I'm trying to figure out how to model a transformer in order to estimate the number of transformers on a bus line. Each transformer is connected in parallel and may or may not have a connected load. I've been able to collect some empirical data from an available device, but I'm having trouble formulating an equation to satisfy that data.
I would assume that, ignoring hysteresis and eddy currents for simplification, calculating a bus like this would be a simple matter of combining the primary-side resistance/reactance with any referred secondary-side resistance/reactance and then adding these resistances in parallel with all other transformers connected in the bus. But when I perform actual measurements, my calculated numbers are off. When testing a circuit with (transformers are a simple 1:1 ratio), the measurement is closer to 75 ohms rather than approximately 71-72 ohms (adding 13.52k + 5k + 3k + 75 in parallel). The measurement will also continue to stay relatively close to 75 ohms rather than dropping to the low 70s/high 60s that I would expect when introducing lower load values.
What exactly am I missing here?