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TAU3 true three-phase transformer winding analyser

With a large power transformer (>100 MVA) you typically require higher excitation voltage and current for accurate and stable turns ratio and winding resistance results.  Whatever your application, there is a TAU3 model to meet your needs.  All TAU3s come with built in tap changer control for minimising test time on transformers with built-in OLTCs.  

Turns ratio is typically the first test performed on a transformer.  It is a pass/fail test. If a transformer fails, it is likely there are significant issues that need to be addressed before other tests are performed.  If the transformer passes the turns ratio test, winding resistance is logically the next test to verify that the mechanical integrity of connections within the transformer, bushing, and tap changers.  A resistance imbalance can lead to faster degradation of the transformer.  Always remember to demagnetize the transformer after winding resistance tests!  Residual magnetization can cause large inrush currents when the transformer is energized, leading to time-consuming and costly nuisance tripping of protection systems.  

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 portable reference devices, the TRS1 and TOS1, for field verification of instrument performance, providing confidence that the correct transformer maintenance decisions can be made.  

Short circuit impedance tests, otherwise known as leakage reactance tests, verify that the transformer winding and core have not physically moved.  In the past, performing this test required disconnecting leads used for TTR or winding resistance tests and applying a physical short between the secondary terminals of the transformer.  Challenges with selecting an appropriately sized short (large cross section cable or busbar) and making solid connections to transformer secondary bushings, have prevented this from becoming a routine test.   With the TAU3’s patent-pending internal shorting arrangement, the short circuit impedance test uses the same connections as the turns ratio and winding resistance tests. There is no need to change lead connections!  

The TAU3 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 TAU3 test set to another or for import into a data management system, such as PowerDB Lite.