So im working on some 500Kva Xfmrs 1

[Magic713Mike]

So im working on some 500Kva Xfmrs and I'm supposed to do an oil sample. Client wants 5L per xfmr. Cool more than usual but ok thing is there is No N2 psi gauge. I'm concerned that draining that much oil could cause the pressure to drop which in turn could cause humidity etc and cause a short. Am I just a dummy or am I thinking properly. Client spec says required accessories temp gauge which is also not there and psi gauge. Asking for a friend Lol

 

[davidbeach]

5cL maybe? 5L is way too much.

When one this sentence into the German to translate wanted, would one the fact exploit, that the word order and the punctuation already with the German conventions agree.

-- Douglas Hofstadter, Jan 1982

 

[Latango]

Standard volume for a DGA sample is usually 0.5L. Maybe the client misread the email from his engineer, or the engineer missed the decimal point? Given that the average 500kVA probably has between 400 and 600 L of oil in it, for a piece of equipment with a 20+yr lifespan and a yearly DGA test requirement, I'm thinking 5L isn't very sustainable...

 

[prc]

Usually, entire oil tests require 1.5 litres of oil. If you are not doing BDV, 500 ml will be sufficient. You should avoid negative pressure at the sampling outlet as air bubbles may enter the transformer. You may top up oil to compensate pressure drop.

 

[Magic713Mike]

So I verified with engineer and client spec because of whatever test it is they are doing is 5L. This is an ABB 500Kva xfmr I mean I'll pull my sample but too me that much is unheard of and then xfmr doesnt have a pressure gauge or temp gauge. Keep in mind these are new installations so testing is required before I can commission them. But my argument is how do they want me tu pull samples without knowing exactly how much N2 pressure I loose so I can know how much to put back. My question is am I wrong for going back and forth with these guys?

 

[bacon4life]

A 5L sounds very strange for that size transformer. If actually want you to take that much, just be sure to convey to the client that you will also be billing them additional costs to replace the sampled volume of oil. You are correct in being concerned about lowering the oil level too low. And not only do you need positive pressure on the tank when you complete the sample, the transformer needs adequate oil volume to account for oil volume shrinking during cold weather. I routinely see low oil alarms from substation transformers during cold snaps due to oil sampling during hot weather.

I have see the need to take way more than 5L that from substation transformers. In order to get representative sample, any oil volume in piping must be drained before taking a sample. In one case, each phase of my LTC had separate piping about 20 ft long. Basically every time we do an oil sample at that substation, we also have refill the transformer conservator. I am now including a requirement in substation transformer specifications for the conservator to be sized large enough to account for 20 years of oil sampling at the manufacturer's recommended sampling schedule.

 

[Magic713Mike]

Thank you all! This has been very helpful in my argument.

 

[davidbeach]

500kVA and I’m picturing a sealed padmount transformer.

When one this sentence into the German to translate wanted, would one the fact exploit, that the word order and the punctuation already with the German conventions agree.

-- Douglas Hofstadter, Jan 1982