The Megger TTRU3-BASIC 3-Phase Transformer Turns Ratiometer is designed to perform three-phase turns ratio measurements using the step-up ratio technique. A single three-phase lead-set connection is all that is required to complete three-phase tests in less than 10 seconds.

The TTRU3 is capable of three-phase excitation and can induce up to 250V on the primary winding, overcoming the voltage dependence seen on larger transformers. The three-phase source allows users to test phase shifting or zigzag transformers and provides users with a guaranteed accuracy of ±0.05% from -20°C to 50°C.

When the TTRU3 is connected to a computer, users can download results or control the instrument remotely. The optional 90029-573 USB Printer (sold separately) for the instrument enables users to print out a hard copy of the results. Users can configure test plans and store results directly on the TTRU3 using the built-in 7 inch daylight-viewable touch screen display. To generate reports, results can be downloaded in Excel and PDF files can be saved to a USB drive.

Variety of Testing to find Typical Problems

With the TTRU3-BASIC and one lead-set connection, users can perform a variety of tests. Users can perform step-up testing for power transformers, phase shift, phase deviation, and polarity. Furthermore, users can perform magnetic balance or flux distribution, excitation current characteristics, and auto vector detection or recognition. An array of problems can be discovered through the variety of tests performed. Typical problems that may arise include loose connections, turn-to-turn shorts, broken strands, winding deformation, tap changer contact problems, and core problems.

Step-Up Turns Ratio Testing Simplified

From IEEE C57.152 2013, under requirement for ratio measurement, the standard states that the term of 'transformer turns ratio' is commonly used despite the actual turns ratio not being measured. With the TTRU3-BASIC, users can now measure the 'transformer turns ratio' as described in the standard. There is no need for higher voltage or heavy instruments that are complex to operate. The TTRU3-BASIC automatically chooses the best test voltage and gives users the correct ratio on the first try.

The technology within the TTRU3-BASIC is based on step-up ratio testing. When compared to traditional 1Ø step-down test instruments, the TTRU3-BASIC removes the inaccuracy associated with test voltage. The user is no longer required to know the 'proper' test voltage required to obtain a 'valid' result. This makes testing much easier, as repetition of testing at proper voltage is no longer required.

Safe With Step Up

Safety is the first priority at Megger, which is why the TTRU3-BASIC is CE Certified to IEC 61010 - Safety requirements for electrical equipment for measurement, control, and laboratory use. During a test, software will perform safety checks before applying full test voltage. In addition, the TTRU3-BASIC utilizes modern hardware to protect the operator in the event of faults.

Polarity

The TTRU3-BASIC quickly and efficiently checks for correct polarity between high and low side windings.

Vector Recognition

The TTRU3-BASIC provides the capability for automatic vector group detection. This is very useful in validating 'expected' versus 'measured' vector group. This does not mean one does not require knowledge about the windings, as this is critical to the proper operation of a transformer. Vector recognition is an effective tool in validating the expected nameplate vector configuration, and should be used as such. Windings such as Zig Zag, can be MISTAKENLY seen as a Delta configuration. This mistake could have catastrophic consequences when line voltage is applied to the transformer, thus supporting the importance of proper use of vector recognition.

Phase Angle Deviation

Phase angle deviation, not to be confused with phase shift, is the phase relationship between in-phase vectors of the high side versus the low side windings. Phase deviation denotes the quality of the core and the winding, and when functioning properly, should exhibit very low values of less than 0.1 degrees. Shorted, partial shorted turns, and a deteriorated or damaged core can cause significant changes in the phase deviation values. Together with ratio error, phase deviation can also be used as a reliable method of quickly verifying accuracy class of PTs and CTs at 'zero burden' rating. This allows for proper validation of accuracy class of incoming CTs or PTs from the factory, or field validation during routine maintenance.

Excitation Current

The excitation current test is very useful in locating problems such as defects in magnetic core balance, magnetic core structure, shifting of windings, failures in the turn-to-turn insulation, or problems in tap changers.

Winding Balance

Winding balance, also referred to as magnetic balance, is performed to assess the health of the windings, core assembly condition, and flux distribution within the transformer. This test, performed safely and efficiently by the TTRU3-BASIC, is a measure of how well balanced electrically the transformer is versus nameplate specifications.

Control Software, Saving, and Printing Results

The intuitive user interface of the TTRU3-BASIC has large, user-friendly buttons. Vectors are displayed on the screen, making it easy to match them to a nameplate and giving users confidence that their test setup is correct. Whether using Quick Test or setting up a Test Plan, minimal training is required. When exported, results are grouped by file name, producing an XLS/PDF report that is easy to read, email, or import into PowerDB. For users needing results on the spot, the optional 90029-573 USB Printer (sold separately) can be utilized.

Automation OLTC

Users can maximize their time in the fields with automation options such as automatic OLTC. Automatic OLTC allows users to run through an entire OLTC with one click. Operation is as easy as confirming the calculated tap voltages in the Test Plan and choosing when the test should stop.