Current Transformer Selection

Definitions as per IEC 60044 & IS 2075

Instrument Transformer a transformer intended to supply measuring instruments, meters, relays and other similar apparatus

Current transformeran instrument transformer in which the secondary current, in normal conditions of use, is substantially proportional to the primary current and differs in phase from it by an angle which is approximately zero for an appropriate direction of the connections

CT classification based on construction

• Wound Type• Bar Type• Dry Type• Liquid Immersed• Hermetically Sealed Current Transformer• Ring Type• Multi-Core Current Transformers• Multi-Ratio Current Transformer

CT classification based on construction

• Wound TypeA current transformer having a primary winding of more than one full turn wound on the core (s).

• Bar TypeA current transformer in which the primary winding consists of a bar of suitable size and material forming an integral part of the current transformer.

• Dry TypeA current transformer which does not require the use of any liquid or semi-liquid material.

CT classification based on construction

• Liquid ImmersedA current transformer which requires the use of oil or other suitable liquid of suitable characteristics as insulating and/or cooling medium.

• Hermetically Sealed Current TransformerA liquid immersed current transformer which is sealed and does not communicate with atmospheric air

• Ring TypeA current transformer which has an opening in the center to accommodate a primary conductor through it.

CT classification based on construction

• Multi-Core Current TransformersA current transformer having more than one secondary core and winding with a common primary winding.

• Hermetically Sealed Current TransformerA liquid immersed current transformer which is sealed and does not communicate with atmospheric air

• Multi-Ratio Current TransformerA current transformer in which more than one ratio is obtainable by reconnection, or tappings, in primary or secondary windings.