strange noise from transformer, partial discharge?
strange noise from transformer, partial discharge?
(OP)
Hi all,
I have been asked to investigate a strange noise coming out of three 3MVA 25kv/600v oil immersed transformers.
There is a small noise coming out of the transformer, like a "ting-ting-ting...", about 160 times a minute.
three out of four transformers are doing it. They are all exactly the same transformer.
Is it possible that partial discharge causes this noise? (it seems to come from inside the tank)
We did gas analysis and everything looked fine exept CO and CO2 were a little high.
thanks for your comments.
JL
I have been asked to investigate a strange noise coming out of three 3MVA 25kv/600v oil immersed transformers.
There is a small noise coming out of the transformer, like a "ting-ting-ting...", about 160 times a minute.
three out of four transformers are doing it. They are all exactly the same transformer.
Is it possible that partial discharge causes this noise? (it seems to come from inside the tank)
We did gas analysis and everything looked fine exept CO and CO2 were a little high.
thanks for your comments.
JL






RE: strange noise from transformer, partial discharge?
Where are you located?
RE: strange noise from transformer, partial discharge?
Also how long has the noise been going on?
RE: strange noise from transformer, partial discharge?
I'm in Canada. The sound is hard to describe. They tried to record it with a digital camera, you can try to hear it, (you need headphones), behind the transformer humm, there's this strange noise about twice per seconds, (it sounded louder on the field).
In case it is partial discharge, what action should be taken. Do you have suggestion of partial discharge tester manufacturer (acoustic test?).
Still in the beginning of investigation , I will update as soon as we get more information.
RE: strange noise from transformer, partial discharge?
PD can be located in oil filled transformers by using HFCT's on the ground combined with magnetically coupled acoustical sensors on the tank. Acurate timing measurements between the 2 sensors are then made and based on the time between the 2 signals and comparing the timing between various locations of the stank sensor the PD location can be triangulated.
ANSI C57.127-2007 has more details on this
My recommendation would be to take DGA samples monthly to track any increase in H2 or other gasses. This one has me curious, keep us updated.
I know a good PD testing company in Canada if you need someone.
RE: strange noise from transformer, partial discharge?
Is it there all the time? I agree with zogzog, it sounds sort of like a bearing problem on a fan or oil pump - are there any fans and/or pumps?
The thing is, if you were hearing a PD through the tank wall, you would be seeing huge amounts of gas in your oil samples.
Phil
RE: strange noise from transformer, partial discharge?
What is the construction? Sealed tank with nitrogen blanket or conservator tank?
Is noise at regular intervals or random?
Is noise present with and without fans and/or pumps running?
RE: strange noise from transformer, partial discharge?
Maybe a high side bushing or external terminations?
jgrirst, PD setection in oil is a common practice, see ANSI C57.127-2007 "Guide for the Detection and Location of Acoustic Emmisions from partial discharge in oil immersed power transformers and reactors"
RE: strange noise from transformer, partial discharge?
One of the four transformer is a lot louder (one is offline, one is outside so hard to hear).
I attached a copy of the oil analysis that have been made on this transformer.
The H2 is high, 215 ppm. Co and CO2 are also high.
Next step will be a complete inspection to make sure its not mechanical noise, and, complete Doble testing of at least two of the four transformer.
RE: strange noise from transformer, partial discharge?
i'm not sure about the transformer construction..
but what I can tell is that the noise is at regular interval and we can hear here it when the fans are not running. (no pumps).
have a look at the DGA , we do see high levels of H2.
Thanks
RE: strange noise from transformer, partial discharge?
High levels of CO and CO2 indicate cellulous breakdown,(see attachment) which would lead to PD activity, your H2 is also high and has been for awhile.
So what dosent make sense is the H2 levels degreasing over time, however that my be due to sampling errors. I would start with a corona scan of the HV bushings and terminations, dont where else the noise would be audible from, then do a full barrage of testing on the transformer, finally degas the oil.
RE: strange noise from transformer, partial discharge?
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: strange noise from transformer, partial discharge?
RE: strange noise from transformer, partial discharge?
Oh, and he said "160" per minute.
Notably when I strip the 60Hz hum out the sound diminishes by the same amount.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: strange noise from transformer, partial discharge?
RE: strange noise from transformer, partial discharge?
Note: May be Gases are generated by normal operation and aging, mostly H2 and CO with some CH4
presents of H2, CO :
-Possible Faults
Thermal fault less than 300 °C in an area close to paper insulation (paper is being heated).
-Possible Findings
Discoloration of paper insulation. Overloading and or
cooling problem. Bad connection in leads or tap changer. Stray current path
and/or stray magnetic flux.
Note:Atmospheric gases (N2, CO2, and O2) can be very valuable in a DGA in revealing a possible leak. Moisture and atmospheric gases will leak inside when the transformer is off and ambient temperature drops.Look for leaks.
Suggestion:
-The weaken point in the Trafo is the tap changer fingers loose ,with time generate a heat and cause gases.open and check.
-check the nature of the load and how is vary or unbalance loads (or overloading)come some times.check if the noise come dowen or not with changing the loads.
-Repeat the DGA for more investigation and comparing results.
I'm interesting to follow this case ,so please keep in touch for any news.
Aimn
RE: strange noise from transformer, partial discharge?
I think that noise is just an acoustical result of the three phases humming or beating in some way. ANY filtering, low pass, equalization, etc., ALL reduce the mystery sound just as quickly as the targeted frequencies. How can this be if it is a true ~3Hz source?
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: strange noise from transformer, partial discharge?
Some 35 years back self was faced with a sound problem in a transformer.It was a 12.5 MVA 132 kv Traction supply transformer.From commmissioning day onwards a tuck-tuck sound was coming from the unit at the time of commissioning and also after switching off.It took couple of minutes for the sound to subside.Initially it was reported that sound was coming from all around,but a close watch showed it from one side.When a wooden rod was used as a stethoscope,moving over the tank surface,sound originating point could be located.It was where a tie -rod connecting upper core frame to lower frame was ending.On internal inspection it was found that the locking nut at the end of the tie rod had loosened and fell down.So the long tie rod still fixed at upper yoke frame was acting as a pendulum and hitting on the side of the hole in the lower yoke clamp.This was happening due to the jerk occurring at the time of switching on or off the transformer.
RE: strange noise from transformer, partial discharge?
Funny thing is, seems the wooden rod found the problem. Nice post prc!
I worked with a guy that was a power system engineer in Russia in the 60's, they did "IR Inspections" on terminations by using a candle on the end of a stick, if the wax melted, the connection was hot.
RE: strange noise from transformer, partial discharge?
since DGA does not show significant increase, we decided to take another oil sample in 6 months.
we wil also do a Doble test on 2 of the 4 transformer at the next maintenance.
I believe it is the only thing we can do for now...
RE: strange noise from transformer, partial discharge?
I don't know that I'd wait six months on the next DGA.
As for locating the source of the sound, you might jump disciplines and see if your MechE folks have a good sonic fingerprinting contractor. I have heard of some interesting findings of transformer noise signatures done by a vibration analyst who was playing around with his technology.
old field guy