Vibration in Power Transformers and Reactors

[hy]

Dear sirs:
I am interested in measuring vibrations in HV Power Transformers and Shunt (line) Reactors.
Could you be kind enough for giving me some help in this?
- where to find information of the tests and analisys?
- which are the most suitable test sensors and equipment?

Thanks in advance
hy

 

[electricpete]

Vibration monitoring of power transformers is not very common. I think the most productive aspect would be monitoring the bearings of associated pumps and fans.

If you were really bored, theoretically you might be able to look for increase in 120hz vibration as a symptom of core problems or overvoltage or unbalanced conditions. Likewise very high frequencies >1mhz acoustic are sometimes associated with internal electrical discharge activity... but that has not been developed as a practical diagnostic tool yet.

The bread and butter tests for monitoring the health of the transformer are oil sampling (including dissolved gas analysis) and off-line electrical testing (power factor, turns ratio, excitation current winding resistance etc).

 

[stevenal]

ANSI C57.12.90 has a method of measuring audible sound in transformers. This is mainly a factory test, since location and ambient noise are important.

 

[electricpete]

Can you explain a little more why you want to monitor vibration of transformers?

 

[hy]

Yes it's not very common, but when you have vibrations enough to fatigue and break conections between conductor and bushings, I really think is something to worry about.
So we are not so bored as you see.

We are aware of bread, butter and coffee tests but, that is another story. Although excitation current and leakage reactance measures are suitable for mechanical movements in core.

Factory test are normally regarding "noise", not vibration.

Also in some 150kV class transformers we had found loosen windings and core wooden separators, due to vibration.

From some of makers we have the points where to take measures, so as to compare with factory tests results, but would want to see if there is anyone who had dealt with this kind of problem, and que test equipment used.

 

[electricpete]

hy - sorry to tell you what you already knew. I didn't understand your purpose, and I've never heard of vibration monitoring used in this manner, although there must be something to it if the manufacturers are talking about it.

From what little I know, the primary factors involved in transformer winding loosening have historically been thought to be through-faults, and thermal aging of the insulation. Related tests as you mention are single-phase leakage reactance and excitationi current and internal inspection. Recently there have been a lot of papers on Frequency Response Analysis for detecting winding movement. I'm certainly not trying to dispute the importance of vibration... I hadn't heard any discussion on that aspect before, but it makes sense that it could be another factor in winding loosening. Also I have never heard of fatigue failures of connections within a transformer.

At our power plant we use Entek IRD Datapak together with desktop software for vibration monitoring of rotating equipment. There is a range of vib monitoring equipment available starting with "vibration pens" sold by skf, giving magnitude only. You can add capability to provide spectrum display, then capability to interface with pc program, do multi-channel analysis, balancing etc). If you have any friends in a power plant or industrial plant with rotating equipment, they will have specialists in vibration monitoring. Vendors include Rockwell/Entek, SKF, CSI and a few others.

One other story that comes to mind on the subject of transformer vibration (not related to your question) ... I heard a report where a generator stepup transformer had a fan blade which apparently developed a crack which went unnoticed.... resulted in increasing imbalance and vibration until the fan blade finally fell apart... shrapnel cut into the cooler tubes resulting, in sucking air into the transformer (cooler was under suction), caused relief valve to lift, and then operators took unit offline in response. Other fan blades showed cracks near the bases of the blade. I have seen similar cracks myself but never a catastrophic failure. It certainly seems like on-line vib monitoring would detect the cracked fan blade as evidenced by vibration at the rotating speed of the fan.

 

[electricpete]

I'm a little curious if the specified measurment locations are on the outside surface of the tank or internal.

 

[prc]

Friends,
You are confusing frequency response analysis and measurement of sound level with measurement of vibration on tank surface.
Tank vibration is more relevant for shunt reactors.There are cases in olden days , when poorly designed or made shunt reactor tanks broke open in service due to severe vibration of tank.So when EHV shunt reactors are tested at factory tank vibration will be measured by puting the sensor on tank surface and applying 110% of rated votageto winding. Limit of vibration will be specified ,say 150 microns etc
Modern trfs,tank vibration is negligible and rarely measured ,even though not uncommon to specify.
You can get test instument from reputed makers like Bruell&Jarr

 

[stevenal]

C57.21 describes a vibration test for shunt reactors over 500 kVA. Briefly for oil filleed units: run reactor at rated voltage and frequency. Divide each tank side into 12 rectangular areas of similar size. Find point of maximum excursion for each area. The average amplitude for the 48 maximum excursion points shall not exceed 60 uM peak to peak. The maximum for any single point shall not exceed 200 uM peak to peak. My copy is from 1990, so is probably not the latest.

 

[jbartos]

Suggestion: Visit

http://www.elexp.com/sec_040b.htm

http://www.cosmotron.se/products/sheets/CMVVS302E.pdf

http://www.grindosonic.com/products.html

etc. for more info