Question

which type of tranformer will made when number of turns in secondary and primaryt coil are same?

Answer 1

It depends on the application.
If you need to transfer signal between two circuits and they cannot be connected with the same ground (i.e. they must work at very different potentials, as you can have for medical application), you need to perform a galvanic isolation. You can understand more on this matter for example reading the Analog Devices document: http://www.analog.com/static/imported-files/tutorials/MT-071.pdf.
In some power equipments, but also for consumer electronics, an "isolation transformer" (with primary and secondary having the same number of turns) ensures safety to a person: if he/she touches an un-isolated part of the circuit, you will not have any closure of the loop person-circuit-earth so that no-current will flow into that person.

Answer 2

Sorry. You can find the MT-071.pdf document at:
http://www.analog.com/en/specialty-amplifiers/isolation-amplifiers/ad215/products/product.html
in the "Documentation" section.