We can often see a large number of pebbles placed under some transformers, so what are these pebbles used for? Just for aesthetics?
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Our common transformers are divided into dry-type transformers and oil-immersed transformers;
Oil-immersed transformers use oil as the main insulation method of the transformer and rely on oil as the cooling medium, such as oil-immersed self-cooling, oil-immersed air-cooling, oil-immersed water cooling and forced oil circulation. The main components of the transformer include core, winding, oil tank, oil pillow, breather, explosion-proof pipe (pressure release valve), radiator, insulating bushing, tap changer, gas relay, thermometer, oil purifier, etc.
Compared with dry-type transformers, oil-immersed transformers have the characteristics of low cost, easy maintenance, and can solve the problem of large-capacity heat dissipation and high-voltage insulation problems of the transformer. However, because the cooling oil of oil-immersed transformers is flammable, it leads to oil-immersed transformers. Transformers have inherent disadvantages, that is, they are flammable and explosive.
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At this time, a series of components such as pebbles came into being; this part under the transformer is usually called the oil unloading pool or oil unloading pit (or similar names), leading to the accident oil pit or accident oil pool.
When an accident occurs, such as oil injection or explosion, the oil from the transformer will be discharged into the oil unloading pit and then flow to the accident oil pool.
Some pools have grilles, and some do not. If the grille is made, the pebbles are placed on the grille; if the grille is not made, the pebbles are placed in the oil unloading pit. Whether to use a barrier or not depends on the transformer type, capacity, and voltage level. There are regulations in this regard.
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When placing pebbles under the oil-immersed transformer, the following seven factors are mainly considered:
1. After the transformer is used for a long time, the parts may have problems such as aging and leakage. Placing a large number of pebbles can absorb the transformer oil leakage and allow the transformer oil to flow back to the accident oil pool smoothly, reducing accidents;
2. In the event of an accident, cobblestones can prevent oil in the transformer from splashing and explosion.
3. When there is an explosion and fire, cobblestones can play an isolation role to prevent the fire from spreading to the ground, which is helpful for extinguishing the fire.
4. Slight cooling effect. When the temperature of the transformer is too high, you can use pebbles to cool it.
5. Pebbles are insulated to facilitate maintenance and inspection by operating personnel.
6. Pebbles have a shock-absorbing effect. The function is the same as the stones on the railway, which can add a layer of buffering.
7. Prevent weeds from growing.
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# There are clear requirements in fire regulations:
1. For outdoor transformers and other oil-immersed electrical equipment with a single oil volume of more than 1,000kg, oil storage pits and oil drainage facilities should be installed.
2. The volume of the oil storage pit should be determined to accommodate 100% of the equipment oil volume or 20% of the equipment oil volume. When an oil storage pit is set up according to 20% of the equipment's oil volume, an oil drain pipe should be installed at the bottom of the pit to drain the accident oil into the accident oil storage pit. The inner diameter of the oil drain pipe should not be less than 100mm. The oil should be able to be drained quickly in the event of an accident. An iron grid filter should be installed at the pipe mouth.
3. The oil storage pit should be equipped with a grid with a net distance of no more than 40mm. The upper part of the grid should be paved with pebbles, the thickness of which should be no less than 250mm, and the particle size of the pebbles should be 50 to 80mm.
When a total accident oil pit is set up, its volume should be determined based on the entire oil volume of the largest piece of oil-filled electrical equipment. When installing a fixed water spray fire extinguishing device, the volume of the total accident oil pit should also consider the amount of water spray and leave a certain margin.
Why is there water in the accident oil pool?
So what exactly is an accident oil pool?
Let me start with a little background.
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At present, among the main electrical equipment in substations,
Oil-immersed power transformer
Be widely used.
When encountering a transformer accident,
In a short period of time,
A large amount of mineral oil splashed out from the transformer.
Falling around.
If special protective measures are not taken,
First, it causes pollution to the substation and surrounding environment;
Second, accidental fuel injection can easily cause a fire.
A large amount of leaked fuel injection will undoubtedly amplify the accident.
therefore,
Whether it is environmental protection,
Or consider it from aspects such as fire safety?
