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Bill Druryis the editor of The Control Techniques Drives and Controls Handbook Second Edition PDF Book.
The functionality of a modern drive is now so diverse that its ability to rotate a motor is sometimes forgotten.
Indeed, some customers buy drives not to control a motor but to utilize the powerfull auxiliary functionality that is built-in.
This is, however, unusual, and the drive remains a key component of the boom in all aspects of automation. Drives are also critical components in relation to energy saving.
For over 30 years the case for energy saving through the use of variable-speed drives has been made by drive companies, and at last, it seems that industry is moving quickly to adopting the technology.
Consider the facts: 55 – 65 percent of all electrical energy is used by electric motors. On average, fitting a variable-speed drive will save 30 percent of the energy used by a fixed-speed motor,
but today only 5 percent of those motors are controlled by variable-speed drives. (The Control Techniques Drives and Controls Handbook Second Edition )
The opportunity is therefore enormous. Drives could save the world, or make a significant contribution to the cause.
Before taking a brief look into the future it is helpful to look back at the relatively short history of drives and see how far and how quickly the technology has come.
1820 Oersted was the first to note that a compass needle is deflected when an electric current is applied to a wire close to the compass; this is the fundamental principle behind an electric motor.
1821 Faraday (Figure P.1), built two devices to produce what he called electromagnetic rotation: that is, continuous circular motion from the circular magnetic force around a wire. This was the initial stage of his pioneering work. The Control Techniques Drives and Controls Handbook Second Edition )
1824 Arago discovered that if a copper disc is rotated rapidly beneath a suspended magnet, the magnet also rotates in the same direction as the disc.
1825 Babbage and Herschel demonstrated the inversion of Arago’s experiment by rotating a magnet beneath a pivoted disc causing the disc to rotate.
This was truly induced rotation and just a simple step away from the first induction motor, a step that was not then taken for half a century. (The Control Techniques Drives and Controls Handbook Second Edition )
1831 Using an ‘induction ring’, Faraday made one of his greatest discoveries – electromagnetic induction. This was the induction of electricity in a wire by means of the electromagnetic effect of a current in another wire. The induction ring was the first electric transformer.
In the second series of experiments in the same year, he discovered magneto-electric induction: the production of a steady electric current.
To do this, Faraday attached two wires through a sliding contact to a copper disc, the first commutator; this was an approach suggested to him by Ampe`re.
By rotating the disc between the poles of a horseshoe magnet he obtained a continuous direct current. This was the first generator. The Control Techniques Drives and Controls Handbook Second Edition )
Faraday’s scientific work laid the foundations for all subsequent electro-technology. From his experiments came devices that led directly to the modern electric motor, generator, and transformer.
1832 Pixii produced the first magneto-electric machine.
1838 Lenz discovered that a d.c. a generator could be used equally well as a motor. Jacobi used a battery-fed d.c. motor to propel a boat on the River Neva.
Interestingly, Jacobi himself pointed out that batteries were inadequate for propulsion, a problem that is still being worked on today.
1845 Wheatstone and Cooke patented the use of electromagnets instead of permanent magnets for the field system of the dynamo.
Over 20 years were to elapse before the principle of self-excitation was to be established by Wilde, Wheatstone, Varley, and the Siemens brothers. (The Control Techniques Drives and Controls Handbook Second Edition )
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1870 Gramme introduced a ring armature that was somewhat more advanced than that proposed by Pacinotte in 1860, which led to the multi-bar commutator and the modern d.c. machine.
1873 Gramme demonstrated, at the Vienna Exhibition, the use of one machine as a generator supplying power over a distance of 1km to drive a similar machine as a motor. This simple experiment did a great deal to establish the credibility of the d.c. motor.
1879 Bailey developed a motor in which he replaced the rotating magnet of Babbage and Herschel by a rotating magnetic field, produced by switching of direct current at appropriately staggered intervals to four-pole pieces. With its rotation induced by a rotating magnetic field, it was thus the first commutator less induction motor.
1885 Ferraris produced a motor in which a rotating magnetic field was established by passing single-phase alternating current through windings in space quadrature. (The Control Techniques Drives and Controls Handbook Second Edition )
This was the first alternating current commutator less induction motor, a single-phase machine that Dobrowolsky later acknowledged as the inspiration for his polyphase machine.
1886 Tesla developed the first polyphase induction motor. He deliberately generated four-phase polyphase currents and supplied them to a machine with a four-phase stator.
He used several types of the rotor, including one with a soft-iron salient-pole construction (a reluctance motor) and one with two short-circuited windings in space quadrature (the polyphase induction motor).
1889 Dobrowlsky, working independently from Tesla, introduced the three-phase squirrel-cage induction motor. The Control Techniques Drives and Controls Handbook Second Edition )
1890 Dobrowlsky introduced a three-phase induction motor with a polyphase slip-ring rotor into which resistors could be connected for starting and control. The speed of these motors depends fundamentally upon its pole number and supply frequency. (The Control Techniques Drives and Controls Handbook Second Edition )
Rotor resistance control for the slip-ring motor was introduced immediately, but this is equivalent to armature resistance control of a d.c. machine and is inherently inefficient.
By 1890 there was a well established d.c.. motor, d.c. central generating stations, three-phase a.c. generation and a simple three-phase motor with enormous potential but which was inherently a single-speed machine.
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