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. 331-597
Mfr. Part No.CT132M40/5-1/3
BrandHOBUT
€13.41
Each
units
40:5 21mm DIN Rail Mounted 65mm 45mm 30mm - - -30°C +85°C - - - -
RS Stock No. 331-474
Mfr. Part No.CT132M50/5-1/1
BrandHOBUT
€13.41
Each
units
50:5 21mm DIN Rail Mounted 65mm 45mm 30mm - - -30°C +85°C - - - -
RS Stock No. 775-2714
Mfr. Part No.CTSCMICRO19-200/5-T-S
BrandHOBUT
€45.13
Each
units
200:5 - Split Core 78mm 58mm 49mm - - -30°C +55°C - - - -
RS Stock No. 914-5290
Mfr. Part No.CTSCMWH30/0.333V
BrandHOBUT
€18.39
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. 819-9779
Mfr. Part No.90AS
BrandEfergy
€11.24
Each
units
- 12mm Split Core - - - - - - - - Data Loggers/DAS, Digital or Analog Meters, DMMs, Recorders - -
RS Stock No. 351-106
Mfr. Part No.MI20
€38.51
Each
units
- - - 45mm 52mm 16mm 2 → 20A - -20°C +60°C - - - -
RS Stock No. 775-2701
Mfr. Part No.CTSCMICRO19-100/5-T-S
BrandHOBUT
€45.13
Each
units
- - - 78mm 58mm 49mm - - -30°C 55°C - - - -
RS Stock No. 914-5307
Mfr. Part No.CTSCMWH250/0.333V
BrandHOBUT
€24.43
Each
units
- 24mm Split Core - - - 250A 333 mV -15°C +50°C 43.5 x 38.6 x 69.6 mm Multi Function Meter Cable -
RS Stock No. 287-3125
Mfr. Part No.CT151M25/5-2.5/3
BrandHOBUT
€15.03
Each
units
25:5 14mm Universal Mounted 75mm 54.5mm 68mm - - -20°C +70°C - - - -
RS Stock No. 287-3131
Mfr. Part No.CT151M40/5-2.5/3
BrandHOBUT
€15.03
Each
units
40:5 14mm Universal Mounted 75mm 54.5mm 68mm - - -20°C +70°C - - - -
RS Stock No. 772-1221
Mfr. Part No.5SV8702-0KK
BrandSiemens
€130.44
Each
units
- 35mm Toroidal Ring 79mm 100mm 58.8mm - - -10°C +50°C - - - -
RS Stock No. 886-2099
Mfr. Part No.XW01-045081S000000
€18.06
Each
units
5:5 - Base Mounted - - - - - - - 62 x 40 x 78 mm - Surface Mount Omega XMER
RS Stock No. 881-7922
Mfr. Part No.CTPROXT200
BrandABB
€21.90
Each
units
- 18mm - - - - - - -5°C +50°C 45 x 96 x 69 mm - BusBar, DIN Rail CT PRO XT
RS Stock No. 857-7432
Mfr. Part No.E83-2050
€453.00
Each
units
100 A:30 mA 12mm Base Mounted 56mm 22.5mm 47.4mm - - -20°C +50°C 56 x 22.5 x 47.4 mm - - -
RS Stock No. 533-0621
Mfr. Part No.CTSCEN200<1000/5
BrandHOBUT
€73.01
Each
units
200:5, 400:5, 600:5, 800:5, 1000:5 - Clip Fit 125mm 132mm 38mm - - -30°C +80°C - - - -
RS Stock No. 819-9798
Mfr. Part No.140AS
BrandEfergy
€14.23
Each
units
- 19mm - - - - - - - - - Oscilloscopes - -
RS Stock No. 250-0142
Mfr. Part No.TRA12UN100
BrandCarel
€10.35
Each
units
- - - 47mm 58mm 33mm - - - - - 24 Vac Controllers Surface Mount -
RS Stock No. 751-1617
Mfr. Part No.93482 P1
€20.17
Each
units
- - - - - - 100A - -20°C +70°C 70 (Dia.) x 36 mm - Stand Alone -
RS Stock No. 399-7244
Mfr. Part No.ASM-010
€4.20
Each
units
- - - - - - 10A - -40°C +120°C 20.4 x 17.2 x 9.53 mm - PCB Mount -
RS Stock No. 881-7998
Mfr. Part No.CTMAX500SELV
BrandABB
€35.44
Each
units
- 30mm - - - - - - -5°C +50°C 70 x 111 x 69 mm - BusBar, DIN Rail CT MAX SELV
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