Fault Current: DC component

Discussion in 'Power Electronics' started by Cerkit, Jul 27, 2016.

  1. Cerkit

    Thread Starter Senior Member

    Jan 4, 2009
    276
    3
    Hi,

    Can someone please explain the DC component of a fault current waveform?

    Is this just a mathematical method of analyzing a fault current waveform or is there an actual DC current involved?

    If it is just a mathematical way of analyzing the fault current waveform then can someone explain why there is the decay?
    The way I view it is that under fault condition there impedance of the system drops rapidly and so the current spikes, as the current spikes the voltage drops, as time progresses the back emf of the inductance in the system inhibits results in a drop in the current and the system comes to a steady state?

    Thanks
     
  2. DickCappels

    Moderator

    Aug 21, 2008
    3,825
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    You have a DC component if when you low pass the the entire waveform with a filter with a corner frequency that is several decades below the frequency of the waveform has a voltage that can be measured on the DC scale of a voltmeter or current meter.

    In other words if the waveform averages to zero there is no DC component, otherwise there is a DC component.

    Does that answer your question?
     
  3. Cerkit

    Thread Starter Senior Member

    Jan 4, 2009
    276
    3
    How do you have a DC component generated in the fault scenario (in an AC system)?
     
  4. DickCappels

    Moderator

    Aug 21, 2008
    3,825
    1,041
    A rectifier through some impedance to earth would create such a fault.
     
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