---
+ Post New Thread
Results 1 to 8 of 8
  1. #1
    Full Member level 4
    Points: 3,762, Level: 14

    Join Date
    Nov 2004
    Posts
    220
    Helped
    9 / 9
    Points
    3,762
    Level
    14

    magnetization characteristics of dc generator

    I was going through an article about DC Shunt Motors when i came up with some unknown concepts... I searched some books but none explained the concepts i needed... can someone please help me with the following:

    1. What are the magnetisation characteristics of a DC Shunt Motor?
    2. What is its Significance?
    3. How to draw the Magnetisation Characteristics given some data about its Open Circuit Voltage and Field Armature Resistance - TABLE
    4. How to calculate the various parameters like Critical Resistance, Critical Speed from the graph and from the data given...
    5. What is Critical Resistance, Critical Speed?

    •   Alt19th January 2005, 19:25

      advertising

        
       

  2. #2
    Full Member level 5
    Points: 7,870, Level: 21
    usernam's Avatar
    Join Date
    Mar 2004
    Posts
    268
    Helped
    132 / 132
    Points
    7,870
    Level
    21

    critical resistance dc generator

    Are you refering to DC shunt motor or DC shunt generator?



    •   Alt19th January 2005, 20:56

      advertising

        
       

  3. #3
    Advanced Member level 2
    Points: 21,612, Level: 35

    Join Date
    Sep 2004
    Posts
    662
    Helped
    72 / 72
    Points
    21,612
    Level
    35

    characteristics of dc motors

    "Critical Resistance" is found to related to DC shunt generator as follows:

    The value of resistance of shunt field winding beyond which the shunt generator fails to build up its voltage is known as critical resistance



    •   Alt19th January 2005, 21:04

      advertising

        
       

  4. #4
    Full Member level 4
    Points: 3,762, Level: 14

    Join Date
    Nov 2004
    Posts
    220
    Helped
    9 / 9
    Points
    3,762
    Level
    14

    characteristics of dc motor

    Sorry...all this magnetisation characteristics are given under the topic DC Shunt Generator...



  5. #5
    Full Member level 3
    Points: 2,542, Level: 11

    Join Date
    Sep 2004
    Location
    Within arm's reach
    Posts
    162
    Helped
    5 / 5
    Points
    2,542
    Level
    11

    critical resistance of dc generator

    Magnetisation characteristics of a DC motor is the plot of variation of torque with speed. it's signoficance lies in the designing of a motor.Of course,there are more factors to be consoidered for a faithful construction of a DC motor.

    Regards
    drdolittle :)



  6. #6
    Full Member level 5
    Points: 7,870, Level: 21
    usernam's Avatar
    Join Date
    Mar 2004
    Posts
    268
    Helped
    132 / 132
    Points
    7,870
    Level
    21

    magnetisation characteristics of dc shunt motor

    Quote Originally Posted by purifier
    Sorry...all this magnetisation characteristics are given under the topic DC Shunt Generator...
    In DC shunt generator the field and armature circuit are in parallel.
    Now say E is the generated armature EMF.
    E=KΦω, where Φ is field flux and ω is generator speed or turbine speed and K is a proportionality constant.

    Now Φ is dependent on I which is the field current.
    Therefore E = GIω where G is a proportrionality factor which varies as the current varies. It depends on the µ of the core material.
    Also I ≈E/Ra where Ra is the armature resistance.
    Now you can generate two graphs for E vs I. One will look similar the B-H curve since B is proportional to Φ and hence depends on E while H is proportional to I.
    The other is a straight line graph with a slope of Ra. The point of intersection of the two graphs gives us E and I.
    Now if Ra is too high the straight line graph will coincide with the linear portion of the B-H curve so the resulting intersection will be at a low E and low I. So to avoid this situation Ra should be lower than a particular critical value. If you draw the two graphs you will understand it better.
    Also in a DC generator some residual magnetism should be present or else when the generator is started Φ = 0 and hence E=0 irrespective of speed and therefore I is always 0. Another important point is that the field magnetism should aid rather than oppose the residual magnetism direction or else once again we'll end up with a Φ = 0 situation when the DC generator starts.



  7. #7
    Full Member level 3
    Points: 1,958, Level: 10

    Join Date
    Aug 2006
    Posts
    155
    Helped
    5 / 5
    Points
    1,958
    Level
    10

    critical speed of dc generator

    critical resistance is tangent to the o.c.c (open circuit curve) curve. beyond critical point machine dosnot perform voltage buldup and prior to critical resistance the machine cannot build up voltage.

    the speed at which critical resistance exist is critical speed of the machine

    both these quantity can be calculated from graph i dont know if they have theoritical formula.

    magnetization charactristics curve are different for generator and motor you can

    find diagrams in any books of electrical machine..........

    there is only one characteristics curve for generator but two in case of motor
    for generator it's voltage-rated current curve
    for motor it's torque-speed curve and torque-armature current characteristics curve...



  8. #8
    Junior Member level 1
    Points: 2,456, Level: 11

    Join Date
    Mar 2011
    Posts
    18
    Helped
    5 / 5
    Points
    2,456
    Level
    11
    Quote Originally Posted by mannnish View Post
    critical resistance is tangent to the o.c.c (open circuit curve) curve. beyond critical point machine dosnot perform voltage buldup and prior to critical resistance the machine cannot build up voltage.

    the speed at which critical resistance exist is critical speed of the machine

    both these quantity can be calculated from graph i dont know if they have theoritical formula.

    magnetization charactristics curve are different for generator and motor you can

    find diagrams in any books of electrical machine..........

    there is only one characteristics curve for generator but two in case of motor
    for generator it's voltage-rated current curve
    for motor it's torque-speed curve and torque-armature current characteristics curve...
    Excellent.. Thanks for the reply..



+ Post New Thread
Please login

LinkBacks (?)