Synchronous driving

Acsium is said to have been designed for use in synchronous drive belt applications. 

The synchronous drive motor (45 MW) at 3000 rpm showed a trouble-free operational behaviour. The same applieds to the asynchronous three-phase motor (4.5 MW) for the start-up. 

The activation of these actuators can be simultaneous (synchronous driving) or selective/controlled (asynchronous driving), which can usually provide higher speed and smoother motion. 

Synchronous drives have an advantage over gears and chains in that they can transmit high loads over a wide range of speeds with low noise and no Inbrication requirements. Synchronous belts, like V-ribbed belts, require closer alignment tolerances in order to avoid premature wear or failure. 

The mechanical secondary pump is of single centrifugal type with cavitation-free impeller, bottom entry flow to the impeller, sodium lubricated hydrostatic lower bearing and a synchronous drive motor cormected with the pump shaft by a cardan shaft with self-aligning couplings. 

Motor nd Drive. The preferred prime mover for a fan is usually an electric motor. Eor fans of low to moderate power, V-belt drives are frequently employed. This permits selection of fans that can be operated over a wide range of speeds rather than being limited to motor synchronous speeds. Furthermore, change of speed is less expensive with V-belt drives. However, fans requiring powerful motors, 37—75 kW (50—100 hp) and higher, are generally directly connected to the motor and driven at synchronous speed. 

The silicon-controlled rectifier with a dc motor has become predominant in adjustable-speed drives for almost all commonly used conveyors when speed adjustment to process conditions is necessary. The low cost of this control device has influenced its use when speed synchronization among conveyors is required. This can also be done, of course, by changing sheave or sprocket ratios. 

Synchronous speeds are calculated by Eq. (29-10). Speeds above the limits given are obtained through step-up gears large high-speed centrifugal compressors are examples. Two-pole (3600 r/min at 60 Hz) synchronous motors can be built but are uneconomical in comparison with geared drives. 

A motor can fall in a generator mode when the machine is energized and is run beyond its synchronous speed, such as when driving a load, travelling down hill or when its speed is reduced to perform a specific duty. The same conditions will appear when a running machine is reversed, whether it is an a.c. or a d.c. machine. 

As a synchronous motor The machine is run primarily to drive a mechanical load and is operated at the synchronous speed and at unity p.f. The efficiency is now better than that of an induction motor. Except in assisting the system by consuming power at unity p.f., it does not help the system to improve its p.f. 

If the field excitation is also lost, the generator will run as an induction motor again driving the primer mover as above. As an induction motor, it will now operate at less than the synchronous speed and cause slip frequency current and slip losses in the rotor circuit, which may overheat the rotor and damage it, see also Section. 1.3 and equation (1.9). A reverse power relay under such a condition will disconnect the generator from the mains and protect the machine. 

Power is generated by the pressurized gas expanding through an 11,000 rpm single-stage, radial-inflow turbine expander, which drives a synchronous generator. Exhaust gas from the expander is liquified by air-cooled condensers and is pumped back to the heat exchangers to repeat the cycle. 

Maximum continuous speed for generator drive duty is synchronous speed. 

Wright, J., A Practical Solution to Transient Torsional Vibration in Synchronous Motor Drive Systems, American Society of Mechanical Engineers, Pub. 75-DE-15. 

Synchronous and induction motors cannot always be compared on an equal speed basis. In geared applications such as high-speed centrifugal compressor drives (above 3,600 rpm), the most economical induction moior speed is usually 1,800 rpm. The most economical synchronous motor speed for the same application might be 900 or 1,200 rpm, depend-... 

Molecular weight, effect on centrifugal sizing, 159 Mollier charts, 27 Monitoring system, 356 Motor, 146 enclosure, 260 equations, 267 insulation, 257 locked rotor torque, 270 selection, 270 service factor, 262 starting characteristics, 270 starting time, 273, 274 synchronous vs induction, 265 variable frequency drives, 27/, 280 voltage, 258 Motors... 

Examination of the drive ratios shows that if both motors have ISOOrpm synchronous speeds that the pony motor is made to operate near 3600rpm when the big motor is operating. This is typically not a problem as to rotor balance or bearing duty because manufacturers make 3600 rpm versions of these same motors. Nevertheless, the duty should be checked and if this is a problem, the small motor can be changed to a 900 rpm model and the synchronous speeds of each motor will not be exceeded. 

Normal electric motor speeds run from the standard induction speeds for direct connection of 3600, 1800 and 1200 rpm to the lower speed standards of the synchronous motors, and then to the somewhat arbitrary speeds established by V-belt or gear drives. For some cases, the pump speed is set by the type of drivers available, such as a gasoline engine. 

Figure 14-4A. Oscillogram shows variation of current to a synchronous motor driving a reciprocating compressor, The compressor is two-cylinder, horizontal, double-acting, and operates at 257 rpm. Line A is the envelope of the current wave. Difference B-C is current variation. Value B-C divided by the rated full load current is the percentage of current variation. (Used by permission Oscarson, G. L. E-M Synchronizer, 200 SYN 52, p. 11. Dresser-Rand Company.)...

For squirrel-cage motors, slip ranges to 5% of the synchronous or constant speed. For variahle-frequency motor drives, see Reference 89. 

Pull-in torque For a synchronous motor, this is the maximum constant torque under which the motor will pull its connected inertia load into synchronism, at rated voltage and frequency, when its field excitation is applied. The speed to which a synchronous motor will bring its load depends on the power required to drive it, and whether the motor can pull the load into step from this speed depends on the inertia of the revolving parts. So, the pull-in torque cannot be determined without having the Wk as well as the torque of the load. 

Figure 14-15 illustrates a synchronous motor used as the drive for a reciprocating compressor. This is a common arrangement. 

Figure 14-14. Selection chart for centrifugal compressor drive. (Used by permission E-M Synchronizer, 200-SYN-52, 1958. Dresser-Rand Company.)...

Important advantages of direct-current motors for machine drives are the adjustable speed over a wide range, the fact that speeds are not limited to synchronous speeds, and the variation of speed-torque characteristics [8]. 

Inverter-AC Motor Drives. An adjustable-frequency control of AC motors provide efficient operation with the use of brushless, high-performance induction, and synchronous motors. A typical system is shown in Figure. 3-14. Such a system consists of a rectifier (which provides DC power from the AC line) and an inverter (which converts the DC power to acljustable-frequency AC power for the motor). Inverter cost per kilowatt is about twice that of controller rectifiers thus the power convertor for an AC drive can approach three times the cost of a DC drive. 

These AC drive systems require the inverters to operate with either low-slip induction motors or reluctance-type synchronous-induction motors.. Such systems are u.sed where DC commutator motors are not acceptable. Examples of such applications are motor operations in hazardous atmospheres and high motor velocities. 

Figure 3-14. Typical invester AC motor drive consisting of rectifier-DC link, adjustable-frequency inverter, and induction of synchronous motor [10].

The supply system for the power plant auxiliaries, including the provision of supplies to any important drives and the provision of standby supply systems. The protection and synchronizing schemes applicable to the generator circuit. 

The foundations of any turbogenerator installation play a significant part in the safe operation of the machine. Industrial turbines will normally operate at above synchronous speed and will drive an alternator via a reduction gearbox. Any vibration or out of balance occurring under both normal or abnormal operation must be accommodated by the foundations, and their design should therefore best be undertaken by a specialist organization. The layout... 

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