IND UCTI VE COORDINA TION 



83 



Table A shows the average harmonics present on three-phase, four- 

 wire industrial and residential feeders under light and heavy load 

 conditions. The reduced magnitudes of the non-triple frequencies in 

 the residual current (neutral and ground-return) are evident. The 

 importance of this as regards noise induction is further indicated in the 

 illustrative examples of the Appendix. 



TABLE A * 



Average Current and Voltage Wave Shapes of 2300/4000-Volt, 

 3-Phase, 4-Wire Distribution Circuits 



Note: Triple harmonics are italicized. 



* Tables 31 &32 — pp. 235 & 236 of Vol. II of Eng'g Reportsof Joint Subcommittee. 



t New weighting — see Engineering Report No. ii of Joint Subcommittee. 



The triple-harmonic currents present on a feeder supplied from a 

 delta-wye substation transformer bank are generally due to the exciting 

 currents of the single-phase load transformers. Under this condition 

 no excessive triples are impressed on the feeder at its source as is some- 

 times the case where the source is a wye-connected, grounded-neutral 

 generator directly connected to the feeder. The exciting currents 

 flow from the individual single-phase transformers toward the delta- 

 wye transformer in the substation. The presence on the feeder of a 

 large three-phase wye-delta load transformer with its neutral con- 

 nected to the system neutral, provides a parallel path for supplying 



