If you are looking to establish interconnections with Oncor at its available transmission levels—69, 138 and 345 kV—below are links to documents that provide facility interconnection requirements. The documents for electric utilities include those that are investor-owned, rural electric cooperatives, river authorities and municipal electric utilities.
Also, here are links to Oncor tariffs:
Retail Customers - Tariff for Retail Delivery Service
Generators and Electric Utilities - Tariff for Transmission Service