How does flux affect armature winding?

How Magnetic Flux Affects Armature Windings

The impact of magnetic flux on armature windings is central to the operation principles of motors and generators. In these devices, changes in magnetic flux induce an electromotive force (EMF) in the armature windings, based on Faraday's law of electromagnetic induction. Below is a detailed explanation of how magnetic flux affects armature windings:

1. Induced Electromotive Force (EMF)

According to Faraday's law of electromagnetic induction, when the magnetic flux through a closed circuit changes, an induced EMF is generated within that circuit. For armature windings, if the magnetic flux varies over time (for example, in a rotating magnetic field), this changing flux induces a voltage in the armature windings. The formula is as follows:

• E is the induced EMF;

• $\mathrm{<span\; style="font-family:\; arial,\; helvetica,\; sans-serif;\; font-size:\; 16px;">N</span>}$N is the number of turns in the winding;

• $\mathrm{<span\; style="font-family:\; arial,\; helvetica,\; sans-serif;\; font-size:\; 16px;">\Phi </span>}$Φ is the magnetic flux;

• $\mathrm{<span\; style="font-family:\; arial,\; helvetica,\; sans-serif;\; font-size:\; 16px;">\Delta </span>}\mathrm{<span\; style="font-family:\; arial,\; helvetica,\; sans-serif;\; font-size:\; 16px;">t</span>}$Δt is the change in time.

The negative sign indicates that the direction of the induced EMF opposes the change in flux that caused it, as per Lenz's law.

2. Induced Current

Once an induced EMF is generated in the armature windings and the windings form a closed circuit with an external load, current will flow. This current, caused by the changing magnetic flux, is known as induced current. The magnitude of the induced current depends on the induced EMF, the resistance of the winding, and any other series impedance present.

3. Torque Generation

In motors, when there is current flowing through the armature windings, these currents interact with the magnetic field produced by the stator, resulting in torque. This is because a current-carrying conductor experiences a force in a magnetic field (Ampère's force). This force can be used to drive the shaft rotation, enabling the motor to perform mechanical work.

4. Back EMF

In DC motors, as the armature begins to rotate, it also cuts through magnetic field lines and generates an EMF that opposes the supply voltage; this is called back EMF or counter EMF. The presence of back EMF limits the growth of armature current and helps stabilize the motor speed.

5. Magnetic Saturation and Efficiency

When the magnetic flux density increases to a certain point, the core material may reach magnetic saturation, where further increases in excitation current do not significantly increase the magnetic flux. Magnetic saturation not only affects motor performance but can also lead to additional energy losses, reducing motor efficiency.

In summary, changes in magnetic flux directly influence the induced EMF, current, and subsequently the torque in armature windings, which are fundamental to the proper operation of motors and generators. Proper design and operation of motors and generators must consider these factors to ensure efficient and reliable performance.