Design consideration of high voltage 3 - phase induction motor.

Design consideration of high voltage 3 - phase induction motor. 


High voltage 3 phase induction motor

1. stator:-

  • Suitable radial air ducts are provided to ensure uniform and efficient cooling.
  • The stator is vacuum pressure impregnated and cured with a specially formulated epoxy resin. This ensures a closed and homogeneous insulation system, which eliminates low dielectric loss, high dielectric strength, excellent heat transfer and serious internal partial discharge.
  • Motors are designed to stay within temperature class F (temperature limit 155°).
  • The windings basic impulse level is kept high and the windings are designed to cope with the highest mechanical stresses.

2. Rotor:- 

  • Minimum vibration is the key to the rotor's long operating life.  This is achieved through strong construction and a delicate balance. 
  • Selecting the shaft material according to the demands of the application and the ambient conditions in which the motor is to operate.
  • Squirrel cages are made of copper, copper alloy or aluminium, depending on the load and customer requirements.
  • More care is taken during manufacture of rotor to minimize stress build-up, and the rotor bars are swaged to provide a very robust construction able to withstand heavy duties. 
  • The added rigidity is provided by the rigid rotor rods, which enable motors to withstand heavy use for longer periods of time.
  • Aluminium bars and end rings are used to ensure optimal characteristics. And, once assembled each rotor is dynamically balanced at full operating speed in accordance with the standards or mechanical vibration.
  • The Proper radial air ducts are provided to ensure uniform and efficient cooling.

3. General:-

  • Strengthening the mechanical structure of the  motor and optimizing the electrical dimensioning in order to increase the permissible starting time and, correspondingly, the permissible load inertia.
  • Many motors are totally enclosed (IP55 to IEC) and are provided with an external fan and cooling ribs (IC411 to IEC). Also special attention is given on the design of the rigid cast iron frame, as this plays an important part in determining the motor's overall cooling efficiency.
  • Unidirectional fans are used for high speed motors in order to reduce the noise level and windage losses while bidirectional fans are used on lower speed motors. The fans are normally made of welded steel plate.

Comments

Post a Comment

Popular posts from this blog

Length of Air Gap ( Factors affecting selection of Air Gap of 3 phase induction motor

Image
Length of Air Gap ( Factors affecting selection of Air Gap of 3 phase induction motor)  Length of air gap is very important in the induction motor as it controls important characteristics of induction motor such as power factor, over load capacity etc.  Following points should be considered while selecting length of air gap: (1) Power factor:- In the performance characteristics of motor this is very important factor. The air gap consumes maximm amount of mmf out of various parts of magnetic circuit of induction mtor. Hence, larger the air gap, more wall be the mmf required to pass the flux through. it can be shown that mmf required to send the flux through air gap is proportional to the product of flux density and length of air gap.  Thus if length of air gap is increased then mmf required I. e. In turm magnetizing current is  increased, which reduces the power factor. Fig  shows the phasor diagram of inductor motor. As length of air gap increases,
Read more

Construction of 3-phase induction motor

Image
Constitution of 3-phase induction motor • Construction of 3-Phase Induction Motor: There are two main parts of a 3-phase induction motor 1.Stator 2.Rotor. 1) Stator: As the name suggests,it is a stationary part of the motor.This part is made or silicon steel stampings(i.e.thin sheets).The stampings are slotted. When complete stator is assembled,the through slots are formed on the inner side of the stator.The slots may be open type,semi-open type or closed type.In these slots,a            3-phase winding (made of super enamcled copper)is accommodated.This winding may be star or delta connected. Three ends of this coil are brought to the terminal box where a three-phase supply can be delivered. The stator windings, stator and the A.C. supply connected to the stator winding is shown in the fig. 2) Rotor: Here two types of induction motors. That are depend on the construction of the rotor. A)  Squirrel cage type B) Wound rotor type
Read more

Methods of Improving Starting Torque

Image
Methods of Improving Starting Torque: Starting torque of induction motor can be increased by increasing the rotor resistance.This can be done by reducing cross sectional area of rotor bars and by changing the conductor material. However, This will reduce the efficiency of motor. This problem can be overcomed by using different design for rotor which gives high starting torque without compromising the efficiency. Following two types of rotor design's are used.  1). Double cage rotors.  2). Deep bar rotors.  1). Double cage rotors : In this type of rotor construction, rotor winding has two cages. As shown in the above Fig, the outer cage uses bars of small cross section, thus it gives high resistance. As this cage is near to the air gap, its leakage reactance is small. The inner cage has bars of larger cross section so it offers less resistance, but as its is away from the air gap it offers high leakage reactance. In this type of motors, division of
Read more