Iron and copper losses

Method

The HV transformer acts once, on the sum of the inverters after the MV line. Its copper loss is the copper fraction of the system's 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 sum of the inverter outputs, or under the cascade reference the power that leaves the MV line. Its 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 two losses.

The math

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

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

where

Symbol	Meaning	Unit
$k_{HV}$	the copper-loss coefficient of the HV transformer	1/W
$f_{HV,Cu}$	the copper loss at the reference power and unit power factor, as a fraction of the reference power	—
$P_{ref,sys}$	the AC power reference of the system: the sum of the inverters' AC nameplates, or the STC reference power (AC power reference step)	W
$\text{PF}$	the power factor	—
$L_{Cu}$	the copper loss	W
$P_c$	the power through the transformer: the sum of the inverter outputs, or the power leaving the MV line under the cascade reference	W
$L_{Fe}$	the iron loss	W
$f_{HV,Fe}$	the iron loss as a fraction of the reference power	—
$L_{HV}$	the HV transformer loss	W

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_hv_transformer = true

Symbols follow the symbol registry.