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Online Leak Repair of HV Apparatus – Oil, SF6 and Nitrogen Leaks

Presented By:
Liisa Colby
Gary Brown
The Colt Group, Power Services Division
TechCon 2017

Abstract / Summary

Leaks develop at various locations on both new and aged equipment; in the past, repair options were limited to draining/de-pressurizing and re-gasketing, welding, applying epoxy or just wrapping with an absorbent material. Today these leaks can be repaired using a time-proven injection method that is completed while the leak is active and in many cases with the equipment in-service. No epoxies or welding are used in this process. The sealant used was specifically developed for use with electric apparatus; it is flexible and easily removed. This approach has been gaining increased recognition and acceptance as a viable solution for repairing oil leaks on transformers and SF6 leaks on circuit breakers and GIS. This paper will explain the methodology with various case stories involving oil and SF6 leak repairs for companies in the USA and Canada.

Why Leaks Occur and Why You Care

Leaks are a common occurrence and can be caused by various factors, including transportation, temperature changes, vibration from normal operations, sudden removal from service, weather and environmental incidents, and animal interference as well as human factors.

The options for dealing with leaks are as follows:

  1. Let it leak. However, if oil or SF6 are leaking out, air and moisture can and often do get in. Moisture can migrate in through several methods; one of the most common is through aged, leaking gaskets. Even though the apparatus is at positive pressure, moisture and air can be drawn in, even though it is leaking in the opposite direction. This has been explained as “capillary action” or “entropic force”. A Chemical Engineer can provide you with a thorough explanation of this effect. The end result of air and moisture infiltrating the apparatus can negatively impact the condition of the unit and lead to serious problems and in the worst cases, catastrophic failures.
  2. Internal repairs – epoxy. Sometimes a company will first attempt their own leak repair using an epoxy product. These products can be effective in certain situations. However, when it comes to HV apparatus leaks, the epoxy approach can create additional obstacles. Many times the epoxy is not effective, then you have the added challenge of epoxy removal to deal with before other repair options can be explored.
  3. Re-gasket or replacement. Re-gasketing or replacement are the number one solutions in a perfect world. However, the resources required to drain the oil or remove the gas often have companies looking for alternative solutions. In addition, online leak repair can often be performed without the need for an outage, or if an outage is required it will be greatly reduced.
  4. Online leak repair by outside specialists. This process has been proven effective for sealing a variety of leaks and is performed by experts who are experienced in working with HV apparatus. The key benefits of this option are that there is no need to drain the oil or remove the gas, and many repairs can be made in service. This does not need be viewed as a temporary repair, many repairs remain in place and effective for 5 – 10 years and longer.

The Benefits of Leak Repair

Leaks do not get better over time. Leaks need to be taken seriously and addressed with a proactive and ongoing maintenance program. Many utilities and industrial companies have learned that online leak repair can be the right fit for certain situations, due to the following reasons:

  • Minimal Outage Required
  • Leaks can often be repaired within hours
  • Many leaks do not require an outage
  • No need to drain oil or remove the gas
  • Sealant is safe for use with HV apparatus and sealant (and clamps) can be easily removed
  • Reduced manpower needs
  • Generally, only a single “safety observer” is required
  • Company personnel is available to work on Capital projects
  • Replacement parts not required
  • Immediate cost savings
  • Work can be scheduled almost immediately
  • And the bottom line: A typical online leak repair costs a fraction of the alternative to re-gasket or replace.

Leak Detection and Repair Program (LDAR) Examples

Some utilities have recognized the advantage of online leak repair and set aside a line item for it in their annual O & M budget. Once leaks are identified, they are prioritized and options are considered, including online leak repair. Here are three examples:

The United Illuminating Company (UI)

UI has worked closely with The Colt Group for over 10 years in a proactive leak repair program. What began as an intensive series of repairs at multiple sites has matured into a more limited, but ongoing inspection and maintenance routine. Some of Colt’s repairs have unintentionally become long-term solutions while other repairs were short-term fixes until UI could properly schedule and complete permanent repairs. Although the Colt repairs are guaranteed for 2 years, many are still in place and working effectively years later. United Illuminating estimates significant savings in annual maintenance costs by utilizing leak repair as an integral part of their overall maintenance strategy and reducing the need for re-gasketing and replacement.

