Lincoln Street Substation Transformer Explosion Burbank, CA - 04/10/2020 8

Seems like smoke is fuming along the 12 kV or (16 kV?) bus and some cable terminations suggesting the fault is somewhere downstream and not detected or cleared by any of the upstream or downstream breakers!...

The question is again where is the primary protection? I guess this is a 132 kV SS?, if the Transformer is delta-wye and that is a single phase fault at the wye side, the delta side will still get some component to sense and trip.

I am interested in reading the fault report, when available.

BTW, around 0:03/0:04 I see a flash to the left. Can I assume that 66kv primary got into the 12kv secondary when the transformer exploded? Just wondering about the extra flash there.

@Power0020: I'm guessing the protection is there, but for some reason it never activated or the DTT signal never got received at the sub-transmission supply end.

Up close video:

Transformer fire normally is not due to any sustained fault on secondary side. It can happen due to low impedance faults inside the transformer ie faults on primary line end of winding so that fault current will not be mitigated by the reactance of windings. The entire fault current of the primary grid will be collapsing inside the tank. Such high energy flow will disintegrate oil, releasing huge volume of combustible hydrocarbon gases at >1000 C. Even before conventional relays pick up the fault, the dynamic pressure wave will shatter the tank weld releasing hot gases. These gases when coming in contact with oxygen in air catch fire, setting fire to oil too.

If fuses are used for protection, two types of fuses are put in parallel on primary side- expulsion fuse ( to protect from over loads and secondary side faults) and current limiting fuses . These later fuses will have very high settings and open out during low impedance faults. These are fast acting and open out during the first peak of current thereby limiting the energy released inside the tank. This will prevent a tank rupture and consequent transformer fire.

Where is Burbank, near Hollywood Studios?

Hi DPC,

Yes, the city of Burbank is located in CA around several movie studios and in close proximity north to the Hollywood sign.

The Lincoln substation is one of the 5 switching station operated by the city of Burbank Water and Power (BWP) municipality powered by local generation and import energy from LADWP. BWP also operates 14 distribution substations,and 138 distribution feeders wit a Summer peak electricity demand of about 320 megawatts. [sub]If anyone is interested to see the site of the station the approximate GPS coordinates are: (34.188575, -118.335159).[/sub]

The Lincoln substation operates with a sub-transmission voltage of 69 kV, 34.5 kV. The failed transformer #1, 69kV/12.47kV creates significant damage to the cable buses and the nearby building that houses a lineup of metal-clad switchgear with upgraded protection and control system in recent years similar to the following Link.

[sub]HELP !!: I do have a few other pictorial information but unable to share it since I can not upload it to Eng-Tips System.[highlight #FCE94F] If anyone knows how to fix that or how to get help from the forum moderator, please let me know.
[/highlight][/sub]

To upload images, you at least need to allow Javascript access to Cloudinary.com. If you are using NoScript it cannot upload with that shut off. It may also require access to cloudflare.com and mathjax.org; try adding them in that order.

@PRC- you describe a padmount transformer. This is a medium sized power transformer, probably somewhere in the 30MVA range. It does not have fuses by the looks of it, instead breaker protection.

Transformer tank rupture can certainly occur from an internal bolted fault and that may be behind the majority of catastrophic failures- but picture a scenario where the relaying has failed and a secondary short circuit occurs outside the transformer. The profound overload will heat the oil until it boils over igniting.

Cuky2000 said:

a lineup of metal-clad switchgear with upgraded protection and control system in recent years similar to the following Link.

Click to expand...

I wonder if that could have caused it. Also wonder if there was any IEC-61850 involved between what would normally might have been copper.


Try uploading the images to IMGUR, then post the link here.

@PRC: I'm confused why you say this or why you have a star. There is clearly a sustained external 12kv fault going on for some time. Any primary 69kv fuses would have blown long before. This looks like a protective relaying failure.

Cucky2000,Thank you for the info. It seems you mistook me for dpc, but I will not complain as dpc is much more famous and well respected in this forum.(though I joined this forum earlier than him!!)
Frankly I was bit scared. Some 20 years back, I had supplied from India, a 56 MVA 34 kV unit to City of Burbank, supplying power to Hollywood. Those days my staff at shop floor used to claim Hollywood stars are shining because of their transformer! I do not know the exact location and I have never been to Los Angeles. (though self seen bit of Silicon Valley & San Francisco)

Mbrooke-I have been studying Transformer Fires for several decades and what I have written is based on my actual experience. Please see a small write up that I wrote some years back . May be useful to Transformer engineers to avoid accidents and fiascos in the field. All these recommendations are based on my actual field experience.

