Magnitude of force | Fleming Left hand rule | DC Machine | Windings in DC Machine

Magnitude of Force:

The magnitude of the force experienced by the current carrying conductor placed in the magnetic field is given by. BII Newton
Equation (5.1.1) tells us that the force is dependent on (proportional to):
The original flux density. B produced by the magnet. Current flowing through the conductor. I Length of the conductor

Direction of Force (Fleming's Left Hand Rule):

[DIEOuestions
State the working principle of DC motor and Fleming's left hand rule.
Q.2 Lu State the Fleming's lert hand ule. (S-10,2 Marks)
The direction of rotation of a motor depends on the direction of force exerted on the armature winding. and the direction of force expenenced by a current carrying conductor is given by Fleming's left hand rule.
Statement of Fleming's left hand rule:
It states that if the first three fingers of the left hand are held mutually at right angles to each other and if the index finger indcates the direction of the onginal field, and if the middle finger indicates the direction of current flowing through thei conductor, then the thumb indcates the directuion of force exerted on the conductor Thus is shown in Fig. 5.1.4(a). Peming's left hand rule is illustrated in a simplfied manner in Fg 5 14(b).

DC Machines :

DC machines are basically of two types : D.C. generator
A dc generator is rotated by a prime mover and produces a dc voltage. So it converts mechanical energy into electrical energy. A dc motor receives energy from a d.c. voltage source and
rotates at a speed proportional to the applied voltage. So a dc motor converts the electrical energy into a mechanical energy.

Windings in a DC Machine:

 5.3 In any dc machine, there are two windings: Field winding
Out of these, the field winding is stationary which does not move at all and the armature winding is a movable winding. The armature winding is mounted on a shaft. So it can rotate freely.i
The construction of a dc generator and dc motor is the same That means we can use the same dc machine cither as a generator or as a motor.
Armature winding.

As shown in Fig. 5.3. l(a), a prime mover supplies mechanical energy to the DC generator which generates electnical output energy.
Fig. 5.3.1 (b) shows the operating principle of a DC motor. It accepts the energy in the electric form from D.C. source and
converts it into mechanical energy at its output (shaft).

Connection of windings for operation as generator:

To operate the dc machine as a generator, the field winding is connected across the dc power supply.
The armature winding is connected to an electrical load such as a lamp load (see Fig. 5.3.1 (a)).

Connection of winding for operation as motor:

 To operate the dc machine as a motor, the field winding is connected across a dc power supply and armature winding also is connected across a dc power supply. The field winding acts as an electromagnet due to dc field current flowing through it and produces flux in the air gap between the two windings.
The armature also carries a dc current and it acts as a current i carrying conductor placed in the magnetic field produced by the field winding.
A mechanical load is applied on the shaft of the dc motor as shown in Fig. 5.3.1(b).