MACHINES & DRIVES

• Charges


  Fundamental charges are carried by electrons (negative) and protons (positive)
• Electrons


  Have a negative electrical charge
• Protons


  Have a positive electrical charge
• Like charges


  Produce repulsive forces - so they repel each other (e.g. electron and electron or proton and proton repel each other)
• Unlike charges


  Produce attractive forces - so they attract each other (e.g. electron and proton attract each other)
• Charge on the electron is - 1.6 x 10-19 C
• Charge on the proton is + 1.6 x 10-19 C
• Direction of the electric field

  Is the same as the direction of the electric force that would be exerted on a positive charge when placed in the electric field
• Current


  The rate of flow of charged particles
• Current = (Number of electrons that pass in one second) ∙ (charge/electron)
• 1 ampere = (6.242∙1018 e/sec) ∙(-1.602 10-19 Coulomb/e)
• An ampere = Coulomb/second
• The current inside the conductor is actually flowing in the opposite direction of the electron flow
• Potential difference


  The potential energy that causes a current to flow through a circuit
• Voltage is always measured as a difference with respect to an arbitrary common point called ground
• Power


  The rate at which energy is transferred from an active source or used by a passive device
• P in watts = dW/dt = joules/second
• P= V∙I = dW/dQ ∙ dQ/dt = volts ∙ amps = watts
• Source


  It delivers the electrical power (electron flows out of + terminal)
• Load


  It absorbs the electrical power (electron flows into + terminal)
• Sources


  • Battery
  • Capacitors
  • Photovoltaic cell
• Loads


  • Resistors
  • Inductors
  • Motors
• Magnetism


  A form of energy that is caused by the motion of electrons in some materials
• Magnets


  • The more lines of force that exist, the stronger the magnet
  • The magnetic lines of force, also called magnetic flux or flux lines, form a magnetic field (Φ) (Wb)
  • Flux density refers to the number of flux lines per unit of area (B=Φ/A) (Wb/m2 ) (Tesla)
• Magnetic induction


  The process of creating a magnet by using a magnet field
• Types of magnets


  • Permanent Magnet
  • Electromagnet
• Electromagnet


  When an iron bar is wrapped with a current carrying wire, the bar becomes a magnet
• Magnetic Field Intensity (H)

  The amount of external force required to induce magnetic field lines on the electromagnet
• H = Ni/l (Amp-Turn/m)
• Magnetic materials


  • Ferromagnetic (μr >> 1 )
  • Paramagnetic (μr > 1 )
  • Diamagnetic (μr < 1)

  
• Permeability (μ)


  The degree of passage of magnetic force through a material
• μ = μr X μ0 → μr = μ/μ0, The permeability of free space is called μ0 , and its value is : 4 X 10-7 H/m

  
• Reluctance


  The resistance to the passage of magnetic force, similar to resistance in an electric circuit
• Magnetization


  The process of making a conductor (soft magnetic materials) into a magnet
• Demagnetization


  The process of removing the magnetism property from some magnetic materials
• Hard magnetic materials


  Materials which retain magnetization and are used for production of permanent magnets
• Hysteresis


  A property of ferromagnetic materials best explained through the magnetization curve
• Electricity and magnetism are different facts of electromagnetism, first elucidated by Faraday and Maxwell
• A static distribution of charges produces an electric field
• Arranging wire in a coil and running a current through produces a magnetic field that looks a lot like a bar magnet, called an electromagnet