Transformer Inrush Measurement
Transformer Inrush Measurement
(OP)
We are setting up to measure a transformer's maximum inrush current. One of our testing contractor offered an equipment called: Dranetz PX5 recorder with 3 TR2500 clamps, memory card and software.
My question is a 5ms measurement enough to detect the transformer inrush with harmonics or do we need less than 4ms measuring capability?
My question is a 5ms measurement enough to detect the transformer inrush with harmonics or do we need less than 4ms measuring capability?






RE: Transformer Inrush Measurement
There was a recent similar discussion at http://www
Gunnar Englund
www.gke.org
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RE: Transformer Inrush Measurement
How about the HIOKI recorder?
RE: Transformer Inrush Measurement
http://www
The difficulty weare having is that there are testing contractors who offers different instruments in measuring the inrush. I would like to get an idea, what should be consider in order to have confidence that their instrument will really capture the peak inrush.
My thanks for any support.
RE: Transformer Inrush Measurement
Shape and magnitude of the inrush event is a function of voltage phase angle and remnant flux in the core, as well as any secondary load. Doing a single measurement is not really going to be definitive.
David Castor
www.cvoes.com
RE: Transformer Inrush Measurement
Both current and waveform captures will be taken on each phase and the switching will be three phase. With this we may compare and see whether the peak current happened at zero voltage period.
My concern is whether the instrument offered will be capable of measuring the harmonics and DC component associated with the transformer inrush and whether the sensors are properly sized so as not to saturate.
Does anyone had any experience on doing this and any suggested instruments will be appreciated.
Do we need NETA Level 3 Tech to do the job?
RE: Transformer Inrush Measurement
There are several USB instruments available. I have a few TiePie four channel instruments that can be used in parallel so that you can build 4, 8, 12 channel recorders with them. Sampling and resolution is similar to the HIOKI.
We also use our own ARCUS. It has ten channels and 12 bit resolution. Not as versatile and fast as the HIOKI and TiePie. But extremely simple to use. And adequate for inrush measurements.
Dranetz is more for power quality. Inrush is somewhat different. And if you want to do other things, the HIOKI is your safest bet.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Transformer Inrush Measurement
http:/
The instrument has an inrush mode and a transient mode. I was thinking on considering a transient mode measurement, which goes down to 5 microsecond measurement. The Tech informed us that we don't need that sensitivity since we are just measuring the peak inrush. I was thinking that a transformer inrush will have harmonic and DC component currents included so a transient wave form capture will accurately indicate the current spike. I am not that familiar with recording instruments so I appreicate an overview on these recorders to guide me as far as transformer inrush measurement is concerned.
Anybody who used Dranetz before for inrush measurement of a transformer?
RE: Transformer Inrush Measurement
Any recoder with a good sample rate can make the measurements. The real problem is the clamp you will use to measure the inrush current. It should have a good frequency response and can not saturate.
So, you need estimate the peak value of the inrush current and use a clamp that not saturate for that peak.
Best regards,
Herivelto bronzeado
RE: Transformer Inrush Measurement
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RE: Transformer Inrush Measurement
However, one manufacturer claimed that they can manufacture a special design that will yield an inrush of almost 100% FLA. Now we are testing the protoype to ensure that what was spec out by them is valid.
RE: Transformer Inrush Measurement
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RE: Transformer Inrush Measurement
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Transformer Inrush Measurement
As I gather, the transformer inrush occurs on a very very short period of time so a high speed recorder like HIOKI would be a good choice. I will check on the clamp rating to ensure that it will not saturate while measuring the inrush. I think the clamps are rated as to the maximum current they are rated to measure.
Does this mean that if my estimated inrush is 720A RMS, I would use a clamp sensor having an accuracy up to 800A?
Regards,
RE: Transformer Inrush Measurement
I've gotten very reasonable recordings of inrush using the oscillography of relays with 16 samples per cycle.
RE: Transformer Inrush Measurement
I would use at least a 1000 A clamp. And make sure it doesn't saturate just above 1000. Most 1000 A clamps are good for 2000 A peak, with a somewhat reduced accuracy.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Transformer Inrush Measurement
This is what is offered:
http:/
RE: Transformer Inrush Measurement
That is a well known issue with UPS and downstream transformers. You are lucky not have blown fuses in the UPS bypass circuit or cause some other damage. It is customary to place the UPS on bypass before energizing the transformers. In data centers, there are means and procedures to prevent automatic re-engergization of PDU transformers, once the power is lost or you can size the UPS accordingly.
But if you can get a unit that limits the inrush within capability of the UPS, that would work too.
Rafiq Bulsara
http://www.srengineersct.com
RE: Transformer Inrush Measurement
By the way, on the current clamp specifications, it is indicated that:
Basic Accuracy: 1% F.S. (48~65 Hz) (%reading + floor spec).
Useable Frequency: 1Hz~20kHz
Max. Non-destructive Current: 4000A
Continuous Current Range: 2A-200A, 20A~2000A.
I am concerned of why the % accuracy is not mentioned for frequencies outside the 48Hz~65Hz window but within the 1Hz~20kHz window. Any reasons why and how does this affect the measurements.
I asked the testing contractor but they gave me a dead end answer that this is what the manufacturer specified.
RE: Transformer Inrush Measurement
Rafiq Bulsara
http://www.srengineersct.com
RE: Transformer Inrush Measurement
I may be wrong but it won't hurt to check efficiency as you evaluate the transformer.
Bill
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"Why not the best?"
Jimmy Carter
RE: Transformer Inrush Measurement
In your technical opinion, will a 256 samples/cycle rate recorder adequate enough to measure a transformer peak inrush current?
Unfortunately, the clamps being used on all our recorders are of Rogowski Coil design and will not capture the DC component of the inrush. Due to time constraints, we are not able to outsource one Hall-Effect CT. Instead, we are looking into a "wide-band" Ferrite CT. Any concerns by experience on this one would be a good help for us.
If we do use the these "clip-on" current sensors and register a peak current on the recorder, is there any other way to approximate the DC component without tedious transient calculations. We had measurements on the same rectifier rating in the past. If the manufacturer claims that they are able to reduce the inrush from 15x to 1x FLA, can we look into it on the basis of approximation looking at the ratios?