Proactive and Preventative Transformer Maintenance: How Destructive Can Rodents Really Be?

By K.C. Radford

Charlotte, NC April 15,2018

How destructive can mice really be to a solar PV system? We hope you never have to find out, but, take our word for it, it’s not pretty. One project, this winter, found out the hard way. It had been a cold and wet winter and rodents had been trying to make their way into a dry and covered space. We discovered, on a site in southern-central Massachusetts, a mouse nest that was built in the interior of a dry type Zig Zag transformer near one of the coils and between two windings.

This buildup of nest material eventually resulted in a fault across the windings of the transformer that caused the failure as seen in the photos (a short between two of the phases on the transformer, tripping the system protection reclosers on an overcurrent event). The dry type transformer used was not sufficiently secured from the ingress of rodents.

The EPC was engaged to replace the failed transformer. A temporary replacement was installed within 2 weeks, and a replacement was ordered and installed approximately 6 weeks after the event. Two weeks of a system being offline in a high value PPA region is a hit to revenue but can be prevented with diligent preventative maintenance. Additionally, this could have been prevented if an oil filled transformer had been employed, since the coils would have been secured and submersed in oil and would not have been susceptible to the ingress of rodents.

We recommend, as a preventative measure for dry type transformers, a more frequent inspection and cleaning schedule to identify and remove any material build up from the transformer. For dry type transformers, Radian recommends, at the very least, quarterly inspections and cleaning.

Have questions for our asset management team? Need help with your projects? Contact us directly at or 415-901-3430