In the last edition of TechTalk, we discussed the typical way to set up the scaling of DNP points on the 70 Series IED. We introduced the CT Scale Factor and the VT Scale Factor as settings that are slightly different from the CT Ratio and VT Ratio settings, but then recommended setting the CT Scale Factor equal to the CT Ratio and setting the VT Scale Factor equal to the VT Ratio. That should be good in most cases. But what happens if the default scale goes into over-range? …or if you’re not satisfied with the default resolution?
The 70 Series supports different approaches to accommodate special range and resolution requirements. In Part 2 of the scaling tutorial we introduce a setting we haven’t talked about before called Calc Types, and we describe how to pick the right Scale Factors to customize the scaling for any range and resolution that you might want.
Rather than continuing to parse out the scaling tutorial into future installments, we’ve decided to go ahead and publish the complete tutorial, Parts 1 through 4, on the NovaTech website with the current edition of TechTalk. Part 3 addresses several types of measurements, like Frequency, Power Factor, and Energy, where the instrument transformer ratios and the Scale Factors aren’t involved in scaling. Then Part 4 provides a brief refresher on what’s meant by “two’s complement” binary numbers and what it means when SCADA comes up with a number that looks bigger than it ought to be.