- In this paper, a laboratory test setup designed to perform transformer insulation experiments at low voltage level is introduced. Monitoring the leakage current flowing through the insulation samples that are taken from an aged distribution transformer is the principle of the investigation. The electrode system utilized and the experimental procedure are described. The test results that highlight important aspects of the insulation behavior concerning incipient fault detection and diagnosis is addressed. The results help identify particular phenomena that might happen when an incipient fault initiates and taking them into account in the characterization of such faults to develop a detection method for the distribution transformer incipient fault.