Shunt dc motor, Electrical Engineering

Shunt DC motor

In this arrangement, the armature and field coils are connected in parallel (the motor is called 'shunt connected').

 

1845_shunt DC motor.png

 

Analysis

With reference to the diagram above,

1226_shunt DC motor  1.png

Normally If is a approxmetely constant and Ra is very small (so V>>Ia.Ra).Therefore the motor speed is approximately constant for a given supply voltage, V. The speed may be controlled by reducing the field If  by increasing the field resistor Rf   is reduced and the so Φ speed  increases.

 

  • If  is approximately constant in this motor configuration, determined by the supply voltage and the resistance of the field coils. 
  • Since Ra is very small, V>>Ia.Ra.Hence, although Ichanges significantly with change in motor speed, (and hence also the torque), the motor speed need only change very slightly to cause a large change of armature current and torque produced. This means that the torque can overcome any imposed mechanical load  with very little change of motor speed (so shunt motor has approximately  onstant speed vs load characteristics)
  • Since the armature winding resistance is small, measures must be taken to limit the surge of armature current when it is first
    switched on (i.e. increase the supply slowly to allow the motor to gain speed before full supply voltage is applied). 
  • Methods for controlling the speed are:

    i)    vary the resistance of the field circuit, Rf . Increasing Rf  a increases the speed.

    ii)   change the applied voltage. Increasing V increases the speed.

    iii)  change Ra by means of an extra (small) resistance in the armature circuit. Increasing Ra  reduces the speed.

    iv)  increasing the mechanical load reduces the speed only slightly. (Approx. constant speed vs load characteristics)

    The preferred method of speed control atconstant supply voltage is method (i)because the field current is low compared to the armature current, and a resistance added in series with the field windings results in less power being wasted.

 

Posted Date: 8/23/2012 12:58:11 AM | Location : United States







Related Discussions:- Shunt dc motor, Assignment Help, Ask Question on Shunt dc motor, Get Answer, Expert's Help, Shunt dc motor Discussions

Write discussion on Shunt dc motor
Your posts are moderated
Related Questions
Discuss DMA operation in brief. The fundamental idea of DMA is to transfer blocks of data directly among memory and peripherals. The data don't suffer the microprocessor but th

Classification of Solids into Insulators, Semiconductor and Conductors A solid can conduct electric current if the electrons can move in it. This is possible only when an ener

Q. Frequency-controlled induction-motor drives ? The converters employed for variable-frequency drives can be classified as: • Voltage-source inverter (which is the only one

trigger capabilities of logic analyser that differentiate it from other devices???

Public safety - Application of Software Defined Radio During emergency situation such as earthquake, tsunami, terrorist attack, public safety officials from different agencies

Determine the load - Thevenins Equivalent Circuit: Determine the load for which the source shall transfer the maximum power if load is connected across the terminal A and B, u

Q.   Explain how phase angle measurement are carried out with vector impedance meter.     Sol. Impedance measurements are concerned with both the magnitude (Z) and the phase

area bounded by the curve y=3x(x-2)^2 and the x-axis

find current across r3 with two voltage as sources

Given: R 1 = R 3 = 1 k_, R 2 = 100 k_ and k = 0.1 A/V, and step-up transformer turns ratio is 10. a) Find the value of the load resistor RL that would maximize the power