Current Transformers

Current transformers (CT) are devices that are used to transform the current from a high current into a lower current so that the power can then be measured and controlled. The transformers consist of a core, a primary and a secondary winding. When an alternating current flows through the primary winding, a magnetic flux is created which then induces an alternating current in the secondary winding. This alternating current is proportional to the current in its primary. Current transformers are also known as a "step-down transformers". Once the current has been reduced it can be safely monitored and measured using an ammeter.

Current transformers can perform circuit control and perform roles for safety protection and current limiting.

Current transformers are found in:

  • Generating stations,
  • Electrical substations
  • Commercial electric power distribution.

Types of Current Transformers

Toroidal Current Transformer - These transformers are shaped like a doughnut they do not contain a primary winding. Instead, the line that carries the current flowing in the network is threaded through a window or hole in the toroidal transformer. Toroidal transformers offer high efficiency with minimal excess noise and little excess leakage inductance.

Wound Current Transformer - The transformers primary winding is physically connected in series with the conductor that carries the measured current flowing in the circuit. The magnitude of the secondary current is dependent on the turns ratio of the transformer.

Bar-type Current Transformer – This type of current transformer uses the actual cable or bus-bar of the main circuit as the primary winding, which is equivalent to a single turn. They are fully insulated from the high operating voltage of the system and are usually bolted to the current carrying device.


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Description Price Current Ratio Inner Diameter Transformer Type Overall Height Overall Width Overall Depth Input Current Output Current Minimum Temperature Maximum Temperature Dimensions For Use With Mounting Type Series
RS Stock No. 124-3879
BrandRS PRO
$2.39
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units
- - - - - - 15A - -40°C +120°C 17.2 x 9.53 x 20.4 mm - PCB Mount -
RS Stock No. 173-0041
BrandRS PRO
$2.091
Each (In a Box of 351)
units
- - - - - - 15A - -40°C +120°C 17.2 x 9.53 x 20.4 mm - PCB Mount -
RS Stock No. 124-3893
BrandRS PRO
$4.60
Each
units
- - - - - - 75 200A - -55°C +130°C 38.1 x 15.9 x 38.1 mm - PCB Mount -
RS Stock No. 173-0217
BrandRS PRO
$32.107
Each (In a Box of 114)
units
- - - - - - 75 200A - -55°C +130°C 38.1 x 15.9 x 38.1 mm - PCB Mount -
RS Stock No. 124-3882
BrandRS PRO
$3.71
Each
units
- - - - - - 1 10A - -40°C +120°C 17.2 x 9.53 x 20.4 mm - PCB Mount -
RS Stock No. 173-0044
BrandRS PRO
$2.244
Each (In a Box of 351)
units
- - - - - - 15A - -40°C +120°C 17.2 x 9.53 x 20.4 mm - PCB Mount -
RS Stock No. 173-0181
BrandRS PRO
$24.132
Each (In a Box of 351)
units
- - - - - - 1 10A - -40°C +120°C 17.2 x 9.53 x 20.4 mm - PCB Mount -
RS Stock No. 173-0045
BrandRS PRO
$2.397
Each (In a Box of 351)
units
- - - - - - 15A - -40°C +120°C 17.2 x 9.53 x 20.4 mm - PCB Mount -
RS Stock No. 124-3881
BrandRS PRO
$2.30
Each
units
- - - - - - 15A - -40°C +120°C 17.2 x 9.53 x 20.4 mm - PCB Mount -
RS Stock No. 124-3880
BrandRS PRO
$2.34
Each
units
- - - - - - 15A - -40°C +120°C 17.2 x 9.53 x 20.4 mm - PCB Mount -
RS Stock No. 171-8858
BrandRS PRO
$36.97
Each
units
20:5 62 x 40mm Clip Fit 78mm 62mm 40mm 20A 5 A -5°C +55°C 62 x 40 x 78 mm - Surface Mount -
RS Stock No. 171-8859
BrandRS PRO
$34.19
Each
units
30:5 62 x 40mm Clip Fit 78mm 62mm 40mm 30A 5 A -5°C +55°C 62 x 40 x 78 mm - Surface Mount -
RS Stock No. 173-0218
BrandRS PRO
$35.674
Each (In a Box of 25)
units
- - - - - - 100 250A - -55°C +130°C 44.5 x 14.3 x 44.5 mm - PCB Mount -
RS Stock No. 171-8860
BrandRS PRO
$43.19
Each
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40:5 74 x 45mm Clip Fit 98mm 74mm 45mm 40A 5 A -5°C +55°C 74 x 45 x 98 mm - Surface Mount -
RS Stock No. 171-8779
BrandRS PRO
$24.71
Each
units
600:5 30 x 10mm Clip Fit 70mm 50mm 31mm 600A 5 A -5°C +55°C 50 x 31 x 70 mm - Surface Mount -
RS Stock No. 171-8805
BrandRS PRO
$57.20
Each
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1000:5 61 x 51mm Clip Fit 110mm 86mm 45mm 1kA 5 A -5°C +55°C 86 x 45 x 110 mm - Surface Mount -
RS Stock No. 173-0219
BrandRS PRO
$44.593
Each (In a Box of 18)
units
- - - - - - 200 500A - -55°C +130°C 55.6 x 20.6 x 55.6 mm - PCB Mount -
RS Stock No. 171-8791
BrandRS PRO
$27.01
Each
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400:5 40 x 11mm Clip Fit 78mm 62mm 40mm 400A 5 A -5°C +55°C 62 x 40 x 78 mm - Surface Mount -
RS Stock No. 171-8751
BrandRS PRO
$21.78
Each
units
60:5 21 x 10mm Clip Fit 65mm 45mm 40mm 60A 5 A -5°C +55°C 45 x 40 x 65 mm - Surface Mount -
RS Stock No. 171-8756
BrandRS PRO
$23.15
Each
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125:5 21 x 10mm Clip Fit 65mm 45mm 40mm 125A 5 A -5°C +55°C 45 x 40 x 65 mm - Surface Mount -
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