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 Bore Size Transformer Type Overall Height Sensor Technology Overall Width Supply Voltage Input Current Overall Depth Output Current Minimum Temperature Maximum Temperature Dimensions For Use With
RS Stock No. 171-8775
BrandRS PRO
$16.67
Each
units
300:5 30 x 10mm Clip Fit 70mm - 50mm - 300A 31mm 5 A -5°C +55°C 50 x 31 x 70 mm -
RS Stock No. 171-8840
BrandRS PRO
$84.67
Each
units
1000:5 101 x 56mm Clip Fit 170mm - 130mm - 1000A 60mm 5 A -5°C +55°C 130 x 60 x 170 mm -
RS Stock No. 171-8822
BrandRS PRO
$61.51
Each
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2500:5 100 x 30mm Clip Fit 155mm - 140mm - 2500A 45mm 5 A -5°C +55°C 140 x 45 x 155 mm -
RS Stock No. 171-8825
BrandRS PRO
$40.77
Each
units
125:5 35mm Base Mounted 87.5mm - 105mm - 125A 38mm 5 A - - 105 x 38 x 87.5 mm MCCB
RS Stock No. 171-8782
BrandRS PRO
$26.64
Each
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125:5 30 x 11mm Clip Fit 78mm - 62mm - 125A 40mm 5 A -5°C +55°C 62 x 40 x 78 mm -
RS Stock No. 171-8778
BrandRS PRO
$18.85
Each
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500:5 30 x 10mm Clip Fit 70mm - 50mm - 500A 31mm 5 A -5°C +55°C 50 x 31 x 70 mm -
RS Stock No. 171-8761
BrandRS PRO
$20.36
Each
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250:5 21 x 10mm Clip Fit 65mm - 45mm - 250A 40mm 5 A -5°C +55°C 45 x 40 x 65 mm -
RS Stock No. 171-8814
BrandRS PRO
$47.97
Each
units
1250:5 80 x 12mm Clip Fit 126mm - 104mm - 1250A 45mm 5 A -5°C +55°C 104 x 45 x 126 mm -
RS Stock No. 171-8763
BrandRS PRO
$18.99
Each
units
80:5 30 x 10mm Clip Fit 70mm - 50mm - 80A 31mm 5 A -5°C +55°C 50 x 31 x 70 mm -
RS Stock No. 171-8833
BrandRS PRO
$43.31
Each
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600:5 45mm Base Mounted 102.5mm - 141mm - 600A 38mm 5 A - - 141 x 38 x 102.5 mm MCCB
RS Stock No. 173-0199
BrandRS PRO
$4.45
Each (In a Box of 133)
units
125:1 - - - - - - 125A - - -55°C +130°C 34.9 x 14.3 x 34.9 mm -
RS Stock No. 171-8815
BrandRS PRO
$66.98
Each
units
1500:5 80 x 12mm Clip Fit 126mm - 104mm - 1500A 45mm 5 A -5°C +55°C 104 x 45 x 126 mm -
RS Stock No. 171-8790
BrandRS PRO
$40.77
Each
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400:1 40 x 11mm - 78mm - 62mm - - 40mm - - - 62 x 40 x 78 mm -
RS Stock No. 171-8754
BrandRS PRO
$33.55
Each
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100:1 21 x 10mm - 65mm - 45mm - - 40mm - - - 45 x 40 x 65 mm -
RS Stock No. 171-8827
BrandRS PRO
$36.81
Each
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160:5 35mm Base Mounted 87.5mm - 105mm - 160A 38mm 5 A - - 105 x 38 x 87.5 mm MCCB
RS Stock No. 171-8784
BrandRS PRO
$27.93
Each
units
300:5 30 x 11mm Clip Fit 78mm - 62mm - 300A 40mm 5 A -5°C +55°C 62 x 40 x 78 mm -
RS Stock No. 171-8841
BrandRS PRO
$89.00
Each
units
1250:5 101 x 56mm Clip Fit 170mm - 130mm - 1250A 60mm 5 A -5°C +55°C 130 x 60 x 170 mm -
RS Stock No. 171-8771
BrandRS PRO
$19.10
Each
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200:5 30 x 10mm Clip Fit 70mm - 50mm - 200A 31mm 5 A -5°C +55°C 50 x 31 x 70 mm -
RS Stock No. 173-0201
BrandRS PRO
$4.273
Each (In a Box of 114)
units
200:1 - - - - - - 200A - - -55°C +130°C 38.1 x 15.9 x 38.1 mm -
RS Stock No. 171-8859
BrandRS PRO
$31.26
Each
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30:5 62 x 40mm Clip Fit 78mm - 62mm - 30A 40mm 5 A -5°C +55°C 62 x 40 x 78 mm -