LABORATORY 4 SINGLE PHASE TRANSFORMERS

Transcription

1 LBORTORY 4 SGLE PHSE TRSFORMERS OBJECTES 1. To determne the tranformer turn rato 2. To erform the no-load and hort crcut tet 3. To calculate the tranformer equvalent crcut FORMTO ngle-hae tranformer wll be nvetgated n th lab. t a te-u tranformer 110/220 wth the rated ower of 1000 and rated frequency of 60 Hz. 1. deal Tranformer tranformer a devce ued to change voltage and current of C electrc ower. n the mlet veron t cont of two wndng wraed around a magnetc core; wndng are not electrcally connected, but they are couled by the magnetc feld, a t hown n Fgure 4.1. When one wndng connected to the C electrc ower, the electrc current generated. Th wndng called the rmary wndng. The rmary current roduce the magnetc feld and the magnetc flux lnk the econd wndng, called the econdary wndng. The C flux through the econdary wndng roduce an C voltage, o that f ome medance connected to the termnal, an C electrc current uled. Fgure 4.1. Sketch of an deal tranformer. Fgure 4.2 how the chematc ymbol of a tranformer. 4-1

2 Fgure 4.2. Schematc ymbol of a tranformer. The mlet model of the tranformer called the deal tranformer and t neglect any ower loe and leakage magnetc fluxe. umng that the rmary wndng ha turn of wre, and the econdary wndng ha turn, the relatonh between the rmary voltage and the econdary voltage ( t) = = a Equaton (4.1) () t where a the turn rato n the rmary and econdary wndng Smlarly, for the rmary and econdary current a = Equaton (4.2) ( t) () t a 1 For C ower the ame can be alo exreed n the haor notaton = a and = Equaton (4.3) 1 = Equaton (4.4) a 2. Real Tranformer The deal model of the tranformer uffcent for aroxmate analy of the electrc crcut only. For full analy a more comlete model needed and t hould nclude: core loe, wndng loe, magnetng current and all leakage magnetc fluxe. t can be hown that the equvalent crcut n Fgure 4.3 fully rereent all thee effect. R X R X R jx c M Fgure 4.3. The model of a real tranformer. 4-2 deal tranformer

3 The retance R rereent the ohmc retance of the rmary wndng and R of the econdary wndng. The reactance X and X model the leakage flux of the rmary and econdary wndng, reectvely. The retance R c reonble for the core loe due to hytere and eddy current, and X M for the generaton of the man flux (magnetng reactance). ll medance on the econdary de of the tranformer can be recalculated for the rmary de. Th alo know a the referrng to the rmary de and reult n the equvalent crcut hown n Fgure 4.4. R jx a 2 R 2 ja X a R c jx M a Fgure 4.4. The tranformer model referred to the rmary voltage level 3. Determnng Equvalent Crcut Exermental determnaton of all element n the tranformer equvalent crcut nvolve three tet: meaurement of the rmary retance oen-crcut tet hort crcut teat 3.1 Meaurement of the Prmary Retance DC ohmmeter hould be connected acro the rmary termnal and R hould be recorded. 3.2 Oen-Crcut Tet The tranformer econdary hould be oen-crcuted and rmary wndng uled wth a full rated voltage (Fgure 4.5). The nut voltage ( oc ), rmary current ( oc ) and ower (P oc ) are meaured. ~ W Tranformer Fgure 4.5. Connecton for tranformer oen crcut tet. 4-3

4 Th tet uffcent to calculate the core retance and magnetng reactance, ung Equaton (4.5) to (4.12). The conductance of the core-lo retor gven by: 1 GC = RC Equaton (4.5) 1 BM = X M Equaton (4.6) Snce thee two element are n arallel, ther admttance add and the total exctaton admttance 1 1 YE = GC jbm = j RC X M Equaton (4.7) The magntude of the exctaton admttance can be determned by the Equaton (4.8) Y E = Equaton (4.8) The angle of the admttance can be found from knowledge of a crcut ower factor. The oen crcut ower factor (PF) gven by: P PF = co ϕ = Equaton (4.9) and the ower factor angle gven by Equaton (4.10) P ϕ = co 1 Equaton (4.10) The ower factor alway laggng for a real tranformer, o the angle of the current alway lag the angle of the voltage by ϕ degree. Therefore, the admttance Y E 1 1 YE = ϕ = co 1 PF = R jx Equaton (4.11) C M 3.3 Short-Crcut Tet The tranformer econdary termnal are hort-crcuted and the rmary voltage uled wth the voltage, much reduced comarng wth the rated value (Fgure 4.6). n ractcal tuaton, th voltage adjuted o that the rmary current aroxmately rated, and the rmary voltage ( c ), rmary current ( c ) and ower (P c ) are meaured. ~ W Tranformer Fgure 4.6. Connecton for tranformer hort crcut tet. 4-4

5 The followng Equaton (4.12) to (4.16) can be ued to calculate element n the rmary and econdary branche. The magntude of the ere medance referred to the rmary de of the tranformer SC Z SC = Equaton (4.12) SC The hort crcut ower factor (PF) gven by: SC co Equaton (4.13) PF = ϕ = and the ower factor angle gven by Equaton (4.14) PSC ϕ = co 1 SC SC Equaton (4.14) Therefore, SC 0 SC Z SC = = ϕ SC ϕ SC Equaton (4.15) The ere medance Z SC equal to Z SC = R jx eq eq Equaton (4.16) P SC SC EQUPMET 1. Sngle-hae tranformer 2. arable C ource 3. Two Dgtal multmeter 4. C wattmeter 1. arable C ource The lab varable C ource hown n Fgure 4.7 a comlex devce, whch degned to rovde afety condton of your exerment. t cont of ngle-hae tranformer, varac and lam bulb connected n ere wth the outut. Fgure 4.7. arable C ource 4-5

