Steam Engines

The advent of electric motors, steam turbines, and other drivers has relegated the steam engine to a minor position as an industrial driver. It does have the advantages of reliability and operating characteristics that are not obtainable with other drivers but also the disadvantage of bulkiness and oily exhaust steam. In the simple nonexpanding engine as used with direct-acting reciprocating pumps, steam is admitted over the entire stroke and does not expand in the cylinder, resulting in...

Electric Motors And Auxiliaries

All electric motors operate on the same basic principle regardless of type or size. When a wire carries electric current in the presence of a magnetic field (at least partially perpendicular to the current), a force on the wire is produced perpendicular to both the current and the magnetic field. In a motor the magnetic field radiates either in toward or outward from the motor axis (shaft) across the air gap, which is the annular space between the rotor and stator. Current-carrying conductors...

Operating Problems

While most turbines have a 10-year-availability record in the range of 95 to 99 percent, troubles may develop in any number of places. The most common are vibration, cycling governor, sticking valve stems, leaky packing, temperature bow, erosion of blading, loss of power, and bearing problems. The causes of vibration have already been discussed. An increase in vibration over a period of time is generally caused by loss of alignment, settling of the foundation, or sticking of some expansion...

Major Gas Turbine Components

Inlet Temperature Gas Turbine 2300

The gas turbine in the simple cycle mode consists of a compressor (axial or centrifugal) that compresses the air, a combustor that heats the air at constant pressure and a turbine that expands the high pressure and high temperature combustion gases and produces power to run the compressor and through a mechanical coupling to the driven equipment. The power required to compress the gases varies from about 40-60 percent of the total power produced by the turbine. Compressors A compressor is a...

Turbine Control

A turbine may be speed-, pressure-, or process-controlled. Some of the terms used are defined as follows Speed-governing system includes the speed governor, the speed changer, the servomotor that moves the valves, and the governor-controlled valves. Speed governor includes only those elements which are directly responsive to speed and position the other elements. The speed changer is a device by means of which the set point may be varied. Steady-state regulation is the change in sustained speed...

Turbine Operation Characteristics

The gas turbine is a high-volume air machine. The compressor air power required is usually between 50-70 percent of the total power produced by the turbine. Thus, the ambient temperature affects the output of the gas turbine. On hot days, the gas turbine produces less output than on cold days. In dry climates, the use of evaporative cooling in the gas turbine decreases the effective inlet temperature and increases the power output of the unit. FIG. 29-39 Performance map showing the effect of...

Selecting A Turbine

The major variables that affect turbine selection are as follows 1. Horsepower and speed of the driven machine 2. Steam pressure and temperature available or to be decided 3. Steam needed for process, so that a back-pressure turbine should be considered 4. Steam cost and value of turbine efficiency, so that consideration can be given to stage and valve options 5. Use of speed-reducing or speed-increasing gears 6. Extraction for feedwater heating FIG. 29-16 Approximate horsepower loss for...

Alternatingcurrent Motors Constant Speed

The majority of industrial drives are constant speed. Typical applications include Pumps Compressors TABLE 29-1 Useful Formulas for Alternating-Current Motors P 0.00173VIye (three-phase) (29-2) P 0.001VIye (single-phase) (29-3) Power input P 0.00173VIy (three-phase) (29-4) P 0.001VIy (single-phase) (29-5) S P y 0.746H ye (29-6b) Line current and power factor e efficiency, decimal H power, hp I line current, A n speed, r min P power, kW S apparent power, kVA T torque, lbf ft V applied voltage, V...

Bearings

Bearing Capacity Dam

Rotating shafts must be supported by the machine housing, not only against gravity, but also against a variety of forces that are imposed on rotors inside machines (including axial thrust). Bearings have a significant influence on the performance of process machines, both because they limit their continuous operation and also since they influence the level of vibration and critical speeds of the machines. It was generally accepted that machinery users do not select bearings (see the sixth...

Types Of Fuel

The life of a gas turbine depends heavily on the type of fuel used. An inherent fuel flexibility is the gas turbine's major advantage. Gaseous fuels traditionally include natural gas, process gas, and low-Btu gas FIG. 29-41 Larson-Miller parameters for turbine blade alloys. FIG. 29-41 Larson-Miller parameters for turbine blade alloys. (coal gas or water gas). Natural gas is the benchmark against which performance of a gas turbine is compared, since it is a clean fuel that promotes long machine...

Motor Control

The basic functions of motor starters are 1. Normal start-stop control of the motor. 3. Protection of the electrical supply system in the event of a motor or motor-feeder short circuit. The fault must be cleared from the rest of the system to prevent further trouble. 4. Electrical isolation to provide accessibility for maintenance. 5. Provision for other control such as master sequence control, protective shutdown devices e.g., bearing overtemperature, overtravel, pump high pressure, remote...

Power Transmission Without Speed Change

Whenever the process machine operates at the same speed as its driver, the two can be directly coupled. This direct coupling still allows for a variable speed, through adjustments of the speed of the driver. Steam turbine speed can be easily adjusted, and electric motor speed can also be varied by the use of special drives that vary the frequency of the power applied to the motor. Whether the speed is fixed or variable, direct coupling of two machine shafts presents the problem of accommodation...

Motor Enclosures

Except for areas with fire or explosion hazards hazardous areas , motor enclosures are designed to provide protection to the internal working parts. The development of improved insulating materials and finishes has affected the required degree of protection and consequently the design and classification of enclosures. Examples of several types of enclosures are shown in Fig. 29-4. Open, dripproof is the standard enclosure for induction, highspeed synchronous, and industrial dc motors. This...