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 1
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Pressure simulation 2
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Pressure simulation 3
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Pressure simulation 4
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Pressure simulation 5
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
Brannforum 2009
Tank rupture process
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 tank The 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
Brannforum 2009
Experience
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 ARC ENERGY (MJ)
RUPTURE
FIRE
1
No
No
2.5
No
No
8.5< < 13
Yes
No
19<
Yes
Yes
20
Yes
No
26< < 67
Yes
Yes
94
Yes
Yes
147
Yes
No
< 23
175 failures resulted in 111 high energy arcs causing 44 tank ruptures and finally 18 fires 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
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SEBK Tests with flashover in oil
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Experience continued 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.
