INTRODUCTION TO ELECTRICAL MACHINES

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.

ELECTRIC MOTOR -

AN ELECTRIC MOTOR IS A MACHINE THAT CONVERTS MECHANICAL ENERGY INTO ELECTRICAL ENERGY. WHENEVER, A CURRENT CARRYING CONDUCTOR IS PLACED IN BETWEEN MAGNETIC FIELD IT EXPERIENCES A FORCE IN A PARTICULAR DIRECTION THIS IS THE PRINCIPLE OF MOTOR.

SIMILAR TO THE GENERATOR MOTOR ALSO CONSIST OF TWO BASIC PARTS ROTOR AND STATOR. MOTORS NEEDS ELECTRIC SUPPLY TO BOTH STATOR AND ROTOR BUT SOME TYPES OF MOTORS LIKE PERMANENT MAGNET MOTOR, INDUCTION MOTORS, ETC. ARE NEEDS SUPPLY TO ONLY ONE WINDING. ELECTROMAGNETIC FORCE BETWEEN TWO WINDING CAUSES IT TO ROTATE IN ONE DIRECTION OF ROTATION HOWEVER DIRECTION CAN BE CHANGED BY SOME METHODS.

TYPES OF ELECTRICAL MOTOR -

• AC MOTOR - AC MOTOR IS A MACHINE THAT USES AN AC ALTERNATING CURRENT SUPPLY FOR ITS MOTORING OPERATION.

• INDUCTION MOTOR

• SINGLE PHASE INDUCTION MOTOR

• SPLIT PHASE INDUCTION MOTOR

• CAPACITOR START INDUCTION MOTOR

• CAPACITOR START AND RUN INDUCTION MOTOR

• SHADED POLE INDUCTION MOTOR

• THREE PHASE INDUCTION MOTOR

• SQUIRREL CAGE INDUCTION MOTOR

• SLIP RING INDUCTION MOTOR

• SYNCHRONOUS MOTOR

• NON-EXCITED SYNCHRONOUS MOTORS

• HYSTERESIS SYNCHRONOUS MOTOR

• RELUCTANCE SYNCHRONOUS MOTOR

• PERMANENT MAGNET SYNCHRONOUS MOTOR

• DIRECT CURRENT EXCITED MOTORS

• DC MOTOR - DC MOTOR IS A MACHINE THAT USES A DC DIRECT CURRENT SUPPLY FOR ITS MOTORING OPERATION.

• SEPARATELY EXCITED DC MOTOR - SIMILAR TO DC GENERATOR IN THIS TYPE OF MOTOR FIELD COIL AND ARMATURE COIL DOES NOT COMES IN CONTACT PHYSICALLY.

• PERMANENT MAGNET DC MOTOR - PERMANENT MAGNET DC MOTOR HAS A ARMATURE WINDING SIMILAR TO OTHER MOTORS BUT IT DOES NOT CONTAINS FIELD WINDING INSTEAD IT HAS FIXED MAGNETS.

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

• SERIES WOUND DC MOTOR - ARMATURE AND FIELD WINDING CONNECTED TO EACH OTHER IN SERIES.

• SHUNT WOUND DC MOTOR - ARMATURE AND FIELD WINDING CONNECTED TO EACH OTHER IN PARALLEL.

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

• CUMULATIVE COMPOUND - IN THIS TYPE OF MOTOR THE SHUNT FIELD ASSIST THE MAIN FIELD FLUX, PRODUCED BY THE MAIN FIELD CONNECTED IN SERIES WITH ARMATURE WINDING. THUS, THE NET FIELD IS INCREASED.

• DIFFERENTIAL COMPOUND - IN THIS TYPE OF MOTOR THE FIELD PRODUCED BY THE FIELD WINDING OPPOSES THE MAIN FLUX PRODUCED BY THE MAIN SERIES FIELD WINDING. THUS THE NET FIELD DECREASES.

TRANSFORMERS -

TRANSFORMERS DO NOT ACTUALLY MAKE CONVERSION BETWEEN MECHANICAL AND ELECTRICAL ENERGY, BUT THEY TRANSFER ELECTRIC POWER FROM ONE CIRCUIT TO ANOTHER CIRCUIT. THEY CAN INCREASE OR DECREASE (STEP-UP OR STEP-DOWN) THE VOLTAGE WHILE TRANSFERRING THE POWER WITHOUT CHANGING THE FREQUENCY, BUT WITH THE CORRESPONDING DECREASE OR INCREASE IN THE CURRENT. INPUT POWER AND OUTPUT POWER OF AN ELECTRICAL TRANSFORMER SHOULD IDEALLY BE THE SAME.

STEP UP TRANSFORMERS INCREASES THE VOLTAGE LEVEL FROM PRIMARY TO SECONDARY BUT WITH THE CORRESPONDING DECREASE IN THE CURRENT. WHEREAS, STEP-DOWN TRANSFORMER DECREASE THE VOLTAGE LEVEL WITH THE CORRESPONDING INCREASE IN THE CURRENT SO AS TO KEEP THE POWER CONSTANT.

