transformer | PartQuest™ Explore

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Electro-Magnetic Components

transformer model comparison -- perfect coupling

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Description

This circuit compares two different ways to specify a two winding transformer. One way is by specifying the inductance of each winding, with a coupling coefficient between the windings.The other way is by specifying the number of windings and the size and permeability of the core on which the windings are wound. For a perfectly coupled transformer, the flux in the core is completely shared by both windings. In the first model, this corresponds to a coupling coefficient of 1.0. In the second model, this corresponds to a single flux path in the magnetic circuit.L = u0*ur*N^2*A/Lu0 = 1.25663706 × 10-6 [m kg s-2 A-2]L_primaryur = 3000 [no units]N = 10 [turns]A = 100.0E-6 [meter^2]L = 100.0E-3 [meter]L_primary =1.25663706E-6 *3000*10^2*1000E-6/100.0e-3 = 3.76991E-04L_secondaryur = 3000 [no units]N = 100 [turns]A = 100.0E-6 [meter^2]L = 100.0E-3 [meter]L_secondary = 1.25663706E-6 *3000*100^2*1000E-6/100.0e-3 = 3.76991E-02The third circuit shows how a magnetic circuit can be used to represent imperfect winding coupling. In this example, the length of the core is divided between the two horizontal core segments. A third (vertical) core segment is also shown. This magnetic path carries flux that is not common to both windings, thus reducing the coupling between the two windings. When the length of this segment is very long, its effect is negligible, approximating the simpler magnetic circuit above it..

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Bridge Rectifier 230 V AC

Designer10

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11 years 11 months

623

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10

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Big fan of VHDL-AMS

Transformer experiment

Designer10

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11 years 11 months

623

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Big fan of VHDL-AMS

Transformer Magnetizing In-rush Current

Designer19

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Member of the PartQuest Explore Development Team. Focused on modeling and simulation of analog, mixed-signal and multi-discipline systems covering a broad range of applications, including power electronics, controls and mechatronic systems.

Description

This transformer design example demonstrates a current in-rush or "peaking" effect that depends on the phase or timing of the AC supply switch closure. A rather counter-intuitive result is shown;Case 1: Set the initial_delay of the digital pulse to 4.17m seconds, which causes the switch to closed when the sinusoidal AC line input voltage is at its peak, one quarter-cycle at its 60 Hz frequency. The current into the primary winding will immediately follow its nominal steady-state no-load profile, with a peak of just under 100mA. Case 2: Set the digital pulse initial_delay to 0 seconds, so that the line voltage is applied to the transformer immediately at its rising zero-crossing. This results in a large non-sinusoidal peaking current which exceeds 500mA on its initial cycle!This is a direct result of saturation in the magnetic core. To produce the necessary "volt-seconds" in Case 2, the magnetic flux in the core must be twice that of Case 1. But if the transformer is sized such that its peak flux density is somewhat close to the the saturation level for nominal steady-state operation, then a start-up transient with the unfortunate timing of Case 2 will result in a large in-rush current.Note that the flux density "b" is displayed for the magnetic core. The core saturation flux density is specified as 1.5 Tesla, a typical value for Electrical Steel. You can also select "B vs. H from Table" to see the performance for a specific type of NGO Electrical Steel -35PN250 from the manufacturer Posco.

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