Instrument Current Transformers Research Articles

Accuracy Standards for Phase-Shifting Transformers for Var Measurement

New accuracy standards are proposed for phase-shifting transformers generally applied in polyphase circuits for var (reactive volt-amperes) measurement. Limiting values of ratio correction factor (RCF) and phase angle defect (PD) are given for three proposed standard accuracy levels, namely, 0.3 per cent, 0.6 per cent, and 1.2 per cent. These levels represent the maximum error in var measurement owing to the phase-shifting transformer. The limiting values appear as circle diagrams. The proposals bring the standards up to the same level of development as those for instrument current and potential transformers.

Current Instrument Transformer Error Calculations

A nonlinear differential equation describing the steady-state operation of a current instrument transformer is formulated based upon a Rayleigh hysteresis loop approximation of the magnetic core effects. Using a harmonic-balance technique, a suitable approximate solution of this equation provides expressions for the RCF (ratio correction factor) and phase angle errors for the transformer directly in terms of the magnetic properties of the core material and the transformer instrument burden.

The Application of a New Nontracking Butyl to High-Voltage Instrument Transformers [includes discussion

A new nontracking butyl insulation which will not carbonize even under severe surface contamination has been applied to 15,000-volt outdoor instrument current transformers, and makes practical still higher voltage outdoor butyl designs. The discovery of a novel principle 1 to overcome the susceptibility of organic materials to carbonization and tracking and the application of this principle to butyl rubber have enabled this major advance to be made.