TRANSFORMER

 TRANSFORMER

A TRANSFORMER IS A STATIC DEVICE THAT TRANSFORMS THE LEVEL OF VOLTAGE/CURRENT FROM ONE LEVEL TO ANOTHER AT THE SAME FREQUENCY. IT IS CALLED A STATIC DEVICE AS THERE IS NO MOVING PART IN IT.

ON LARGE SCALE IT IS USED IN POWER TRANSMISSION AND DISTRIBUTION. BASICALLY, TRANSFORMERS ARE PLACED AT THE SENDING END OF THE TRANSMISSION LINE TO INCREASE THE VOLTAGE LEVEL AS THE VOLTAGE LEVEL WILL DECREASE DURING THE PASSAGE FROM ONE END TO OTHER DUE TO LOSSES OCCUR IN TRANSMISSION LINE PARAMETERS.

AT RECEIVING END ALSO TRANSFORMER IS KEPT TO DECREASE THE VOLTAGE LEVEL AS A LOW VOLTAGE LEVEL HAS TO BE DISTRIBUTED TO THE CONSUMERS.

AT A LOW SCALE, TRANSFORMERS ARE USED IN RECTIFIERS, VOLTAGE STABILIZERS, MEDICAL ELECTRONICS, TELECOMMUNICATION ETC.

APPLICATION

1. USED AS AN IMPEDANCE MATCHING DEVICE

2. TO MEASURE VOLTAGE AND CURRENTS THESE ARE KNOWN AS INSTRUMENT TRANSFORMERS

CONSTRUCTION OF TRANSFORMER:-

CONSTRUCTION OF TRANSFORMER CONSISTS OF VARIOUS CIRCUITS AND AUXILIARIES:-

#MAGNETIC CORE

#CONDUCTING WIRES

#CONSERVATOR TANK

#BREATHER

#TANK AND TANK OIL

#HV AND LV BUSHINGS FOR INPUT AND OUTPUT COME

#COOLING FINS AND WHEELS

MAGNETIC CORE

THE MAGNETIC CORE OF A TRANSFORMER IS MADE UP OF STACKS OF THIN LAMINATION (0.35MM THICKNESS)

THIS MATERIAL ALLOWS THE USE OF HIGH FLUX DENSITIES (1-1.5T) AND ITS LOW LOSS PROPERTIES TOGETHER WITH LAMINATED CONSTRUCTION REDUCE THE CORE LOSS TO FAIRLY LOW VALUES.

LAMINATIONS ARE OVERLAPPED SO THAT TO AVOID THE AIR GAP AT THE JOINTS BY (L) SHAPED OR (I) SHAPED LAMINATION STRUCTURE.

TRANSFORMER CORE BUILT-UP OF OVERLAPPING OF L-SHAPED STRUCTURE ARE KNOWN AS CORE-TYPE TRANSFORMER AND that BUILT-UP E AND I SHAPED STRUCTURE OVERLAPPING ARE KNOWN AS SHALL TYPE TRANSFORMER.

ELECTRIC CONDUCTORS/WIRES USED

THE HV OR LV WINDING ARE WOUND ON THE CORE AND ARE ELECTRICALLY INSULATED FROM EACH OTHER FROM THE CORE.

BASICALLY, TWO TYPES OF COILING IS DONE

- CYLINDRICAL CONCENTRIC COILS

-SANDWICHED COILS

CONSERVATOR TANK

IT IS A SMALL SIZE TANK. IT IS PARTIALLY FILL WITH OIL. THE CONSERVATOR TANK TAKES THE PRESSURE OF OIL CONTRACTION AND EXPANSION BY THE CHANGE IN THE TEMPERATURE.

BREATHER

OIL IS NOT ALLOWED TO COME IN CONTACT WITH THE ATMOSPHERIC AIR WHICH MAY CONTAIN MOISTURE. THE MOISTURE SPOILS THE INSULATING PROPERTIES OF OIL.

WHEN THE TRANSFORMER COOLS, THE OIL LEVEL GOES DOWN AND THE AIR IS DRAWN IN IT.

THIS IS KNOWN AS BREATHING. THE AIR COMING IN IS PASSED THROUGH A DEVICE CALLED 'BREATHER' FOR THE PURPOSE OF EXTRACTING MOISTURE.

TANK AND TANK OIL

THE CONSTRUCTION OF THE TRANSFORMER HAS TO ENSURE EFFICIENT REMOVAL OF HEAT FROM THE CORE AND WINDINGS SO THAT TEMPERATURE RISE IS LIMITED TO THAT ALLOWED FOR THE CLASS OF INSULATION EMPLOYED.

THIS IS ARCHIVED IN POWER TRANSFORMERS BY IMMERSING THE BUILT-UP TRANSFORMER IN A CLOSED TANK FILLED WITH NON-FLAMMABLE INSULATING OIL CALLED TRANSFORMER OIL.

HV AND LV BUSHINGS

CONNECTION OF INPUT(SUPPLY) AND TO THE OUTPUT(LOAD) ARE NOT MADE DIRECTLY WITH THE HV/LV WINDINGS FOR THE SAFETY PURPOSE.

