Iron and copper losses

Method

The transformer at each inverter has two losses on every timestep. The copper loss is the copper fraction of the reference power, times the square of the ratio of the power through the transformer to the reference power, divided by the square of the power factor. That power is the inverter output, or under the cascade reference of the AC resistive reference step, the output after the AC wiring. The iron loss is the iron fraction of the reference power, drawn on every timestep while the transformer is connected. With the night disconnect on (Losses tab) the transformer is connected only on timesteps with export. The row adds the losses of all inverters.

The math

1. Copper-loss coefficient
2. Copper loss
3. Iron loss
4. Row

$$k_{Cu} = \frac{f_{Cu}}{P_{ref}\,\text{PF}^2} \tag{1}$$ $$L_{Cu} = k_{Cu}\,P_c^2 \tag{2}$$ $$L_{Fe} = \begin{cases} f_{Fe}\,P_{ref} & \text{connected} \\ 0 & \text{disconnected at night} \end{cases} \tag{3}$$ $$L_{MV} = N_{inv}\,(L_{Cu} + L_{Fe}) \tag{4}$$

where

Symbol	Meaning	Unit
$k_{Cu}$	the copper-loss coefficient of one transformer	1/W
$f_{Cu}$	the copper loss at the reference power and unit power factor, as a fraction of the reference power	—
$P_{ref}$	the AC power reference of one inverter: its AC nameplate, or its share of the STC reference power (AC power reference step)	W
$\text{PF}$	the power factor	—
$L_{Cu}$	the copper loss of one transformer	W
$P_c$	the power through the transformer: the inverter output, or the output after the AC wiring under the cascade reference	W
$L_{Fe}$	the iron loss of one transformer	W
$f_{Fe}$	the iron loss as a fraction of the reference power	—
$L_{MV}$	the medium-voltage transformer loss of the system	W
$N_{inv}$	the number of inverters	—

References

1. IEC 60076-1:2011, Power transformers, Part 1: general (no-load and load losses)
2. PVsyst 8 help, External transformer losses

API

ac_losses.use_mv_transformer = true

Symbols follow the symbol registry.