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. 124-3880
BrandRS PRO
TWD47.00
Each
units
15:1 - - - - - - 15A - - -40°C +120°C 17.2 x 9.53 x 20.4 mm -
RS Stock No. 121-8178
Mfr. Part No.CSLA2EL
BrandHoneywell
TWD1,609.00
Each
units
20:1 - - 57.4mm - 44.4mm 6 → 12 V dc 20A 15.7mm Maximum of 550 A -25°C +85°C - -
RS Stock No. 198-841
Mfr. Part No.AT 5 B5
BrandLEM
TWD2,127.00
Each
units
5:1 16mm - 67mm - 44.5mm - 5A 36.5mm - -20°C +60°C - -
RS Stock No. 715-7024
Mfr. Part No.53030C
TWD59.00
Each
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10:1 - - - - - - 10A - - -40°C +125°C 8.3 x 7.2 x 5.4 mm -
RS Stock No. 497-378
Mfr. Part No.AT 50 B10
BrandLEM
TWD2,938.00
Each
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50:1 16mm - 67mm - 44.5mm - 50A 36.5mm - -20°C +60°C - -
RS Stock No. 397-9117
Mfr. Part No.BZCT035
TWD1,246.00
Each
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- 35mm - 74mm - 64mm - - 40mm - -20°C +60°C - Broyce Type A Earth Leakage Relays
RS Stock No. 331-373
Mfr. Part No.CT164M500/5-5/0.5-001
BrandHOBUT
TWD792.00
Each
units
500:5 28mm DIN Rail Mounted 78mm - 60mm - 500A 45mm 5 A -30°C +85°C - -
RS Stock No. 173-0052
Mfr. Part No.AC-1025
TWD129.50
Each (In a Box of 120)
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25:1 - - - - - - 25A - - -40°C +120°C 30.2 x 14.3 x 30.2 mm -
RS Stock No. 452-9325
Mfr. Part No.DK 400 B10
BrandLEM
TWD10,684.00
Each
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400:1 21.7mm - 57.2mm - 89.7mm 20 → 50 V dc, 22 → 38 V ac 400A 30mm - -20°C +50°C - -
RS Stock No. 169-7654
Mfr. Part No.CSLA2EL
BrandHoneywell
TWD1,229.80
Each (In a Box of 50)
units
- - - 57.4mm - 44.4mm 6 → 12 V dc - 15.7mm Maximum of 550 A -25°C +85°C - -
RS Stock No. 914-5301
Mfr. Part No.CTSCMWH500/0.333V
BrandHOBUT
TWD1,382.00
Each
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500:1 35mm Split Core - - - - 500A - 333 mV -15°C +50°C 51.2 x 51.2 x 83.5 mm Multi Function Meter
RS Stock No. 124-3897
BrandRS PRO
TWD128.00
Each
units
50:1 - - - - - - 50A - - -40°C +85°C 19 x 11.5 x 21.5 mm -
RS Stock No. 715-7077
Mfr. Part No.56T100C
TWD57.00
Each
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10:1 - - - - - - 10A - - -40°C +85°C 16.79 x 8.89 x 20.19 mm -
RS Stock No. 886-2124
Mfr. Part No.XM02-185071S000000
TWD426.00
Each
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100:5 21mm Base Mounted - - - - - - - - - 45 x 40 x 65 mm -
RS Stock No. 919-4707
Mfr. Part No.LF 2010-S
BrandLEM
TWD8,013.00
Each
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3000:1 - - 135mm Closed Loop 170mm ±14.25 → ±25.2 V 3000A 52mm ±0.6 A -40°C +85°C - -
RS Stock No. 533-0637
Mfr. Part No.CTSCM40-100/5
BrandHOBUT
TWD1,376.00
Each
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100:5 - Clip Fit 104.5mm - 116mm - - 35.5mm - -30°C +80°C - -
RS Stock No. 198-829
Mfr. Part No.AT 20 B5
BrandLEM
TWD2,127.00
Each
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20:1 16mm - 67mm - 44.5mm - 20A 36.5mm - -20°C +60°C - -
RS Stock No. 527-8545
Mfr. Part No.DHR 300 C10
BrandLEM
TWD8,431.00
Each
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300:1 32mm - 70mm Open Loop 90mm 20 → 50 V dc 300A 25mm - -40°C +70°C - -
RS Stock No. 914-5297
Mfr. Part No.CT132TRAN150A-4/20MA
BrandHOBUT
TWD1,570.00
Each
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150:1 21mm - 65mm - 45mm 15 → 30 V 150A 30mm 4 → 20 mA -15°C +50°C - -
RS Stock No. 321-6309
Mfr. Part No.LAH 100-P
BrandLEM
TWD783.00
Each
units
100:1 - - 21mm Closed Loop 33.3mm 12 → 15 V 100A 14.93mm 50 mArms -25°C +85°C - -