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
TWD47.00
Each
units
- - - - - - 15A - -40°C +120°C 17.2 x 9.53 x 20.4 mm - PCB Mount -
RS Stock No. 173-0041
BrandRS PRO
TWD38.70
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. 124-3888
BrandRS PRO
TWD170.00
Each
units
- - - - - - 25 75A - -55°C +130°C 30.2 x 14.3 x 30.2 mm - PCB Mount -
RS Stock No. 124-3897
BrandRS PRO
TWD141.00
Each
units
- - - - - - 50A - -40°C +85°C 19 x 11.5 x 21.5 mm - PCB Mount -
RS Stock No. 173-0197
BrandRS PRO
TWD154.90
Each (In a Box of 176)
units
- - - - - - 25 → 75A - -55°C +130°C 30.2 x 14.3 x 30.2 mm - PCB Mount -
RS Stock No. 124-3880
BrandRS PRO
TWD47.00
Each
units
- - - - - - 15A - -40°C +120°C 17.2 x 9.53 x 20.4 mm - PCB Mount -
RS Stock No. 173-0044
BrandRS PRO
TWD41.50
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. 171-8849
BrandRS PRO
TWD1,418.00
Each
units
250:5 33 x 23mm Base Mounted 106mm 93mm 40mm 250A 5 A +20°C +70°C 93 x 40 x 106 mm - Surface Mount -
RS Stock No. 124-3887
BrandRS PRO
TWD110.00
Each
units
- - - - - - 20 60A - -55°C +130°C 23.8 x 11.12 x 23.8 mm - PCB Mount -
RS Stock No. 124-3893
BrandRS PRO
TWD201.00
Each
units
- - - - - - 75 200A - -55°C +130°C 38.1 x 15.9 x 38.1 mm - PCB Mount -
RS Stock No. 171-8771
BrandRS PRO
TWD347.00
Each
units
200:5 30 x 10mm Clip Fit 70mm 50mm 31mm 200A 5 A -5°C +55°C 50 x 31 x 70 mm - Surface Mount -
RS Stock No. 171-8801
BrandRS PRO
TWD904.00
Each
units
600:5 41 x 41mm Clip Fit 98mm 74mm 45mm 600A 5 A -5°C +55°C 74 x 45 x 98 mm - Surface Mount -
RS Stock No. 171-8850
BrandRS PRO
TWD1,467.00
Each
units
300:5 33 x 23mm Base Mounted 106mm 93mm 40mm 300A 5 A +20°C +70°C 93 x 40 x 106 mm - Surface Mount -
RS Stock No. 124-3900
BrandRS PRO
TWD149.00
Each
units
- - - - - - 10A - -40°C +120°C 17.2 x 9.53 x 20.4 mm - PCB Mount -
RS Stock No. 171-8828
BrandRS PRO
TWD831.00
Each
units
200:5 35mm Base Mounted 87.5mm 105mm 38mm 200A 5 A - - 105 x 38 x 87.5 mm MCCB Surface Mount -
RS Stock No. 173-0200
BrandRS PRO
TWD89.80
Each (In a Box of 133)
units
- - - - - - 50 → 125A - -55°C +130°C 34.9 x 14.3 x 34.9 mm - PCB Mount -
RS Stock No. 171-8767
BrandRS PRO
TWD513.00
Each
units
- - - - - - - - - - - - - -
RS Stock No. 173-0218
BrandRS PRO
TWD132.60
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
TWD768.00
Each
units
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. 124-3894
BrandRS PRO
TWD144.00
Each
units
- - - - - - 100 250A - -55°C +130°C 44.5 x 14.3 x 44.5 mm - PCB Mount -