The growing number of distributed energy resources (DER) connected to power systems can lead to an overload condition on the distribution substation transformers. Bidirectional power flow, alternating charge/discharge states at each DER site, and remote and rural DER locations all make substation transformer overload protection difficult. 

This presentation offers a transformer overload protection approach based on wireless communication between the head-end station and multiple DER sites with perspectives from PG&E. IEC 61850 GOOSE messages are used to communicate ramp-down and trip signals, as well as DER state and status information. The scheme uses directional overpower (32) function and voltage-supervised overcurrent (50) elements. Custom logic was developed to support selective ramping down and tripping of DERs operating in the detected overpower direction only.

Wireless point-to-multipoint communication was chosen due to its ability to reach remote DER locations without building a wired communication infrastructure, coupled with sufficient reliability and security of its operation. 

This presentation will also cover:

• Design, including protection elements, logic, and communications configuration
• Test results for the proof of concept system, covering communications, protection, and custom logic
• The benefits of applying wireless communication-assisted transformer overload protection