27-10-2016, 09:35 AM
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DC Machine is an industrial design and machining center that designs and manufactures close tolerance components
History Of DC Machines:
With the invention of the battery (Allessandro Volta, 1800), the generation of a magnetic field from electric current (Hans Christian Oersted, 1820) and the electromagnet (William Sturgeon, 1825) the foundation for building electric motors was laid. At that time it was still open whether electric motors should be rotating or reciprocating machines, i.e. simulate a plunger rod of a steam engine.
The first rotating device driven by electromagnetism was built by the Englishman Peter Barlow in 1822 (Barlow's Wheel).
After many other more or less successful attempts with relatively weak rotating and reciprocating apparatus the German-speaking Prussian Moritz Jacobi created the first real rotating electric motor in May 1834 that actually developed a remarkable mechanical output power. His motor set a world record which was improved only four years later in September 1838 by Jacobi himself. His second motor was powerful enough to drive a boat with 14 people across a wide river. It was not until 1839/40 that other developers worldwide managed to build motors of similar and later also of higher performance.
Already in 1833 the German Heinrich Friedrich Emil Lenz published an article about the law of reciprocity of the magneto-electric and electromagnetic phenomena, i.e. the reversibility of electric generator and motor. In 1838 he provided a detailed description of his experiments with a Pixii-generator that he operated as a motor.
In 1835 the two Dutchmen Sibrandus Stratingh and Christopher Becker built an electric motor that powered a small model car. This is the first known practical application of an electric motor. In February 1837 the first patent for an electric motor was granted to the US-american Thomas Davenport.
The DC motor was not created from these engines, but rather from the development of power generators (dynamometers). The foundations were laid by William Ritchie and Hippolyte Pixii in 1832 with the invention of the commutator and, most importantly, by Werner Siemens in 1856 with the Double-T-anchor and by his chief engineer, Friedrich Hefner-Alteneck, in 1872 with the drum armature. DC motors still have a dominant market position today in the low power (below 1 kW) and low voltage (below 60 V) range.
Today, the three-phase synchronous motor is used mostly in highly dynamic applications (for example in robots) and in electric cars. It was developed first by Friedrich August Haselwander in 1887.
The highly successful three-phase cage induction motor was built first by Michael Dolivo-Dobrowolsky in 1889. Today, this is the most frequently produced machine in the power range of 1 kW and above.
Types Of DC Motors:
This is major and widely used classification system or type for both D. C. Motor and D. C. Generator.
D. C. Motor are of four types :
• Separately Excited D. C. Motor
• Series D. C. Motor
• Shunt D. C. Motor
• Compound D. C. Motor
Separately Excited D. C. Motor :
This type of DC motor is constructed such that the field is not connected to the armature. This type of DC motor is not normally used.
Applications:
Industrial Uses:
• Cranes
• Elevators
• Air compressor
• Vacuum cleaner
• Hair drier
• Sewing
• machine
Current and Voltage Equations of dc shunt motor
• Current Equation: The current supplied to the motor is divided into two paths one through the armature and the other through the field windings. So we can say that , IL = Ia + Ish
• Voltage Equation : We already know that V = Ish Rsh where, V is the supply voltage , Ish and Rsh are shunt field current and shunt field resistance respectively.
Compound D. C. Motor :
A compounded DC motor is constructed so that it contains both a shunt and a series field. This particular schematic shows a cumulatively-compounded" DC motor because the shunt and series fields are aiding one another. Sometimes in D. C. Motors the magnetic field is produced by an inductor or a solenoid type electrical component connected in both series and parallel with the armature coil. This arrangement is called D. C. Compound Motor.
Q. 01: Why laminated core is used in D.C Machine?
Ans:Motor armatures have to be made of thin laminations of iron to work efficiently. By using an armature made of very thin iron laminations, the eddy currents can be reduced to an acceptable minimum level
Q.02: What is the function of commutator?
Ans:The commutator is used to change the direction of
current to cater the problem of torque
Q.03: What is the function of Carbon Brushes?
Ans: The brushes transfer the electricity from outside the motor to the spinning winding in the center of the motor. They undergo quite a lot of friction, and after a while wear out. Carbon is used as it is a reasonable conductor
Q. 04: How should a generated be started?
Ans: it has pull start with rope. and i want alternate start with self start..
Q.05: how about a series generator ?
Ans: it usually brought up to speed with tht help of driving engin called prime-mover.
Q.06: What is the procedure of shutting down a generator?
Ans: first should be the lood gradully reduced.if possible easing down the driving engin then when the generator current little or zero the main switch should be opend.