Multifunction testers are a familiar idea. One could argue that power factor/tan delta (PF/TD) test instruments, which have been in the market for decades, are multifunctional, providing the ability to perform PF/TD tests, excitation current tests, and even modified TTR tests. But those tests have in common the requirement for an AC voltage source and an instrument’s ability to measure AC current. Multifunction power test instruments, meanwhile, provide multiple test sources and measuring circuits. A TTR test instrument requires an AC voltage output and an AC voltage input, while a DC winding resistance tester requires a DC current output and a DC voltage input. So beyond the advantages enumerated in the About the Product section, what technical merit exists for combining these two tests?
A TTR test is universally popular. Beyond detecting short-circuited winding turns, TTR testing assures an operator that when that transformer returns to service and picks up load, the transformer will transform voltage as expected. Therefore, the industry routinely performs this test as part of practically every transformer outage. Meanwhile, as transformer diagnostic tests go, DC winding resistance tests are among the most important. According to the 2012 CIGRE Transformer Reliability Survey, transformer windings constitute the number one failed transformer component. Therefore, Megger recommends performing this very searching winding assessment test at every transformer outage. For this reason, among others, what a perfect pairing!