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 12:57:37 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
Determine the value of maximum power: Determine the value of load resistance, R L for which the source shall transfer the maximum power. Also determine the value of maximum p

Determine self inductance of coil: A flux of 0.5 m Wb is generated by coil A of 600 turns wound on a ring with a current of 2 A in it. Determine (a) self inductance of coil A,

what do we mean when we say that an equation is dimensionally correct?

ferroelectric materials are charatrised by

Q. What is the voltage gain? voltage gain is the ratio of output voltage to input voltage. It is represented as Av,vo-voltage output,Vi-voltage input,Ic-collector current,Ie

What is the use of modem control unit in 8251? The modem control unit handles the modem handshake signals to coordinate the communication among the modem and the USART.

How is bias compensation in transistor is done using thermistors and sensistor

Q. A 300-kVA transformer has a core loss of 1.5 kW and a full-load copper loss of 4.5 kW. (a) Calculate its efficiency corresponding to 25, 50, 75, 100, and 125% loads at unity

Central Energy Conservation Fund This fund is to be set up at the Centre to develop the delivery mechanism for large-scale adoption of energy efficiency services like as perfo