FOWLER CHAPTER 12 LECTURE 12 TRANSFORMERS

TRANSFORMERS CHAPTER 12 TRANSFORMERS ARE MULTIPLE WINDING INDUCTORS. WORK ON THE PRINCIPLE OF MUTUAL INDUCTANCE. TRANSFORMERS ARE 2 OR MORE COILS LINKED BY MAGNETIC FLUX. PRIMARY COIL INDUCES A VOLTAGE IN A SECONDARY COIL BY MUTUAL INDUCTANCE. THE AMOUNT OF MUTUAL OR SELF INDUCTION IS MEASURED IN HENRY’S.

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SYMBOLS

TRANFORMER WINDINGS

TRANSFORMERS TRANSFER POWER FROM PRIMARY TO SECONDARY WINDINGS. PRIMARY TAKES ELECTRICAL ENERGY AND CONVERTS IT TO MAGNETIC ENERGY SECONDARY TAKES MAGENTIC ENERGY AND CONVERTS IT TO ELECTRICAL ENERGY. THERE IS NO PHYSICAL COUPLING BETWEEN THE PRIMARY AND SECONDARY WINDINGS.

STEP UP/DOWN TRANSFORMERS STEP UP STEP DOWN

COEFFICIENT OF COUPLING (COC) THE PORTION OF FLUX THAT LINKS ONE COIL TO ANOTHER. COC CAN VARY FROM 0 TO 1. AT 1, ALL THE FLUX IS COUPLED. COC CAN ALSO BE EXPRESSED. AS A %. 100% = COUPLING OF 1. COUPLING IN Fe CORE TRANSFORMERS IS NEARLY 100%. SINCE THERE IS LITTLE FLUX LEAKAGE INTO THE AIR. AIR CORE TRANSFORMERS HAVE LOW COC DUE TO THE HIGH RELUCTANCE OF AIR, CAUSING A LARGE AMOUNT OF LEAKAGE. THIS IS CALLED LEAKAGE FLUX. THIS CAN BE CONTROLLED SOMEWHAT BY SPACING THE COILS CLOSER TOGETHER. IF COILS ARE PERPENDICULAR TO EACH OTHER COC IS CLOSE TO ZERO.

CHANGING VOLTAGE VAULES STEP UP, STEP DOWN TRANSFORMERS. WITH 100% COULPING THE TURNS RATIO AND VOLTAGE RATIO ARE EQUAL.

20KV 500A 10 MW STEP UP TRANSFORMER AT POWER PLANT 400KV 25A 10 MW LONG DISTANCE TRANSMISSION LINES 400KV 25A 20KV 500A 10 MW STEP DOWN DISTRIBUTION TRANSFORMER AT SUBSTATION TO LOADS AND OTHER STEP DOWN TRANSFORMERS. ADVANTAGES OF HIGH VOLTAGE TRANSMISSION LINES

EFFICIENCY OF TRANSFORMERS IN THE REAL WORLD CORES AND COILS OF TRANSFORMERS CONVERT SOME ELECTRICAL ENERGY INTO HEAT. EFFICIENCY OF TRANSFORMERS IS EXPRESSED IN TERMS OF POWER. EX.12-3 P309 WHAT IS THE EFFICIENCY OF A TRANSFORMER WITH A INPUT OF1880W INTO THE PRIMARY COIL AND 1730W OF OUTPUT FROM THE SECONDARY COIL. 150W LOSS, CALLED POWER LOSS.

POWER LOSS IN TRANSFORMERS IS CAUSED BY: 1.HYSTERSIS LOSS : CAUSED BY RESIDUAL MAGNETISM LEFT IN THE CORE EACH TIME THE FIELD REVERSES, WHICH CAUSES HEAT LOSS.

Steel has a "fat" hysteresis loop. It is difficult to demagnetize, so steel is used for permanent magnets. Substances, such as soft iron, with thin hysteresis loops, are used for transformer cores. HYSTERSIS LOOP, THE NARROWER THE LOOP, THE LESS THE LOSS. HYSTERSIS LOSSES INCREASE WITH THE FREQUENCY OF PRIMARY CURRENT. Eddy Currents, Magnetic Braking and Lenz's Lawhttp://

2. EDDY CURRENT LOSS ARE INDUCTED CURRENTS IN THE CORE FROM ITS OWN MAGNETIC FLUX. THESE EDDY CURRENTS FLOWING THRU THE CORES RESISTANCE PRODUCES HEAT. What Is Eddy Current

HOW CAN WE REDUCE EDDY CURRENT LOSES? BY INSULATING EACH LAMINATION OF THE CORE WITH A THIN LAYER OF OXIDE. THIS INCREASES THE RESISTANCE OF THE CORE WHICH REDUCES HEAT LOSS SINCE, Eddy Current Demo.

