Transformer models in EMTP/ATP

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Core representation • Attached to the fictitious N+1th winding • Topologically “correct” core model, with nonlinear inductances representing each leg and limb – Triplex – 3- and 5-legged core • Flux linkage-current relation by Frolich equation and relative lengths and areas. • Fitting to Test Report λ i λ = a' + b' ⋅| i | i R o L l R l L o R y L y L l R l R y L y L l R l R o L o 15 / 19 11/6/2012 Transformer modeling at high frequency • Transformer models in EMTP are valid for frequencies up to 2 kHz • To study phenomena with characteristic frequency in range of 2 - 30 kHz, capacitive coupling among windings and to ground must be added • Above 30 kHz a more detailed representation of internal winding arrangement is required – Interwinding and interturn/disks capacitances must be taken into account • Above 100 kHz the presence of ferromagnetic material has just secondary importance.
Transformer modeling guidelines PARAMETER/ EFFECT Low Frequency Transients Slow Front Transients Fast Front Transients Very Fast Front Transients Short-circuit impedance Very important Very important Important Negligible Saturation Very important Very Important (1) Negligible Negligible Iron losses Important (2) Important Negligible Negligible Eddy currents Very important Important Negligible Negligible Capacitive coupling Negligible Important Very important Very important (1) Only for transformer energization phenomena, otherwise important (2) Only for resonance phenomena 17 / 19 11/6/2012 Application: CT modeling ip’ Rp Lp Rs Ls Es is im imr Rm imx Lm Rl 18 / 19 11/6/2012
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Transformer models in EMTP/ATP

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