A Major Hydro Generation Station

This Hydro Station is located in a very remote area, with a limited timeframe for outages. They have found online leak repair to be the most cost-effective and convenient solution to seal oil leaks on multiple GSUs and other oil-filled HV apparatus. Every year, oil leaks are prioritized and matched to the planned outage schedule. The online leak repair team is scheduled to come on site to coincide with the critical outages and perform top and upper level repairs on the outage units at that time. Lower level repairs are done on the same mobilization, without the need for outages. Inspections and planning for the next year are part of each annual visit.

SF6 Leak Mitigation at ConEd’s West 49th Street GIS

ConEd’s West 49th Street station is one of the oldest GIS in the USA. Online leak repair was determined to be a cost-effective solution to sealing SF6 leaks due to the difficulty to obtain outages and perform “permanent” repairs. Over 100 custom clamps and enclosures have been installed on leaking flanges, bypass valves and other various locations over the last ten years. Many of these repair clamps are still in place and continue to effectively seal the leak.

Some examples of ConEd leak repairs are included later in this paper.

The History of Online Leak Repair

Online leak repair was first developed during World Wars I and II, when the ships were steam driven. Sailors needed to find a way to slow steam leaks whilst at sea, in order to remain in operation until a more permanent repair could be effected. Robert Furman at the Newport News Shipping Yard developed a DIY kit which could be used out at sea. Years later this process evolved and was adapted specifically for use with transformers, circuit breakers and GIS.

Two different methodologies are used for online leak repair on HV apparatus – either a “Drill & Tap” using injection valves, or custom-fabricated clamps and enclosures. The Drill & Tap technique is used for oil leaks, the enclosures are used for certain oil leak applications, or for SF6 and nitrogen leaks. The sealant used in both these methods is not an epoxy. Specially formulated for use with high voltage electrical apparatus, the sealant is flexible and easily removed. It maintains a “memory” that allows for expansion and contraction as needed due to temperature changes and vibration. The substance has excellent dielectric properties as documented by test results from an independent laboratory.

Drill & Tap Injection

In the “Drill & Tap” method, an experienced technician will drill and tap a 1/16” blind hole in between the bolt holes to intersect the groove or gasket. Next, they install an injector valve into the tapped hole. This injector allows the technician to control any oil flow that may occur during the next step. Using a 1/8” drill bit he will then insert the drill into the injector and drill a hole into the seal area. The bit is then removed and the injector is turned to the closed position. This process is repeated with additional injection valves; the objective with the multiple ports being to carefully control the amount of sealant which is injected.

A two-part compound, the sealant has the consistency of peanut butter when it is first mixed. It is injected into the positioned valves one by one, using a manually controlled gun with pressure gauge. It takes approximately one hour for the sealant to cure. Once the sealant has cured, the injection valves are removed and Teflon-coated pipe plugs are inserted in the threaded holes.

On repairs that have a grooved or recessed area where the O-ring or gasket lies, there is a perfect spot to penetrate using the Drill and Tap technique. By intersecting this grooved area, there is a channel where the sealant can travel around and create a seal. This process can be used on tap changer handles, tap changer flanges, cover plates, belly bands, bushing mounting flanges and other locations. Depending on the location of the leak, some of these repairs can be made with the unit energized. An example of a common in-service leak repair might be the bottom of a tap changer flange, or lower radiator flanges.

Drill & Tap Injection of a 4-bolt flange

Drill & Tap Injection of a 4-bolt flange. After the sealant cures (1-2 hours) the injection valves are removed.

Custom Clamps and Enclosures

The second leak repair methodology involved is a custom fabricated clamp or enclosure. This creates a barrier around the leaking component and injecting the cavity of that piece of hardware to obtain a seal. This special hardware allows the sealant to be injected under pressure to successfully seal the leaks. For enclosure repairs, two brief outages are typically required – on the morning of Day One, a 1-hour outage is taken for the leak seal technician to take precise measurements for the enclosure. The device can be fabricated that same day and shipped overnight to the client. A second outage of 4 – 6 hours is taken to install the enclosure. Sealant is injected into a channel inside the clamp to seal the leak. The clamp remains in place, and can be easily removed when needed.

