Power Restoration Actions After Potential Device Start to Fail.

[cuky2000]

From the operation standpoint, what actions are recommended temporarily and permanently for winter power restoration in a large ring bus transmission substation after a potential device started fail located close to a salt-fog area.

Example:

· Will be OK to isolate the line and temporarily operate with ring bus open.
· Is cleaning, silicon grease or replacement of the potential device is viable options.

Please fill free suggest any procedure, site with info or share any experience in this matter.

 

[RalphChristie]

cuky

I am no expert regarding failures due to contamination, but just a few comments:

What is failing and where is it situated? Insulators? On a line or on the bus?
Is the failure due to contamination? (salt spray)
What kind of insulators do you use? Ceramic or non-ceramic?

A few remedies:

Washing
Substation or line insulators can be washed when de-energised or when energized. Automatic washing schemes and helicopters have been used for this purpose. The costs are usually prohibitive.
Greasing
A thin layer if silicone grease, when applied to ceramic insulators, increase hydrophobicity of the surface. Pollution particles that are deposited on the insulator surface are also encapsulated by the grease and protected from the moisture. Disadvantage of greasing is that the spent grease must be removed and new grease be reapplied, more or less yearly.
Coatings
Room temperature cured silicon rubber coatings are available to be used on ceramic substation. These coatings have good hydrophobic properties when new.
Increase creapage distance
If clearances allow, additional discs may be added to increase the reliability of a line. In the case of longrod and post insulators the increased creepage length must not result in an inadequate shed spacing. This solution is usually not possible and will be expensive.
Replace hydrophilic with hydrophobic insulators
This solution is expensive and it must be known with certainty that the original problems are contamination/pollution related.

In my opinion, depending on the seriousness of the near-failing device, isolation of the faulty part (thus an open ring) sounds fair. However, immediate action must be taken to repair/replace the faulty device as soon as possible to prevent any outages due to other possible failures. (you are entering a critical time with possible failures higher than normal)

Regards
Ralph

 

[cuky2000]

Thanks RalphCristie.

There is any special procedure to wash insulator during wintertime?

The primary goal in any power restoration process is the keep the light on quick in a safe manner.

 

[RalphChristie]

Insulators can be washed with fixed or hand-held equipment. The hand-held equipment can be operated from the ground, from a platform or from a helicopter. For effective washing, care should be taken with the design of the spray nozzles and in the case of live washing, the conductivity of the water is also extremely important. Manual washing requires a sharply focused jet, and cleaning is commenced at the bottom of the insulator or string. With automatic systems the spray must be such that the full length of the insulator is uniformly wetted. Water conductivity must be very low. The maximum conductivity that can be safely tolerated will depend on the nozzle design and the water flow rate. The NEC has commissioned a project on the detailed design of washing systems - I do not know if the report is already released.

Washing as an anti-pollution measure requires a high capital investment, but generally the annual cost is less than the cost of greasing.

Regards
Ralph