What is the waveform of the armature MMF in a dc machine?

What is the waveform of the armature MMF in a dc machine?

The armature MMF waveform of a dc machine is. Pulsating. Rectangular.

What is the nature shape of a dc armature magnetomotive force wave form?

Now, when the machine is loaded, the armature flux is directed along the inter polar axis (the axis in between the magnetic poles)and is triangular in wave shape.

How should the field MMF with respect to armature MMF to reduce the armature reaction?

How should the field mmf be with respect to armature mmf to reduce the armature reaction? Clarification: To reduce the armature reaction, the field system should be designed such that the field mmf should be dominant over the armature mmf. If the armature mmf becomes low, the armature reaction reduces.

What are the materials used for brushes in DC machines?

Metal Graphite Brushes are generally made from natural graphite and finely divided metal powders. Copper is the most common metallic constituent but silver, tin, lead and other metals are sometimes used. These brushes are often ideal for a wide variety of applications because of their low resistivity.

Why Copper brushes are not used in DC machines?

The function of a commutator in a dc generator is to collect the current generated in armature conductors. Brushes are usually made from carbon or graphite, but copper brushes are preferred in low voltage high current requirements.

What is MMF wave?

In electrical generators ac windings are place where electromotive force (EMF) should be induced. In electrical motors, primarily ac windings goal is to produce rotating magneto-motive force (MMF) wave.

Which of the following correctly defines the magnetomotive force MMF )?

Magnetomotive force (MMF) is a component or part of the equation of magnetic flux in magnetic circuits. As an analogy to electromotive force, MMF “drives” magnetic flux through a magnetic circuit. Magnetomotive force is also known as magnetic potential.

How can induced emf in the armature conductors of a dc generator be made unidirectional?

In a DC motor, the alternating current is produced by the rotation of the commutator. In the generator, the commutator facilitates the collection of current from the armature conductors and converts the alternating emf induced (AC) in the armature conductors to unidirectional emf (DC) in the external load circuit.

What is the nature of induced emf in the armature conductors of a dc generator?

The nature of the induced emf for a conductor rotating in the magnetic field is alternating. As conductor rotates in a magnetic field, the voltage component at various positions is different. Hence the basic nature of induced emf in the armature winding in case of dc generator is alternating.

What should be the range of the field mmf in armature mmf ratio at full load Mcq?

The maximum value of the ratio should be not greater than 1.25.

Why is armature winding placed on the rotor of a DC machine?

The armature winding of a dc machine is placed on the rotor to facilate commutation ie to convert the alternating voltage produced in the winding into direct voltage at the brushes. In a DC machine one part has to rotate with respect to the other.

What is the shape of the armature MMF of distributed armature winding?

The armature mmf of a distributed armature winding of a dc machine is triangular in shape as shown in Fig. In a D.C. machine, the armature M.M.F. wave has its maximum value at fixed points between the main poles, and its chief effect is to increase the flux density on one side of the pole and reduce it on the other

What is the shape of distorted triangular waveform?

Distorted triangular waveform shape is that of flux distribution under poles, which is due to the armature reaction. Explanation: It is cross magnetizing in nature which happens due to interaction between stator and field mmf.

Is MMF Traingular or trapazoidal?

First of all i want ot correct you that the armature MMF is not excatly traingular but some sort of trapazoidal. This is bacause it is AC what is needed at the armature to rotate and due to saturation of the iron core it cannot reach its peak. Hence it looks like trapazoidal. 8 clever moves when you have $1,000 in the bank.

What happens to the armature flux when the machine is loaded?

Now, when the machine is loaded, the armature flux is directed along the inter polar axis (the axis in between the magnetic poles)and is triangular in wave shape. This results an armature current flux directed along the brush axis and causes cross magnetization of the main field.