Impact of Quasi-DC Currents on Three-Phase Distribution Transformer Installations

Abstract

This report summarizes a series of tests designed to determine the response of quasi-dc currents on three-phase power distribution transformers for electric power systems, In general, if the dc injection is limited to the primary side of a step-down transformer, significar_t harmonic distortion is noted and an increase in the reactive power demand results. For dc injection on the secondary (load) side of the step-do,arn transformer, the harmonic content at the secondary side is quite high and saturation occurs with a relatively low level of dc injection; however, the reactive p(.,wer demand is significantly lower, These tests produced no apparent damage to the transforn',ers. Transfornmr damage is dependent on the duration of the dc excitation, the level of the excitation, and on the thermal characteristics of the transformer.

Evaluation Transportability Testing of the Joint Modular Intermodal Platform (JMIP) Unit #4, TP-94-01, Transportability Testing Procedures

“…Measurements of E 3 responses were also made on a mock-up of a three-phase 480-V/12.47-kV/208-V power distribution system [14]. A 480-V/12.47-kV 300-kVA Y-Y step-up transformer was connected to a 12.47-kV/208-V 75-kVA Y-Y step-down transformer, and dc current was injected into the neutrals of the transformers.…”

“…For an assumed peak MHD-EMP E-field strength of just 20 V/km, this results in a current of 8 A, which is above the levels of current observed to cause harmonic distortion in ref. [14]. Similarly, for a 500-kV power transmission line which is =NoDC =25ADC=50ADCE75ADC 50- ......... ..... ... ........ ..................................................... A2 10 2 .…”

“…Similarly, measurements of the reactive power on the distribution system in ref. [14] were also made, and these results are summarized in Figure 39. Note that the vertical scale in figure 39 is in Kvar/phase.…”

“…Measured Harmonic Content for DC Injection in the Neutral of a Three-Phase 480-V/12.47-kV/208-V Power Distribution System, from Ref. [14]. 69 Figure 38.…”

“…Reactive Power Demand for the 480-V/12.47-kV/208-V Power Distribution System, from Ref. [14]. 71 Measured Geomagnetic Field at Ottawa, Canada, from Ref.…”