Smart Maintenance of Power Transformers

State-of-the-art test systems and a smart software solution for diagnostic testing, condition assessment and easy data management help to evaluate the status of a power transformer faster and more reliably than ever before…

Growing energy demand, increasing distributed generation and an aging asset infrastructure are all part of the major challenges facing electric utilities today. Asset and maintenance managers need to ensure the reliability of their assets in an environment which is experiencing increasing cost pressure. Since power transformers are among the most critical and cost intensive components in electric energy networks, life-cycle management programs are becoming more and more common. Thereby, a two-step approach is often utilized to keep the lifecycle management process more cost efficient.

Initial Screening

  In an initial screening step, you can evaluate power transformers by monitoring the most critical components and using test methods which can indicate a wide range of problems. The most powerful screening method is the Dissolved Gas Analysis (DGA). Due to the fact that this method can be used to detect a very broad spectrum of problems related to the active part makes it the most widely accepted and used measurement routinely performed on power transformers. If performed frequently, it also allows detection of developing failure modes by trending over time and evaluating the rate of change of certain gas concentrations.

  In many cases, bushings reach the end of their life before the power transformer itself. However, the diagnostic reach of DGA related to bushings is limited. Therefore, power/dissipation factor and capacitance measurements should be included in the screening process as part of the lifecycle management program.

  Based on this condition information, you can assign the probability of a failure to each asset. In the second step, you can conduct a more detailed condition assessment for the high risk assets including diagnostic testing.

Diagnostic Testing

  Additional test methods have to be employed to further evaluate the condition and decide on maintenance, repair or replacement measures. In addition to the above mentioned DGA and power/dissipation factor tests, you can use a variety of electrical test methods to diagnose different problems within the power transformer.

  As you can see, each type of test gives you another piece of information about the overall status of your power transformer. Comparisons with fingerprints and previous measurements provide additional information.

  So, in order to have a picture that is as complete as possible, you need to find a way to make these pieces fit together. In the past this was often only possible by transferring data manually from the individual test devices to one common file. Comparisons and reports also had to be prepared manually.

  Therefore, OMICRON developed software that supports users in smart power transformer maintenance.

Picture 1: One software for all common chemical, electrical and dielectric diagnostic tests on power transformers

Primary Test Manager™ – the software for smart maintenance

  OMICRON’s Primary Test Manager™ (PTM) software is optimized for the initial screening, diagnostic testing and condition assessment of medium and high-voltage assets, including power transformers and associated equipment such as bushings and on-load tap changers (OLTC). The PTM software assists you in testing and assessing your assets according to applicable international IEEE and IEC standards and guidelines, while keeping your testing time to a minimum.

  It is, therefore, the ideal software tool for supporting your efforts to complete your transformer diagnostic testing with much greater speed.

Picture 2: The PTM software assesses DGA results using interpretation methods such as Duval’s triangles or gas ratio methods according to IEEE C57.104 and IEC60599

One Software for Chemical, Electrical & Dielectric Tests

  Meanwhile, the comprehensive PTM software supports you in all common chemical, electrical and dielectric diagnostic tests performed with OMICRON test systems and the corresponding condition assessment, such as the assessment of dissolved gas analysis test data:

• Power factor/dissipation factor and capacitance
• Excitation current
• Short-circuit and zero sequence impedance
• Transformer turns ratio
• DC winding resistance
• Dynamic OLTC Scan (DRM)
• Demagnetization
• Dielectric (frequency) response analysis
• Insulation resistance
• Polarization index and dielectric absorption ratio
• Sweep frequency response analysis
• Gas-in-Oil analysis

  So, you only have to get comfortable with one type of testing software, which also means less training effort.

  Combined with the time-saving advantages of new test systems such as, for example, the 3-phase power transformer test system TESTRANO 600 or the DIRANA for dielectric frequency response analysis, power transformer testing can be done in a fraction of the time needed in the past.

Efficient Data Management

  The PTM software provides a well-structured database for managing all power transformer related data to get a comprehensive overview of its condition. You can enter information about the location, as well as nameplate parameters such as serial number, vector group, or voltage and current ratings. Alternatively, you can import data about location or asset from other systems, for example ERP, maintenance or asset management systems. Once the data is entered, it can be re-used for all future tests. You can find the transformer you’re looking for with just a few clicks – everything is quick and easy.

  The PTM DataSync function guarantees that all test data created in the field is synchronized to a central database. This provides guaranteed access to tests that have already been carried out, plus the associated connection diagrams and test reports, at any time, regardless of whether the tests were carried out by you or any other member of your test team.

Picture 3: Trend analysis and side-by-side comparisons with reference values or previous results.

Preparation Increases Quality & Saves Time

  The testing procedure using the PTM software is based on a four-step concept that covers everything from the preparation stage right through to the test report.

  Using PTM, you can make thorough preparations for the testing day and reduce the amount of time spent outside in the field. Thanks to the central database, any test procedures or measured data from previous asset tests can also be accessed during the preparation stage.

Step 1: Customized test plans

  Based on the nameplate values entered in the database, PTM generates a customized test plan according to current standards and guidelines for each asset. Thereby, PTM provides you with a comprehensive test plan to thoroughly assess the condition of your transformer. By selecting or de-selecting individual tests, you can tailor the test procedure to your specific needs with minimum effort. At the same time, test plans can be configured in advance to enable fast and effective measurements.

Step 2: Safe and automatic test execution

  Clear connection diagrams help the user ensure the test equipment is set up correctly. Not only does this keep errors to a minimum and speed up the testing process, but it also provides protection for the user.

  PTM enables you to control the connected test set and to execute the defined test directly from a computer. You are prompted wherever a user interaction is required, otherwise the execution of the tests is fully automatic. All results are displayed as diagrams and tables in real time, and the system also shows the progress of the measurements as well as the tasks that are still remaining.

Step 3: Automatic assessment, comparison and trending

  Limit values can be selected according to applicable guidelines or defined based on your individual customized limit profiles. An instant ‘pass/fail’ assessment of the test results is displayed based on specified limit values. In addition, a tooltip informs you which test parameters should be investigated.

  Having said this, often it is not the absolute value that has been measured once that is of importance, but the change of the value over time – the trend. With PTM you can do a trend analysis for power/dissipation factor or DGA values for example. Additionally, you can do side-by-side comparisons with reference assets or sister units.

Step 4: One report for all tests

  Once the tests are done, PTM automatically generates a report including all asset related information and test results. This gives you a comprehensive overview of the power transformer that has been tested, the test results and the assessment. You can easily adapt this test report, for example, by choosing from different types of result tables and diagrams and by providing comments on every test.

Reliable and fast transformer diagnostics

  Using the combination of several diagnostic tests helps to get an unambiguous picture of the status of a power transformer and define the required measures precisely. Thereby, state of the art test systems and a smart software solution for diagnostic testing, condition assessment and easy data management help to evaluate the status of a power transformer faster and more reliably than ever before.

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