6 2. C Wattmeter Electrc ower meaured by mean of a wattmeter. Th ntrument of the electrodynamc tye. t cont of a ar of fxed col, known a current col, and a movable col known a the otental col. mlfed electrodynamc wattmeter crcut hown n Fgure 4.8. ~ R Fgure 4.8. mlfed electrodynamc wattmeter crcut. The current col (tatonary col) of the wattmeter connected n ere wth the crcut (load), and the otental col (movable col) connected n arallel wth the load. When lne current flow through the current col of a wattmeter, a feld et u around the col. The trength of th feld roortonal to the lne current and n hae wth t. The actuatng force of a wattmeter come from the feld of t current col and the feld of t otental col. The force actng on the movable col at any ntant (tendng to turn t) roortonal to the ntantaneou value of lne current and voltage. That why t very mortant to erform a roer connecton of the begnnng and the end of each col. The begnnng of the both current and voltage col of the lab wattmeter have red connector marked wth gn a t hown n Fgure 4.9 Fgure 4.9. Lab C wattmeter PRE-LBORTORY PREPRTO Read the nformaton ecton of the lab manual and lab ntrument decrton. Be ready to anwer queton related to the tranformer theory and ractcal meaurement. 4-6

7 PREDURE 1. Rated Quantte From the tranformer namelate, note the rated value of S 1, 1, and 2. Calculate the rated maxmum current for the ammeter on the rmary and econdary de-do not exceed thee value. 2. Retance Meaurement Ung an ohmmeter, meaure the retance of the tranformer rmary (R 1 ) and econdary (R 2 ) wndng. 3. Turn Rato The turn rato of a tranformer equal to the rato of rmary and econdary voltage at no-load P P0 a = = Equaton (4.15) where: P0 rmary voltage S0 econdary voltage S S 0 n order to determne the turn rato, connect the crcut a hown n Fgure The tranformer uled wth a varable voltage and both rmary and econdary voltage are meaured and recorded. Do not turn the ower on before your crcut ha been checked by your T! When the layout ha been comleted, have your T to check your crcut connecton and get h/her gnature n your log book C P0 S0. RC TRSFORMER Fgure Tranformer rato meaurement Startng from P0 =20 turn the varac knob and lowly ncreae the nut voltage. 4-7

8 Meaurement and calculaton of the turn rato hould be done for P0 = 20, 40, 60, 80, 100 and 120. Comlete all the data n Table 4.1. P0 () S0 () Turn Rato verage Turn Rato Table 4.1. Tranformer turn rato meaurement and calculaton 4. Oen Crcut Tet 4.1. Connect the aaratu a hown n Fgure ly the rated nut voltage to the rmary wndng and meaure nut voltage, current, ower, and outut voltage. Do not turn the ower on before your crcut ha been checked by your T! When the layout ha been comleted, have your T to check your crcut connecton and get h/her gnature n your log book. oc W oc 120 C oc 2 RC TRSFORMER Fgure Tranformer oen crcut tet meaurement 4.2. Startng from oc =20 turn the varac knob and lowly ncreae the nut voltage. Comlete all the data n Table Determne the arameter of the magnetng branch ung Equaton (4.5) to (4.11). 4-8

9 oc () oc () P oc (W) 20 () Y E 1/Ω co ϕ Table 4.2. Tranformer oen crcut tet meaurement and calculaton. R eq Ω X eq Ω 5. Short-Crcut Tet 5.1. Short-crcut the econdary wndng through an ammeter a hown n Fgure Do not turn the ower on before your crcut ha been checked by your T! When the layout ha been comleted, have your T to check your crcut connecton and get h/her gnature n your logbook Slowly and gradually ncreae the aled voltage and carefully watch the rmary and econdary current. Meaurement and calculaton rato hould be done for hort crcut current value ecfed n Table Calculate the hort crcut medance a meaured from the rmary ung Equaton (4.12) to (4.16). Show your calculaton n your lab reort. Comlete all the meaurement and calculaton n Table c W c 120 C c 2. RC TRSFORMER Fgure Tranformer hort crcut tet meaurement 4-9

10 c () c () P SC (W) 20 () Z SC Ω co ϕ R C Ω X M Ω Table 4.3. Tranformer hort crcut tet meaurement and calculaton. REPORT Record n a lab book crcut dagram and reult for all exerment Calculate average turn rato Calculate arameter of the equvalent crcut Your Lab reort due one week later. Pleae ubmt t to your T n the begnnng of your next lab eon. ote: You mut coy/rnt the Sgnature and Markng Sheet from your manual before comng to the lab eon. 4-10

11 SGTURE D MRKG SHEET LB 4 To be comleted by T durng your lab eon Student ame: T ame: Student # : Check Tak Max. Granted T boxe Mark Mark Sgnature Pre-lab comleted 0 Turn Rato tet comleted 6 Oen Crcut Tet comleted 7 Short-Crcut Tet comleted 7 Overall Reort Prearaton 80 TOTL MRKS