= Instrument Transformers: Technical Information and Application Guide by ABB
https://library.e.abb.com/public/e2462bd7f816437ac1256f9a007629cf/ITTechInfoAppGuide.pdf
Primary ABB guide. Technology Review, Performance Characteristics, printed pp.8–9, discusses equivalent excitation and through impedances. Burdens, printed p.13, defines secondary loading and its effect on ratio/phase errors, distinguishes standard from actual burdens, and tabulates impedance and VA at specified secondary current. No present-day accuracy standard is inferred from this historical guide.
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