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Nan issue when energizing a 3 phase 2 winding transformer with YY configuration
Hi. I am trying to model a transformer inrush during energization. I do not have saturation data from the manufacturer, but I have the basic data like leakage reactance, vector group, and voltage rating. The configuration is as follows
An inverter is connected to an isolation transformer with the vector group Dy11. The Delta side of this transformer is connected to a YY step-down transformer (12.47 kV to 0.48 kV) with no-load connected on the secondary. The sequence is that the Dy11 transformer is connected all the time. The source is ramped up until it reaches a steady state. After this, the step-down transformer is connected by closing the breaker. As soon as the breaker is closed, the transformer current and voltage results in nan with a very high value. If I change the transformer winding configuration from YY to DD, then the issue disappears. I am using the same saturation parameters in both cases which are as follows
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Open Mar 24, 2025 - 02:02 AM
Transformer Inrush current, Transformer saturation
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Apparently the screenshots did not attach to the original post, so here are the parameters
Place Saturation on Winding = Middle
Hysteresis = Basic model
Air core reactance = 0.115 pu
Magnetizing current = 1 %
Knee Voltage = 1.17 pu
Remanent Flux Core 1 = 0.1
Remanent Flux Core 2 = 0.2
Remanent Flux Core 3 = 0.1
3 Phase Transformer MVA = 7 MVA
Base Operation Frequency = 60 Hz
Positive Sequence Leakage Reactance = 0.0575 pu
Ideal Transformer Model = Yes
Eddy Current Losses = 0.003 pu
Copper Losses = 0.01 pu
Tap Changer on Winding = None
Graphics Display = Single line (windings)
Winding 1 Line to Line voltage (RMS) = 12.47 kV
Winding 2 Line to Line voltage (RMS) = 0.48 kV
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