Re: Harmonic filter for better power quality

Home Electrical Engineering Forum General Discussion Harmonic filter for better power quality Re: Harmonic filter for better power quality


Hi, Joe,

It looks like the last response I posted for you did not make it here. So, I will do it again.

Contactors and circuit breakers deisgned for AC voltage systems operate on the principle of breaking the voltage before the current is interrupted. In this manner the energy supply – voltage – has been removed and the contacts open stopping current (and voltage).

If current leads voltage, the contacts must break the current before it breaks the voltage. This causes the source (voltage) to continue as the current is interrupted. The result of this is a high energy arc according to the level of voltage broken. As the power factor goes more leading the instantaneous voltage rises on the AC voltage waveform toward the peak voltage at 90 degrees.

The issue is what happens to the contacts when the voltage is still present and supplying energy. This energy must arc to between the contacts. Each arc lifts the metal content at the point of arc. Over time the contact becomes heavily pitted.

At some point one of two results will occur. One is the conatcts will weld closed and prevent opening the contacts. Thus continued supply of power to the load. The other is if the contacts are open, they may not close because there is an irregular surface and lock in cannot occur.

Regards, Jim