This standard covers the design requirements and operator interface for steam turbine bypass systems for drum and once-through steam generators and combined cycle plants. Hardware configurations are suggested to obtain the minimum design requirements to obtain a safe and operable system. Both fixed percentage bypass and variable pressure systems are covered.

It is applicable to boilers with steam capacities of 200,000 lb/hr (25 kg/s) or greater.

Purpose

This standard establishes the minimum requirements for design specifications to implement steam turbine bypass systems and hardware configurations for drum and once-through, fossil fuel power plant boilers.

The turbine bypass system should provide for cold start-up, warm start, hot restart, load rejection, turbine shutdowns, and unit trips. The system shall be designed to provide pressure, temperature, and flow control of steam around and through the turbine by controlling each bypass valve, isolation valve, and associated desuperheater. The desuperheating function may be integral with the bypass valve. The turbine bypass system does not interface with the turbine control and supervisory system. The turbine bypass system is set to maintain steam pressure, and any coordination with the turbine is through interaction with the process as the turbine demands more or less steam. There is no direct interconnection of control systems.