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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