Kjell Carrander

03.02.2009 Brannforum 2009

B

i

Sikkerhetsløsninger

Hvordan sikre seg mot

sprengning av

transformatorkassen?

How to avoid transformer

tank rupture?

Kjell Carrander

Brannforum

Stavanger

2009-02-03

Agenda

Fire status today

Fire triangle

Tank rupture process

Cigré brochure

Pressure simulations

Experience HQ, SEBK, GE

Conclusions

Brannforum

2009

Background … fires

Not too many explosions and fires during latest 20 years…

…but many in the last 2 years.

Even 10 - 20 fires per year are resulting big impacts in damages,

revenues and capital losses plus public attentions.

Big impact for the owners if it happens

Transformer origin or victim of a fire

The concerns for fires and its consequences are increasing

Many sessions and conferences in all countries

CIGRE WG A2.33 Transformer Fire Safety Practices

Many Power Plants have Fire Protection high on the agenda

Insurance companies have started to put questions

Brannforum

2009

Fire triangleBrannforum

2009

Tank rupture - fire process

Example

An electrical fault occurs

Arc is created, less than 1 μs, temperature > 3000 ºC

Oil displacement

Oil cracking – gas generation

Pressure wave: 1) shock (fast) wave 2) secondary (slow) wave

Peak pressure of the shock wave: >10-20 bar

Peak pressure of the secondary wave depends on position

Tank opening (shock wave), bulging (secondary wave)

If tank ruptures, then . . .

Liquid is spilled

Air is entering the tank

Many options: Breaker operates, Arc is melting the conductor

Liquid level is lowered, conductor still hot, ignites a fire

Brannforum

2009

Cigré Technical Brochure

Working Group within Cigré (WG A2.33)

”Transformer Fire Protection Practice”

Technical Brochure ready 2010

Content

1. General about fire risks and different types of transformers

2. Different risks with different types of transformers

3. Bushings

4. Tap Changers

5. Pressure processes

6. Substation types

7. Prevention types

8. Tank design

9. Damage control, substation design

Brannforum

2009

Pressure simulation 1Brannforum

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Pressure simulation 2Brannforum

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Pressure simulation 3Brannforum

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Pressure simulation 4Brannforum

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Pressure simulation 5 Brannforum

2009

Tank openings by SIMULATIONS

Once the pressure wave reaches the tank wall, if the wave is strong enough, it

breaks the wall and goes out

Parametric model

Tank rupture processBrannforum

2009

Tank opening

The tank breaks when a strong shock wave hits the wall. The opening process can be subdivided in two parts:

Standard first opening of the tankThe first opening is created by the shock wave which wants to flow out.

Opening until the break reaches the final shape The opening continuously expands because gas and oil flow out. It further expands until to reach the final shape..

Examples of first opening and final shape of the breaks

Level of Energy by 25 years of EXPERIENCE

The following results come from failure statistics of Hydro-Quebec over 25 years in their 735kV systems

175 failures resulted in 111 high energy arcs causing 44 tank ruptures and finally 18 fires

Brannforum

2009

ARC ENERGY (MJ) RUPTURE FIRE

1 No No

2.5 No No

8.5< < 13 Yes No

19< < 23 Yes Yes

20 Yes No

26< < 67 Yes Yes

94 Yes Yes

147 Yes No

Experience

COMPONENT FAULTS RUPTURES FIRES

HV bushing 41 19 13

Windings 57 21 3

Core 3 2 1

OLTC 2 1 0

Others 7 1 1

SEBK Tests with flashover in oil Brannforum

2009

GE 1976

Test with distribution transformers with air under the cover.

Measured 22 bar at the bottom at flashover and 1 bar in the air.

Hydro Quebec 2007

At the rupture of the tanks it was observed that 2/3 of the pressure

relief valves had not opened.

Brannforum

2009 Experience continued

ConclusionsBrannforum

2009

Thank you !