Three terminal operation of the Pacific HVDC intertie for dc circuit breaker testing

The Pacific Intertie HVDC System has been operated in a voltage-limited three terminal configuration suitable for dc circuit breaker testing. A rectifier at Celilo, Oregon, delivered power down-line 847 miles to a current-controlling inverter at Sylmar, California. Part of the rectifier current was taken by that inverter and returned to Celilo via the ground path. The remainder of the rectifier current returned to a current-controlling inverter at Celilo along the other pole. The system approximated a 1694 mile tapped monopolar line having an inverter at the midpoint. Changes in system configuration, control, and protection are described. Results of close-in and remote fault tests are compared against computer transient simulations. The system operated essentially as predicted and as such, this modification of an existing bipolar dc system has made possible the means to make a meaningful field test of a dc circuit breaker.