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Why is it desirerable to have a many coils of wire and commutator segments on the armature of a d-c generator?
Wiki User
∙ 16y ago
The short answer is that with more individual coils in the rotor (and the increased number of commutator segments necessary to support them), the motor will run more smoothly. At each transition, the rotor will want to slow down a bit, but with a large commutator and lots of coils in the armature, the motor will transition more quickly to the next segment (for a given RPM) than a motor with fewer segments. The motor runs more smoothly. The drawback in making a motor like this is the increase in cost. A more economical motor is constructed using fewer windings in the rotor. The trade offs must be considered based on application and the economics of that application.
Wiki User
∙ 16y ago
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Name two reasons for arcing at the commutator?
1) When the armature is open. 2) When the Field is open. 3) Commutator segments are internally short.
How commutator converts AC to DC?
There is no conversion of AC to DC a commutator is the key to creating straight DC voltage. "The commutator rotates with the loop of wire just as the slip rings do with the rotor of an AC generator. Each half of the commutator ring is called a commutator segment and is insulated from the other half. Each end of the rotating loop of wire is connected to a commutator segment. Two carbon brushes connected to the outside circuit rest against the rotating commutator. One brush conducts the current out of the generator, and the other brush feeds it in. The commutator is designed so that, no matter how the current in the loop alternates, the commutator segment containing the outward-going current is always against the "out" brush at the proper time. The armature in a large DC generator has many coils of wire and commutator segments. Because of the commutator, engineers have found it necessary to have the armature serve as the rotor(the rotating part of an apparatus) and the field structure as the stator (a stationary portion enclosing rotating parts). Which is the inverse of an AC Generator."
Why commutator are not used in ac motors?
Because, the commutator segments are used for converting AC to DC.
Remedies for Armature reaction?
Since an armature is wound with coils of wire, a magnetic field is set up in the armature whenever a current flows in the coils. This field is at right angles to the generator field, and is called cross magnetization of the armature. The effect of the armature field is to distort the generator field and shift the neutral plane. The neutral plane is the position where the armature windings are moving parallel to the magnetic flux lines. This effect is known as armature reaction and is proportional to the current flowing in the armature coils. The brushes of a generator must be set in the neutral plane; that is, they must contact segments of the commutator that are connected to armature coils having no induced emf. If the brushes were contacting commutator segments outside the neutral plane, they would short-circuit "live" coils and cause arcing and loss of power. Armature reaction causes the neutral plane to shift in the direction of rotation, and if the brushes are in the neutral plane at no load, that is, when no armature current is flowing, they will not be in the neutral plane when armature current is flowing. For this reason it is desirable to incorporate a corrective system into the generator design. These are two principal methods by which the effect of armature reaction is overcome. The first method is to shift the position of the brushes so that they are in the neutral plane when the generator is producing its normal load current. in the other method, special field poles, called interpoles, are installed in the generator to counteract the effect of armature reaction. The brush-setting method is satisfactory in installations in which the generator operates under a fairly constant load. If the load varies to a marked degree, the neutral plane will shift proportionately, and the brushes will not be in the correct position at all times. The brush-setting method is the most common means of correcting for armature reaction in small generators (those producing approximately 1000 W or less). Larger generators require the use of interpoles.
Why carbon brushes are most used in dc?
Carbon is used because it is soft and does not damage the commutator. This means that the brushes must be replaced at intervals, and the powdered carbon scraped out from between the segments of the commutator.
Give the function of its part of dc generator?
An AC generator generally called an alternator because it is generating a alternating current, consist of a rotor, field stator, slip ring assembly or rectifier bridge mounted in the place of the slip ring, in the case of a brushless alternator and an AVR (Automatic Voltage Regulator)
What is the function of carbon brushes in dc machine?
The carbon (graphite) brushes in a generator are used to connect external circuits in the generator to the rotor through the commutator. But you want to know what that means, right? Darn it, we always see these "trick" questions here. Okay, this is the scoop. The rotor in a generator is (usually) a group of windings. These are coils of wire. But they need to be connected to the "outside" or non-moving parts. Each coil has two ends, and these ends are connected to copper segments (sometimes called "lands") on the commutator. The segments are all in a ring around the end of the rotor, and the brush or brush sets ride on them. The other end of the brush(s) is(are) connected to wires to electrically connect them to appropriate places in the non-moving parts of the generator. The brush is conductive (naturally), and it is soft enough to provide a good "wear point" against the copper segments. The brushes do most of the "wearing away" in this application, and it is a fairly easy and straight forward evolution to replace them. In the motors of power tools, some of the units have a way to access the brush holder without taking the housing apart. Particularly the older ones. Anyway, it is said that a picture is worth a thousand words. Use the link below and take a look at the pictures. It's all there.
What is the difference between a synchronous motor and a generator?
A DC generator is Direct Current most common in industrial environments. Limited to DC equipment such as motors, cranes, certain types of lighting etc. A AC generator is Alternating Current can be used in virtually every environment. These are used for virtually everything from residential dwellings to large steel manufacturing facilities.
What happen applying dc supply to ac induction motor?
It depends on whether the field winding of the dc motor is connected in series or in shunt with the armature winding.If it is connected in series,the motor will rotate since the torque,which varies as the product of the armature and field current is always positive.Thus,a positive average torque causes the motor to rotate,however the pulsating nature may cause the commutator segments and brushes to wear out. Thus only small sized dc motors may be used with ac supply.
What is a carbon brush used for?
Some kinds of single phase ac electric motor use commutators. They are the kind where the field winding is connected in series with the armature and they are typically used in non-battery-powered electric drills, hair dryers and home vacuum cleaners.
Can a DC motor work on an AC supply?
There is a motor that is known as Universal motor which works on DC or AC .You might find one in a drilling machine or a domestic grinding machine .But there is a disadvantage ,in that there will be sparking at the commutator between the brushes and the commutator segments due to a shift in the magnetic neutral axis while on AC operation.
What causes three phase induction motor fails to start?
One possable reason for failure to start could be as simple as a brush not making contactwith the commutator. Also if the commutator segments are dirty this could also contribute to the problem
