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
Q A wire with n = 10 30 electrons/m 3 has an area of cross section A = 1mm 2 and carries a current i = 50 mA. Compute the number of electrons that pass a given point in 1 s, and

Dielectric: Insulator that is used among the two plates of a capacitance is called as dielectric.  Electric field exists in the dielectric and the flux density depends on th

Q. Sketch the idealized (asymptotic) Bode plot for the transfer function Find the angular frequency at which H(ω) is 0dB and the angular frequency at which θ(ω) = -60°.


Q. Show Advantage of digital control system over analog system? Sampled data and digital control offer several advantages over analog systems: • More compact and lightweight

Consider Chebyshev Type I versus Chebyshev Type II (also called inverse Chebyshev) Ölters. Which one should be used based on the following criteria? (If there is no difference betw

Types of cells and batteries are:- a.  Carbon-zinc cell b. Nickel-cadmium cell c.  Alkaline celld.  d.  Edison cell e.  Mercury cell

Determine phase - voltage and power: A balanced star connected load is supplied from a symmetrical 3-phase 440 Volt system. The current in each of the phase is 40 Amp and lags

Q. How time slot interchange switch works in time multiplexed time switching, Elucidate using schematic. Ans: Switches for which inlets and outlets are trunks that carry tim

Define Stability - Characteristics of Discrete Time Systems? The LTI system is stable if its impulse response satisfies the condition This condition is satisfie