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Fast-acting control systems - for actuators in turbine control systems

Fast-acting control systems

Fast-acting control systems are installed when an actuator in the normal operating state (closed, open, or control position) must immediately assume a defined safety position following signal output. This fast-acting control system is specially designed for actuators in turbine control systems.

Basic principle of control systems

A control cylinder which is mounted on a gas or steam valve is hydraulically pretensioned against a spring and moves to the designated working position.

If the gas or steam valve must be closed or opened quickly, the preloaded cylinder chamber is relieved to the zero-pressure side of the cylinder via a hydraulic cartridge valve. The spring moves the cylinder piston to the designated safe open or closed position of the gas or steam valve.

Safety aspects of control systems

Output of the signal for quickly closing or opening a gas or steam valve is usually based on a turbine operating state that requires a quick and safe response (e.g. load rejection). This is why hydraulic cartridge valves are almost always installed in a dual-channel configuration for redundancy.

Safety Circuit Structures

Hydraulic dual-channel valve structures (1oo2 safety circuits) are complemented by additional circuit structures that are used with respect to the required safety loop (IEC 61508 IEC 61511 ) of a gas or steam valve: For example 1oo1, 1oo2, 1oo3, 2oo2, and 2oo3 (oo = out of).

For a 2oo3 safety circuit, for instance, three actuation elements (e.g. directional valves) must be installed to execute a function. Only two actuation elements (2 out of 3) are required to safely execute the function. Thus one element can fail without compromising the function itself.