Vernon Main Transfer Trip Addition

Vernon Main Transfer Trip Addition

Location: Texas

Client: American Electric Power

Completion Date: 2009

Burns & McDonnell performed the engineering design for the installation of transfer trip capability on both 138-kV transmission lines at the Vernon Main Substation and upgraded line relays from electromechanical to solid state. Buswork, cable jumpers and switches also were upgraded to increase the current capacity of the 138-kV portion of the substation.

  • Engineering design

This existing 138/69/12-kV substation is in Vernon, Texas. The project involved upgrading the 138-kV breaker disconnect switches and buswork to increase the current rating of the 138kV yard. Coupling capacitor voltage transformers (CCVTs), line traps and line tuners were added on the two 138-kV transmission lines to allow transfer trip, and line relay protection for both lines was upgraded.

The physical portion of the engineering design involved specifying switches and CCVTs and determining where the new equipment would be located. A steel pole was also installed for a SCADA communications antenna.

The protection and control portion of the engineering design involved upgrading the 138-kV line relaying from electromechanical relays to solid-state relays. Each 138-kV line had a TC-10 for transfer trip functions, an SEL-351S for breaker protection, a GE D-60 for primary line protection and an SEL-421 for secondary line protection. The GE D20 RTU was upgraded to a newer model, and settings were completed for both breaker SEL-351S relays. Because new direct current loads were added in the relay upgrade, the battery charger and battery sizes were checked to ensure that there was sufficient battery capacity at the substation.