What is armature MMF in dc machine?

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.

What is armature reaction in dc machine explain with the help of MMF and flux density waveform?

Definition: The armature reaction simply shows the effect of armature field on the main field. The armature flux causes two effects on the main field flux. The armature reaction distorted the main field flux. It reduces the magnitude of the main field flux.

What is the direction of generated EMF in the armature coil of a dc machine?

In case of a motor a generator action also takes place and the direction of generated emf can be derived by flemming’s right hand rule which is exactly opposite to the supply current in the armature i.e. we can say the direction of generated emf in the armature coil of a dc machine is the same as that of the current in …

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 is the armature reaction in dc generator?

3.10 Armature reaction in d.c. generators. Armature reaction is the effect on the main field flux of that flux set up by the currents in the armature winding. The effect is the same for both lap- and wave-wound machines.

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 in armature reaction?

This m.m.f. sets up a magnetic flux and the effect of this flux on that set up by the main poles is called armature reaction. The armature m.m.f. is acting on a relatively small airgap under the main poles and on a long air path of high reluctance between the poles. Resultant flux in the air gap of a d.c. machine.

What is armature constant?

In DC motors, the back EMF, denoted Ea, is proportional to the flux, times the shaft speed. The torque developed by the armature is proportional to the product of the magnetic flux and the armature current. The constant of proportionality is the armature constant.

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.