Report

EE 306 TRANSFORMERS Instructor: Dr. Mahamed Shwehdi Done By: Ahmad Saleh Al-Owied 1 Transformers Very large three-phase network transformer. 2 Transformer electromagnetic device (mutual induction) 1. components: -- 2 adjacent coils -- coils not physically connected to each other 3 Transformer (cont.) 2. operation: a) AC in primary coil produces D B b) Secondary coil receives a D in I & V S N S N 4 Transformers Wye / Wye connection IA Ia A a V AB B C V BN V an V AN N V CN V bn n V cn V ab b c 5 Transformers Three-phase network supplies a load through a transformer. Transform er S upply N etw ork Load Y -Y V net_ A N X n et V AN V an X tr_ s A a Ia IA V lo ad _a n Equivalent circuit of the wye-wye n N S upply N etw ork T ra nsform er X tr_s X net V n et_A N IA L oad V AN V an Ia V load _an Single-phase equivalent circuit for phase A of the three-phase wye-wye transformer system 6 Wye / Delta connection Ia IA A a a V AB V CA V AN VBN B V CN N V BC C I ac c I ba b Ib V ab b Icb Ic V ca V bc c 7 Transformers V AN T ran sfo rm er A IA I ba AC V BN V AN V AB V CA B IB a V ab Ia V ab V ca I cb b Ib I ca I ac AC V CN C AC S u p p ly V BN V BC IC V bc I ac V CN V bc c I ab I bc Ic V ca L oad N Wye-delta connected transformer 8 Transformers R tr_ p X tr_p T IA V p_ A N Rc Xm spe X tr_ s V an V AN R tr _s Ia V s_a n Y -D Single-phase equivalent circuit of a wye-delta transformer. 9 Delta / Wye connection IA A V AB V CA B a IAB n IB IC A V BC C Ia V bn IC IB C V an Ib V cn Ic V ab b V ca V bc c 10 Delta / Delta connection IA A Ia a Ib a IAB V AB B V ab ICA I ac b c C 11 Transformers Three-phase Transformer Relations Transformer Connection Primary and Secondary Voltage Phase Relation Wye-Wye VAN is in phase with Van Zero A and a Wye-Delta VAN is in phase with Vab 30° A and ab Delta-Wye VAB is in phase with Van –30° AB and a Delta-Delta VAB is in phase with Vab Zero AB and ab Phase Shift* Windings Placed on the Same Leg * Note: Phase shift lead between line-to-line voltages, VAB and Vab, and line-to-neutral voltages, VAN and Van, and line currents, IA and Ia. 12 Transformer Turns Ratio ratio of the # of turns in the secondary coil to the # of turns in the primary coil TR NS NP numerical factor indicating relative change in PD across a transformer TR > 1 = V (step up) TR < 1 = V (step down) 13 Transformer Law (change in voltage in a transformer) D in V is directly proportional to the ratio of the # of turns in the secondary to the # of turns in the primary Formula: NS NP = VS VP NS secondary coil turns NP primary coil turns VS secondary voltage VP primary voltage direct relationship 14 Transformer Current Current in a transformer will be inversely proportional to the TR of the transformer IP primary coil current formula: N S IP NP = IS IS secondary coil current I vs. V = inverse relationship VS VP = IP IS 15 Types of Transformers Based on TURNS RATIO 1. step-up turns ratio > 1 VS > VP IS < IP 2. step-down turns ratio < 1 VS < VP IS > IP 16 Transformer Types (cont.) Based on STRUCTURE OF COILS 1. air core -- inside area of coil is empty -- inefficient induction 2. open core -- ferromagnetic material inside coils -- B = induction 17 Transformer Types (cont.) 3. closed core -- ferromagnetic ends connected -- B induction 4. shell -- lazy square eight -- overlap of coils on same ferromagnetic core 18