I strongly suggest you to go through a small 139 page book by CIGRE on Transformer fires-Technical Brochure No.537-2013 "Guide for Transformer Safety Practice" It gives a lot of info on cause and mitigation measures for Transformer Fires. IEEE Std C57.156-2016 Tank Rupture _Mitigation is also a good source to understand failure modes leading to transformer fires. If you become a CGRE member (annual fee less than 100 USD) you can down load all their technical Brochures free of charge ( more than 100,000 pages of technical literature on Power Generation and Transmission)
Your thinking long duration secondary fault will "boil" the oil inside the tank and it will start burning is simply not true. Remember Thermal time constant of an oil filled unit is 2-3 hours ! Any arcing inside the transformer ( say from interturn faults) will not cause oil to catch fire though at the core of arc, temperature may be more than 3000 C ) Remember we were using oil as an arc quenching medium in oil circuit breakers !

So you are trying to tell me a transformer will not catch fire if short circuited indefinitely?

Here's an "internal" fault - stray flux.

The wall was heated by eddy currents until the oil boiled, lifted the relief valve. the oil vapor ignited upon exposure to the atmosphere, burning the exterior of the transformer to destruction.

When untanked at the factory, the windings were intact. There was evidence of charring on the barrier board between the winding and the tank wall. Nobody at the factory saw the failure mode, so we replaced the transformer with an identical unit.

Five years later the replacement transformer started the same behaviour but this time an observant operator noticed the paint discoloring on the transformer wall. Based on the discoloration of the paint and the charring of the PVC jacket of flex conduit in contact with the hot spot on the wall, temperatures exceeded 250C.

We took the transformer out of service, the supplier bought my finding of stray flux issues, and rebuilt the transformer under warranty, changing from a three-legged to a five-legged core.

At no time during these events did transformer currents come close to pickup of the overcurrent elements.

old field guy

oldfieldguy- Very interesting case; was the original unit a Y-Y unit without tertiary winding? MVA rating? Y-Y were solidly grounded or un grounded or grounded through resistor? Was there unbalanced loading between phases?

oldfieldguy, I have seen aluminium plates covering the inside of the transformer tank walls in large transformers. These are supposed to provide low resistance path for eddy currents.
I thought 5-legged core is for reducing the height of large transformers. It seems, from your details, that it can also reduce the leakage flux inside the transformer.
Interesting share.

@PRC, in your opinion, what happened at Burbank?

@prc-

Bingo! 34.5-13.8 Y-Y. After I practically had to beat an vendor engineer over the head to get him to acknowledge the failure mode, somebody in their shop announced that it was a not-too-uncommon issue with that configuration.

The re-engineered replacement has a five-legged core and a tertiary winding.

It's a fun situation. The transformer feeds a natural gas compressor station - 7000 HP on a VFD. If the unit is running, we might use 5000 kVA, but if the unit is down, we're running HVAC and lighting loads - maybe 20 kVA.

old field guy

oilfieldguy,
From the photograph that you posted, it looks like a 5-6 MVA Distribution Transformer. In these transformers there is no chance of stray flux heating of tanks, because such stray flux volume is negligible. Stray flux is the leakage flux from windings (zero at no-load and maximum at full load) that may impinge tank and core creating local heating. Normally this heating is mild even in large transformers. But tank is shielded in large units by silicon steel laminations (magnetic shielding) or by copper or aluminum sheets(electro-magnetic shielding) to reduce the stray losses created in metal by these fluxes.( 10-35 % of I2R losses)

But in large distribution transformers of YNyn connection (this connection used to reduce ferro-resonance) tank heating can occur due to zero sequence exciting flux from core( 1978-Distribution Transformer Application Considerations by Westinghouse presented at Power System District Engineers ) With this connection and in case fuse is opened in one phase, a zero sequence voltage of about 30 % of winding line to ground voltage will be impressed on transformer creating 30 % exciting zero sequence flux in core. These zero sequence fluxes in three limbs, being unidirectional, can return only through tank and heating it up. By using a 4 limb or 5 limb core, we can provide path for this zero sequence flux and prevent tank heating. The above famous paper mentions cases of tank heating and blistering of painting due to this type of zero sequence flux.

But this is the first time a tank fire attributed to tank heating is seen.