An SDG&E trailer (shown at extreme left) is being used to suppress the project training fire at the Flammable Liquid Firefighting School in Texas.

SDG&E Responds to Transformer Fires

Aug. 1, 2013
Utility implements emergency response plan to prepare for potential equipment fires in its service territory.

A transformer burst out in flames at a San Diego Gas & Electric (SDG&E) power plant three years ago. The 230-kV transformer, which contained about 15,000 gallons of combustible mineral oil, was quickly consumed by the fire at the Palomar Energy Power Plant facility. Following this event, the utility worked closely with the local fire jurisdiction to respond rapidly to the situation, implement a plan of action, and determine how to best respond to a future emergency. As a result of lessons learned in the transformer fire, the utility modified its emergency response plan.

Learning from Past Experience

After the fire, SDG&E learned that several factors prevented the aggressive and timely extinguishing of the transformer fire. Through an internal and external after-action review of the incident, the utility found it needed to improve its pre-emergency response planning, have proper suppressants for flammable liquids in large enough quantities readily available and provide increased training in this specialized form of fire suppression.

At the time of the incident, SDG&E didn’t have Class B foam and dry chemical extinguishing agents in a large enough quantity on site or anywhere close to the fire. Also, the utility discovered that the local firefighting community had limited experience or training with this low-frequency but high-risk event.

A crash-rescue truck from a nearby marine base was unsuccessful at extinguishing the Palomar Energy transformer fire.

A few hours after the fire began, a crash-rescue truck from Camp Pendleton Marine base arrived on the scene. Two failed attempts at suppression led to the decision to let the fire free-burn until the oil was gone. The primary firefighting tactic was to prevent additional damage with exposure protection. The fire burned for more than 24 hours before the flammable liquid fire was over, however Class A combustibles within the transformer continued to burn well beyond that time.

The blast walls, designed to protect adjacent equipment, were effective but very close to compromise at the fire’s end and required total replacement. Pollutants and air quality were also a constant concern, and the equipment received collateral damage as a result of the fire.

Creating a Response Team

After much thought, research and consideration, SDG&E issued a contract for Industrial Fire Brigade (IFB) services on a full-time basis. This program incorporates aspects to mitigate each concern surfaced in the after-action review of the Palomar Energy event.

The 13 full-time participants in a specialty fire academy focused on flammable liquid firefighting and, more specifically, electrical equipment-related fires of this type. Members of the team also attended a formal Flammable Liquid Firefighting School at a Texas A&M extension facility.

SDG&E also tasked the IFB with creating comprehensive pre-emergency response plans for high-asset facilities. The utility has just passed the one-year anniversary of working with the IFB, and it has already played a key role in five significant electrical equipment-related fire incidents.

To promote safer incidents, the utility invites its IFB personnel to attend substation safety meetings, train together with linemen at its mock substation and make field visits to substations with the crews during routine maintenance activities. The interchange of knowledge between the two groups has heightened their skills and, more importantly, created an increasing trust factor for each other’s expertise.

The Palomar Energy transformer fire free-burned throughout the night.

In addition, SDG&E purchased four specialized trailers with 300 gal of Class B foam, 500# of Purple-K dry chemical extinguishing agent, a 500-gpm self-educting monitor, and two self-educting foam hand lines with two 4-inch supply line intakes. The utility strategically placed the trailers throughout the service territory to allow for sufficient supply in the event of any incident.

Minimizing and Containing Oil Fires

SDG&E not only purchased trailers and contracted with an IFB, but the utility also took a close look at the cause of the fires at its substations. The utility discovered that more often than not, these fires were due to equipment filled with oil instead of insulation, which can be easily isolated and put out.

With advent of SF6 gas as a replacement medium for oil, most of the legacy oil-filled equipment such as circuit breakers have been converted to SF6 gas over the years. Other equipment such as oil bushings, potential transformers and oil-filled pot heads have been replaced mostly with solid insulation material. This has contributed to drastically lowering the risk of oil fires.

On the other hand, transformers still use oil for insulation and because of to sheer volume, it could be cause for concern, says William Assurian, a principal engineer for SDG&E’s electric transmission and distribution engineering group.

“At SDG&E, we try to minimize the risk of transformer oil fire by incorporating safety features in design of our facilities,” he says.

For example, the utility incorporates setbacks from the property line to the substation fence or wall and also inside the fence between the transformers. The engineers also design the transformer foundations with a oil-containment moat around them to collect the running oil in case of an unexpected rupture or fast leak. The oil containment is normally compensated to account for rain water.

The company also installs firewalls to separate large transmission class transformers from each other and other adjacent equipment. Other design features include transformer oil level gage and pressure sensors, which will produce an alarm or trip and isolate the transformer if the oil level inside the tank gets below a certain level or the internal pressure increases suddenly.

At newer substations, SDG&E has installed cameras to look for fire aftermath of an incident. These measures have been proven successful in case of a few oil fire incidents that have been experienced. For example, SDG&E had another incident in early 2013. In case of the recent Miguel transformer fire, the fire walls and the oil containment performed as expected; fire was contained with no damage to adjacent equipment and caused no safety hazard.

Responding to Another Emergency

The fire at the 500-kV Miguel substation happened in February 2013. On Valentine’s Day, a transformer with more than 26,000 gal of combustible mineral oil erupted into flames. This was a very similar event to the previous one at Palomar Energy, but only with much more oil involved.

The fire response was initiated and with concurrence from the jurisdictional fire agency. The SDG&E IFB was deployed with personnel, equipment and two foam firefighting trailers. A unified command was established with the local fire chief and an SDG&E supervisor in joint leadership.

The utility then held a comprehensive safety briefing with all in agreement what would take place for safety purposes prior to suppression taking place. De-energization and grounding for safety actually took longer than expected but was never compromised.

At about three hours after ignition, following an additional safety briefing, SDG&E initiated suppression action. After a brief problem with the water supply and a minor adjustment in suppression tactics, the fire was completely knocked down in less than one hour with salvage and overhaul completed shortly thereafter.

The county air quality personnel responded and had no concerns regarding pollutants in the atmosphere or containment breach or run-off. The blast wall was also fully effective and required no replacement or repair, and no peripheral damage or fire extension occurred.

Although some new minor lessons learned, SDG&E considered it a completely successful event, validating much of the course and direction taken by the company post-Palomar Energy fire. The utility will continue to integrate new lessons learned and is confident that its skills and abilities for these types of events will be all the better for it in the future.

Hal Mortier ([email protected]) is the fire program manager for San Diego Gas & Electric. He has more than 40 years of wildland fire experience.

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