Testing Tranformer Oil Rated for 50Hz Power Trafo at 60Hz Test Voltage

The chemical test for oil impurities is no more frequent than several months. What test do you think you are performing?

We only need to measure kV. Just wanted to know if test voltage at 60Hz affects the results in any way.

Thanks

The dielectric strength of any insulating material may be a function of frequency. However, at such low frequencies as 50 and 60 Hz, I do not suspect a change of more than a few percent.

http://electrical-engineering-portal.com/what-standards-to-use-for-transformer-oil-testing

From what I can gather, (1) contact the supplier of your test equipment and see is the test source frequency can be switched from 50 Hz to 60 Hz (or vice versa).

The important thing is detecting problems arising from impurities, to ensure transformer safe operation.

To my knowledge no.

You may need to add a note in your procedures documenting you are using a 60Hz test instead of a 50Hz test along with a justification comment (or comments). Really purely for audit purposes or in the event something happens and your test procedure is questioned for legal or insurance claim purposes (not sure if this is a big thing in Pakistan).

Yes audit is one of the purpose. Good observation.

Most testers operate in a range of voltages and hz....The dielectric property of the oil is tested by determining the insulating quality of the oil using high voltage....the voltage is continually increased until an arc occurs signaling oil insulation failure...

"To assess the insulating property of dielectric transformer oil, a sample of the transformer oil is taken and its breakdown voltage is measured. The lower the resulting breakdown voltage, the poorer the quality of the transformer oil.

• The transformer oil is filled in the vessel of the testing device. Two standard-compliant test electrodes with a typical clearance of 2.5 mm are surrounded by the dielectric oil.
• A test voltage is applied to the electrodes and is continuously increased up to the breakdown voltage with a constant, standard-compliant slew rate of e.g. 2 kV/s.
• At a certain voltage level breakdown occurs in an electric arc, leading to a collapse of the test voltage.
• An instant after ignition of the arc, the test voltage is switched off automatically by the testing device. Ultra fast switch off is highly desirable, as the carbonisation due to the electric arc must be limited to keep the additional pollution as low as possible.
• The transformer oil testing device measures and reports the root mean square value of the breakdown voltage.
• After the transformer oil test is completed, the insulation oil is stirred automatically and the test sequence is performed repeatedly: typically 5 repetitions, depending on the standard.
• As a result the breakdown voltage is calculated as mean value of the individual measurements."

https://en.wikipedia.org/wiki/Transformer_oil_testing

The tester is automated. It does the 5 tests in the same way you mentioned just by pressing of a button. At the end we saw the print out results which mentioned the test voltage applied at 60Hz.

Just want to know if 60Hz test voltage affects the results in anyway.

Thanks

No....The machine is calibrated to do the test with 50 or 60 hz...

I don't know what tests you are trying to do. But I bet if you asked the individual who drew up the test procedure, you'd get a useful answer. Care for a wager? Shall we say, 50 Francs?

50 Franks? How about 50 Sheilas, that's a bet I would take you up on, but no Fanks

Di-electric strength test. Measuring the oil breakdown voltage (kV).

You haven't told me what the individual who wrote the procedure said. I mean, you used the word "we". So there's got to be someone else involved. So I win by default. I'll see you at René's humble café in half an hour so I can collect.

You did not specify a make and model number, but many BDV (Break Down Voltage) test sets are built around a Variac driving a step up transformer. If yours is like that then the output frequency will be equal to the input frequency, but you might need to recalibrate the kV and mA meters just to be sure.

If you're a certified test lab it must be recalibrated by a recognized third party, or just relist it on EBay and read the fine print before you make your next purchase from there.

"If you're a certified test lab" you would have ordered the proper tester and not be asking this lame question.

The Megger guide to insulating oil dielectric breakdown testing

http://www.slideshare.net/piyujwr/8-ee7-hve-lab-manual

Lame question? I already mentioned that we made a mistake in procurement. No need to remind. And no we're not a certified test lab.

Thanks

If you're all not a certified test laboratory then why on earth are you all testing?

I would hazard a guess that it's never been done, and they want to see what condition the oil is in, or there has been an incident and this is the knee-jerk reaction.

Planned maintenance as we all know is a necessary evil, but an important requirement that many people either forget about or ignore.

Testing the oil will give them a heads up on the condition of the oil, and while they may not be certified, and its not a legal requirement, it better than nothing.

