CURRENT TRANSFORMER TYPES IN POWER SYSTEM TUTORIALS

Current Transformers are instrument transformers intended to have its primary winding connected in series with the conductor carrying the current to be measured or controlled. High and even medium voltage are quite dangerous levels for instrumentation, controls, and measurements.

Instrument transformers are intended to reproduce in its secondary circuit, in a definite and known
proportion, the current or voltage of its primary circuit with the phase relations substantially preserved. Instrument transformers such as current transformers, then transforms their current or voltage levels into a level than can be safely utilized.

Below are the types of current transformers in the manner of construction and applications.

Bar-type Current Transformer
Bar Type CT

One that has a fixed and straight single primary winding turn passing through the magnetic circuit. The primary winding and secondary winding(s) are insulated from each other and from the core(s) and are assembled as an integral structure.

Bushing-type Current Transformer
Bushing Type CT

One that has an annular core and a secondary winding insulated from and permanently assembled on the core but has no primary winding and no insulation for a primary winding. This type of current transformer is for use with a fully insulated conductor as the primary winding. A bushing type current transformer usually is used in equipment where the primary conductor is a component pan of other apparatus.

Window-type Current Transformer
Window Type CT

One that has a secondary winding insulated from and permanently assembled on the core, but has no primary winding as an integral part of the structure. Primary insulation is provided in the window, through which one turn of the line conductor can be passed to provide the primary winding.

Wound-type Current Transformer
Wound Type CT

One that has a primary winding consisting of one or more turns mechanically encircling the core or cores. The primary winding(s) and secondary winding(s) are insulated from each other and from the core(s) and are assembled as an integral structure.

Current Transformer could either be:

Indoor current transformer: One that, because of its construction, must be protected from the
weather.

Outdoor current transformer: One of weather-resistant construction, suitable for service without
additional protection from the weather.

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