SLOTS PRESENT ON ITS OUTER PERIPHERY. THUS IT CAN BE USED AT HIGH SPEED. IT HAS ONLY 2 OR 4 NUMBER OF POLES.

•  DC GENERATOR = THIS GENERATOR CONVERTS MECHANICAL ENERGY INTO DC CURRENT. DC GENERATORS HAVE ROTATING ROTOR AND STATIONARY FIELD.

• SELF EXCITED DC GENERATOR - IN THIS TYPE FIELD COIL IS CONNECTED WITH ARMATURE IN EITHER SERIES OR PARALLEL OR SERIES-PARALLEL COMBINATION. 

• SERIES GENERATOR - FIELD WINDING IS CONNECTED IN SERIES WITH ARMATURE WINDING.

• SHUNT GENERATOR - FIELD WINDING IS CONNECTED IN PARALLEL WITH ARMATURE WINDING.

• COMPOUND GENERATOR - FIELD COILS ARE CONNECTED IN SERIES AND PARALLEL WITH THE ARMATURE WINDING.

• SHORT SHUNT GENERATOR.

• LONG SHUNT GENERATOR.

• SEPARATELY EXCITED GENERATOR  - IN THIS TYPED OF GENERATOR THE FIELD WINDING DOES NOT COME IN CONTACT WITH ARMATURE WINDING PHYSICALLY, THE SOURCE IS SEPARATELY PROVIDED TO FIELD WINDING.