Відео

About <=2% the FLA.

it's not always necessary to change the port settings on the PC

You might be able to do this with only an AC voltage source and (2) precision voltmeters. One for the voltage source on the primary and one for the secondary voltage. This might work great for a single-phase transformer. However, when you get into a 3-phase transformer testing, your meters and your source are going to have to become a bit more complex. You will now have to monitor both phase-to-phase and phase-to-neutral voltages and their phase relationships to one another. This is dealt with by having the test equipment (TTR) apply the appropriate vector math for the configuration of the transformer being tested. You will find that most of these pieces of test equipment will calculate accuracies or % error based on having entered in nameplate information. Probably the most significant response to this question is that commercially available test equipment will by necessity have certain safety and convenience features built into them. Automatic Discharge Single Equipment Grounding Point Demagnetizing Feature Easy Access to transformer configuration selections and connection Diagrams Pass/Fail indications based on imbedded industry standards and programed nameplate data. Finally, with a piece of test equipment designed for performing TTR tests, you can have an electronically generated report available for your customer within minutes.

Thank you!

You're welcome!

From Bret Hammonds: The best approach to demagnetizing a transformer has been being debated for as long as I can remember. The answer might actually be based on who you ask. If I understand your comments correctly, it is as you stated. Demagnetizing from the secondary side of the transformer will require a greater amount of current than it would from the primary, even though it can be performed from either side of the transformer. However, I took it upon myself to contact a test equipment manufacturer concerning this question. Their recommendation was to demagnetize from the primary of the transformer. They also recommended that you demagnetize the transformer on each of the phases, and not just one. The best recommendation that I might give is to contact the specific equipment manufacturer and get their input regarding this matter.

Bret Hammonds from Protec answering: Excitation tests with a TTR are valid if you can establish a pattern such as a High-Low-High relationship of excitation values between phases. You may not be as successful at trending specific excitation values if you are not using the same instrument to perform your testing each time. The reason being that the specific excitation values are voltage dependent and will not trend if you use a TTR to do the testing at perhaps 8 to 120 volts on one occasion and a 10 kV power factor test set on another occasion. Regarding your question about an excitation current value of zero (0) on one phase of a three-phase transformer, the fact that you were able to perform winding resistance testing with good results confirms that you were able to saturate the core of the transformer and were not struggling with a tap connection or open winding issue. It’s difficult to say exactly why you may have gotten a zero-excitation test result on one of the phases. It may be that a low voltage instrument such as a TTR was, in this case, simply not adequate to properly perform excitation tests on this transformer. This would of course be only one possible explanation and may require further investigation to establish the actual cause of this test result.

Hi Mark, thanks for your question. From Bret Hammonds: The technology behind TDRs is ideally suited for two conductors separated by a homogeneous (equivalent) insulation such as what you would find in either a shielded cable or one with a concentric neutral. The case that you have presented is less than ideal for use of a TDR since it is only able to detect very significant changes in impedance such as an open circuit or a short circuit. Having said that, it might be possible under some very unique circumstances for a TDR to be helpful in finding a fault in such a situation as what you have described. Those circumstances would include: - Using either a grounded conductive conduit for your return or the two separate cables that are running through the conduit. In either case you would NOT have a homogeneous (equivalent) impedance throughout the distance of the cable run. AND - A significant fault that is either completely open circuited ( ~ ∞ ohms) or a very low impedance (for all practical purposes considered to be a short circuit between the conductors.) If the fault is a high impedance fault, which is often the case, then the TDR will NOT be able to see the fault without being integrated into a more elaborately featured cable fault locating system.

The attached “Battery Testing Guide” from Megger does a good job of addressing this question. The explanation is on page 15 and references Figure 1(page 6): protecequip.com/media/7183/meggerbatterytestingguide.pdf

Thank you for the generous praise! Glad to have you and your experience on commissioning!

Thanks for your question. If the values associated with this type of testing are questionable, perhaps it would merit further investigation such as reviewing previous test results to establish a trend, performing a tip-up tests as an indication of voltage dependency for partial discharge. It may even be helpful to perform PD testing prior to moving into more impactful maintenance measures.

Thanks for your question. A transformer that has a resistive LTC on the secondary will display this kind of characteristic that increases as you move away from the nominal position in either the raise or lower direction. In either of the extreme positions (16R or 16L), all of the regulating winding will be included in the circuit and represent the highest winding resistance values. Each step away from the neutral position will represent a slightly larger amount of winding slightly increasing the winding resistance. In the case of a 16 raise and 16 lower tap switches with a neutral position in the middle, the difference between the raise and lower tap positions is a reversing switch. While that polarity of the winding included in the circuit may be opposite for the raise and lower taps, the amount of winding resistance would be comparable to the corresponding position in the opposing polarity.

Glad it was helpful!

Thank you for the comment and question. The greater the number of turns in a winding the less of an impact one or two shorted turns may have on the ratio of the transformer and may not be significant enough to cause it to fail the (+/- 0.5%) industry standard for pass and fail criteria. However, it may cause enough of a change in comparison to previous excitation current tests or comparison to excitation tests of other phases to merit further investigation. This is why, in many cases if we perform one of these tests, we’ll perform both. It would be great if we had one test or one piece of equipment that would give us a full picture of the health of a transformer, but it just isn’t so. It sometimes takes 2 or 3 pieces of the puzzle to give us a clear representation of what’s going on with a transformer and its health. The number of shorted turns may not be significant enough to fail the ratio test, but other tests such as the excitation tests and winding resistance tests will produce results that perhaps cause enough concern to merit further investigation as to why test results aren’t more comparatively acceptable. Hope this helps!

Thanks for watching!

Thanks for watching!

Hi, you should contact Megger sales within your country to get a quote for purchase. megger.com/. If you are within the US and looking for a rental, you can contact us at (866) 352-5550 to get a rental quote. Thanks!

I’m not completely sure of the context of this question, but I am suspecting that it may have been related to the difference in how measurements may at one time have been made as opposed to the way they are currently made from a concern for safety. If we were to apply a voltage to the secondary and measure the voltage across the primary of a transformer, the potential at the primary could be lethal and perhaps more difficult to meter. However, if we were to apply a voltage to the primary and compare it to the secondary, then the voltage is much lower and less difficult to meter on the output of the instrument, perhaps making it more accurate and safer than if we applied a voltage to the secondary.

Glad you like it! We will be doing another webinar on Transformer Winding Resistance this Thursday and will be adding it to the UA-cam library next week!

Maybe...if you are going to use more than 60 cells, you have to connect back from the last BVM to the power and signal module. Additionally, you need to make sure the first BVM goes on the NEGATIVE terminal of the string. Finally, if the BVMs continually read up to a particular BVM, check the input and output ports of that BVM.

Thanks!

You are so welcome!