Explain about elementary direct-current machines, Electrical Engineering

Assignment Help:

Q. Explain about Elementary Direct-Current Machines?

A preliminary discussion of dc machines, including Equations. The location of the brushes on the commutator arrangement connected to the armature winding ensures that the rotor and stator mmf axes are at all times at right angles to one another, as shown in Figure. The expression for torque given by Equation is applicable to the dc machine, provided the constant K is adjusted for the nonsinusoidal mmf distributions and sin δ is made equal to unity. Not only are the conditions for constant torque fulfilled, but also the condition for maximum torque and hence for maximum energy conversion is satisfied, since δ = ± π/2, depending upon whether generator or motor action occurs for a given direction of rotation.

1098_Explain about elementary direct-current machines.png

Since both armature and field circuits carry direct current in the case of a dcmachine, they can be connected either in series or in parallel. When the armature and field circuits are connected in parallel, the machine is known as a shunt machine. In the shunt machine, the field coils are wound with a large number of turns carrying a relatively small current. When the circuits are connected in series, the machine is known as a series machine. The field winding in the series machine carries the full armature current and is wound with a smaller number of turns. A dc machine provided with both a series-field and a shunt-field winding is known as a compound machine. In the compoundmachine, the series fieldmay be connected either cumulatively, so that itsmmf adds to that of the shunt field, or differentially, so that the mmf opposes. The differential connection is used very rarely. The voltage of both shunt and compound generators (or the speed, for motors) is controlled over reasonable limits by means of a field rheostat in the shunt field. The machines are said to be self-excited when the machine supplies its own excitation of the field windings, as in the cases just defined. The field windings may be excited separately from an external dc source, however. A small amount of power in the field circuit can control a large amount of power in the armature circuit. The dc generator may then be viewed as a power amplifier.


Related Discussions:- Explain about elementary direct-current machines

Flex routing , Flex Routing : You can see that your labour will have bee...

Flex Routing : You can see that your labour will have been in vain unless you take steps to ensure that flexes are routed safely and well clear of possible sources of danger.

Decision making, Decision  Making The rhombus diamond symbol  is used...

Decision  Making The rhombus diamond symbol  is used to represent  the decision making  process  as shown  below.                                          Figure  De

Explain thermosetting plastic materials, Explain Thermosetting Plastic Ma...

Explain Thermosetting Plastic Materials. Thermosetting Plastic Materials: They undergo huge changes while subjected to high temperatures for rather sometimes. They are call

High level language - third generation language , High Level Language ( thi...

High Level Language ( third Generation Language ) The difficulties of low  level  languages are overcome  by high  level languages. In  assembly  language  mnemonics  were used

Explain diffusion, Explain Diffusion. Diffusion : Though, the mobili...

Explain Diffusion. Diffusion : Though, the mobility of the carriers in a semiconductor is greater than the electrons in metals, the conductivity in the former is much less t

Explain by using a circuit diagram a darlington pair, Q. Explain by using a...

Q. Explain by using a circuit diagram, a ‘Darlington Pair'. Mention its advantages? THE DARLINGTON PAIR : This is a very special way of direct coupling of two transistors. The

Back emf, Transistor Switching Circuit Design a) Sketchy a schematic d...

Transistor Switching Circuit Design a) Sketchy a schematic diagram showing how a transistor can be used to control the operation of a relay b) Determine what is meant by ba

Impact of abnormal solar winds on the earth, (a) Provide examples of intent...

(a) Provide examples of intentional electromagnetic sources and examples of unintentional sources. (b) Describe the process of the formation of lightning. (c) Reduce each of

What are the predefined interrupts in 8086, What are the predefined interru...

What are the predefined interrupts in 8086? The predefined interrupts are, DIVISION BY ZERO (type 0) Interrupt. SINGLE STEP (type 1) Interrupt. NONMASKABLE (ty

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd