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. 123-6720
Mfr. Part No.XN35-235031S000000
HK$228.46
Each
units
160:5 31mm Base Mounted - - - 160A 5 A - - 105 x 38 x 87.5 mm MCCB BusBar, DIN Rail, Plug In Omega
RS Stock No. 331-569
Mfr. Part No.CT143M500/5-5/0.5-001
BrandHOBUT
HK$186.47
Each
units
500:5 24mm DIN Rail Mounted 70mm 49mm 45mm - - -30°C +85°C - - - -
RS Stock No. 123-6721
Mfr. Part No.XN35-245031S000000
HK$228.46
Each
units
200:5 31mm Base Mounted - - - 200A 5 A - - 105 x 38 x 87.5 mm MCCB BusBar, DIN Rail, Plug In Omega
RS Stock No. 175-6203
Mfr. Part No.4NC5433-0DH21
BrandSiemens
HK$1,322.90
Each
units
1200:1 - Window 84.1mm 112mm 127.5mm 1.2kA 1 A -30°C +55°C 112 x 127.5 x 84.1 mm Sentron Power Monitoring Devices Chassis Mount Sentron
RS Stock No. 833-2743
Mfr. Part No.DM0T0050
BrandLovato
HK$166.80
Each
units
50:5 22mm Base Mounted 66mm 44mm 32mm - - -25°C +50°C - - - -
RS Stock No. 123-6730
Mfr. Part No.XS01-225221S 000000
HK$332.68
Each
units
150:5 33 x 23mm Clip Fit - - - - - - - 93 x 40 x 106 mm - Surface Mount Omega10
RS Stock No. 173-0237
BrandRS PRO
HK$39.738
Each (In a Box of 351)
units
- - - - - - 10 20A - -40°C +85°C 17.2 x 9.53 x 20.4 mm - PCB Mount -
RS Stock No. 833-2774
Mfr. Part No.DM3T1000
BrandLovato
HK$419.48
Each
units
1000:5 30mm Base Mounted 81.5mm 71mm 62.5mm - - -25°C +50°C - - - -
RS Stock No. 174-3477
Mfr. Part No.1033485
HK$4,510.17
Each
units
- - DIN Rail Mounted 70.4mm 22.5mm 85mm 1 kA, 1.5 kA, 2 kA, 4 kA, 100 A, 250 A, 400 A, 630 A 0 1 A -30 °C, -20 °C +70 °C, +80 °C 22.5 x 85 x 70.4 mm Retrofitting DIN Rail PACT RCP
RS Stock No. 123-6739
Mfr. Part No.XS03-375105S 000000
HK$554.61
Each
units
800:5 120 x 80mm Clip Fit - - - - - - - 155 x 40 x 198 mm - Surface Mount Omega10
RS Stock No. 897-6930
Mfr. Part No.4 121 52
BrandLegrand
HK$2,191.10
Each
units
2500:5 - Base Mounted - - - - - -25°C +50°C 160 x 125 x 40 mm Ammeter, Electricity Meter, Measurement Control Unit Surface Mount -
RS Stock No. 124-3883
BrandRS PRO
HK$57.66
Each
units
- - - - - - 5 50A - -40°C +120°C 32 x 20.5 x 35 mm - PCB Mount -
RS Stock No. 175-6204
Mfr. Part No.4NC5433-2DH21
BrandSiemens
HK$1,008.45
Each
units
1200:5 - Window 84.1mm 112mm 127.5mm 1.2kA 5 A -30°C +55°C 112 x 127.5 x 84.1 mm Sentron Power Monitoring Devices Chassis Mount Sentron
RS Stock No. 171-8789
BrandRS PRO
HK$122.75
Each
units
300:5 40 x 11mm Clip Fit 78mm 62mm 40mm 300A 5 A -5°C +55°C 62 x 40 x 78 mm - Surface Mount -
RS Stock No. 175-6213
Mfr. Part No.4NC5438-0CJ21
BrandSiemens
HK$1,313.52
Each
units
2000:1 - Window 84.1mm 112mm 127.5mm 2kA 1 A -30°C +55°C 112 x 127.5 x 84.1 mm Sentron Power Monitoring Devices Chassis Mount Sentron
RS Stock No. 136-6368
Mfr. Part No.XM22-405151S000000
HK$241.40
Each
units
1200:5 72mm - 104mm 104mm 45mm 1.2kA 5 A - - 104 x 45 x 104 mm - BusBar, Cable Mount, DIN Rail, Wall Mount Omega
RS Stock No. 175-6149
Mfr. Part No.4NC5122-2FC21
BrandSiemens
HK$680.07
Each
units
200:5 - Window 65.6mm 60mm 75.3mm 200A 5 A -30°C +55°C 60 x 75.3 x 65.6 mm Sentron Power Monitoring Devices Chassis Mount Sentron
RS Stock No. 881-8001
Mfr. Part No.2CSG226035R1101
BrandABB
HK$296.11
Each
units
- 30mm - - - - - - -5°C +50°C 70 x 111 x 69 mm - BusBar, DIN Rail CT MAX SELV
RS Stock No. 833-2746
Mfr. Part No.DM0T080
BrandLovato
HK$170.59
Each
units
80:5 22mm Base Mounted 66mm 32mm 44mm - - -25°C +50°C - - - -
RS Stock No. 881-7910
Mfr. Part No.CTPROXT100
BrandABB
HK$196.25
Each
units
- 18mm - - - - - - -5°C +50°C 45 x 96 x 69 mm - BusBar, DIN Rail CT PRO XT