A Quick Guide to Selecting a Current Transformer

When you’re planning to install an ammeter in an existing electrical circuit that transmits high voltage electricity, you will need to also install a current transformer. This is a device that reduces the voltage of the electricity flowing through the system to protect the measuring device and the person installing it from electrocution. However, choosing a current transformer suitable for the circuit is not that simple.

First you have to consider the currents flowing in both primary and secondary coils. Normally, primary and secondary currents in a typical current transformer are indicated by 1 A or 5 A, each suiting a particular condition. 1 A is suitable when the measuring instrument (ammeter) is to be installed more than 30 feet away from the current transformer. The reason for this is that the wire resistance, which affects the accuracy of the result of current measurement, is great at high amperages and long distances.

After learning about the transformer ratio (primary/secondary) and determining the ratio that you need for your system, you can now look for the type of current transformer that matches the voltage of your electrical source. Knowing that increasing the voltage will also increase the current, you can assume that you’ll measure a huge amount of current if your system’s voltage is high. For high voltage electricity, it’s advisable to use a flexible current transformer as this does not need to be attached directly to the transmission line, therefore reducing the risk of electrocution.


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