New
MTOU3 three-phase winding resistance ohmmeter
Dual winding excitation for fast and accurate primary and secondary winding measurements.
Less ladder climbs, keep personnel safe and healthy
Industry first confirm vector functionality in a standalone winding resistance ohmmeter
About the product
The MTOU3 uses a safe, one-time connection for complete winding resistance assessment of power, distribution, and instrument transformers with automatic adaptive demagnetization, eliminating the risk of tripping system protection when the transformer is put back into service.
Perform vector confirmation, winding resistance, and demagnetization tests with the same one-time lead connection.
Guided by color-coded leads and extendable clamps with on-screen vectors that match the transformer nameplate, the easy-to-follow setup ensures the right result the first time - just click start!
Auto vector confirmation before every test ensures that the proper transformer vector is selected.
FAQ / Frequently Asked Questions
With a large power transformer (>100 MVA) you typically require higher excitation voltage and current for accurate and stable winding resistance results. Whatever your application, there is an MTOU3 model to meet your needs. All MTOU3s come with built in tap changer control to minimize test time on transformers with built-in OLTCs.
The MTOU3 uses a demagnetization process called adaptive demagnetization. Adaptive demagnetization uses volts DC to quickly demagnetize any transformer, reducing the time required by more than half on large power transformers. Each MTOU3 comes with auto demagnetization enabled and intuitively demagnetizes the transformer after the completion of winding resistance tests.
When you have questionable results, the next step is to check that the connections from the test set to the transformer are clean and tight. After this, customers often question the reliability/accuracy of the test set. Megger has a portable reference device, the TOS1, for field verification of instrument performance, providing confidence that the correct transformer maintenance decisions can be made.
The MTOU3 provides data in three formats. Reports of the tests performed are available as Excel or PDF files. These can be used as evidence of work completed and transformer assessment. Also created is a json file. This contains asset and test information and can be used to move data from one TxU test set to another or for import into a data management system, such as PowerDB Lite.
Further reading and webinars
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Troubleshooting
- Ensure the power cord is connected to the device
- Ensure the power cord is connected to an appropriate outlet
- Ensure the power switch is set to the on position
- Check that the leads connected to the MTOU3 are connected properly
- Check that the leads are connected to the transformer and connected to the correct phases
Interpreting test results
Winding resistance results should be within 2% when compared phase to phase. If winding resistance results exceed 2% error, ensure that the correct current and stability time are being used. When testing delta windings, it is important to allow sufficient stabilization time. If measurements are not allowed long enough to stabilize, results may not be accurate. This is typically a problem on larger transformers and transformers with derated tertiaries.
Demagnetization is an important step after winding resistance tests. These tests saturate the transformer core with DC voltage and use DC current to perform measurements. This magnetizes the transformer core. If this magnetization is not removed after testing, the transformer may be subjected to large inrush currents when reenergized. This could cause protection equipment to trip and lead to significant amounts of time being wasted trying to determine the root cause of the trip – which could have been avoided! The TAU3 displays before and after magnetic remanence, ensuring that the transformer is in the proper state to be reenergized.