2mx2m 11kV cable tunnel -ventilation method

[byju1982]

Hello friends!

I have 2m x 2m Power cable tunnel running for 300m under a road. It has 11kV cables arranged in trefoil on cable trays approx 50 numbers. What kind of ventillation system should I consider for this tunnel ?

Thank you !

 

[BenMacier]

Natural and weatherproof. Easy and simple, always.

* Finding a solution is great * Knowing how to implement it is fantastic * Believing it is the only one and best is naive ?

 

[byju1982]

Hi BenMacier,

Request to provide some more details. Since it is directly running under the road for 350m, so we are finding it difficult to plan the ventillation. Can the manholes provided for maintenance access be treated as ventillation points ?

Thank you !

 

[chicopee]

Your inquiry about a ventilation system for the tunnel appears that you have concerns about a temperature rise, high relative humidity or some hazardous vapors from underground. Can you explain your concern.

 

[byju1982]

Hi Chicopee,

My concern is about temperature rise and associated derating of cables.

Thank you.

 

[IRstuff]

How far down is the tunnel?

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[MintJulep]

It might be important to identify how much heat is generated in the tunnel.

It might be important to identify the highest allowable temperature inside the tunnel.

It might be important to identify the cooling media, and its initial temperature.

 

[LittleInch]

byju,

Your methods of cooling will vary depending on your requirements.

so work those out first.
How much power is being released as heat in your cables? - I2R calculation
Max temp you want to avoid?
Ambient air temperature?
Any other air entry / exit points on your 350m?
Space for any air trunking?
space available at the end for ventilation?
Does the space need to be suitable for personnel for regular access or only occasionally?
At depths of >1m the ground temperature is fairly constant so there is some heat loss into the ground. how much depends on the type of ground, so you need to know that as well - wet ground is better.

You may well need some sort of chilled water AHU and cooling system if you've got 50 cables. I can't see an air driven scheme over 350m being enough air to avoid a high temperature increase at the exhaust end. But then you need to pump out condensate.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[byju1982]

Thank you Littleinch, MintJulep! That was good information to do some homework.
@ IRstuff, top of tunnel is 2meter below road surface.

 

[SAK9]

Typically for cable tunnels two types of cooling methods are employed:

1.Air based:This is usually a push -pull type of ventilation system.A fresh air shaft/chimney with complete with fans are provided.An exhaust shaft complete with exhaust fans are provided at a different location. Typically temperature rise of8-10 deg centigrade is used.The distance between fresh air and exhaust shaft is decided based on the heat rise of ventilation air.These fans also provide smoke control should a fire develop in the tunnel
2.Water based:Cables are buried in a trough/channel filled with sand.Cold water circulating pipes are buried adjacent to the cables and carry away the heat generated by the cables.Cooling towers are provided at intermittent locations that cool the hot water returning from the sand trough.

Both systems coexist in most cable tunnels.A detailed thermal modelling is required to determine what percentage of the heat generated will be removed by the cooling water loop and how much will be left for the air based ventilation system to remove.

 

[byju1982]

Thank you SAK9 !
Happy to know the professional techniques in use around the world. Cable tunnel Hvac engineering indeed requires careful analysis and planning to avoid problems at advanced stages.

I am closing the thread now as I got sufficient aspects to think about and proceed.

Once again thanking all the members for their precious time spent on replying my query !
Happy engineering !