Motor Induction

An electric motor turns because of Induction. Induction is a process that includes an altering magnetic field in or near a circuit or coil and it’s used to generate electricity in many different devices and motors for example a car alternator or turbines in a power station. For induction to work a current is placed in a magnetic field where it experiences a force that involves the conversion of electrical energy to mechanical energy which makes the electrical motor work. Since induction occurs because of magnetic force It becomes a electromagnetic induction which is the production of voltage across a conductor moving threw a magnetic field.

For the electric motor to turn there needs to be magnetic force between a stationary electromagnet called the stator and a rotating electromagnet called the rotor. To do this two magnetic fields need to be placed, one on the stationary pole windings and the other in the rotor conductors. After that a motor effect occurs which is the force produced on the magnetic conductors from the interaction of the magnetic fields which makes the axis rotary motion.

In an induction motor, the current is induced in the rotor without contacts by the magnetic fields to transform the voltage. The current in the primary side created an electromagnetic field which interacts with the electromagnetic field of the secondary side to produce a resultant torque, there by transforming the electrical energy into mechanical energy.

There are many type of motors such as...

The Universal Motor:

• Can run on D.C or A.C power
• The armature windings and both field windings are in series
• Mostly found in hand drills, mixers anything that needs a variable speed and low cost.
• The two magnetic fields are produced by voltage
• Motor can reverse its rotating direction by changing the armature winding or the field windings input and output polarity's but not both.
• Voltage and current are applied directly to the armature  windings through the brushes.
  

Capacitor Start, Capacitor Run (CSCR):

·  This type of motor is a quite motor and is good for heavy duty loads.

·  Two capacitors are connected in parallel but are also connected to the start winding in series.

·  This motor runs using both windings

·  It is like Capacitor Start, Induction Run (CSIR) the phase angle between the start winding current and the main winding current is increased to 90 degree.

·  The reversed rotation is achieved by reversing the main winds polarities.

Permanent Split Capacitor (PSC):

·  Has no centrifugal switch due to the capacitors positioning in the circuit.

·  Starts using a capacitor but the start windings are permanently connected to the power supply along the run windings.

·  This type of motor is mainly used in blowers and ceiling fans as a variable speed is required.

·  Reverse rotating direction is achieved by reconnecting the supply phase from one position to another.

Shaded Pole Motor:

• A.C single phase motor.
• Small squirrel cage rotor in which the auxiliary winding is made from a copper ring which surrounds each pole.
• Auxiliary winding is called shading pole.
• Current in the shading coil produces a magnetic flux in a part of the pole which produces a rotating magnetic field.
• Direction of the rotation is from unshaded side of pole to the shaded side of pole.
• Cannot be reversed unless has two sets of shading coils with switches.
• These motors have only a single winding and no capacitor.

 

Capacitor Start, Induction Run (CSIR):

·   A spilt-phase induction motor

·  Capacitor is connected in series with the start winding

·  Motor starts up using both windings

·  As motor comes up to speed the relay removes the start winding and capacitor from the circuit.

·  Reverse rotation of capacitor start induction run is same as common split phase motor RSIR.

Repulsion Start, Induction Run (RSIR):  

·  A repulsion motor similar to universal motor.

·  Needs a sweep of flux around the stator poles so the induced voltage and current in the rotor conductors will be in a positive direction.

·  Has a centrifugal switch that shorts all segments so the motor operates as an inductor motor once it has met its full speed.

·  Both windings are placed at a 30 degree angle and are connected directly to the supply and the current through each of those windings is out of phase by approximately 30 degrees.

·  To reverse the rotating direction of this motor you have to change the polarity of either the start winding or run winding but not both.

Test Questions

Three Heat Switch:

If the 2 elements each have a Resistance of 20.2ohms, and the voltage is 230V. What will its power output be in the low setting? (give your answer in kW)




Simmerstat:


A simmerstat has a fault, It is permanently ON and never turns OFF

Motors:


I don't know what my motor is when its on its running fine but when its turns off it makes no noise


Network:


If you leave a heater on in your house (230v), and it has a resistance of  79 Ohms.
If the power supply company charges you  14.3  cents for a unit, and you leave it on for 7 days  and 5 hrs , How much will it cost?
Give the answer in dollars.



Appliance Testing:

What is a safe resistance to operate an appliance



Protection:

What is the purpose of a fuse   a) short circuit   b) overload

Conductors and Insulators

1. Four conductors used mostly in the electrical industry is Copper, Silver, Aluminium and Steel.

2. Four Insulator materials used mostly in the electrical industry is Air, Rubber, Glass, and Plastic.

  3. There is many different conductors and insulators available in the electrical industry this is because due to the environmental factors in electrical work you have to use certain types of insulators and conductors to suit the condition of work being done, and to keep yourself safe.

  4. Environment factors do affect conductors and insulators through aspects such as temperature. Conductors have a positive temperature so a increase in temperature increases their resistivity and resistance. Whereas Insulators have a negative temperature so they are liable to decrease their resistivity and resistance with an increase in temperature.  A simple way to calculate the resistance of a conductor is to use the formula R=p*L/A=ohms.

  5. In electronic manufacturing the conductors used are cooper and aluminium and semi conductors such as silicon and germanium which is used in transistors and diode.

About Me

Hi my name is Brendan Harris and i am studying at Unitec doing a Certificate in Electro technology so I can become a Electrician one day. So far I am enjoying the course and finding it very interesting. My Hobbies are body building, rugby, car enthusiastic swimming and being active. I would really like to travel the world in the future and have my own electrical business. So far I have made heaps of cool friends in this course and cant wait to graduate and get my career started in the Electrical Industry.