The Mighty 477 Blog

The brown box to the right is one of the PTs or Power Transformers. The PT transforms the 18,000 volts of the Isophase Bus to 69.3 volts Phase to Ground (120 volts phase to phase). This voltage is sent to the Generator Protection Panel in the STG E-house, where it is monitored for proper level and frequency. The device on the left is a lightning arrestor which is also connected to the Isophase. The Silver ring through with the Isophase is passing through is one of the CTs or Current Transformers. The ratio of the transfomer is 10,000 to 5, so that if 2000 amps is flowing on the Isophase, 1 amp of current will circulate through the CT circuit back to the Generator protection panel where relays will monitor the current level, phase angle, phase imbalance, phase fault distance, and most important, current differential.
Posted by Scott Collins (Click to Enlarge Photo)