PPL Electric Utilities (PPL Electric) has established thresholds on utility-owned secondary transformer sizing. Transformers are important pieces of electric equipment directly connecting the electric utility and our customers. Therefore, maintaining the health and reliability of this key asset is critically important. Based on third-party findings and available data illustrating an increase in Distributed Energy Resources (DERs) and corresponding two-way power flow on the grid, these third-party researchers have found that loading of transformers leads to significant life-span reductions. This potential overloading directly affects reliability, safety, and cost impacts for customers.
Update: PPL Electric Utilities set new thresholds on utility-owned secondary transformer sizing for new applications received on or after 8/23/2024. At that time, it was set to 90% of maximum transformer rating. Based on new findings, PPL Electric has revised this overloading amount to 95% of maximum transformer rating for new applications received on or after 01/21/2025.
Traditional transformer loading standards are derived based on the internal oil temperature and the breakdown of the paper insulation on the transformer windings. Typically, a transformer is expected to experience two peaks within a 24-hour load period. It is similarly assumed the transformer will experience an overnight cooling period. When interconnecting a solely generating solar customer to PPL's distribution system, a different load profile must be considered. A transformer interconnected to a solar installation is anticipated to be in constant reverse loading throughout the daytime generation period, with minimal load present at night. The standard below, confirmed by a third-party engineering firm, considers the loading pattern of these solar DER customers:
This formula will be applied for any transformer size that PPL allows (up to a 2500 kVA maximum pad-mounted 480Y/277 V transformer size).
PPL Secondary Transformer maximum name plate connected generation.