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 Inner Diameter Transformer Type Overall Height Overall Width Overall Depth Input Current Output Current Minimum Temperature Maximum Temperature Dimensions For Use With Mounting Type Series
RS Stock No. 819-9779
Mfr. Part No.90AS
BrandEfergy
$22.03
Each
units
- 12mm Split Core - - - - - - - - Data Loggers/DAS, Digital or Analog Meters, DMMs, Recorders - -
RS Stock No. 250-0142
Mfr. Part No.TRA12UN100
BrandCarel
$17.71
Each
units
- - - 47mm 58mm 33mm - - - - - 12/24Vac controllers Surface Mount -
RS Stock No. 819-9798
Mfr. Part No.140AS
BrandEfergy
$25.10
Each
units
- 19mm - - - - - - - - - Oscilloscopes - -
RS Stock No. 745-7995
Mfr. Part No.TRA2400001
BrandCarel
$20.60
Each
units
- - - - - - - - -10°C +50°C - 12/24Vac controllers Surface Mount -
RS Stock No. 399-7339
Mfr. Part No.AS-104
$5.69
Each
units
- - - - - - 15A - -40°C +120°C 17.2 x 20.4 x 9.53 mm - PCB Mount -
RS Stock No. 775-2701
Mfr. Part No.CTSCMICRO19-100/5-T-S
BrandHOBUT
$96.15
Each
units
- - - 78mm 58mm 49mm - - -30°C 55°C - - - -
RS Stock No. 775-4909
Mfr. Part No.AZ-0500
$9.31
Each
units
- - - - - - 25A - -40°C +85°C 19.0 x 11.5 x 21.5 mm - Flying Lead -
RS Stock No. 173-0066
Mfr. Part No.AZ-0500
$8.239
Each (In a Box of 84)
units
- - - - - - 25A - -40°C +85°C 19.0 x 11.5 x 21.5 mm - Flying Lead -
RS Stock No. 533-0621
Mfr. Part No.CTSCEN200<1000/5
BrandHOBUT
$229.49
Each
units
200:5, 400:5, 600:5, 800:5, 1000:5 - Clip Fit 125mm 132mm 38mm - - -30°C +80°C - - - -
RS Stock No. 399-7244
Mfr. Part No.ASM-010
$7.70
Each
units
- - - - - - 10A - -40°C +120°C 20.4 x 17.2 x 9.53 mm - PCB Mount -
RS Stock No. 537-4485
Mfr. Part No.AC-1005
$5.896
Each (In a Pack of 5)
units
- - - - - - 5A - -40°C +120°C 23.8 x 23.8 x 11.12 mm - PCB Mount -
RS Stock No. 668-4067
Mfr. Part No.CT105F250/5-2.5/1
BrandHOBUT
$72.32
Each
units
250:5 21mm Base Mounted 79mm 105mm 53mm - - -30°C +80°C - - - -
RS Stock No. 331-339
Mfr. Part No.CT132M100/5-2.5/1
BrandHOBUT
$34.07
Each
units
100:5 21mm DIN Rail Mounted 65mm 45mm 30mm - - -30°C +85°C - - - -
RS Stock No. 914-5290
Mfr. Part No.CTSCMWH30/0.333V
BrandHOBUT
$36.12
Each
units
- 10mm Split Core - - - 30A 333 mV -15°C +50°C 28.7 x 26.4 x 41.7 mm Multi Function Meter Cable -
RS Stock No. 537-4520
Mfr. Part No.AC-1020
$5.896
Each (In a Pack of 5)
units
- - - - - - 20A - -40°C +120°C 23.8 x 23.8 x 11.12 mm - PCB Mount -
RS Stock No. 331-597
Mfr. Part No.CT132M40/5-1/3
BrandHOBUT
$23.44
Each
units
40:5 21mm DIN Rail Mounted 65mm 45mm 30mm - - -30°C +85°C - - - -
RS Stock No. 397-9123
Mfr. Part No.BZCT070
$127.97
Each
units
- 70mm - 117mm 105mm 40mm - - -20°C +60°C - Broyce Type A Earth Leakage Relays Surface Mount BZCT
RS Stock No. 828-5209
Mfr. Part No.BZCT050
$88.53
Each
units
- 50mm - - - - - - -20°C +60°C - Broyce Type A Earth Leakage Relays Surface Mount BZCT
RS Stock No. 331-474
Mfr. Part No.CT132M50/5-1/1
BrandHOBUT
$24.29
Each
units
50:5 21mm DIN Rail Mounted 65mm 45mm 30mm - - -30°C +85°C - - - -
RS Stock No. 533-0643
Mfr. Part No.CTSCM40-200/5
BrandHOBUT
$100.67
Each
units
200:5 - Clip Fit 104.5mm 116mm 35.5mm - - -30°C +80°C - - - -
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