This part of the oil must be
Safely move to a dedicated facility,
Isolate it from external flammable materials,
Cool down and store,
To be separated and recycled in the future,
Process and reuse.
Generally, the accident oil pool in a substation looks like this.
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In the photo above, the 200 cubic meters written on the nameplate is the total volume of the accident oil pool.
It is not the maximum oil storage volume of the accident oil pool~
The entrance to the accident oil pool,
With the main transformer base oil pit,
That is, the cobblestones underneath the transformers are connected.
The oil from the main transformer passes through the oil drain pipe
Transported to the accident oil pool.
So see here
I guess many people will ask again,
We have all seen the pebbles under the transformer;
But why cobblestones at all?
Is it okay to use gold, silver and jewelry?
Okay, let me explain again,
First of all, there is not that much money. . . . .
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Let's get down to business,
The pebbles actually play an isolation role.
When a transformer catches fire,
It can help reduce the intensity of the fire.
Secondly
High temperature transformer oil
After the pebbles have cooled,
It can also reduce the intensity of the fire.
Good for putting out fires.
Okay, so what is the principle of the accident oil pool?
Let us first take a look at a cross-sectional view of the accident oil pool.
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simply put,
The accident oil pool is a connector.
In the absence of accident oil,
If there is water in the accident oil pool,
The water levels in both pools AB are the same.
Oil and water have different densities,
Immiscible with each other and able to separate on their own.
Since oil is less dense than water,
So oil will float on water
(I believe anyone who can cook knows this)
Once accident oil is discharged into the accident oil pool,
The oil will be on the main reservoir side,
Since pressure is generated on the water surface of pool A,
Forcing water through the drain to the other side,
Pool B moves,
As the amount of accident oil increases,
The water will be forced into the sewage well.
If you still can't understand it,
no problem,
Never doubt your own IQ,
After all, it is indeed a bit difficult to pronounce.
So let's use pictures below
To be concise and clear
Let's describe this process~
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The initial state of the accident oil pool contains water.
Main transformer, high resistance to fire,
Start the sprinkler system,
A large amount of insulating oil and oil-water mixture
Flow into Pool A from the entrance.
After standing and separation in pool A,
Oil floats at the top of pool A and water sinks at the bottom.
Under the action of oil pressure,
Pass through the water outlet and enter Pool B.
Discharge through the outlet.
Finally, we reach the following Buddhist state:
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This will keep the oil in pool A,
Convenient for analysis and utilization after the accident.
If there is no water in the accident oil pool,
A large amount of oil leakage occurred first in the main transformer and high resistance.
A large amount of insulating oil enters the oil pool,
Then the main transformer and high resistance caught fire.
Start the water sprinkler system,
A large amount of oil-water mixture enters pool A.
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After standing and separation in pool A,
The water sinks to the bottom and the oil floats in the upper part of pool A.
But the small amount of oil in the upper part of pool B
Calculated based on the oil pool of Dieling Station, the maximum is about 1.7m³
It will eventually be discharged from the outlet into the surrounding environment.
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After the oil in pool B is drained,
And finally reached the previous one
A very Buddhist state (as shown below),
Meet the design requirements.
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There should always be water in the pool.
According to GB 50229-2006
"Code for Fire Protection Design of Thermal Power Plants and Substations"
Regulation:
When equipped with oil-water separation measures
Total accident oil storage tank,
Its capacity should be determined based on 60% of the capacity of a fuel tank.
It means this accident oil pool
I should be able to let it go
60% of a transformer is oil.
So let's do the math:
For example:
The single-phase oil volume of main transformers in DL stations #2 and #3 is 65t.
The single-phase oil volume of #4 main transformer is 60.5t.
The high-resistance oil volume is even less, 13t.
Therefore, the #2 and #3 main transformer phases are used as the standard for calculation.
Density of transformer oil
Through investigation, it can be found that it is 0.895kg/m³.
According to ρ=m/V, 65t of oil is 72.6m³.
The 60% capacity of the tank is 43.56m³.
Accident oil pool at DL station
The maximum oil storage volume is calculated by
is 47.55m³>43.56m³,
Therefore it complies with the standard.
After seeing this, I believe everyone already understands
Have you learned the structure and principle of the accident oil pool?