COOLING FINS AND WHEELS

TO FACILITATE NATURAL OIL CIRCULATION AND TO INCREASE THE COOLING SURFACE EXPOSED TO THE AMBIENT, TUBES, OR FINES ARC PROVIDED ON THE OUTSIDE OF TANK WALLS

PRINCIPLE OF TRANSFORMER OPERATION

CONSIDER TWO COILS 1 AND 2 WOUND ON A SIMPLE MAGNETIC CIRCUIT. THESE TWO COILS ARE INSULATED FROM EACH OTHER AND THERE IS NO ELECTRICAL CONNECTION BETWEEN THEM.

LET N1 AND N2 BE THE NUMBER OF TURNS IN COILS 1 AND 2 RESPECTIVELY.

WHEN A SOURCE OF ALTERNATING VOLTAGE V1 IS APPLIED TO COIL 1, AN ALTERNATING CURRENT Io FLOWS IN IT. THIS ALTERNATING CURRENT IS PRODUCED ON ALTERNATING FLUX IN THE MAGNETIC CIRCUIT. THE FLUX LINKS THE TURN N1 OF THE COIL AND INDUCES IN THEM AN ALTERNATING EMF E1 BY SELF INDUCTION.

NEGLECTING CORE AND COPPER LOSSES, WE FIND THAT ALL THE FLUX PRODUCED BY COIL 1 ALSO LINKS N2 TURNS OF COIL 2 AND INDUCES AN EMF E2 BY MUTUAL INDUCTION.

IF THE COIL 2 IS CONNECTED TO THE LOAD THEM AN AC WILL FLOW THROUGH IT AND ENERGY WILL BE DELIVERED TO THE LOAD. THUS, ELECTRICAL ENERGY IS TRANSFERRED FROM COIL 1 TO COIL 2 BY A COMMON MAGNETIC CIRCUIT.

HENCE THERE IS NO RELATIVE MOTION BETWEEN THE COILS, THE FREQUENCY OF THE INDUCED EMF IN COIL 2 IS EXACTLY THE SAME AS THE FREQUENCY OF THE APPLIED VOLTAGE TO THE COIL.

COIL 1 WHICH RECEIVES ENERGY FROM THE SOURCE OF AC SUPPLY IS CALLED THE PRIMARY WINDING.

COIL 2 WHICH IS CONNECTED TO THE LOAD AND DELIVERS ENERGY TO THE LOAD IS CALLED SECONDARY WINDING.

TYPES OF TRANSFORMER

1. CORE TYPE

2. SHELL TYPE

1. CORE TYPE TRANSFORMER

IN THIS TYPE THE CORE IS SURROUNDED BY WINDING AND HAVING 2 LIMBS OR LEGS.

FOE THE GIVEN OUTPUT AND VOLTAGE RATING THIS TYPE REQUIRES LESS IRON BUT MORE CONDUCTOR MATERIAL. IN THIS LEAKAGE FLUX IS REDUCED BY PLACING HALF OF THE WINDING OVER ONE LEG AND THE OTHER HALF OVER THE SECOND LEG.

TO MINIMIZE INSULATION LV WINDINGS ARE PLACED ADJACENT TO THE STEEL CORE AND HV WINDINGS OUTSIDE.

2. SHELL TYPE TRANSFORMER

IN THIS TYPE, WINDING IS SURROUNDED BY THE CORE AND THE CROSS-SECTIONAL AREA OF OUTER LIMB IS Y2 OF THE MIDDLE LIMBS.

IT IS AN ECONOMICAL FOR LOW VOLTAGE AND HIGH CURRENT RATINGS.

#THESE ARE PREFERRED FOR LOW POWER APPLICATIONS.

#THIS LV AND HV WINDINGS ARE WAND OVER THE CENTRAL LIMB.

#THE BOTTOM AND TOP LV COILS ARE OF 1/2 THE SIZE OF OTHER LV COILS

#THEY DEPEND UPON THE APPLICATIONS

1. DISTRIBUTION TRANSFORMER

2. POWER TRANSFORMER

3. AUTO TRANSFORMER

4. ISOLATION TRANSFORMER

STEP-UP TRANSFORMER

A TRANSFORMER IN WHICH THE OUTPUT (SECONDARY) VOLTAGE IS GREATER THAN ITS INPUT (PRIMARY) VOLTAGE IS CALLED STEP-UP TRANSFORMER

STEP DOWN TRANSFORMER

A TRANSFORMER IN WHICH THE OUTPUT (SECONDARY) VOLTAGE IS LESSER THAN ITS INPUT (PRIMARY) VOLTAGE IS CALLED STEP DOWN TRANSFORMER

DISTRIBUTION TRANSFORMER

THE PURPOSE OF A DISTRIBUTION TRANSFORMER IS TO REDUCE THE PRIMARY VOLTAGE OF THE ELECTRIC DISTRIBUTION SYSTEM TO THE UTILIZATION VOLTAGE SERVING THE CUSTOMER.