Power transformer - gravel

[Jorge3pe]

You have often seen that there are gravels below transformer and around large Transformers, do you know what is the reason behind the same?, What standard request it? IEC, IEEE, NFPA?

 

[bacon4life]

Three kinds of rocks might be used:
1) Round, washed rock of about 3-4 cm is used for fire suppression. The there is enough space between the rocks that the whole volume of transformer oil will go below ground level, allowing an oil fire to be extinguished. With this design, there is a huge underground vault to contain the oil.

2) Large angular rock of 2-5 cm with minimal fines is used for a high resistive surface. The minimal contact area between rocks makes the surface have a high resistance, which helps protect works from step and touch potentials. Check out IEEE 80 for more info.

3) Normal gravel with fines (small particles) is good for walking/driving as well as for structural support. Sometimes normal gravel is incorrectly substituted for the other two kinds of rocks.

 

[thermionic1]

I've seen some installations where the rock is used as a berm, in conjunction with an underlying membrane as oil containment.

 

[Jorge3pe]

Bacon4life:
1) Round, washed rock of about 3-4 cm is used for fire suppression. The there is enough space between the rocks that the whole volume of transformer oil will go below ground level, allowing an oil fire to be extinguished. With this design, there is a huge underground vault to contain the oil.

Comment: It is the answer I need, but I need the standard or bibliography (IEC,NEC,IEE) that talk about the fire suppression.

 

[waross]

2) Large angular rock of 2-5 cm with minimal fines is used for a high resistive surface. The minimal contact area between rocks makes the surface have a high resistance, which helps protect works from step and touch potentials.

This is used as well for switching or equi-potential mats.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[RRaghunath]

I think IEC 61936 is the reference you are looking for.
"International Standard IEC 61936-1 has been prepared by IEC technical committee 99: System
engineering and erection of electrical power installations in systems with nominal voltages
above 1 kV a.c. and 1,5 kV d.c., particularly concerning safety aspects."

 

[prc]

The relevant standards are IEEE 979-2012 Guide for Substation Fires; IEEE 980-2021-Guide for Containment and Control of oil spills in Substations; CIGRE Brochure 537-2013 Transformer Fire Protection; IEC 61936-2021- Power Installation- Common Rules