50 A transformer ohmmeter

  • Capable of testing transformers up to 1000 MVA
  • DC test current up to 50 A maximum
  • Integrated demagnetisation feature
  • Computer control and internal data storage
  • Validates proper operation of on-load tap changers
  • Protected against accidental current lead disconnection (through potential leads)

The MTO250 50 A transformer ohmmeter is a line-operated, field-portable instrument designed specifically to measure the resistance of all types of magnetic windings safely and accurately. It tests transformers, shunt reactors, and rotating machine windings, and it performs low resistance measurements on connections, contacts, and control circuits.

The dual set of potential inputs enables the resistance measurement of either two primary, two secondary windings, or of a primary plus a secondary winding simultaneously. This dual reading, dual injection characteristic, is a highly efficient method of completing tests in a timely manner.

The MTO250 is useful for testing the winding plus contact resistance of load tap changers (LTC) as well as assessing the 'make-or-break' transition event. LTCs are the only moving part of a transformer and, as they are mechanical devices, are one of the most vulnerable parts of a transformer. LTCs result in more failures and outages than any other component and so require frequent testing and attention to ensure reliable and safe operation. Operating the LTC to change taps while DC test current is applied helps validate proper make-or-break transition. This test diagnoses possible issues such as aggressive pitting, weak springs, and misalignment of contact mechanisms.

Applying DC current to highly inductive objects is a potentially dangerous test. To protect you, the asset under test, and the intrument itself while working, the MTO250 has multiple built-in safety features. These include auto-discharge in the event of input power loss, automatic discharge in the event of inadvertent disconnection of a test lead, safety interlock which places test into discharge when interrupted, and an optional high voltage strobe which warns personnel of presence of a dangerous condition.