BASIC TYPES OF TRANSFORMER -

DEPEND UPON OUTPUT :

1. STEP UP TRANSFORMER - IT GIVES BOOSTED VOLTAGE AND DECREASED CURRENT AT ITS OUTPUT.
2. STEP DOWN TRANSFORMER - IT GIVES BOOSTED CURRENT AND DECREASED VOLTAGE AT ITS OUTPUT.

DEPEND UPON PHASES - ACCORDING TO THIS TRANSFORMER CLASSIFIED IN TWO TYPES AS FOLLOWS,

1. SINGLE PHASE TRANSFORMER - THIS TYPE OF TRANSFORMERS USED FOR 230V 1-PHASE OR BELOW.
2. THREE PHASE TRANSFORMER - THIS TYPE OF TRANSFORMERS ARE USED MOSTLY IN INDUSTRIES FROM 400V TO 11KV 3-PHASE SUPPLY.

DEPENDING UPON VOLTAGE LEVEL :

1. POWER TRANSFORMER - THIS TYPE OF TRANSFORMERS ARE USED FOR HIGH VOLTAGE TRANSMISSION LINE, AT GENERATOR PLANTS, ETC. THIS TRANSFORMER WITH HIGH EFFICIENCY WHEN LOADED AT FULL LOAD CAPACITY.
2. DISTRIBUTION TRANSFORMER - THIS TYPE OF TRANSFORMERS ARE USED FOR MEDIUM VOLTAGE LEVEL AT CONSUMER/UTILITY END.FOR EX. DISTRIBUTION STATION, POLE MOUNTED DISTRIBUTED TRANSFORMER.THIS TRANSFORMER GIVES FULL EFFICIENCY WHEN LOADED AT 50% OF IT'S FULL LOAD CAPACITY.
3. INSTRUMENT TRANSFORMER - THIS TYPE OF TRANSFORMER IS USED FOR MEASUREMENT OF HIGH VOLTAGE AND CURRENT WITH THE HELP LOW SCALED/ RESOLUTION METERS.

DEPENDING UPON WINDING :

1. TWO WINDING TRANSFORMER - HAS A TWO SEPARATE WINDINGS WITH THE RATIO GREATER THAN. EASY TO DESIGN AS BOTH WINDINGS ARE PLACED ON DIFFERENT LIMBS.
2. AUTO-TRANSFORMER - HAS A SINGLE WINDING WHICH ACT AS BOTH PRIMARY AND SECONDARY WINDING WITH RATIO LESS THAN 2. COMPLICATED TO DESIGN AS SINGLE WINDING HAS TAPPING ON IT WHICH SEPARATES IT IN TWO PARTS PRIMARY WINDING AND SECONDARY WINDING.

DEPENDING UPON LOCATION :

1. OUTDOOR TRANSFORMER - THIS TRANSFORMERS HAS NO LIMITATION OF SIZE AND WEIGHT. THIS CAN INCLUDE HIGH VOLTAGE TO LOW VOLTAGE LEVEL TRANSFORMERS. ENVIRONMENTAL EFFECTS OF TRANSFORMER ARE MORE BECAUSE IT IS EXPOSED TO ATMOSPHERE.
2. INDOOR TRANSFORMER - THIS TRANSFORMER HAS DESIGNED AT CERTAIN SIZE AND WEIGHT CRITERIA WHICH IS GIVEN BY THE CONSUMER/UTILITY. THIS CAN BE DESIGNED AND USED FOR MEDIUM VOLTAGE LEVEL TO LOW VOLTAGE LEVEL. LEAST ENVIRONMENTAL EFFECTS ON TRANSFORMER, AS IT IS NOT EXPOSED TO ATMOSPHERE.

DEPENDING UPON COOLING SYSTEM :

1. OIL COOLED - THE COOLING IS PROVIDED WITH THE HELP OF CIRCULATING MINERAL OIL. LOW VISCOSITY OIL GIVES BETTER COOLING TO THE TRANSFORMER.
2. AIR COOLED - ATMOSPHERIC AIR IS USED AS A COOLANT FOR THIS TRANSFORMER.THIS TYPE OF TRANSFORMERS HAS WINDOWS ON ITS OUTER BODY IN ORDER TO KEEP THE GOOD AIR FLOW THROUGH CORE AND WINDINGS OF TRANSFORMER.

DEPENDING UPON TYPES OF CORE :

1. CORE TYPE - THIS TYPE OF TRANSFORMER HAS TWO WINDINGS HV AND LV PLACED ON TWO SEPARATE LIMBS OF YOKE/BODY OF TRANSFORMER. THUS THE DESIGN PROVIDES ONLY ONE WINDOW(SINGLE MAGNETIC CIRCUIT).
2. SHELL TYPE - THIS TYPE OF TRANSFORMER HAS TWO WINDINGS HV AND LV PLACED ON CENTRAL LIMB WHILE OTHER TWO LIMBS ACT AS A PATH FOR MAGNETIC LINES(DOUBLE MAGNETIC CIRCUIT).
3. BERRY TYPE - THIS TYPE OF TRANSFORMER HAS A CORE WHICH LOOKS LIKE THE SPOKES OF A WHEEL. THE  METAL SHEET TANKS ARE USED FOR HOUSING THIS TYPE OF TRANSFORMER. IT HAS TRANSFORMER OIL FILLED INSIDE FOR COOLING PURPOSE.