This sensor allow to analise the current used by high voltage devices.
This built demonstration is made by Denis. With this sensor you will be available to analize quality of the Mains, including low voltage to high voltage inverters and power generators.
Device power consumption also can be calculated by using some math.
Built and Test Video
Parallel with the output of the transformer you should connect a 2kΩ resistor as load, better if 1/2W or more.
Considering the KCT-10 model 5A – 2.5mA, this will generate a voltage of 5V when the current is 5A. In this way you can use the full input scale of the oscilloscope (±5V).