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Ageing power grid: the importance of Fire Protection systems for electrical transformers

As modern society takes uninterrupted electricity supply for granted, electrical utility providers are increasingly measured by the reliability of the infrastructure used to deliver power to consumers. In the last 6 months, hot weather conditions and high power demand resulted in massive outages in multiple suburbs all around WA. In response to these outages that affected over 34,000 households and businesses last summer, Western Power will be investing about $4.6 billion in the network in the five years to 2027*. The massive capital investment program will aim to replace and modernise an ageing network, including power transformers.*

* ref. ‘Five years, $4.6bn for ageing grid’ Business News article by Matt Mckenzie, 14/03/2022

 

What are electrical transformers and where are they used?

They are an essential piece of our electrical infrastructure for the transmission, distribution, and utilisation of alternating current electric power to domestic or commercial users.

Power transformers are used to transfer energy between different circuits, either increasing (stepping up) or reducing (stepping down) the voltage. They are designed to reduce the voltage of conventional power circuits to operate low-voltage devices and to raise the voltage from electric generators so that electric power can be transmitted over long distances. 

Transformers are a critical part of electrical distribution; however, as they often contain oil as an insulator and coolant, fire and blast protection is required in the unlikely event of a malfunction.

 

What happens when a transformer fails?

When a transformer fails, it can have catastrophic consequences and lead to a major power blackout. If the failure was not caused by an existing fire, the potential for a new fire resulting from the failure is extremely high. 

A power substation consists of multiple transformer tanks, each containing a large volume of extremely flammable mineral oil. The ignition of the transformer oil can generate heat and pressure sufficient to cause the tank to rupture.

Once a rupture has occurred, air rushes into the tank and the oil explodes resulting in a blast of intense radiation scattering flaming oil, steel shrapnel, gaseous decomposition products, solid insulation, and molten conductors onto the surrounding area.

The effect of the explosion and radiation is instantaneous and can ignite neighbouring transformers more than 15 metres from the initial fire.

 

image of a power plant fire due to a transformer explosion

 

What are the main causes of transformer explosions and burns?

There might be several factors that can trigger a transformer failure, including electrical failure, insulation deterioration, line surges, overloading, material failure, and oil contamination.

Ageing power plants have higher risks of transformer explosions as a portion of the power transformers in service are often in poor or bad condition, needing replacement or refurbishment due to age and other factors.

Another reason why transformers explode and burn is accidents caused by lightning strikes and other extreme weather conditions such as strong winds, bushfires and rains. Lightning strikes can often damage the wiring and transformer equipment, causing it to overload and explode. Extreme bad weather conditions such as strong winds, bushfires and rains can cause trees to fall on transformers, causing explosions.

When damage occurs in a transformer, there can be an overload in the supply of electricity flowing into the transformer or an overheating of insulation fluid (mineral oil) past its flash point or fire point.

 

What are the fire safety regulations in power substations?

All substation and high voltage installations in Australia must comply with the Australian Standards, specifically AS2067:(Substations and high voltage installations exceeding 1 kV). 

The Australian Standard defines the fire risk zones and safety measures required around the transformer compound.  Fire resistance level (FRL) walls and separation distance (clearance) are two mitigation strategies commonly utilised in the industry. 

The Australian Standard also provides the minimum separation distance required between transformers and other buildings or equipment. The separation distance is affected by the following factors:

  • Installation location – indoor or outdoor,
  • Volume of transformer insulating liquid,
  • Fire Resistance Level of building, and
  • Type of transformer.


Fire Barrier**
To reduce the size of the fire risk zone and mitigate the fire risk associated with an electricity network substation, a fire-rated barrier can be installed, to the following specification:

  • A 2-hour fire-rated barrier (FRL 120/120/120) adjacent to the building,
  • The vertical extent of the fire barrier is required to be 7.5m tall; and
  • a minimum horizontal distance of 1.5m away from the transformer compound

**Ref ‘Western Power’s Asset Management System Distribution Substation Plant Manual 2019 Chapter 5 – Fire Clearances / 4. Transformer fire risk mitigation

 

How can transformer blasts be prevented in power substations?

While it’s difficult to determine whether or not a transformer explosion will occur, anticipating and planning for transformer failure is essential to minimise damage to other nearby transformers, equipment, structures and property. This can be achieved by installing appropriate fire protection systems for power stations.

In the past transformers were often placed adjacent to each other and without a firewall barrier in between. Nowadays, installing fire blast walls between transformers has become common practice to protect other transformers in the event of an explosion. 

High-voltage transformer fire barriers or transformer firewalls are outdoor countermeasures against cascading failures in an electric grid. The purpose of these barriers, like common fire barriers in building construction, is compartmentalisation of transformer fires, and compartmentalisation of transformer and bushing explosions―in which the fuel source of both fires and explosions is the transformer oil. 

Effective transformer firewalls must be made from materials that can withstand the intense heat and long duration of transformer oil fires. They must also be designed such that both thermal and mechanical requirements are met before, during, and after the fire.

 

Promat Durasteel barrier systems, a cost-effective and space-saving solution for electrical transformers

Commercial, industrial buildings and most large residential developments have electrical substations with power distribution transformers installed either within the building or in close proximity. Many are critical energy networks and with the implications of a total power failure to the banking, government, transport, defence, hospitals or business sectors, we can see how vital it is to install a system that maintains power supply, with little or no interruption.

Promat DURASTEEL® barriers are used to prevent catastrophic damage in the event of power transformer blasts and can also be installed between transformers, isolating the blast and minimising subsequent disruption. 

Promat DURASTEEL® barriers systems offer both cost and space savings when used on transformer applications. They are particularly effective when installed between transformers located adjacent to each other in the traditional manner, as they help isolate the blast and potential damage by preventing it from spreading via a domino effect.

The relatively lightweight of the Promat DURASTEEL® barriers allows simpler and smaller foundations to be used when compared to traditional poured concrete or concrete block barriers and this can generate significant cost savings. This is a particular benefit for retrofit transformer applications where space may be limited and existing underground service foundations cannot be disturbed. Promat DURASTEEL® barriers can also be demounted and reinstalled which greatly simplifies the task of transformer replacement.

Promat DURASTEEL® is a fully certified composite system of fibre-reinforced cement with punched steel sheets mechanically bonded to both outer surfaces. This delivers the strength and resistance required to withstand high impact and blast pressures, maintain structural integrity and provides up to four hours fire protection. It is an extremely durable design with high energy absorption which has testing to AS 1530: Part 4 and has been used extensively throughout the country over the last 25 years.

 


05 Apr 2022