3. COPPER LOSS POWER LOSS IN THE WINDINGS OF THE TRANSFORMER. CAN BE FOUND FROM P= I²R, R IS THE OMIC RESISTANCE OF THE WINDING TURNS. LOSS AND EFFICIENCY TRANSFORMERS ARE MOST EFFICIENT WHEN FULLY LOADED. EFFICIENCY DECREASES AS THE LOAD DECREASES. WHY? CURRENT FLOW IN THE TRANSFORMER PRIMARY DOES NOT DECREASE IN DIRECT PORPORTION TO THE DECREASE IN LOAD. PRIMARY CURRENT CAUSES CORE AND Cu LOSS WHEN LIGHTLY LOADED.

TRANSFORMER CORES. CLASSIFIED BY CORE MATERIALS. SUCH AS Fe AND AIR CORE, I AND E LAYERS ALTERNATE IN STACKING WHEN BUILDING THE CORE. MAKES AN AIR GAP WHICH HELPS KEEP THE INDUCTANCE MORE CONSTANT FOR DIFFERENCE CURRENTS. Disassembling laminated transformer core

TYPES OF TRANSFORMERS CLASSIFIED BY USE: POWER 60Hz, FROM 115 TO 1000’S VOLTS. USED FOR POWER DISTRIBUTION AND LIGHTING.

CONTROL TRANSFORMERS : USED BY SMALLER RECTIFIERS AND CONTROL CIRCUITS USING RELAYS SOLENOIDS.

AUDIO TRANSFORMERS. WORK AT FREQUENCIES UP TO 20KHz.

RF TRANSFORMERS f (RADIO RANGES) CAN BE Fe OR AIR CORE.

CONSTANT VOLTAGE TRANSFORMERS : PROVIDE STABLE SECONDARY VOLTAGE, DESPITE VARING PRIMARY VOLTAGE.

ISOLATION TRANSFORMER HAVE EQUAL PRIMARY AND SECONDARY VOLTAGE, USED TO ISOLATE ELECTRICAL EQUIPMENT FROM THE POWER DISTRIBUTION SYSTEM.

VARIOUS ISOLATION TRANSFORMERS

MORE ISOLATION TRANSFORMERS

AUTO TRANSFORMER: PRIMARY WINDING IS PART OF THE SECONDARY WINDING AND VICE-VERSA.

1,000 MVA, 1050/525kV single-phase autotransformer

VARIABLE TRANSFORMER: WORK AT POWER FREQUENCIES. THESE ARE AUDIOTRANSFORMERS WITH AN ADJUSTABLE SECONDARY.

IMPEDANCE MATCHING (IM) P.317 THIRD MOST COMMON USE FOR TRANSFORMERS IS IM WHY? WHEN IM OF SOURCE IS MATCHED TO IM OF THE LOAD. MAX. POWER TRANSFER OCCURS. A TRANSFORMER CAN MAKE A LOAD APPEAR TO THE SOURCE LARGER OR SMALLER THEN IT ACTUAL IS. REFLECTED IMPEDANCE (Z) FROM THE SECONDARY APPEARS TO THE PRIMARY AS BEING EQUAL.

TRANSFORMER RATINGS VOLTAGE RATING ARE SPECIFIED FOR PRIMARY AND SECONDARY WINDINGS UNDER LOAD AND NO LOAD CONDITIONS. POWER RATINGS: GIVEN IN WATTS GOING TO A RESISTIVE LOAD

Full Load Current Ratings of Self-CooledThree-Phase Transformers V Line to Line Voltage kVA , ,3881, ,0821, ,0002,7762,4061, ,5004,1643,6081,8041, , ,8112,4061, , ,0072, , ,6092, , ,5113, , ,8111, , ,8041, , ,4061,388802

SERIES AND PARALLEL WINDINGS P.230 SOME TRANFORMERS CAN BE BUILT WITH MULTIPLE PRIMARY AND SECONDARY WINDINGS WHICH CAN BE CONNECTED IN SERIES OR PARALLEL.

3 PHASE TRANSFORMERS

500 KVA 3 PHASE TRANSFORMERS

3 PHASE TRANSFORMER UNDER CONSTRUNTION

ULTIMATE USE FOR TRANSFORMERS: A SUPERCONDUCTING FUSION REACTOR

MAGNETIC CONFINMENT CONTAINTER FOR A PLASMA FUSION REACTOR

DRAWING SHOWING HOW MAGNETIC FIELDS COMPRESS 1 MILLION DEGREE PLASMA

INTERIOR OF A FUSION REACTOR