We do not supply these. This page is here because the question comes up and the answer is hard to find written plainly. What we do supply is three phase and single phase pad mounted distribution transformers from 25 to 2500 kVA.
What it actually does
A current transformer produces a small, precisely proportional current from a large one. A 600 to 5 ratio unit carrying 600 amps in the primary gives 5 amps out of the secondary, which a meter or a protective relay can handle. It is an instrument, not a means of supplying a load, and it is sized in ratio and accuracy class rather than kVA.
Never open the secondary while it is energised
This is the one safety rule that matters. With the primary carrying current and the secondary open circuited, the core saturates and a very high voltage appears across the open terminals, high enough to kill and to destroy the unit. Short the secondary before disconnecting a meter. Every CT has shorting provisions for exactly this reason.
Where they appear on our equipment
Pad mounted transformers are sometimes ordered with metering provisions, and a CT is what makes that work. The CT sits on the secondary conductors inside the low voltage compartment and feeds a utility meter. It is an accessory on the order, not the transformer itself.
How to specify one
Ratio, for example 600 to 5. Accuracy class, metering classes are tighter than relaying classes. Burden, which is what the secondary circuit loads it with. Insulation class for the system voltage. Window size if it is a donut style that slips over an existing conductor.
Common questions
What is a current transformer used for
Measuring and protection. It scales a large primary current down to a small, proportional secondary current, normally 5 amps or 1 amp at full rating, so a meter or a protective relay can work with it safely.
Why should you never open circuit a current transformer secondary
Because the core saturates and generates a dangerously high voltage across the open terminals, which can injure someone and destroy the unit. Always short the secondary before disconnecting anything in that circuit.
What is the difference between a current transformer and a distribution transformer
A current transformer is an instrument that measures. A distribution transformer supplies power to a load. A CT is rated in ratio and accuracy class, a distribution transformer in kVA.
Free to cite with a link to this page.