Rotor systems and

The prime vendor for the PRT shall perform lateral, torsional, and rotor response to unbalanee analyses of the eomplete rotor system and shall issue reports of these analyses to the Purehaser. 

In the baseline O M strategy mostly main components are defined on a system level, except the rotor system and drive train, where the major subsystems are included in the breakdown. The failure... 

With a view to achieve yet more standardization in motor design, NEMA Standard MG-1 has also recommended the maximum locked rotor current of single-speed three-phase motors for the various rotor designs A, B, C, and D, for various recommended torque values. These have been derived for a 415 V a.c. system and are shown in Table 2.2. 

The inverter may be a current source inverter, rather than a voltage source inverter (.Section 6.9.4) since it will be the rotor current that is required to be vtiried (equation (1.7)) to control the speed of a wound rotor motor, and this can be independently varied through the control of the rotor current. The speed and torque of the motor can be smoothly and steplessly controlled by this method, without any power loss. Figures 6.47 and 6.48 illustrate a typical slip recovery system and its control scheme, respectively. 

The unbalanced voltage will produce an additional rotor current at nearly twice the supply frequency. For example, for a 2% slip, i.e. a slip of 1 Hz, the negative sequence stator current, due to an unbalanced supply voltage, will induce a rotor current at a frequency of (2/- 1) = 99 Hz for a 50 Hz system. These high-frequency currents will produce significant skin effects in the rotor bars and cause high eddy current and hysteresis losses (Section 1.6.2(A-iv)). Total rotor heat may be represented by... 

Figure 5-13. The Elliott TH expander is a single-stage hot gas expander with an axial inlet and vertical exhaust. The TH-line expanders range in horsepower from 4,000 to 50,000 and are of overhung rotor construction. The expander consists of four major components the inlet casing and its supports, the exhaust casing, the bearing housing and support system, and the rotor.

In this automatic thrust balancing system, the pressure behind the compressor wheel is controlled to a value between the compressor suction pressure and the wheel peripheral pressure. As the expander inlet pressure increases above the compressor suction pressure level, the resulting thrust force pushes the compressor wheel, and hence the rotor system, towards the compressor suction. In the reverse situation, when the pressure behind the compressor wheel is reduced below the wheel peripheral pressure level, the rotor system moves toward the expander. 

Squeeze film dampers have long been used to combat rotor dynamic and stability problems that conventional bearings cannot solve on turbomachinery rotor systems. The use of squeeze film dampers in problem process machinery has tainted it as a treat-the-symptom solution, and many users shy away from using squeeze film dampers for this reason. Also, their limited use is explained by the difficulty in accurately predicting performance, particularly with o-ring supported dampers. 

Critical speeds correspond to the natural frequencies of the gears and the rotor bearings support system. A determination of the critical speed is made by knowing the natural frequency of the system and the forcing function. Typical forcing functions are caused by rotor unbalance, oil filters, misalignment, and a synchronous whirl. 

There are many types of forees that aet on a rotor-bearing system. The forees ean be elassified into three eategories (1) easing and foundation forees, (2) forees generated by rotor motion, and (3) forees applied to a rotor. Table 5-2 by Reiger is an exeellent eompilation of these forees. 

In a real rotor system the amount and location of unbalances cannot always be found. The only way to detect them is with the study of rotor vibration. Through careful operation, the amount and the phase angle of vibration amplitude can be precisely recorded by electronic equipment. The relation between vibration amplitude and its generating force for an uncoupled mass station is... 

One is the so-called A-plane approach. This approach states that only A-planes are necessary for a rotor system running over Ncritical speeds. The other technique, called the (N + 2)-plane approach, requires two additional planes. These two additional planes are for the two-bearing system and are necessary in this school of balancing. 

The inventory of these plants can run into over 20,000 items, including over 100 complete rotor systems. The field of spare parts is changing rapidly and is much more complex than in the past. A group of plants have gotten together in a given region and formed Part Banks. ... 

The manufacturer will have carried out a full mathematical investigation into the system vibration response. One quality control requirement will be to establish whether the correct assumptions have been made Rotor assembly and component weights should be obtained during man ufacture and verified against mathematical data used. 

A typical excitation system includes a voltage regulator, or exciter, protection circuits, and measurements transducers. If the terminal voltage decreases below rated value, the conU ol system increases the rotor cuiTent and thus the magnetic field as shown in Faraday s law, the generated voltage is thus forced up to the desired value. 

Figure 12-110A. A typical cross-section showing the spiral screw rotors, lubrication system, and other details of internal construction. (Used by permission 1961. Roots Division, Dresser Industries, Inc.)...

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