The CT series toroidal transformers allow to sense the leaking currents to earth. These transformers have been designed to be coupled to the maximum earth leakage current relays of the ELR series.
The T/T’s should be installed upstream of the lines or loads to be protected and/or supervised. All active wires (phase and neutral)of the three phase or single phase lines should pass through the internal core of the transformers. It senses, in this way, the currents vectorial addition, in order to transmit the earth leakage current to te secondary.
The current T/T’s are made of an optimum quality magnetic core, which allows to detect leakage currents of a very low value even. There are two windings coupled in the core, one to detect the signal of a leakage in the line (to be sent to the relay), and the other for performing the Test.
The selection of the transformer should be made on basis of the dimensions of the wires or bars that should pass through its innerhole. There are split core types available, which allow their installation without disconnecting the actual wiring.
All phases should pass through the inner part of the T/T, even the neutral if same is distributed. The earthing wire shouldn’t passthrough the T/T.
The passage direction of all wires has to be the same, but in those applications which do not use Current Transformers in parallel, itis not necessary to respect the introduction direction.
Should the case be of using the split core transformers, it is necessary to supervise that the contact faces of the half-cores are properly clean, so as the tightening of the fixing side screws andthe right electrical wire connections between both half-cores.
In the case that the cables are shielded or they have metal protection, these should be earthen downstream of the toroidal transformer. If the shielding of the cable passes through the inner hole ,the shielding connection to earth should pass again in the inverse direction by the inner hole.