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What is Needed in Transformer Models? U I ECE524 Lecture 37 Amount of detail depends on frequency of desired response Power flow stability often just model leakage, perhaps winding resistance » Tap changing » Perhaps wye-delta phase shift Transformers Spring 2016 What is Needed in Transformer Models? U I ECE524 Lecture 37 Fault studies require more information » Connection info – wye – delta – zig-zag – autotransformer – etc. » Grounding » Possible impact of tertiary Transformers Spring 2016 1 U I Low Frequency Transients ECE524 Lecture 37 Similar modeling info to fault programs » Connection information more important Magnetizing branch » Saturation Core loss term Not using per unit » Need to include turns ratio » Divide leakage L, winding R between windings Transformers U I Spring 2016 Single Phase Equivalent Circuit ECE524 Lecture 37 Winding resistance Leakage inductance Core loss--total losses Non-linear inductor model for magnetizing branch Transformers Spring 2016 2 U I ECE524 ATP Options Lecture 37 Ideal transformer component Saturable transformer component BCTran -- preprocessor that converts description of transformer to coupled RL Can also create manually using coupled RL branches Transformers Spring 2016 Ideal transformer component U I ECE524 Lecture 37 Combines ideal transformer with ideal source » Simply enter transformation ratio » Can be used to implement floating source too » Uses frequency from basic ATPDraw settings – Need to make sure this matches system frequency – Setting “Branch = 0” forces ATP to use this frequency – “Branch = 1” can avoid this (Vm=1E-20) Transformers Spring 2016 3 U Accessing Transformer I Models ECE524 Lecture 37 Note that three phase and single phase options Transformers U I Transformers Spring 2016 ECE524 Dialog box Lecture 37 Spring 2016 4 U I ECE524 Text Entry Lecture 37 C ...........................Source data ...................................... C Bus--><I<Amplitude<Frequency<--T0|Phi0<---0=Phi0 <----Tstart<----Tstop 14NodeJ C NodeL><-|---n----><NodeK<NodeM<NodeX 18 The 18 card need to follow the 14 Node X can be used for current measurement Transformers U I Spring 2016 ECE524 Adding R, L Terms Lecture 37 The balance of the regular transformer model can be created by: » Adding external R, L for series terms » Shunt resistor for core loss term » Saturable inductor component for Lm Create winding connections externally Can also add capacitance Transformers Spring 2016 5 U I ECE524 Limitations Lecture 37 Limited to two winding transformers It is very easy to create numerical problems in the simulation with the ideal transformer Transformers U I Spring 2016 ECE524 Saturable Transformer Lecture 37 Model has built-in circuit elements » Winding resistance » Leakage inductance (can’t enter 0) » Core loss resistance » Magnetizing branch – not entered as an L in mH » Can set all except leakage to 0 to simplify » Enter winding to winding ratios Transformers Spring 2016 6 U I Single Phase Saturable Base Attributes ECE524 Lecture 37 Io, Fo are steady-state point on saturation characteristic for initial Lm RMS = 0 or 1: determines how the saturation characteristic is entered. Output is information about mangetization branch Transformers U I Saturation Characteristic Spring 2016 ECE524 Lecture 37 If RMS = 0, this is current versus flux If RMS = 1, this is RMS current versus RMS voltage at frequency of first source in the system The 0,0 point is assumed by the program Up to 10 points can be entered » Better to limit to 3-5 Transformers Spring 2016 7 U Viewing The Saturation I Characteristic ECE524 Lecture 37 If RMS = 0, this is current versus flux If RMS = 1, this is RMS current versus RMS voltage at frequency of first source in the system The 0,0 point is assumed by the program Up to 10 points can be entered » Better to limit to 3-5 for better numerical behavior » Does not include hysteresis Transformers U I Spring 2016 ECE524 Three Phase Model Lecture 37 Icon changes with the connection type. Here is three winding with all WYE Here is 2 winding with delta-wye Note that there is a point to connect to measure magnetizing branch voltage Three leg core option Transformers Spring 2016 8 U I ECE524 Three Phase Model Lecture 37 Enter data for each winding Select Y, D, or Zig-zag Three leg option here, but better to use specific case from pulldown menu. Transformers U I Spring 2016 Three Phase ModelThree Leg Core ECE524 Lecture 37 Option to model homopolar reluctance » Saturable-Three Leg Much additional information needed. See help menu. Transformers Spring 2016 9 U I ECE524 BCTRAN Interface Lecture 37 Produces coupled RL model Based on SC and OC test data » Linear Lm internally » Need to add external nonlinear Transformers U I Additional BC Tran Data Transformers Spring 2016 ECE524 Lecture 37 Spring 2016 10 U I Y Y ECE524 Hybrid Transformer Lecture 37 XFMR Y Transformers U I Spring 2016 ECE524 Nonlinear Devices Lecture 37 Models for resistors and inductors » Differ model implementation The Type 98 and Type 93 inductors do not include hysteresis » Same user data as saturation in saturable xfmr » Set with initial conditions Transformers Spring 2016 11 U I Type 96 reactor with hysteresis ECE524 Lecture 37 Option to enter residual flux along with steady-state Transformers U I Spring 2016 ECE524 Example Lecture 37 SRC1 Transformer with saturation Transformers SRC2 U SRC B12 B13 Spring 2016 12 U Results from increasing I voltage ECE524 Lecture 37 200 [V ] 150 100 50 0 -50 -100 6 -150 [mA ] -200 0.00 0.02 (f ile Exam pl1.pl4; x-v ar t) v :B13 0.04 0.06 0.08 [s] 0.10 4 v :B12 2 0 -2 -4 -6 0.00 0.02 (f ile Exam pl1.pl4; x-v ar t) c :SR C Transformers 0.04 0.06 0.08 [s] 0.10 -B12 Spring 2016 13