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. 106-8532
Mfr. Part No.56100C
HK$13.25
Each (In a Tube of 25)
units
- - - - - - 10A - -40°C +85°C 16.79 x 8.89 x 20.19 mm - Through Hole -
RS Stock No. 397-9123
Mfr. Part No.BZCT070
HK$544.54
Each
units
- 70mm - 117mm 105mm 40mm - - -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. 287-3232
Mfr. Part No.CT153M500/5-2.5/1
BrandHOBUT
HK$197.34
Each
units
500:5 26mm Universal Mounted 75mm 54.5mm 68mm - - -20°C +70°C - - - -
RS Stock No. 886-2134
Mfr. Part No.XM02-285081S000000
HK$115.20
Each
units
300:5 21mm Base Mounted - - - - - - - 45 x 40 x 65 mm - Surface Mount Omega XMER
RS Stock No. 287-3210
Mfr. Part No.CT153M300/5-2.5/1
BrandHOBUT
HK$171.26
Each
units
300:5 26mm Universal Mounted 75mm 54.5mm 68mm - - -20°C +70°C - - - -
RS Stock No. 715-7055
Mfr. Part No.54100C
HK$21.48
Each
units
- - - - - - 15A - -40°C +125°C 10.8 x 9 x 8.2 mm - Surface Mount -
RS Stock No. 287-3226
Mfr. Part No.CT153M400/5-2.5/1
BrandHOBUT
HK$206.04
Each
units
400:5 26mm Universal Mounted 75mm 54.5mm 68mm - - -20°C +70°C - - - -
RS Stock No. 897-6857
Mfr. Part No.4 121 54
BrandLegrand
HK$2,104.96
Each
units
4000:5 - Base Mounted - - - - - -25°C +50°C 160 x 125 x 40 mm Ammeter, Electricity Meter, Measurement Control Unit Surface Mount -
RS Stock No. 775-4928
Mfr. Part No.AX-1000
HK$30.77
Each
units
- - - - - - 10A - -40°C +120°C 12.7 x 17 x 9.53 mm - Through Hole -
RS Stock No. 331-480
Mfr. Part No.CTSCM40600/5-5/1
BrandHOBUT
HK$379.01
Each
units
600:5 - Clip Fit 104.5mm 116mm 35.5mm - - -30°C +80°C - - - -
RS Stock No. 257-830
Mfr. Part No.CT173M400/5-2.5/1-002
BrandHOBUT
HK$205.81
Each
units
400:5 40mm Base Mounted 95mm 70mm 55mm - - -30°C +85°C - - - -
RS Stock No. 913-9738
Mfr. Part No.METSECT5CC020
HK$469.04
Each
units
200:5 21mm Tropicalise - - - - - -25°C +60°C 65 x 44 x 30 mm - DIN Rail -
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. 715-7068
Mfr. Part No.56050C
HK$13.63
Each
units
- - - - - - 10A - -40°C +85°C 16.79 x 8.89 x 20.19 mm - Through Hole -
RS Stock No. 729-5517
Mfr. Part No.AC-1100
HK$55.26
Each
units
- - - - - - 100A - -40°C +120°C 44.5 x 14.3 x 44.5 mm - Through Hole -
RS Stock No. 775-2714
Mfr. Part No.CTSCMICRO19-200/5-T-S
BrandHOBUT
HK$425.00
Each
units
200:5 - Split Core 78mm 58mm 49mm - - -30°C +55°C - - - -
RS Stock No. 123-6719
Mfr. Part No.XN35-225031S000000
HK$228.46
Each
units
150:5 31mm Base Mounted - - - 150A 5 A - - 105 x 38 x 87.5 mm MCCB BusBar, DIN Rail, Plug In Omega
RS Stock No. 833-2740
Mfr. Part No.DM2T0100
BrandLovato
HK$177.78
Each
units
100:5 23mm Base Mounted 65.5mm 52mm 46.5mm - - -25°C +50°C - - - -
RS Stock No. 123-6729
Mfr. Part No.XS01-185031S 000000
HK$332.68
Each
units
100:5 33 x 23mm Clip Fit - - - - - - - 93 x 40 x 106 mm - Surface Mount Omega10
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