Experimental test of a load model in the presence of harmonics

Field tests were conducted at an industrial plant to see whether the voltage and current waveforms at the input transformer supplying power to the plant would agree with computer generated predictions. The latter were made by using a simple simulation procedure, previously published, for analysing a power system that supplies a substantial nonlinear load. The plant demand was about 300kW. Very good agreement was obtained between the measured waveforms and those predicted using the simulation procedure, from the presumed composition of the load. However, in many practical situations the composition of the load is not known. In general, in such cases, the load composition may be deduced from the known current waveforms of the individual load components. This is achieved by adding them together in the proper proportions so that the RMS difference between the measured current waveform and the predicted one is minimised. The work described provides the basis for a next step: integration of the simulation scheme into a large multibus system so that a standard load-flow program may be used to account for the effects of harmonics on the system.