When I worked for a Steel company in the UK, we regularly took samples of Tx oil for testing as part of our PM and especially after the BH relay tripped.
But UK legislation requires a certified lab report, which happened every 12 months

We made a mistake in procurement. Its BAUR Oil tester, model: DTA100C. Though it operates on 220V~/50Hz but there is no mention of test voltage frequency either in its brochure or detailed manual.

We wanted Megger in the first place. But you know procurement departments and how those people are like.

I don't want my testing done by an uncertified facility that cannot order the right tester for the job. Let me know who you are and I'll take my business elsewhere.

I am slightly puzzled by your poser. You are only trying test OIL- taken out of a transformer to test for degradation in properties. It does not matter whether you extracted the oil from a 50 Hz trafo or a 60 Hz trafo.

You say, you have purchased an equipment which applies 60Hz test voltage!!!! Trafo oils are tested by chemical analysis, FDS, PDC etc- where different voltages, at different frequencies are applied.

Pl check exactly what tests are you doing, why you are doing, what you are looking for etc etc.

Puzzled why?

We only need to measure the di-electric strength (kV). We realized that the oil tester applies test voltage at 60Hz after we saw the result it printed out. It mentioned tests taken at 60Hz.

I just want to know if this makes any difference in the di-electric strength (kV) results for oil used in transformer rated at 50Hz.

Thanks

again the very short answer is, NO!.. the operating Hz that the tester produces the high voltage is of no consequence!

You should ONLY be concerned with the recorded VOLTAGE at which the oil breaks down.
That in turn, when checking with the oil manufacturers specifications will give you the amount of contamination & dielectric strength of the oil.

the short answer is No!

You are over thinking this perceived problem

OK, thanks. :)

So the premise that the original poster opened with is wrong. Good show!

The actual breakdown event usually occurs because of transient voltages that have time periods that are much shorter than the operation frequency of the device. Orders of magnitude shorter in fact. SO, the answer is NO. The frequency of the test is not a factor.

I saw one paper while researching this topic that clearly stated the conclusion that DC breakdown voltage was 15-20% lower than the pulse train breakdown. What do you make of that?

Interesting....I would then look at the phase angle between the applied voltage and the current. DC of course has a 0deg phase angle and infinite wavelength. In a pulse situation on an inductive system, you would need a higher peak voltage long enough over time for the current to catch up and arc through the dielectric. 15-20% sounds like the difference between peak and RMS and RMS is an approximation of DC. That's my off the cuff opinion anyway.

"As with any dielectric, the breakdown voltage (BV) of liquids tends to increase under short pulses, although not consistently [5], [9]. It was reported in an early investigation [9] that, for transformer oil, the BVs under pulses of several milliseconds duration and very low pulse repetition rates (PRRs) were higher than for AC (60 Hz) by a factor of approximately 1.5 to 2, with larger increases for shorter pulses."

http://www.spellmanhv.com/~/media/Files/Technical-Resources/Articles/Comparison_of_Dielectric_Strength_of_oil.ashx

Pretty interesting stuff, huh.

We used to use an RF oscillator to study the dielectric properties of various organic liquids in physical chemistry lab I assisted as T.A.

Back in 1970, I tested the dielectric constant of plastic disks I cast and ground flat.

The equipment resembled a Rube Goldberg lash up with a wooden case and huge analog dials with some precision flat plate vise to hold the sample.

I'm sure it a hand held piece of something now.

Yes sir, times have changed immensely some of the trappings, and now all the little magic boxes render up few clues how they actually work....made just for Little Johnny.

...as an aside, speaking about circuit breakers....

..."The maximum arcing time that is possible during a short circuit fault at 50 Hz may exceed the 60 Hz tested values by up to 1.7 milliseconds. As a result, before applying a circuit breaker that has been rated for 60 Hz into a 50 Hz application, consideration should be given to the equipment being protected to ensure that the potential additional 1.7 milliseconds of arcing time will not result in unacceptable increased equipment damage. In most practical applications, this increase in time is inconsequential."...

http://www.eaton.com/ecm/idcplg?IdcService=GET_FILE&allowInterrupt=1&RevisionSelectionMethod=LatestReleased&Rendition=Primary&dDocName=WP131002EN

Or injury to unsuspecting technician, either.