Exposed MV Termination on Transformer

M

myntz

Member
Location
New Jersey
Occupation
Engineer
Curious to know if anyone had came across where MV substation transformer have both exposed lightning arrestor and HV (35kV) terminals Mounted on top of the transformer. This is exposed to the environment. The incoming HV feeder comes from overhead copper bus-tube with adapter for conductor. I am looking to see the best way run the feeder from the bus-tube to lightning arrester to HV terminal. The distance between each point is pretty short, maybe 22" or so. This mean it will be pretty tough to use Shield MV cable with stress cones given the distance. Has anyone done this with just bare copper (not sure if this is code violation) or know of any insulated but non-shielded 35kV cable for short run like this?

The transformer sits inside a locked fence yard with sufficient height.
 
myntz said:
Curious to know if anyone had came across where MV substation transformer have both exposed lightning arrestor and HV (35kV) terminals Mounted on top of the transformer. This is exposed to the environment. The incoming HV feeder comes from overhead copper bus-tube with adapter for conductor. I am looking to see the best way run the feeder from the bus-tube to lightning arrester to HV terminal. The distance between each point is pretty short, maybe 22" or so. This mean it will be pretty tough to use Shield MV cable with stress cones given the distance. Has anyone done this with just bare copper (not sure if this is code violation) or know of any insulated but non-shielded 35kV cable for short run like this?

The transformer sits inside a locked fence yard with sufficient height.
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I believe non insulated components with that higj voltage have to either be guarded or elevated 8'7" or so
 
Jpflex said:
I believe non insulated components with that higj voltage have to either be guarded or elevated 8'7" or so
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I wasn't aware of the height requirement, thank you for that. The yard has a high fence 10ft+ with exposed component at roughly 16 ft+ from ground level.
 
jim dungar said:
If this is open air, why do you want insulated conductors?
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I am under the impression that if the conductor is shielded and insulated with stress cones, this could prevent environmental corrosion that is seen on bare conductor (not sure if this is true).
 
myntz said:
I am under the impression that if the conductor is shielded and insulated with stress cones, this could prevent environmental corrosion that is seen on bare conductor (not sure if this is true).
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Not true.
Stress cones are used to reduce the voltage gradient (stress) caused by insulated conductors.
Corrosion comes from the environment which might be mitigated by the use of 'coated' conductors.
 
jim dungar said:
Not true.
Stress cones are used to reduce the voltage gradient (stress) caused by insulated conductors.
Corrosion comes from the environment which might be mitigated by the use of 'coated' conductors.
Click to expand...
What is the primary purpose of shields (which are often grounded) for cables

Is it to mitigate inductive heating effects, noise etc?
 
Jpflex said:
What is the primary purpose of shields (which are often grounded) for cables

Is it to mitigate inductive heating effects, noise etc?
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Shielding equalizes and evenly distributes electrical stress across the conductor insulation, which allows less dielectric material and more reliable operation. This is a good summary on cable theory, particularly starting around 13:00. Then a look at the importance of stress cones or some other termination at 18:15.

 
Jpflex said:
What is the primary purpose of shields (which are often grounded) for cables

Is it to mitigate inductive heating effects, noise etc?
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Without shield, voltage could build up on the surface of the insulation and possibility discharge randomly. With shield and grounded, the build up can be drained to ground.
 
myntz said:
Without shield, voltage could build up on the surface of the insulation and possibility discharge randomly. With shield and grounded, the build up can be drained to ground.
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Discharge as jump onto someone nearby or metal but how many feet do you think?
 
Jpflex said:
high voltage but very low current?

Almost like a capacitor where insulation acts as dielextric but current passes?
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Pretty much but without a shield the insulation would need to be much thicker making the conductor unwieldy.
 
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