Transcript Al-Owied
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 VAB B C VBN Van VAN N VCN Vbn n Vcn Vab b c 5 Transformers Transformer Supply Network Three-phase network supplies a load through a transformer. Load Y-Y Vnet_AN Xnet VAN Van Xtr_s A a Ia IA Vload_an Equivalent circuit of the wye-wye n N Supply Network Transformer Xtr_s Xnet Vnet_AN IA Load VAN Van Ia Vload_an Single-phase equivalent circuit for phase A of the three-phase wye-wye transformer system 6 Wye / Delta connection Ia IA A a VAB VCA VAN VBN B VCN N VBC C Iac c Iba b Icb Ib Ic a Vab b Vca Vbc c 7 Transformers VAN Transformer A IA AC VBN VAN VAB VCA B IB Vab Ia Vab Vca Icb VBN VBC C AC Supply a b IC Vbc Iac Ica VCN Vbc c Iab Ib Iac AC VCN Iba Ibc Ic Vca Load N Wye-delta connected transformer 8 Transformers Rtr_p Xtr_p spe T IA Vp_AN Rc Xm Xtr_s Van VAN Rtr_s Ia Vs_an Y-D Single-phase equivalent circuit of a wye-delta transformer. 9 Delta / Wye connection A VAB VCA B VBC C IA Ia Vbn a IAB n IB IC ICA IBC Van Ib Vcn Ic Vab b Vca Vbc c 10 Delta / Delta connection IA A Ia a Iba IAB VAB B C Vab ICA Iac b 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 NS TR 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: N S VS = NP 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 = IS secondary coil current NP IS I vs. V = inverse relationship VS IP = VP 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