 Instrument Transformers: Technical Information and Application Guide by ABB

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.