Microgrid DER ( Distributed Energy Resources ) Transformer

Other Considerations

In addition to the transformer configuration, the design of the DER transformer also takes into account three other important factors:

Electrostatic shield: 

• The transformer is crucial in managing the noise produced by the inverter, which arises from insulated gate bipolar transistor switching patterns.

• This noise is categorized into two: 

  1. Differential mode noise 

     • Handled by an inductor that forms part of the LCL filter, integrated into the DER inverter. 

  2. Common mode noise 

     • Extra consideration from the transformer's design. 

     • To stop this common mode noise, the transformer must be designed with a grounded electrostatic shield. 

       • This shield, situated between the transformer's primary and secondary sides 

       • Enables the common mode noise to circulate between the grounded shield and the DC ground within the inverter, effectively curtailing its propagation. 

K factor: 

• The K-factor rating is an index of the transformer’s ability to handle harmonic content while operating within its temperature limits. 

• Transformers with a K factor are crucial when serving loads are non-linear that generates harmonics that can impact the transformer's performance.

MVA rating: 

• Consider the fluctuating operation of inverter-based DERs and bidirectional power flow 

• DER transformers should be oversized to increase their life expectancy. 

• For example, a transformer for the PV farm was oversized by 125% and the transformer for BESS was oversized by 150%.