Hi
I am working on a design in which we need to have very good coupling from primary to secondary of a transformer.
The transformer is used as a current transformer and we must have very high accuracy from primary to secondary, so we have the same current on the output also.
We are using a toroid xformer with bifilar windings (4 wires in parallel to yield a transformer with 4 windings). We have used the entire circumsphere for the winding to have good coupling. We cannot add many layers, but are there other hints to get a very good coupling?
From a seach on the web:
Although the coupling coefficient K is 1 in an ideal current transformer, K is about 0.95-0.99 in actual current transformers at RL of 100=CE=A9 or less, under the influence of the internal resistance of windings, load resistance, a leaked magnetic flux, the non-linearity of a permeability, etc. Because the K value is low if there is a gap in a magnetic circuit, a toroidal core with no gap can provide an ideal current transformer having the largest degree of coupling. The larger cross section area S, the larger number N of a secondary winding, and the smaller load resistance RL provide the K value closer to 1. This K value also varies depending on the through-current I0. In the case of micro-current I0 of 100 mA or less, the K value tends to be low. Particularly when a low-permeability material is used for the magnetic core, this tendency is large. Accordingly, when the micro- current should be measured at high accuracy, a high-permeability material is used for the magnetic core
(us7473325)
Thanks
Klaus