Turbine Bypass Research Articles

A PWR hybrid computer model for assessing the safety implications of control systems

As part of the ORNL study of safety-related aspects of control systems, a hybrid computer model was developed to trace the dynamic impact of single and multiple component failures on the control system and remainder of the plant. Since the thrust of this program is to investigate control system behavior, the controls are modeled in detail to accurately reproduce characteristic response under normal and off-normal transients. The balance of the model, including neutronics, thermohydraulics and component submodels, is developed in sufficient detail to provide a suitable support for the control system. The model is being used primarily to address mild to moderate transients that can occur at least partially under action of the non-safety control system. Attention initially focused on overfill events that assumed single or multiple failures of feed valves or the generator low and high level setpoints and trips that regulate the valves. In general, these calculations showed that for single-generator overfeed, water inventory in the affected generator increased to a sufficiently high level to saturate the generator fluid, quench superheat, and inject water into the steam line. Overcooling of the primary side was modest. Other events studied with the model include: insufficient main feedwater cooling induced by a steam generator high level setpoint failing low, potentially drying out the generator; secondary side depressurization induced by turbine bypass valves failing open in loop A or in combination with loop B, at low and high power levels; and steam generator tube ruptures in combination with overcooling incidents.

Propulsion systems for civil transport aircraft

The aero engine has developed from the piston engine and propeller through the pure jet turbine and high bypass turbofan to a possible re-emergence of the advanced turbopropeller engine. The author traces the evolution of propulsion systems for civil transport aircraft and suggests how fuel efficiency could be improved

OTEC Plant Response and Control Analysis

An analysis is presented which allows prediction of closed-cycle OTEC power plant system response and control. Two basic operational control schemes are presented, which are primarily related to the type of seawater pumps employed. Variable flow seawater pumps allow optimization of the OTEC thermal-cycle state points for maximization of net generated power. Constant flow pumps are cheaper and simpler, but do not allow direct control over the evaporator and condenser operating temperatures. A system of nonlinear differential equations representing the basic elements of a constant seawater flow OTEC plant with turbine bypass flow control has been formulated for computer solution. Typical normalized response curves are presented for pressures, temperatures, mass flow rates, and generator speed for a small-scale, 50-kW OTEC plant design.

Design and Dynamic Performance of a Steam Turbine Bypass Control System for a Large Fossil-Fired Power Generating Unit

This paper describes the design and the dynamic performance of a novel limited capacity bypass control system proposed for two-shift operation of a 500 MW oil-fired generating unit employing a G.E. turbine. Direct digital controls with analog back-up are applied.

Acoustics, stability, and compensation in boiling water reactor pressure control systems

An analysis is provided of the effects of steam pipe acoustics on the control of steam pressure in boiling water reactors. A model is developed for the process which encompasses the reactor vessel, the main steam piping, the bypass system piping, the turbine throttle valve and bypass valve, and associated control equipment. It is shown that instability of the closed loop can occur unless the acoustics are suitably accounted for. Moreover, it is shown that although classical compensation schemes may lead to adequate controller designs in some situations, such regulators are limited in their ability to provide fast pressure recovery and can thus contribute to undesirable oscillations between reactor pressure and water level control loops. State variable methods are shown to lead to fundamentally different control structures which eliminate this difficulty but other considerations are noted which can limit their application. These are, however, minor when compared to the benefits attainable.

A Fixed-Head Concept Diesel Engine

This high-speed automotive diesel engine was designed to achieve the greatest possible reliability in operation, low operating and maintenance costs and maximum versatility of component and auxiliary arrangements, based on long experience of large-scale manufacture of engines for commercial vehicles and the increases in power output and time between overhauls made possible by improvements in design, materials, manufacturing processes, fuels and lubricants. Elimination of the cylinder high-pressure joint was a radical departure from current practice and promised considerable advantages in cooling, reducing thermal stress and freeing restrictions in cylinder-head porting layout. Thus the potential for operating at the highest rating now in use and for future development was improved. This paper deals with the design aims, describes the engine and outlines the development work with single and multi-cylinder engines that has been undertaken to ensure that each commercial variant meets the requirements of its rating. Vertical and horizontal configurations are used in naturally aspirated and pressure-charged versions. For automotive work, using mechanical transmissions, the drooping characteristic of the normal turbocharged engines torque curve at low speed is a serious disadvantage. Measures taken to overcome this are described. These included variations in camshaft timing, automatic variable control of injection timing and boost pressure control of fuel injection quantity to avoid undesirable smoke in the exhaust emission in addition to the normal development work of ensuring the highest practicable standards of mechanical, volumetric and combustion efficiency. Other methods such as special turbocharger matchings, including the waste-gate system of turbine by-pass, the system of auxiliary hydraulic drive of the turbocharger at low engine speeds and, as alternative to turbocharging, pressure charging by an aerodynamic pulse-converter are discussed. At the other end of the scale, considerable attention has been paid to increasing the maximum engine output by turbocharging with intercooling which promises to increase naturally aspirated power by over 100 per cent, if in road vehicles the problem of the intercooler, air/air or air/water, can be dealt with satisfactorily.