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. 666-8214
Mfr. Part No.CKSR 50-NP
BrandLEM
TWD633.00
Each
units
50:1 - - Closed Loop 5.25 V 50A - 16.5mm -40°C 21.91mm +105°C 13.4mm - -
RS Stock No. 451-1396
Mfr. Part No.LF 1005S
BrandLEM
TWD7,684.00
Each
units
1500:1 40.5mm - Closed Loop 15 → 24 V 1500A 200 mArms 95mm -40°C 110mm +85°C 34.3mm - -
RS Stock No. 532-9205
Mfr. Part No.HTFS 200-P
BrandLEM
TWD879.00
Each
units
300:1 22mm - Open Loop 5 V 300A - 46mm -40°C 40mm +105°C 17mm - -
RS Stock No. 751-1627
Mfr. Part No.93486 P1
TWD563.00
Each
units
300:1 - - - - 300A - - -20°C - +70°C - 62 (Dia.) x 20 mm -
RS Stock No. 435-8684
Mfr. Part No.HX 03-P/SP2
BrandLEM
TWD438.00
Each
units
9:1 0.6mm - Open Loop 12 → 15 V 9A - 20.5mm -25°C 19mm +85°C 15.4mm - -
RS Stock No. 715-7061
Mfr. Part No.56100C
TWD54.00
Each
units
10:1 - - - - 10A - - -40°C - +85°C - 16.79 x 8.89 x 20.19 mm -
RS Stock No. 179-6667
Mfr. Part No.LA 100-P
BrandLEM
TWD890.00
Each
units
150:1 12.7 x 7mm - Closed Loop 12 → 15 V 150A 50 mArms 27.6mm -40°C 36.5mm +85°C 14.45mm - -
RS Stock No. 301-9473
Mfr. Part No.LTS 25NP
BrandLEM
TWD597.00
Each
units
80:1 3.2mm - Closed Loop 5 V 80A - 24mm -40°C 22.2mm +85°C 10mm - -
RS Stock No. 446-0636
Mfr. Part No.DK 300 B420
BrandLEM
TWD15,516.00
Each
units
300:1 21.7mm - - 20 → 50 V dc, 22 → 38 V ac 300A 4 → 20 mA 57.2mm -20°C 89.7mm +50°C 30mm - -
RS Stock No. 532-9182
Mfr. Part No.HAIS 400-P
BrandLEM
TWD719.00
Each
units
600:1 15 x 8mm - Open Loop 5 V 600A - 29.5mm -40°C 33mm +85°C 14mm - -
RS Stock No. 331-468
Mfr. Part No.CT132M120/5-2.5/1
BrandHOBUT
TWD518.00
Each
units
120:5 21mm DIN Rail Mounted - - 120A 5 A 65mm -30°C 45mm +85°C 30mm - -
RS Stock No. 729-5517
Mfr. Part No.AC-1100
TWD218.00
Each
units
100:1 - - - - 100A - - -40°C - +120°C - 44.5 x 14.3 x 44.5 mm -
RS Stock No. 435-8634
Mfr. Part No.HX 05-P
BrandLEM
TWD425.00
Each
units
15:1 0.8mm - Open Loop 15 V 15A - 20mm -25°C 19mm +85°C 15.4mm - -
RS Stock No. 173-0061
Mfr. Part No.AC-1100
TWD193.00
Each (In a Box of 27)
units
100:1 - - - - 100A - - -40°C - +120°C - 44.5 x 14.3 x 44.5 mm -
RS Stock No. 435-8640
Mfr. Part No.HX 10-P
BrandLEM
TWD425.00
Each
units
30:1 1.1mm - Open Loop 15 V 30A - 20mm -25°C 19mm +85°C 15.4mm - -
RS Stock No. 181-2129
Mfr. Part No.CSLA2CD
BrandHoneywell
TWD688.00
Each
units
- 10.9mm - Open Loop 6 → 12 V dc - - - - - - - - -
RS Stock No. 206-2381
Mfr. Part No.HAL 50-S
BrandLEM
TWD1,583.00
Each
units
150:1 20 x 15mm - Open Loop 15 V 150A - 41mm -25°C 41.27mm +85°C 31.3mm - -
RS Stock No. 832-9879
Mfr. Part No.L01-8009
BrandAlttec
TWD468.00
Each
units
250:5 21.5mm Clip Fit - - - - 65mm - 45mm +40°C 30mm 65 x 45 x 67 mm -
RS Stock No. 477-4711
Mfr. Part No.CSNS300M
BrandHoneywell
TWD3,356.00
Each
units
600:1 26mm - Closed Loop 15 V 600A 150 mA 61.2mm -40°C 67.5mm +85°C 19mm - -
RS Stock No. 162-0255
Mfr. Part No.B82801B0504A050
BrandEPCOS
TWD44.20
Each (On a Reel of 900)
units
20:1 - - - - 20A - - -40°C - +125°C - 8.13 x 7.11 x 5.08 mm -