XHYZ1668T On-Load Tap Changer Tester| Transition Resistance & Waveform Analyzer The on-load tap changer is the only moving part connected to the transformer circuit, which is why OLTC inspection is taken so seriously. Handover and preventive test procedures for electrical equipment require verification of the tap changer action sequence and switching time. The XHYZ1668T measures the OLTC transition waveform, transition time, instantaneous transition resistance values and