What Is a Winding CT (Bushing CT)?
Quick answer — A bushing CT is a current transformer mounted around the bushing (or the winding lead) of a power transformer. It senses the current without breaking the circuit and feeds the protection (differential, overcurrent) and metering relays. Multiple cores can provide different ratios for protection and metering.
What is a winding or bushing current transformer?
What it does
It reproduces, at a smaller current, the primary current for relays and meters. Being fitted around the bushing, it is compact and needs no separate primary conductor.
Use in protection
Differential protection compares bushing CTs on the HV and LV windings to detect internal faults; overcurrent protection uses them for back-up and protection.
Considerations
Accuracy class, ratio, burden and saturation behaviour matter so the CT saturates correctly under fault and does not misoperate the protection.
References & standards
- IEC 60044-1 (instrument transformers)
- IEC 60076-1
Related
Related manufacturers
Prolec GE (GE Vernova) · Prolec GE Waukesha · Hitachi Energy USA · Siemens Energy · Eaton · Virginia Transformer Corp
Related components
Technical content is prepared from engineering references, standards frameworks, manufacturer documentation and industry sources. Contractual or compliance decisions should refer to current official standards. TransformerPath Technical Editorial.
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