Asynchronous motors

Describe the factors that influence the strength of skeletal muscle contraction including multiple motor unit summation, asynchronous motor unit summation, frequency of nerve stimulation, length-tension relationship, and diameter of the muscle fiber... 

Multiple motor unit summation involves recruitment of motor units. As the number of motor units stimulated at any given moment increases, the strength of contraction increases. Asynchronous motor unit summation refers to the condition in which motor unit activation within a muscle is alternated. In other words, at one moment, some of the motor units within the muscle are activated, while other motor units are relaxed. This is followed by the relaxation of previously activated motor units and activation of previously relaxed motor units. Consequently, only a fraction of the motor units within the muscle generate tension at any given moment. Therefore, this type of summation may generate submaximal contractions only. 

The Venturi Astrolab is called a high-performance solar-electric commuter car. It has two seats in tandem for better balance on the road, a 16 kW asynchronous motor and a hydride metal nickel 72V battery that gives it a 110-km range and a 120 km/hour top speed. 

The capacity of a motor is defined by the distance (mm) between its drive shaft and bed plate. This distance is termed its frame size. For asynchronous motors there is a standard (IEC standard) that defines frame size. For example, if a motor has a diameter of 800 mm, its frame size is 400. Motors produced according to this standard are termed standard motors. 

Asynchronous motors can operate directly on the AC network current. The resulting speed is constant and dependent on the number of pole pairs and network frequency. However, an extruder drive should at least have variable speed. For this, a frequency converter is used. 

With a frequency converter, stator voltage and frequency of the asynchronous motor can be varied infinitely. This transforms a standard motor into a variable speed drive system. An asynchronous motor equipped with a rotor position sensor, magnetization calculation, and the impression of the corresponding stator currents (vector regulation) has the properties of a servo drive. 

Standardized asynchronous motors are designed for operation on AC network current. That means they have high starting torque (current displacement grooves) and are trimmed for... 

Asynchronous motors are the most widely used industrial motors. They can be plugged directly (with a motor starter) into AC network current, are very robust, and simple to build. Thanks to these desirable characteristics, this drive is internationally standardized and produced in large quantities all over the world. 

Nominal motor speed is an important parameter for configuring the drives of an extruder. Many contemporary extruders offer screw speeds of 1200 rpm. At 60 Hz mains network frequency, the synchronous speed of an asynchronous motor per number of pole pairs is... 

Often, synchronous motors are used instead of asynchronous ones. They are more expensive than asynchronous motors, but they have the advantage of requiring less starting current and can be used to compensate blind current. This makes it possible to do without the usual system for compensating blind current. 

Asynchronous motors (squirrel cage induction motors, the rotor-stator part of slipring induction motors) and the rotor-stator part of synchronous motors are within the scope of increased safety due to the omission of sparks and arcs assuming an appropriate construction of rotor and windings. Tire standards IEC 60079-7 and EN 50019 contain mechanical and thermal requirements that follow this aim. 

Following this route, the dynamical stresses of switchgear, busbars and load terminals due to short-circuit currents can be massively reduced, if a protective device responds in an adequate time and prevents the short-circuit current rising to its prospective value. There is no longer a need for an additional reactance as a short-circuit current limiting device, which unfortunately impedes the run-up of large asynchronous motors. 

Energy saving due to variable speed solution depends a lot from thermal loads if at maximum load performances are similar to fixed speed solutions, the main benefit appears at reduced loads. The economical threshold between brushless and asynchronous motors is today around 150 watts under this limit brushless technology is competitive in terms of costs to asynchronous motors above such limits asynchronous motors are used and the motor speed could be changed by inverters. 

ASYNCHRONOUS MOTOR - An induction motor, whose speed is not synchronous with the frequency of the suppiy iine. 

Primary coolant circulation is provided by main coolant pumps (MCP) with canned asynchronous motors that are installed on the reactor cover. As an additional benefit, simple configuration and short length of the primary circuit path permit to sustain high flow rate of... 

Coal mine has humidity, high temperature, flammable gas, coal dust and other big issues, in which the boring machine, scraper conveyor, belt conveyors, fans, pumps, hoists and other equipment should be driven by explosion-proof three-phase asynchronous motors. Whats worse, the universal converters are forbidden to use directly in these occasions, and these equipment s control methods are direct start and mechanical speed control, which will cause a great Impact to the current and voltage of the power supply system. ... 

SPEED-SENSORLESS VECTOR CONTROL OF ASYNCHRONOUS MOTORS... 

The estimated speed of asynchronous motor can be achieved from equation (32) to realize speed-sensorless operation. Meanwhile, the system has a good control performance. 

Figure 34.26. The left picture shows a schematic of the ARTEMIS furnace facility. A cylindrical sample sticks at the bottom and the top in two independent heaters and in between it is fully surrounded by a silica aerogel having a cylindrical hole. The right photo gives a picture of such a furnace assembly mounted in a vacuum chamber. The sample and the surrounding aerogel can be seen. There are six eoils, which form an asynchronous motor and thus...

The recirculation system is based on the use of internal glandless pumps driven by wet, asynchronous motors, supplied individually with "variable frequency - variable voltage" power from frequency converters. This type of pumps has been operating reliably (for more than three million operating hours) since 1978. Within a couple of years such internal pumps will be in use also by other BWR vendors, in the ABWR plants. 

Number of cooling or recirculation pumps 4 Type Centrigual, Single-stage, Glandless with two-speed asynchronous motor... 

The primary circuit blower consists of a single-stage radial compressor. A speed-controlled asynchronous motor is provided as drive. The motor is cooled with water. The blower with motor is installed in the blower pressure vessel section as a slide-in unit with vertical shaft and hanging impeller. A blower flap is located on the suction side of the blower. The blower increases the pressure of the helium sucked in from the steam generator outlet side by approx. 1.5 bar. 

Sen, P. C. Principles of Electric Machines and Porver Electronics. 2d ed. New York John Wiley Sons, 1997. An advanced textbook providing a thorough treatment of electromagnetic machine principles, including magnetic circuits, transformers, DC machines, and synchronous and asynchronous motors. 

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