Distributed Photovoltaic Grid Transformers

13

Magnetic Inrush Current in Distributed Photovoltaic Grid Power Transformers

Magnetic inrush currents in distributed photovoltaic grid transformers (DPV-GTs) can be as high as 10 to 20 times the nominal current. This is primarily driven by the inductive nature of the transformer coils on the HV and LV sides. The approximate formula for peak inrush current is given by

$I_{\text{max}\text{peak}}=\left(1000\times L\times B_s\right)/\left(5.2\times N\right)\text{in}\text{Amps}$

(13.1)

where

$\begin{array}{l}{B}_{\text{s}}=\text{flux density in air space}=\left(A_{\text{c}}/A_{\text{s}}\right)\left(B\text{residual}\text{+}\text{2}\times B_{\max }=130{\text{kL/in}}^{\text{2}}\right)\hfill \\ A_{\text{c}}=\text{Area of core in square inches}\hfill \\ A_{\text{s}}=\text{Area of air space (core to winding) in square inches + core area in}\text{square inches}\hfill \\ N=\text{Number of turns in winding (solenoid length) inches}\hfill \\ B\text{residual in variable = assume}30{\text{kL/in}}^{\text{2}}\left(\text{i}\text{.e}\text{.,}\text{5}{\text{kL/cm}}^{\text{2}}\right)\hfill \\ \text{Saturation of iron core assumed at 130 ...}\hfill \end{array}$