Many transformer labs will be familiar with processing emergency samples, but usually it is a small batch of 1 or 2 at a time that are actually an emergency. However, I was surprised to have 27 samples arrive in one evening as an emergency.
It had been bad weather and there had been a few storms over the previous 24 hours in the UK. So bad that 7 customers in fact sent emergency samples at once because of lightning strikes, environmental damage, flooding etc all to check the condition of the units and confirm they were good to go before bringing back online. The lights were literally waiting on us to be able to switch on.
To describe all of these in one post might be overkill so let’s cover two of these stories which could have had a gruesome ending fitting of Halloween.
The sample of Dr Frank N Stein
Frank works in power generation research and development. His business has sudden high demands for energy from relatively low base load. In fact sometimes he needs to go from near nothing to peak load almost instantly. Whilst testing one of his new projects, which requires very high energy consumption during a thunderstorm he found his electrobiochemical process had not worked. There had been a lot of lightning and he suspected his power distribution at the facility may have been hit.
Frank knew for when failure is not an option he needed to call Oil Analysis Laboratories with its TransDGA programme.
He telephoned the lab and said his 4 samples would be at the lab at about 10.30pm as he was going to have the sample driven to us through the evening.
The main test of significance was the dissolved gas analysis (DGA) which detected a slightly high hydrogen in one sample. Hydrogen is seen in most transformer faults to some degree but 3 key causes are:
- Partial discharges, where discharges occur between the insulating medium e.g. within gas bubbles etc.
- Stray gassing, a relatively modern phenomenon in its discovery in that oils can spontaneously generate gases without serious faults.
- Lightning strikes, but can also be linked to cases of re-energising and loading changes to give a similar effect.
In this case the Hydrogen rise didn’t seem particularly high compared to historical trended rises and the customer was told if no other factors appeared abnormal it was safe to re-energise. They were asked to sample again every 2 weeks for the next 2 months just to keep an eye on the hydrogen which actually began to fall after the second sample.
The case of D. Racula
The next customer was one who works in the storage of medical products. The facility holds large quantities of red liquid products and they have to be constantly refrigerated. Mr Racula works night shifts, which has no windows and hence no natural lighting. His facility uses constant electric lighting. So his facility’s load is fairly constant, but has a high energy consumption. He has a backup generator on site to ensure constant energy load as he needs 24/7/365 power.
That evening severe weather conditions had caused flooding on site. The power had cut about 6pm. The UPSs kept the refrigeration going uninterrupted but the lights went out for about a minute before the generator kicked in. He had until daylight before the fuel in the generator would need to be refuelled and any electrical fixes made so he needed to work out what was wrong with the transformer before dawn.
He went to the transformer and took a sample. The area where the transformer was situated was raised so protected from the flooding on site.
However when he took the sample he noted even after flushing the sample point well there was lot of strange black bits in the sample.
Mr Racula knew that when there is something strange in your transformer oil, who you going to call? Oil Analysis Laboratories! And that’s what he did.
The laboratory tested the sample and found the breakdown voltage was 18kV, with over 30kV being the recommended voltage and usually the previous samples had over 50kV. So this was a significant drop. The IEC method for breakdown runs the test 6 times, but we repeat the test of 6 a total of 3 times so have an average of 18 different results to make sure we have the most accurate breakdown voltage to quote to the customer.
The water content of the sample was found to be 36ppm, usually <10ppm and an alarm limit of <30ppm. The particle count of the sample was 22/19/16 with the code usually around 17/15/12, so it was a total of ~16 times dirtier than usual.
The dissolved gas analysis found nothing unusual though suggesting nothing was electrically wrong although the oil was very contaminated. Speaking to Mr Racula he confirmed the system had not been near the flood water, which we suggested checking the breather condition as that would be the most likely point of entry. Indeed the breather was found to be in a very poor state with the desiccant completely soaked and in need of replacing.
The customer replaced the breather and contacted the filter supplier who popped round the following morning to perform some offline filtration on the system with a water removal unit. Strangely enough Mr Racula had a pressing engagement and couldn’t come outside to meet the filter supplier during the day whilst they performed the filtration work, but popped out after dusk to inspect the work.
More real than you think.
Although the names might have been slightly changed for dramatic effect for this spooky tale, we did receive 27 emergency transformer samples in one day. Below is the picture I took at 3am of the lab instruments hard at work processing the last of those samples before going to get some sleep for a few hours ready to then review the last of the data produced and telephone through the results. One of the customers did require refrigeration of medical supplies, similar to Mr D Racula. The sample of the real Dr Frank N Stein was from a suspected lightning strike sample from a chemical manufacturing customer who sometimes needs to go to peak load very fast and at short notice.
Trick or treat?
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