Transformer purging after tripping off line

[SparkyPete]

When we have a distribution transformer clear the system due to fault indications on the transformer, we test the cover gas head space before we perform any testing on the transformer. The gas tester tests for hydrogen and level is given out in percent LEL. What is your process for purging the head space of hydrogen gas and what is an acceptable limit of hydrogen concentration before performing tests? The tests we start off with is meggar, ratio and TTR

 

[RRaghunath]

SparkyPete,
The term 'Purging' is not used with transformers. The oil is degassed / dried using an transformer oil processing plant to remove the dissolved gases and moisture (if any) as well as other impurities.
Before that, since you are finding H2 in the gasses evolved from the transformer oil, you may want to inspect the transformer to diagnose the cause of gasses. You may also want to have DGA done on an oil sample for identifying the gasses in detail with the individual gas concentration levels.
It is not recommended to energise the transformer ithout identifying and addressing the underlying cause.

 

[SparkyPete]

We also do DGA samples but the question is removing hi hydrogen concentration in the gas headspace to enable us to perform transformer testing?

 

[DTR2011]

How about purging the space with nitrogen.

 

[waross]

How about purging the space with nitrogen.

Or the heavier CO[sup]2[/sup], admitted low while the H[sup]2[/sup] is drawn off high.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[waross]

This is what happened when a generator was improperly purged of hydrogen.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[SparkyPete]

Waross,
That’s exactly what we want to prevent. I want to know what the industry thinks is a safe percentage of H2 gas in the head space before testing. Also we fill the head space with N2 to 8-10lbs through the 1/4”pipe fill valve and regulator and then vent through the same pipe and test for H2.

 

[Palletjack]

Why is the transformer creating hydrogen in the first place?
Your XF overloaded?
Oil supersaturated and creating gas bubbles?
Partial discharge an issue?

I believe I would try to find the underlying cause before I worry about just purging and replacing an N2 blanket

 

[mc5w]

By the way, some power plant generators are cooled with pressurized hydrogen because it is a very efficient heat transfer fluid both because of its ability to convey heat and it requires less power to blow it around than air. Also, hydrogen without any oxygen or moisture protects the generator from moisture and oxygen degradation ( rust, etc. ) .

I am u too late. See you next week.

 

[prc]

Sparkeypete, It looks like your transformer failed and the extent of failure is not known to you. The arcing must have produced hydrogen and other combustible hydrocarbon gases. In power transformers, it is a general guideline never to start low voltage testing immediately after any low impedance fault inside the transformer.

https://www.linkedin.com/pulse/a38-how-prevent-power-transformer-accidents-p-ramachandran

In distribution transformers, energy levels will be low and chances of excess combustible gases are low. My suggestion will be to purge out nitrogen and do fresh gas filling if you detect even slight levels of hydrogen and other gases. Wait for a couple of days before testing.

 

[stevenal]

While hydrogen in the gas space is not a good sign, why do you wish to purge it prior to testing? Hydrogen and nitrogen is not an explosive mixture. Do you have reason to believe oxygen is present?

 

[prc]

Nitrogen or air will dissolve in oil and transformers in service may contain 8-10 % dissolved air in oil. In nitrogen-sealed transformers chances of dissolved oxygen is remote but purging nitrogen may be an extra safety margin.

 

[unclebob]

Not only H2 is a flammable gas. CO, methane, C2H2, C2H4 are too. Your last DGA should show a % value of combustible gas in the oil sample.

 

[FacEngrPE]

Rule of thumb is 10% of the LEL. Devices measuring % LEL are not sensitive to the particular gases being measured.

https://safels.com/19-facts-you-should-know-about-lel-monitor-and-lel-meter/

I would consider energizing a faulted transformer risky, even with testing devices risky. Follow the advice above please.