Overspeed protection

In contrast to steam turbines, in which runaway overspeediug is always a problem, pump-turbines operating at design head go to zero torque at about 130 to 140 percent of design speed. Thus, overspeed protection may not be necessary if the pump-turbine can withstand 140 to 150 percent of design speed and it is the sole driver. When a steam-turbine helper is used, it should be provided with the usual overspeed trip-out mechanism. 

Service tank Low level Engine inlet Low pressure Overspeed protection ... 

ISO3046/IV Reciprocating internal combustion engines Performance. Part 1 Specifications for standard reference conditions and declarations of power, fuel consumption and lubricating oil consumption. Part 2 Test methods Part 3 Specification of test measurements. Part 4 Speed governing. Part 5 Torsional vibrations. Part 6 Specifications for overspeed protection. Part 7 Specifications for codes for engine power. 

OVERSPEED TRIP - On steam turbines, a mechanism that provides absolute reliable overspeed protection by shutting off the steam supply. 

In addition to the normal speed control function provided by the turbine control system, a separate turbine overspeed protection system is included to minimize the possibility of turbine failure and high energy missile damage. 

Module-speed Measurement Module - Fuel Flow Module - Overspeed Protection Module - T1/P1 Module - FMV Module - Fuel Metering... 

Overspeed Protection. To prevent damage to a driven machine, materials in the industrial process, or the motor, overspeed protection is provided by controlling the power-supply frequency in ac motors and by hmiting the maximum shunt field resistance or armature voltage in dc motors. Typical applications include paper and printing plants, steel mills, processing plants, and the textile industry. 

Overspeed protection during load rejection and emergencies... 

Steam turbines are equipped with an emergency overspeed protection system that is separate from the main governing system. In the event of excessive rotor speed, this system shuts down the steam flow to the steam turbine by closing both the stop and control valves. This is an electronic failure detection system that is redundant and can be tested during operation. 

The plant arrangement assumed for the two Brayton system heat balance is illustrated in Figure 5-27. This system has two converter loops each with one turboaltemator, recuperator, and gas cooler. No cross-strapping of converter loop components is assumed. Each turboaltemator Is sized to produce the entire 200 kWe required for full power. The recuperator and gas cooler are appropriately sized to meet this power requirement. One converter loop is normally operating while the other is an idle spare A check valve is located at the outlet of each compressor to prevent backflow through the idle loop to maximize system efficiency, minimize bypass cooling flow around the reactor, and prevent potential damage to turbomachinery due to reverse rotation. An isolation valve installed the outlet of each compressor enables loop shutdown and startup evolutions and provides Brayton overspeed protection for certain electric plant casualties. 

Various protective instruments are used to provide a shutdown signal (to a fast-acting trip valve at the expander inlet) that senses various things, such as overspeed, lubricant pressure, bearing temperature, lubricant temperature, shaft runout, icing, lubricant level, thrustbearing load, and process variables such as sensitive temperatures, levels, pressures, etc. However, too many safety shutdown devices may lead to excessive nuisance shutdowns. 

Mechanical protective equipment, such as overspeed trips. 

The unit is fully protected with safety valves at necessary points. In addition the compressor has water temperature and pressure shutoff switches, and a suction pressure switch, which will shut it down in the event the system runs low on gas. This protects against line bursts or major leaks, or operator negligence in providing gas supply. The expander has overspeed and oil-pressure protection. The expander and compressor are linked with a unique electrical circuit, which permits them to be started separately, but which shuts down both units in case of automatic shutdown of either one. Thus any failure will close down the entire system, preventing damage to either compressor or expander. 

If the bond between the copper tube and the A286 support tube is neglected, the centrifugal pressure of the copper on the overwrap is 2.52 MPa (366 psi) at 12,000 rpm, which produces a hoop stress of 298 MPa (43,200 psi) in the composite overwrap. The hoop stress in the overwrap itself, due to the 12,000-rpm rotation, is 150 MPa (21,700 psi). Hence, the combined hoop stress in the overwrap is 447 MPa (64,900 psi) at design speed and 541 MPa (78,500 psi) at the overspeed (13,200 rpm) condition. The observed tensile strength in the hoop direction for the composite at 77 K was —896 MPa (130,000 psi). Hence, sufficient structural protection under rotation should be provided by the overwrap. Warm tests on the complete generator were recently conducted up to 12,000 rpm with no apparent problems with the shield construction. 

Full Supervision (FS) is the normal mode providing a full protection against overspeed and... 

Thermal and overspeed cutout devices are coimnonly used to protect electrical equipment (and thus the operator). A thermal cutout is simply a temperature-sensitive switch with a preset limit designed to interrupt power when the temperature exceeds a certain value. As its name implies, an overspeed switch operates when it senses that a motor or other device is operating at too fast a speed. Obviously, excessive speed may create dangerous conditions and indicate failure of equipment. The overspeed switch operates to shut down an overspeeding device by interrupting power to it. 

Critical interlock While identifying the hazards it is important to categorize critical interlocks (for new plants, data/experience from similar plants may be helpful) for which sufficient backup may have to be arranged as a safety measure. In many of these cases, in addition to software interlock, hardware interlocks are also provided. In some cases, even mechanical protection is provided. A critical trip interlock pertinent to a turbine is an example. For turbine overspeed, condenser vacuum, etc., in addition to electronic interlock (with sufficient hardware/software redundancy), mechanical interlocks are provided so that the equipment is saved. Choke and kill in offshore is also an example of this. Regulations To meet the requirement of a regulatory board or company standards, measures are taken to enhance overall safety. Incorporation of these safety measures does not always mean that risk is adequately reduced. These measures could make the system acceptable for use, and a local regulatory board may require additional precautions. An example will elaborate the situation. Many turbine manufacturers give low forward power relays or reverse power... 

Protection strategies are needed against overtemperature and overspeed, etc. 

Control systems generally contain many automatic protection and alarm systems. A typical protection system includes a main stop valve which is spring-loaded to close and is mounted ahead of the turbine inlet valve. Hydrauhc oil keeps this valve open if several protection devices all indicate safe operation. These include an overspeed governor, bearing oil pressure relay, a manual trip relay, and where apphcable, a low-vacuum relay and nonreturn valve relays. 

Another concern with internal combustion engines is that they could possibly overspeed from the intake of additional combustible vapors during an unexpected combustible vapor cloud release at a facility The engines may accelerate and overspeed, but most are provided with protection devices to protect against this occurrence and additionally those engines who drive electrical generators would have an increase in voltage frequency that would also cause them to automatically shutdown. 

FIG. A-37 Trigger criteria for protection against overspeed. (Source J.iM. Vbilh GmbH.)... 

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