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Used Instrument Transformers

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Overview

Instrument transformers (current and voltage transformers) reduce high voltages or currents to safe, measurable levels for metering, protection, and control. They must meet accuracy classes, insulation ratings, and short-circuit withstand requirements for their application. Buyers look for clear nameplates, calibration records, standards compliance (IEC/ANSI), and the right mounting or enclosure type. Available options include oil-filled or dry-type designs, single- or three-phase units, and various secondary ratios.

FAQ

What should I check when buying a used instrument transformer?

Verify nameplate data (ratio, class, burden, insulation level), calibration and test reports, physical condition, and history of overloads or faults. Confirm standards compliance and whether secondary terminals and accessories match your protection/metering equipment.

How do I ensure instrument transformers meet accuracy and safety requirements?

Request recent accuracy and insulation test certificates, lightning impulse and routine test results, and evidence of IEC/ANSI class ratings. For protection CTs, confirm T‑class or accuracy at specified fault currents and verify secondary burden compatibility.

What are best practices for shipping instrument transformers?

Securely brace units to prevent movement, protect bushings and terminals, and use moisture barriers for oil-filled types. Follow carrier rules for heavy loads, declare oil-filled equipment and hazardous materials if applicable, and insure for transport damage.

What maintenance and testing should be done after delivery?

Inspect for shipping damage, verify insulation and continuity, perform ratio and polarity checks, and run insulation resistance and power-frequency / excitation tests. For oil-filled units, sample oil and check for moisture and dielectric strength. Recalibrate as needed per manufacturer recommendations.