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 Sensor Technology Supply Voltage Input Current Output Current Overall Height Minimum Temperature Overall Width Maximum Temperature Overall Depth Dimensions For Use With
RS Stock No. 499-5536
Mfr. Part No.AP 50 B10
BrandLEM
TWD4,317.00
Each
units
50:1 18mm - Closed Loop 24 V dc 50A - 69mm -20°C 67mm +60°C 55mm - -
RS Stock No. 331-474
Mfr. Part No.CT132M50/5-1/1
BrandHOBUT
TWD478.00
Each
units
50:5 21mm DIN Rail Mounted - - 50A 5 A 65mm -30°C 45mm +85°C 30mm - -
RS Stock No. 331-597
Mfr. Part No.CT132M40/5-1/3
BrandHOBUT
TWD486.00
Each
units
40:5 21mm DIN Rail Mounted - - 40A 5 A 65mm -30°C 45mm +85°C 30mm - -
RS Stock No. 497-271
Mfr. Part No.HTR 200-SB
BrandLEM
TWD4,497.00
Each
units
400:1 21mm - Open Loop 12 → 15 V 400A - 69mm -10°C 46mm +70°C 21.5mm - -
RS Stock No. 207-2984
Mfr. Part No.LA 205-S
BrandLEM
TWD3,115.00
Each
units
300:1 22.7 x 17.4mm - Closed Loop 12 → 15 V 300A 100 mArms 56.3mm -10°C 66mm +85°C 56.5mm - -
RS Stock No. 435-8628
Mfr. Part No.HX 03-P
BrandLEM
TWD425.00
Each
units
9:1 0.6mm - Open Loop ±15 V 9A - 20mm -25°C 19mm +85°C 15.4mm - -
RS Stock No. 886-2128
Mfr. Part No.XM02-195071S000000
TWD393.00
Each
units
120:5 21mm Base Mounted - - - - - - - - - 45 x 40 x 65 mm -
RS Stock No. 180-7357
Mfr. Part No.LA 55-P
BrandLEM
TWD823.00
Each
units
70:1 - - Closed Loop 12 → 15 V 70A 50 mArms 27.6mm -40°C 36.6mm +85°C 14.45mm - -
RS Stock No. 173-0060
Mfr. Part No.AC-1200
TWD280.80
Each (In a Box of 27)
units
200:1 - - - - 200A - - -40°C - +120°C - 55.6 x 20.6 x 55.6 mm -
RS Stock No. 729-5520
Mfr. Part No.AC-1200
TWD312.00
Each
units
200:1 - - - - 200A - - -40°C - +120°C - 55.6 x 20.6 x 55.6 mm -
RS Stock No. 286-361
Mfr. Part No.LV 25-P
BrandLEM
TWD1,961.00
Each
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14:1 - - Closed Loop 12 → 15 V 14A 25 mA 16.45mm 0°C 26mm +70°C 29.2mm - -
RS Stock No. 399-7317
Mfr. Part No.AS-103
TWD69.00
Each
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15:1 - - - - 15A - - -40°C - +120°C - 17.2 x 20.4 x 9.53 mm -
RS Stock No. 731-5270
Mfr. Part No.HTA 600-S
BrandLEM
TWD2,068.00
Each
units
600:1 32mm - Open Loop ±15 V 600A - 70mm -25°C 90mm +85°C 27.5mm - -
RS Stock No. 301-9489
Mfr. Part No.HAS 50S
BrandLEM
TWD849.00
Each
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150:1 20.4 x 10.4mm - Open Loop 15 V 150A - 30mm -10°C 40mm +80°C 30mm - -
RS Stock No. 207-2912
Mfr. Part No.HTA 400-S
BrandLEM
TWD2,271.00
Each
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1000:1 32mm - Open Loop 15 V 1000A - 70mm -25°C 90mm +85°C 27.5mm - -
RS Stock No. 751-1617
Mfr. Part No.93482 P1
TWD673.00
Each
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100:1 - - - - 100A - - -20°C - +70°C - 70 (Dia.) x 36 mm -
RS Stock No. 532-9148
Mfr. Part No.HAIS 100-P
BrandLEM
TWD771.00
Each
units
300:1 15 x 8mm - Open Loop 5 V 300A - 29.5mm -40°C 33mm +85°C 14mm - -
RS Stock No. 451-1352
Mfr. Part No.LF 205S
BrandLEM
TWD4,618.00
Each
units
420:1 15.6mm - Closed Loop 12 → 15 V 420A 100 mArms 51.63mm -40°C 61mm +85°C 26.19mm - -
RS Stock No. 207-2940
Mfr. Part No.HTA 1000-S
BrandLEM
TWD2,821.00
Each
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1000:1 32mm - Open Loop 15 V 1000A - 70mm -25°C 90mm +85°C 27.5mm - -
RS Stock No. 321-6292
Mfr. Part No.LAH 50-P
BrandLEM
TWD694.00
Each
units
50:1 - - Closed Loop 12 → 15 V 50A 25 mArms 21mm -25°C 33.3mm +85°C 14.93mm - -