# Fault Current: DC component

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

1. ### Cerkit Thread Starter Active Member

Jan 4, 2009
275
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
2,755
665
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.

3. ### Cerkit Thread Starter Active Member

Jan 4, 2009
275
3
How do you have a DC component generated in the fault scenario (in an AC system)?

4. ### DickCappels Moderator

Aug 21, 2008
2,755
665
A rectifier through some impedance to earth would create such a fault.