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. 173-0070
Mfr. Part No.AX-0500
HK$32.574
Each (In a Box of 250)
units
- - - - - - 5A - -40°C +120°C 12.7 x 17 x 9.53 mm - Through Hole -
RS Stock No. 173-0058
Mfr. Part No.AP-1500
HK$26.822
Each (In a Box of 250)
units
- - - - - - 10A - -40°C +85°C 17.2 x 9.53 x 20.4 mm - - -
RS Stock No. 914-5301
Mfr. Part No.CTSCMWH500/0.333V
BrandHOBUT
HK$313.23
Each
units
- 35mm Split Core - - - 500A 333 mV -15°C +50°C 51.2 x 51.2 x 83.5 mm Multi Function Meter Cable -
RS Stock No. 819-9798
Mfr. Part No.140AS
BrandEfergy
HK$134.08
Each
units
- 19mm - - - - - - - - - Oscilloscopes - -
RS Stock No. 881-7900
Mfr. Part No.CTPROXT40
BrandABB
HK$165.08
Each
units
- 18mm - - - - - - -5°C +50°C 45 x 96 x 69 mm - BusBar, DIN Rail CT PRO XT
RS Stock No. 832-9857
Mfr. Part No.L01-8001
BrandAlttec
HK$119.09
Each
units
50:5 21.5mm Clip Fit 65mm 45mm 30mm - - - +40°C 65 x 45 x 67 mm - - -
RS Stock No. 751-1636
Mfr. Part No.93487 P1
HK$163.02
Each
units
- - - - - - 400A - -20°C +70°C 80 (Dia.) x 20 mm - Stand Alone -
RS Stock No. 881-7932
Mfr. Part No.CTPROXT40SELV
BrandABB
HK$192.35
Each
units
- 18mm - - - - - - -5°C +50°C 45 x 96 x 69 mm - BusBar, DIN Rail CT PRO XT SELV
RS Stock No. 782-6809
Mfr. Part No.8-1611461-1
HK$207.95
Each
units
- - - - - - - - - - 6.67 x 5.54 x 6.65 mm - Chassis -
RS Stock No. 751-1614
Mfr. Part No.93481 P1
HK$241.61
Each
units
- - - - - - 60A - -20°C +70°C 70 (Dia.) x 36 mm - Stand Alone -
RS Stock No. 745-7995
Mfr. Part No.TRA2400001
BrandCarel
HK$97.47
Each
units
- - - - - - - - -10°C +50°C - 12/24Vac controllers Surface Mount -
RS Stock No. 313-817
Mfr. Part No.CT174M600/5-2.5/1-001
BrandHOBUT
HK$222.28
Each
units
600:5 40mm Base Mounted 95mm 70mm 55mm - - -30°C +85°C - - - -
RS Stock No. 729-5517
Mfr. Part No.AC-1100
HK$35.36
Each
units
- - - - - - 100A - -40°C +120°C 44.5 x 14.3 x 44.5 mm - Through Hole -
RS Stock No. 886-2171
Mfr. Part No.XM19-315131S000000
HK$233.15
Each
units
400:5 50mm Base Mounted - - - - - - - 86 x 45 x 110 mm - Surface Mount Omega XMER
RS Stock No. 510-9152
Mfr. Part No.7KT1201
BrandSiemens
HK$1,849.39
Each
units
- 13mm Straight Through - - - - - - - - - DIN Rail -
RS Stock No. 173-0061
Mfr. Part No.AC-1100
HK$26.715
Each (In a Box of 27)
units
- - - - - - 100A - -40°C +120°C 44.5 x 14.3 x 44.5 mm - Through Hole -
RS Stock No. 881-7913
Mfr. Part No.CTPROXT60
BrandABB
HK$173.77
Each
units
- 18mm - - - - - - -5°C +50°C 45 x 96 x 69 mm - BusBar, DIN Rail CT PRO XT
RS Stock No. 828-5209
Mfr. Part No.BZCT050
HK$465.95
Each
units
- 50mm - - - - - - -20°C +60°C - Broyce Type A Earth Leakage Relays Surface Mount BZCT
RS Stock No. 832-9854
Mfr. Part No.L01-8000
BrandAlttec
HK$119.09
Each
units
50:1 21.5mm Clip Fit 65mm 45mm 30mm - - - +40°C 65 x 45 x 67 mm - - -
RS Stock No. 173-0057
Mfr. Part No.AX-1000
HK$23.053
Each (In a Box of 250)
units
- - - - - - 10A - -40°C +120°C 12.7 x 17 x 9.53 mm - Through Hole -