matlab simulink电气仿真集.7z

%% Three-Phase Core-Type Transformer % % This example shows the use of the Three-Phase Transformer Inductance % Matrix Type block to model a three-phase core-type saturable transformer. % It also shows that using three single-phase transformers to simulate % a Yg/Yg core-type transformer is not acceptable. % % Gilbert Sybille (Hydro-Quebec, IREQ) % % Copyright 1997-2012 Hydro-Quebec, and The MathWorks, Inc. %% open_system('power_Transfo3phCoreType') %% Description % % The model shows two identical circuits with a three-phase transformer rated 225 kVA, 2400 V/600V, 60Hz, connected to a 1 MVA, 2400 V power network. % A 45 kW resistive load (20 % of transformer nominal power) is connected % on the 600 V side. Each phase of the transformer consists of two windings both connected in wye with a grounded neutral. % % The transformers in circuit 1 and circuit 2 use two different models: % % 1) Circuit 1 uses a *physical model* (yellow block) where the core geometry and the B-H characteristic of the iron used % to build the core are the basic parameters used for modelling the magnetic properties of the transformer. % % 2) Circuit 2 uses the *Three-Phase Transformer Inductance Matrix Type (Two Windings)* block (blue block) % for modelling the linear part of the model. Saturation is modelled in the "Saturation" subsystem (cyan block) % by three single-phase saturable transformers connected on the primary side of the linear transformer model. % % In order to minimize the quantity of iron, the transformer core uses the core-type construction. % Contrary to a three-phase transformer built with three independent units, % the three phases of a core-type transformer are coupled. % Because of these couplings, the transformer reactances in positive- and zero-sequence are quite different. % When the three voltages applied on primary side are balanced, (positive-sequence voltage) the fluxes set up in each limb % are also balanced and they stay trapped inside the magnetic core. % However, when the voltage source or the load is unbalanced, a zero-sequence voltage is added to the % positive- and negative sequences voltages. % This zero-sequence voltage produces three flux components in phase in each limb, resulting in a zero-sequence flux component % which has to circulate outside the iron core, through the air and transformer tank or casing. % Due to the high reluctance (low permeability) of the flux return path through the air, the zero-sequence no-load excitation current is much higher % than in positive sequence. For this particular model, zero-sequence excitation current exceeds 3 times the nominal current (344 %), % as compared to only 2.2 % in positive sequence. Excitation current, no load active losses and short-circuit impedance R+j*X % (where R=winding resistance, X=leakage reactance) have been measured for the physical model of circuit 1. % Results are shown in the table below. % % positive-sequence zero-sequence % ------------------ ------------------- % No-load excitation current % (% of nominal current) 2.28 % 353 % % % No load active power losses % (winding losses + iron losses) % (% of nominal power) 2.0 % 14.0 % % % Short-circuit impedance % R+jX (pu) 0.02 + j*0.10 pu 0.0168 + j*0.0914 pu % % Note : % You can verify these values by using the "Sequence Measurements" block provided in the model. Specify either "Positive " or "Zero" % sequence in the block menu. To perform the no-load measurements you must % disconnect the load and use an infinite voltage source (source impedance bypassed), either in positive-sequence % or a zero-sequence. In order to apply a zero-sequence voltage % connect all three terminals of B1 measurement block to the same A terminal of the source. % Also, in order to initialize fluxes in zero-sequence, specify the following % vector of *Voltages for flux initialization* in the block menu: % % [VmagA VmagB VmagC (pu) VangleA VangleB VangleC (deg)] =[ 1 1 1 0 0 0] % % A schematic of the core geometry specified in the physical model is shown below. % % L2 L2 % =================== % || || || % || || || % A B C L1 % || || || % || || || % ==================== % % L1 = average height of the three limbs bearing the windings (2 windings per limb) = 53 inches % L2 = average length of the core yokes interconnecting the limbs = 21 inches % A1=A2 = cross section of the limbs and yokes = 45.48 square inches % Number of turns of high-voltage windings (2400/sqrt(3)= 1386 V) = 128 % Number of turns of low-voltage windings (600/sqrt(3) = 346.4 V)= 32 % % Look under the mask of the transformer of circuit 1 to see how the electrical and magnetic circuit models are built. % The electrical part is implemented by six controlled current sources (one source per winding). % These current sources are driven by the magnetomotive force developed by each winding. % The "Core" subsystem uses the electric/magnetic analogy to implement the magnetic circuit % which consists of 7 steel elements (3 limbs and 4 yokes in blue) and 7 air elements (in green) % representing flux leakages for each of the six coils and flux zero-sequence return path. % % The three figures below show respectively: % % *1) Iron B-H characteristic* % openfig('power_Transfo3phCoreType_BH') %% % *2) Saturation characteristics* for the three phases % (flux in pu as function of peak magnetizing current in pu) when the transformer % is excited in positive sequence (3 balanced voltages). % These saturation characteristics obtained in positive sequence are used % in the three single-phase saturable transformers to model saturation of % the core-type transformer. % openfig('power_Transfo3phCoreType_Sat') %% % Using the positive-sequence saturation characteristics to model core saturation % gives acceptable results even in presence of zero-sequence voltages. % This is because the magnetic circuit used for conducting zero-sequence % flux is mainly linear due to its large air gap. % The large zero-sequence currents required to magnetize the high reluctance air path % are taken into account in the linear model. % Therefore, connecting a saturable transformer outside the three-limb linear model % with a flux-current characteristic obtained in positive sequence will produce % currents required for magnetization of the iron core. % % *3) Waveforms of excitation currents* when a 1.5 pu voltage is applied % at the 2400 V terminals. openfig('power_Transfo3phCoreType_iexc') %% % Notice on Figure 2 that, because of the core asymmetry, the magnetizing current of phase B is % lower than the current obtained for phase A and phase C. % See for example on Figure 3 the excitation currents obtained with 1.5 pu voltage. %% Simulation % % In order to emphasis the importance of a correct representation of transformer zero-sequence parameters, % the transient performance of the Inductance Matrix Type transformer of circuit 2 is compared % to the physical model of circuit 1 when a single-phase to ground fault is applied on phase A. % A six-cycle fault is applied at 2400 V terminals at t=0.05 sec and cleared at t=0.15 sec. % % Before starting simulation, open the Three-Phase Transformer Inductance % Matrix Type block menu. Check that the "Core type" parameter is set to % "Three-limb or five-limb core". Now, select the "Parameters" tab and check % that the positive- and zero-sequence parameters are set according to % the table given in the Circuit Description section. % % *1. Comparison of transient performance of transformer operating in linear region* % % Start the simulation. Observe on Scope1 and Scope2 respectively for % circuit 1 and circuit 2 the following waveform