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The Importance of Three-Phase Testing for Electrical Applications

Three-phase testing devices, like the OMICRON Testrano 600, are crucial to completing tests quickly, accurately, and safely. Because you can run three tests simultaneously, you’ll have to set up for that round of tests just once, as opposed to going back and forth to the power transformer each time. There’s less margin for error with fewer trips made, and when you’re spending less time setting up between tests, you can shave your time by one-third of what it would be with a conventional, single-phase transformer test set. Testing on three-phases opens up the possibility to conduct more tests, simultaneously. Here are just a few you could run concurrently on a three-phase power transformer.
 

Transformer Turns Ratio (TTR) Measurement


Transformer turns ratio tests (or TTR for short) are able to verify the operating principle of a power transformer in effort to detect shorted turns or open-circuited conditions. It’s an AC low voltage test that determines the ratio of high voltage to all other winding at no-load. Measured ratio variations should fall within 0.5% of the nameplate markings. Test values outside of that range indicate a shorted or open transformer winding.
 

Short-Circuit Impedance/Leakage Reactance Measurement


A three-phase power transformer test system really comes into play when measuring the leakage reactance (aka short-circuit impedance) of a transformer. This test is used to detect any potential deformation or displacement of windings. With a three-phase system, you can test all three phases in parallel, without rewiring each time. It saves time and reduces the number of trips.
 

DC Winding Resistance Measurement


DC winding resistance measurements help calculate winding temperature and power losses in the transformer, determine abnormalities due to loose connections and broken strands, and serve as a benchmark for assessing possible damages in the field. Three-phase transformer test sets enable you to measure all three phases of a wye-connected winding simultaneously, cutting testing time to one-third of what it would take with a single-phase transformer test set.
 

Dynamic Resistance Measurement (DRM)


DRM is a test used to diagnose the condition of a resistive-type on-load tap-changer (OLTC) and its associated components (such as the diverter switch, diverter switch contacts, and transition resistors).  Three-phase transformer test sets can run diagnostic OLTC tests simultaneously alongside DC winding resistance tests for maximum efficiency.
 

Core Demagnetization


Once the DC Winding Resistance measurement is complete, the transformer core will remain magnetized.  A magnetized core may result in higher inrush currents upon transformer energization, which results in unnecessary mechanical stress on the transformer.  As a precaution, it is recommended that the transformer core be demagnetized before the unit is placed back into service.
A magnetized core may also contaminate the test results of some electrical diagnostic tests, including the exciting current, SFRA, and TTR tests.  Therefore, it is useful to have a tool that quickly and accurately demagnetizes the core, in order to rule out the effects of residual magnetism on the diagnostic test results.
 

Power Factor/Dissipation Factor (PF/DF) and Capacitance Measurement


PF/DF and capacitance measurements are taken in order to determine the insulation condition of power transformers and bushings. These tests are able to locate weaknesses in the electrical insulation or any hazards within the device, before an impending failure takes its course. They can measure dielectric loss, AC resistance, presence of bad insulation (even if there are patches of good insulation), and assessment of insulation under normal frequency (60 Hz), moisture, and aging. PF/DF and capacitance tests allow you to spot issues before they have a chance to shut down an entire power system.
Streamline your testing process with a power transformer that can handle your work load. Three-phase power transformers enable you to conduct more tests, in less time and with fewer interruptions, which saves money and effort. Advanced Test Equipment Rentals carries a selection of three-phase power solutions for optimized testing, including the new OMICRON Testrano 600. Have questions about power transformers, or electrical test equipment in general? Feel free to contact us by email or at (800) 404-2832. 
Posted: 4/18/2017 2:18:04 PM