I'd say that using piezoelectric transducer plus signal conditioning circuitry would serve the detection. However, it may sound easy as it may seems, but in actual situation is rather different. There are many sources of vibration generator, i.e. from windings, from structure and from surroundings. It is very difficult task for one to differentiate which kind of signal that is of interest.

I got such devise but I could not install it on the body of the Transformer it is a very small device . moreover , I do not know where to send its output signal , I mean what kind of devices could be used to measure its output signal ?

It depends on what final shape has your piezo device. In principle you need a charge amplifier, so something that has an extremely high input impedance, that is low input current (thinking of bias and offset current of an Op Amp). See e.g. datasheet and app. note for LMC6001 (National).

Alternatively, you may use an accelerometer, that outputs an already conditioned signal that can be read with an oscilloscope.

Or, if you are interested in locating the frequency and less in the amplitude, a microphone like the ones for cellular phones and similar applications using an electret (made e.g. by Panasonic).

If you don't want to go too high in frequency than you can used also a strain gauge and measure it with a Wheatstone bridge and again an oscilloscope.

Thank you Andrea for these information. Thank you .

@Adel. You're welcome Adel. If you need some more help, don't mind. You can also write me at name.surbame AT unige dot it OR name.surname AT gmail dot com.

Thank you Andrea very much. Sure , if I need more help I will write to you right away .

I is beautiful when you find such people in the world who wants to help the other people without knowing them and for free. and also Thanks for Research Gate who made this window to make the people help each other without knowing each other.

really appreciated. Thanks again

For more of the same thing see

http://www.digikey.com/us/en/techzone/sensors/resources/articles/fundamentals-of-piezoelectric-sensors.html

http://www.digikey.com/product-detail/en/VR001/VR001-ND/2402863?cur=USD

and

http://www.arduino.cc/en/Tutorial/Knock

and

http://www.electroschematics.com/6023/vibration-sensor-circuit/

Thank you Diana , it is a very good information .