Mini Current Transformer Key Parameters
Mini Current Transformer Key Parameters
Usually, our current transfromers (CTs) are customized according to clients’ requirements. Here, we introduce some important parameters which should be specified by the users.
Accuracy Class
Most of our CTs are 0.1 class, which is precision enough for measurement in normal energy meters or other electrical devices, and the cost is nearly the same as that of 0.2 or 0.5 class. We can also manufacture CTs with better accuracy class (0.05 or 0.02 class), but the cost is much higher.
Burden Resistance
The resistance burden in electrical circuit is imporant, as it has close relationship with the accuracy class of a mini CT. The typical resistance of a burden ranges from 5 Ω to 100 Ω.
Turns Ratio
The winding coils have turns range from a few hundred (such as zero phase CT) to more than 25000 as below post. But the typical turns ratio is 1:1000, 1:2000 or 1:2500.
Max. Primary Current
The test range of a CT depends on the max. primary current. In most cases, max. current of 100A is sufficient for measurement. But max. current as high as 600A are also available.
DC Immunity
DC immune CTs usually require winding cores of composite cores, which are combination of nanocrystalline and amorphous rings.
Encapsulation
Plastic case CTs are suitable for mass production, but the suitable cases are not always available. So, for samples or pilot run, the CTs wrapped by insulation tape is good choice. Metal cases are usually required for anti-magnetic current transformers.
Busbar Type
Busbar built-in CTs can be easily assembled in the meter cases, but the cost is higher, as the busbar is usually made of copper. Ring type CTs can be combined with flexible cable which serve as primary wire.
Output Wires
The lead wires pass the sensing current to the circuit of measurement module. Each wire’s end should be tinned, but we can add the wires to connectors or plugs, which can be easily assembled on the PCB. The range of output current (seconday current) depends on the max. current and turns ratio.
Summary
These important parameters are listed as the table below.
| Max. Primary Current | 10~600 A |
| Output Current | 1~40mA |
| Turns Ratio (typical) | 1:1000~1:25000 |
| Burden (Rb) | 5~100 Ω |
| Accuracy Class | 0.02/0.05/0.1/0.2 Class |
| Core Inside | Nanocrystalline / Silicon Steel / Composite Core |
| Encapsulation | Plastic/Metal Case, Double Insulation, PCB Mounting Type |
| Busbar Type | None/Built-in/Removable |
| Mounting Method | Tinned Wire/Metal Pin/Connector Plug |