The Winding Ohmmeter & Tap Changer Test Set RMO100TD is designed for resistor type on-load tap changer analysis and resistance measurement of inductive test objects. RMO100TD generates true DC ripple free current. Both injection of current and discharge of energy from the inductance are automatically regulated.
RMO100TD injects current with a voltage as high as 60 V. This ensures that the duration of test is as short as possible, and that the desired test current is reached faster. Two independent channels enable testing of two series windings, or primary and secondary windings. There is enough memory within RMO100TD instrument to store 500 measurements. All measurements are time and date stamped.
The set is equipped with thermal and overcurrent protection. The RMO100TD has very high ability to cancel electrostatic and electromagnetic interference in HV electric fields. It is achieved by very efficient filtration. The filtration is made utilizing appropriate hardware and software.

The RMO100TD can be used to measure winding resistance of individual taps of a power transformer’s tap changer. It can also check whether the OLTC switches without an interruption. The moment a tap position is changed from one tap to another, the device detects a sudden, very short drop of the current. A properly working OLTC differs from a malfunctioning one. This is obvious from an interruption during the change, by the magnitude of the current ripple and also by the transition time. Malfunctioning behaviour of OLTC will result in much higher current ripple value and by changed transition time than a properly functioning OLTC.

Using DV-Win software, tests could be performed from a PC, and results can be obtained directly at a PC. The DV-Win software allows results to be arranged in an Excel spreadsheet, which can be shown later as a diagram and printed for a report, or ASCII format. This software can control the RMO-T instrument, allowing a condition assessment of OLTC analyzing the graph which represents dynamic resistance during the tap change. Using DV-Win and RMO100TD it is possible to perform heat run test on distribution and power transformers.