SF6 Leak Repairs

When an SF6 leak is identified and immediate re-gasketing or replacement are not feasible, leak repair can provide a viable alternative solution. Utility management has been increasingly vigilant in recent years monitoring these gas leaks and looking for quick response. In the case of ConEd’s West 49th Street Station, online leak repair has been utilized due to the difficulty in obtaining outages, the desire to limit unnecessary gas handling and contamination, and to limit manhours and overtime. The Colt Group has worked closely with ConEd to reduce costs and eliminate emergency charges yet still provide expedited service.

This photo shows one section of the West 49th Street GIS and the locations of multiple repair clamps.

This photo shows one section of the West 49th Street GIS and the locations of multiple repair clamps.

It is not always aging equipment that presents a problem. In the following example, the Manufacturer contacted The Colt Group to repair an SF6 leak on a GIS bus flange at a Southern California Edison’s Valley GIS. Leak repair was determined to be the best solution, as alternatives would have increased down time and cost, and the leaking section of apparatus was scheduled to be replaced in two years. The bus work had originally been installed in 2003, so the repair was within the 10 year manufacturer warranty.

The leaking joint consisted of two painted aluminum flanged sections mated vertically with an approximately 0.5 inch thick insulator sandwiched between the flanges. Since this was considered an insulated joint, the Colt solution needed to be non-conductive. Diameter of each flange is 25 inches x 2 inches thick. Diameter of pipe is 20 inches. Internal pressure is 67 psig SF6.

SF6 leaking from the flange as indicated by a red arrow in the photo below. It is right behind the surge arrester in the photo. The leak was found using an SF6 detection camera. Maintenance attempted to slow the leak using epoxy, but it did not work. SCE was adding about 66 lbs of SF6 per month to this section.

Client photograph of leak location

Colt’s solution required the surge arrester to be removed and relocated in order for a custom enclosure to be installed on the flange.

Inspection & Measurements

Colt technician made on-site inspection, took additional photos and precise measurements.

Colt Technician Drawings and Measurements

Colt Custom Enclosure Design Plan

Colt’s first plan was for a custom aluminum enclosure, with .150” thick nylon shims between the pipe OD and the aluminum of the end plates to insure a .150” insulating gap. These shims would be placed 1-2 inches apart around the OD on both end plates (upper and lower). This approach evolved into Colt’s final design, which was to engineer a nylon ring to fit inside the aluminum enclosure. This strategy ensured more distance and insulation between the aluminum surfaces. Rubber seals were set in the nylon rings to attach to the aluminum pipe above and below the leaking flange, providing ample clearance from the aluminum of the Colt enclosure to the aluminum pipe.

Colt Custom Enclosure – Final Design

The installation plan called for the Colt enclosure to be centered so that no electrical contact would be made between it and the pipe on both sides. Nylon spacers were placed in between the bolts on the top flange; the enclosure would rest on these to prevent any metal-to-metal contact.

Installation

The Manufacturer removed the Surge Arrester. Colt installed the custom enclosure. Sealant was poured in via one inch ports incorporated into the top of the enclosure. Colt hydraulically injected additional sealant through injection valves along the sides of the enclosure. The Manufacturer re-installed the Surge Arrester in its new location. Status of leak was subsequently checked with an SF6 camera, then the section was bagged and monitored for 12 hours to ensure the leak was fully sealed and the repair was effective. The repair remained in place and successfully sealed the leak for the two years needed until replacement. The following photographs outline the installation process.

The following photographs outline the installation process

Ongoing Research and Development

The Colt Group is working with various utilities and research facilities in the USA and Canada to continue exploring new and improved solutions for online leak repair.

References

“Taking Leaks Seriously”, Jon Allen and Anthony Picagli, The United Illuminating Company, T&D World Magazine, October 2013

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