Electrical Control Features of the Avon Supercritical-Pressure Unit

The trend toward increased electrification inside the modern power plant is evidenced by the Avon supercritical-pressure unit. The application of electrical controls to economically and reliably accomplish equipment protection and interlocking functions directly, or in combination with hydraulic and pneumatic control devices, has been demonstrated on commercial subcritical pressure units. They will continue to do so on the supercritical-pressure units. 1. Basically, the over-all trip protection for the supercritical-pressure turbine and steam generator is not radically different from that for large subcritical units, except for several important additions. 2. Automatic transfer of selected auxiliary motors to the start-up source becomes more important. 3. The monotube once-through steam generator requires a large number of hydraulic and remotely operated electrical controls. 4. Automatic starting of boiler feed pump prime movers and other auxiliaries may increase the over-all reliability of the main unit while adding little complexity to the control system which is designed for complete remote operation. 5. The complexity and number of electrica controls required on main control room panels for a supercritical unit far exceeds those required for a large conventional highpressure high-temperature unit.