MTO250 50 A transformer ohmmeter

Overview

The MTO250 50 A transformer ohmmeter (discontinued) is a line-operated, field-portable instrument designed to measure the resistance of magnetic windings safely and accurately. It provides DC test current up to 50 A and is stated as capable of testing transformers up to 1000 MVA. Automation: Yes; Single-phase capability: Single-phase. The instrument includes integrated demagnetization, computer control, and internal data storage. A dual set of potential inputs enables resistance measurement of either two primary windings, two secondary windings, or a primary plus a secondary winding simultaneously (dual reading, dual injection). It is protected against accidental current lead disconnection through the potential leads. Built-in safety features include auto-discharge in the event of input power loss, automatic discharge if a test lead is inadvertently disconnected, a safety interlock that places the test into discharge when interrupted, and an optional high voltage strobe to warn personnel of a dangerous condition. Product documents available: MTO250_DS_US.pdf (pdf 1.6 MB) and User-guide-MTO250.pdf (pdf 1.88 MB). The MTO250 is used to test the resistance of transformers, shunt reactors, and rotating machine windings, and to perform low resistance measurements on connections, contacts, and control circuits. It validates the resistance of two windings simultaneously using dual reading/dual injection. The instrument is also used to test winding plus contact resistance of load tap changers (LTC) and to assess the make-or-break transition event by operating the LTC while DC test current is applied, diagnosing issues such as aggressive pitting, weak springs, and misalignment of contact mechanisms.