Electrical and Magnetic Circuits: Principles and Applications

Posted on Dec 20, 2024 in Electronics

Electrical Circuit

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Current Flow in an Electric Circuit

  • I = V/R
  • I = Q/t
  • Unit = Ampere [A]
  • Current cannot flow through air.
  • Electromotive force (EMF) is responsible for the flow of current through an electric circuit.
  • Resistance opposes the flow of current in an electric circuit.

Magnetic Circuit

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  • Flux flow in a magnetic circuit.
  • Φ [Flux] = B x A
  • Unit = Weber [Wb]
  • Flux can flow through air.
  • Magnetomotive force (MMF) is responsible for the flow of flux through a magnetic circuit.
  • Reluctance opposes the flow of flux in a magnetic circuit.

Working Principle of a Universal Motor

  1. Initially, an AC or DC supply is given to the field winding of the motor.
  2. Due to this, current will start flowing through the field winding.
  3. This current magnetizes the field poles, producing a magnetic flux that passes from the north pole to the south pole.
  4. A second AC/DC supply is given to the armature winding through the brush. This magnetizes the armature conductors, and flux is produced around each conductor in a clockwise or anticlockwise direction, depending upon the direction of current flowing through it.
  5. If the two fluxes are in the same direction, they will add to each other. If the two fluxes are in opposite directions, they will subtract from each other.

Factors Affecting Earth Resistance

  1. The resistivity of soil: If the soil is too dry, the resistance is high. Pour water through a funnel as per the moisture of the soil.
  2. Material of the plate: If a copper plate is used, the resistance is lower compared to other materials because copper has a very low resistance.
  3. Temperature of soil: If the temperature is greater than 0°C, soil resistivity increases as the temperature decreases.
  4. Depth of the electrode: One very effective way of lowering ground resistance is to install ground electrodes deeper.

Series Magnetic Circuit

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  • When flux flows through only one part of the magnetic circuit.
  • Equation: S = S1 + S2 + S3
  • When MMF is applied, the same flux flows through the entire circuit.

Parallel Magnetic Circuit

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  • When flux flows through multiple parts of the magnetic circuit.
  • Equation: 1/P = 1/P1 + 1/P2
  • When MMF is applied, the flux divides between the paths of the circuit.

MCB (Miniature Circuit Breaker)

  1. MCBs can usually be reused.
  2. MCBs are used for low-voltage circuit protection.
  3. MCBs are more expensive.
  4. MCBs are slower.
  5. Applications:
    • Lighting circuits
    • Residential setups
    • Industrial systems
    • Domestic purposes

Fuse

  1. Fuses usually cannot be reused.
  2. Fuses are suitable for varying voltages, from very low to very high.
  3. Fuses are less expensive.
  4. Fuses are faster than MCBs.
  5. Used to protect electrical equipment from excessive current and to prevent short circuits.

Necessity of Earthing

  • The main reason for earthing is safety. When all metallic parts in electrical equipment are grounded, then if the insulation inside the equipment fails, there are no dangerous voltages present on the equipment case.
  • Safety for human life: To save human life, buildings, and equipment from the danger of electrical shock or death by providing an alternative path for the fault current to flow so that it will not endanger the user.
  • To protect buildings, machinery, and appliances under fault conditions.
  • To ensure that all exposed conductive parts do not reach a dangerous potential.

Working of a Stepper Motor

  1. Initially, the supply is given to the motor and is supplied to the load through the shaft. The first starter winding is given, denoted by ‘A’. The stator pole will get magnetized, producing a north pole. The rotor has a south pole, which will be attracted toward the north pole.
  2. Now, the supply is given to the starter winding denoted by ‘D’. The stator pole will get magnetized and again produce a north pole. The rotor will move through 90° in an anticlockwise direction. Thus, the rotor will rotate in an anticlockwise direction, given a step angle of 90°.
  3. The step angle can be varied by changing the number of poles on the stator.

Working Principle of a DC Motor

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