Your premier source for all things related to
stator cooling water systems

 

With the arrival of spring (at least in name, if not temperatures for some of us) comes the time to prepare your generator for Summer operation. A good look at the stator cooling water system can ensure a trouble free Summer.

Those of you that saw our presentation on stator cooling water system (SCWS) monitoring at the last EPRI workshop on Amelia Island saw in detail how best to monitor your SCWS.

We've been busy at SvoBaTech this winter and have further tested and developed our process. We had the opportunity to visit a nuclear power plant and assist by cleaning their stator cooling water channels - all during operation and without losing a kWh of electricity produced!

Our talk titled “Flow restrictions in water-cooled generators: causes, prevention, and removal” will shed some light on this common problem with water-cooled generators.

For more details click here.

We will present “Chemical cleaning of generator stator windings” on Wednesday, June 10.

For more information about the conference, click here.

—> Did you know?

How to eliminate Stator Cooling Water System plugging

 

In our last newsletter we talked about how to recognize plugging in stator cooling water systems.

If plugging has been identified the system should be cleaned. Doing nothing bears a significant risk of the hollow conductors plugging completely and not being accessible for less intrusive forms of cleaning. In other words, doing nothing will likely cause more problems. The correct question to ask is which cleaning method should be used.

Cleaning can be done both mechanically and chemically. Each method has its unique strengths and weaknesses described below.

» Mechanical cleaning methods

Hot reverse flushing is the least intrusive - and least effective - method for removing oxides from the stator cooling water channels. It works well for loose blockages such as debris or foreign objects, but has the potential to break loose copper oxide layers and plug up the hollow conductor even more.

More intrusive methods include dry ice blasting or scraping with wire brushes or metal rods. These methods are effective to break open passages, but require at least partial disassembly of the connectors. Depending on design, access can be problematic.

—> Next newsletter topic: “Useful instrumentation for the SCWS”

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» Chemical cleaning methods

Historically, various acids have been used to remove copper oxides from the hollow conductors. This, however, often removes significant amounts of material that preferably whould have stayed in place – namely, copper and braze. Acid cleaning does not remove material evenly, but the removal rate depends on local turbulences and can result in erosion.

» Recommended methods

In most cases, a global chelant cleaning will restore full flow and remove all errant copper oxides from the system. In extreme cases where adverse conditions have gone unnoticed or ignored, and hollow conductors are completely plugged, mechanical cleaning is often the only answer. This can be combined with targeted chemical flushing and should always be followed by a global chemical cleaning of the whole stator cooling water system.

As proper application is important to ensure the situation is actually improved and not worsened, specialists should be hired for this work. This is not a place to cut corners, as the consequences can be expensive and range up to partial rewinds.

An online cleaning should be carried out by experienced experts; a turbine trip, or worse, may result from improper application.

Chemical cleaning of stator cooling water systems our specialty. We bring a combined experience of over 70 years, from the beginnings of SCWS cleaning in the early 80s.

SvoBaTech can provide you with single bar chemical cleanings, offline chelant cleanings or state-of-the-art online chelant cleanings that allow you to stay in production throughout the cleaning process. We also offer support before and during a mechanical clean.

Our passion is stator cooling water systems Let our passion work for you!

EDTA molecule with CuStator bar with hollow conductorsCleaning success, before and after

A better agent to use in chemical cleaning was found in chelants. The name chelant comes from the Greek word chēlē, meaning “claw”, and that is precisely what they do with the copper oxides; they surround them like a claw and keep them in solution.

The most useful chelant for this application is EDTA. This substance is used routinely in food and cosmetics. It poses much lower risks to the machine, as well as to personal health, than the acids previously used.

There are other advantages to EDTA use over acid use. The effect is not concentration dependent which makes it possible to apply during operation of the machine. The reaction can be precisely controlled and monitored, and finally it only removes the copper oxides while leaving the hollow conductors and other vital parts unaffected.