Capacitor required for harmonic filter duty will be required to accept given magnitude of various orders
of harmonic current which will increase the nominal line current & hence the thermal duty on capacitor.
In addition, voltage due to these harmonic currents will appear across the capacitor & will cause an increase in the R.M.S. voltage.
Some degree of derating is, therefore , necessary for capacitors used as harmonic filters. |
The normal current overload permitted in typical power capacitor specification is 1.3 multiplied
by nominal current , & in determining this factor due attention has been paid to the fact that a capacitor
connected to an ac power system may be required to accept an unknown magnitude of unspecified harmonic
currents. In the case of a properly designed harmonic filter the magnitudes & orders of the harmonic currents
are known & hence, provided that the permitted over - voltages & KVAR loading are not exceeded ,
the de-rating factor for the capacitors may not be as great as would be expected. |
