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I was reading an interesting document made by S&C about the calculation of a transformer inrush current based on the impedance and the short-circuit available at the primary side of the transformer: http://www.sandc.com/webzine/2003/012003_1.asp We usually use a 8 to 12x nominal value for 0.1s...

Thank you for your answers! Yes, indeed, for the capacitor. I also thought about that later yesterday, it was obvious after all! As for the measured value for the reactor, 66mH instead of the 115mH mentioned by the manufacturer, I think it is because the value measured on a single phase does...

I am currently reading a report talking about the test and sizing of an harmonic filter. I have a couple of questions about how they managed to get their results. Here we go. The filter is made of one 3-phase reactor, with a value on the plate of 115 uH. In series with this reactor are four...

I am currently working on the coordination study of a factory's emergency network. They have 2 500kW generators and 1 MW turbo-generator. I was able to get all the information I need about the 2 generators as they are only a few years old. But unfortunately, the turbo-generator was made in the...

I was looking for informations about T-T connected transformers because I saw a couple of them in the last months. I found this thread via google where it was briefly discussed: thread238-151261 Some manufacturers like "Marcus Transformers" (http://www.marcustransformer.com), also found with...

Of course, we use the cts and vts when available, which is most of the time. I must say I don't really enjoy the idea of taking measurements on live medium voltage cables. Even if every and all precautions are taken, there is still a higher risk than working on cts and vts. But we have...

We would like to take measurements on a 25kV transmission line (voltage and current). Other than installing permanent current and voltage transformers, is there something else we can use to record those values over a short period of time? A few months ago, I remember receiving a publicity...

We also already do that, we clean the jar and syringe with the transformer's oil three times, after removing the 1-2 liters ;) We take a lot of precautions to avoid contamination when taking the samples. That's why I wondered if the higher result *could* be real in some cases..

We regularely take oil samples from our clients transformers in order to analyse their dissolved gas content and oil properties. Sometimes (and it happens a couple of times in the last few months), we see a sudden change in water content (for example from 10 ppm to about 50 ppm a year later)...

I was looking for the book dpc talked about on amazon.com, Protective Relaying (Power Engineering, 5) by J. Lewis Blackburn: http://www.amazon.com/Protective-Relaying-Power-Engineering-5/dp/0824799186/sr=8-1/qid=1158934286/ref=pd_bbs_1/002-1679553-7031209?ie=UTF8&s=books I saw another...

Thanks for all the valuable information, i will study it very thoroughly. I will try to find more information about the CT type in order to predict what would happen during a 6kA fault.

I have a question about current transformers saturation. Here's the situation. The building has a medium voltage breaker with its protection relays, on the primary side of its main transformer. The current transformers used by the relay have a ratio of 50:5A. The maximum short-circuit current...

rbulsara: The tests were done as an annual inspection and verification. Both transformers were online before the tests and they are online as we speak. The units are about 30 years old and are delta-wye. We have no history about earlier testing. Unclebob: MB told me the same thing, but there...

rbulsara: the dielectric strength was about 33 to 35 kV (standard test) Zogzog: The voltage was applyed for 1 minute. I know the voltage is not high, but that doesn't explain why we got those results. The polarization index was not calculated. By the way, all cables were disconnected during...

Hello everyone, We just tested 2 PCB transformers: ratio, winding resistance, PCB dielectric breakdown and insulation test (megger @ 1kV). All the tests gave good results on both transformers, but the insulation tests we're pretty low on -both- transformers primary side (about 8 to 9 MegOhm...

The person who took the sample tells me it was done correctly, but we'll double check with a new sample. Good idea to confirm with our dielectric tester ;) I talked to Morgan Schaffer about those results and they told me it was most likely a water contamination in the plastic jar (even if the...

Hi Scott, Thanks for the reply. You think that the water content can be significant in this case? It has raised by 11 ppm to reach 15 ppm in 2 years, which I believe is not that much. I don't think a 15 ppm water content could create such a drastic change in the oil properties.. I have seen...

I just received the results of the oil analysis we made on a 2.5 MVA transformer. I'm a little puzzled by the results and I would like to have your opinion. We have the results from the last 4 years. The DGA show stable gasses (low concentrations) and no problem have been observed on that...

The high concentration of ethane, ethylene and methane points toward overheating oil. But we must be extremely careful when we have only a single analysis like this one. What is really indicating a trouble or a potential dangerous situation is not the gas itself but the variation of those...

Well, to be honest, I don't really have more details than what I wrote in my message. I'm not the one responsible for that job. I'm doing those researches for a colleague who just told me that last week. I understood from the few information I received that he talked to a guy at S&C a few...