Harmonic compensation due to a non-linear load
Your current sensor is not in fact looking at the "main current" (by which I presume you mean the fundamental frequency). Instead it is simply converting a measurement of current into a voltage. The resulting voltage waveform will contain the same spectral information as the current signal - in other words the voltage signal will have the same harmonics as the current waveform.

To analyse the level of harmonics in any signal, you need to look at the spectral content of the signal - how much power there is at any given frequency. This is achieved by converting the time domain signal to the frequency domain. Performing an FFT (Fast Fourier Transform) of the signal is one way to achieve this.

Once you have converted your signal to the frequency domain, you will be able to see exactly what harmonics are presented and at what strength.