The simplest current transformer (CT) consists of two copper windings, isolated from each other and wound on a steel core. Each of the windings has a certain number of turns, the ratio of which determines the current transformation ratio. Errors that arise when converting the primary current into a secondary one, allow the CT to be attributed to one of the accuracy classes.
Instructions
Step 1
Currently, there is a huge variety of TT. There are several classifications: by place of installation, by construction, by type of insulation, etc. It will be quite difficult for a person untrained in this area to immediately determine which species this or that TT belongs to. The easiest way to determine the type of CT is to decipher the symbol indicated on the plate attached to the CT itself (see Fig. 1).
Step 2
However, very often, for some reason, there is no nameplate with factory data on the TT case. In this case, you can use the factory documentation. Find the passport-protocol for this type of equipment. The TT type will be indicated on its first page. In addition, the required information is often indicated in the electrical schematic diagrams of this connection (circuit).
Step 3
In the event that this method does not give the desired result, you can try to load this CT, that is, remove the current-voltage characteristic from it. This will require special equipment: a loading unit, a clamp meter, a volt-ampere-phase meter (VAF), an alternating current voltmeter.
Step 4
To correctly take readings, it is necessary to supply current either to the terminals of the primary winding (high current) and to remove the current and voltage values from the secondary winding, or, conversely, to supply a small current to the terminals of the secondary winding of the CT, and from the primary to remove large values of current and voltage. Then, based on the data obtained, you will need to build curves that determine the dependence of voltages on primary and secondary currents, as well as determine the current transformation ratio and the absolute error of this CT.
Step 5
By the appearance and the data obtained, using reference materials, you can approximately determine the type of this CT, its condition (good / bad), as well as the accuracy class. However, in order to avoid mistakes, it is still better to contact a qualified specialist. He will not only save you time, but he will also give recommendations on the use, method of connection and maintenance of this device.
