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. 820-0444
Mfr. Part No.2904923
TWD11,586.00
Each
units
4000:1 8.3mm - - 24 V dc 4000A 0 → 1 A 70.4mm -30°C 22.5mm +80°C 85mm - -
RS Stock No. 715-7989
Mfr. Part No.2308030
TWD9,354.00
Each
units
200:1 32mm - - 20 → 30 V dc 200A 4 → 20 mA 70mm -40°C 90mm +65°C 33.8mm - -
RS Stock No. 793-4629
Mfr. Part No.CTSR 0.3-P
BrandLEM
TWD1,272.00
Each
units
21.6:1 20.3mm - - 4.75 → 5.25 V 21.6A 300 mA 44.6mm -40°C 41.35mm +105°C 17.9mm - -
RS Stock No. 169-7656
Mfr. Part No.CSLA2DK
BrandHoneywell
TWD1,164.40
Each (In a Box of 50)
units
- - - - 6 → 12 V dc - Maximum of 400 A 44.5mm -25°C 35.6mm +85°C 14.2mm - -
RS Stock No. 198-829
Mfr. Part No.AT 20 B5
BrandLEM
TWD2,127.00
Each
units
20:1 16mm - - - 20A - 67mm -20°C 44.5mm +60°C 36.5mm - -
RS Stock No. 886-2124
Mfr. Part No.XM02-185071S000000
TWD426.00
Each
units
100:5 21mm Base Mounted - - - - - - - - - 45 x 40 x 65 mm -
RS Stock No. 207-2990
Mfr. Part No.LA 305S
BrandLEM
TWD2,579.00
Each
units
500:1 25.5mm - Closed Loop 12 → 15 V 500A 120 mArms 73.4mm -10°C 86mm +85°C 46.4mm - -
RS Stock No. 106-8537
Mfr. Part No.56T100C
TWD52.60
Each (In a Tube of 25)
units
10:1 - - - - 10A - - -40°C - +85°C - 16.79 x 8.89 x 20.19 mm -
RS Stock No. 715-7043
Mfr. Part No.53200C
TWD59.00
Each
units
10:1 - - - - 10A - - -40°C - +125°C - 8.3 x 7.2 x 5.4 mm -
RS Stock No. 124-3888
BrandRS PRO
TWD168.00
Each
units
75:1 - - - - 75A - - -55°C - +130°C - 30.2 x 14.3 x 30.2 mm -
RS Stock No. 650-560
Mfr. Part No.CSLA1CF
BrandHoneywell
TWD1,087.00
Each
units
- 10.9mm - Open Loop 8 → 16 V dc - - - - - - - - -
RS Stock No. 446-0642
Mfr. Part No.DK 400 B420
BrandLEM
TWD15,516.00
Each
units
400:1 21.7mm - - 20 → 50 V dc, 22 → 38 V ac 400A 4 → 20 mA 57.2mm -20°C 89.7mm +50°C 30mm - -
RS Stock No. 173-0055
Mfr. Part No.AX-1500
TWD119.90
Each (In a Box of 250)
units
15:1 - - - - 15A - - -40°C - +120°C - 12.7 x 17 x 9.53 mm -
RS Stock No. 206-2432
Mfr. Part No.HAL 400-S
BrandLEM
TWD1,540.00
Each
units
1000:1 20 x 15mm - Open Loop 15 V 1000A - 41mm -25°C 41.27mm +85°C 31.3mm - -
RS Stock No. 451-1403
Mfr. Part No.LF 2005S
BrandLEM
TWD12,056.00
Each
units
2000:1 60.5mm - Closed Loop 15 → 24 V 2000A 400 mArms 68.5mm -40°C 170mm +85°C 52mm - -
RS Stock No. 731-5261
Mfr. Part No.HTA 300-S
BrandLEM
TWD2,050.00
Each
units
300:1 32mm - Open Loop ±15 V 300A - 70mm -25°C 90mm +85°C 27.5mm - -
RS Stock No. 351-106
Mfr. Part No.MI20
TWD3,591.00
Each
units
20:1 - - - - 20A - 45mm -20°C 52mm +60°C 16mm - -
RS Stock No. 527-8545
Mfr. Part No.DHR 300 C10
BrandLEM
TWD8,431.00
Each
units
300:1 32mm - Open Loop 20 → 50 V dc 300A - 70mm -40°C 90mm +70°C 25mm - -
RS Stock No. 173-0052
Mfr. Part No.AC-1025
TWD129.50
Each (In a Box of 120)
units
25:1 - - - - 25A - - -40°C - +120°C - 30.2 x 14.3 x 30.2 mm -
RS Stock No. 666-8201
Mfr. Part No.CKSR 15-NP
BrandLEM
TWD684.00
Each
units
15:1 - - Closed Loop 5.25 V 15A - 16.5mm -40°C 21.91mm +105°C 13.4mm - -