Dear members,

Has any site using micro switch for the compressor air bleed valve? Is yes please share the details.

Our limit switches are frequently failing due to high temperature.

Unit:GE Frame 9E, Control system: Mark V

Take care,
g.rajesh

 

grajesh,

If you're using OEM switches, or the exact same switches as provided by the OEM, it's pretty unusual for them to fail due to high temperature--UNLESS the temperature in the turbine compartment is abnormally high. That could be because of leaks of hot air/combustion gases into the compartment, the failure of gravity-operated dampers to allow sufficient air into the compartment (some GE-design Frame 9E heavy duty gas turbines did use motor-operated dampers for incoming air, and if the units at your site use them have they been checked for proper operation?), or a failure of the Turbine Compartment Vent Fans to adequately cool and ventilate the compartment. It could very well be a combination of two or more of these conditions, as well.

It's also pretty common for the vent fans to be rotating in the wrong direction after re-installation after an outage. This happens often because the common type of centrifugal fan used is a reverse-tangential fan in which the fan blades are shaped opposite to what would normally be expected. These fans move a lot of air when running in the proper direction. And when they are rotated in the WRONG direction they don't move very much air BUT they do draw a LOT of current, which usually results in unknowing engineers re-setting or replacing or jumpering the fan motor thermal overloads/switches. And, this leads to a lower-than-normal air flow, which leads to higher than normal compartment temperatures. (There are often small direction-of-rotating arrows painted on the fan housing--but they either get painted over, or they fade with time and sun and temperature.)

So, be sure the fans are rotating in the proper direction (by checking motor current draw versus motor nameplate value--if the current is higher than rated, then it's pretty certain the motor/fan is rotating in the wrong direction; the current drawn by the motor should be slightly below motor nameplate rating when the fan is running in the proper direction--and the air flow will be much higher when running in the proper direction).

But, under normal operating circumstances the limit switches provided by the OEM are more than adequate for the application/environment. It is very common that sites have sourcing personnel which are easily persuaded that this or that component is exactly the same as the one used by GE when in fact they are not. But if it looks similar and is cheaper, the sourcing people usually buy it--and then the instrumentation technicians have to deal with the consequences while the sourcing people get accolades for "saving money", when the real cost of multiple replacement and failures and lost generation is never considered. So, if the switches are repeatedly failing and they weren't purchased from the OEM or known to be exact replacements, then it's pretty likely (because it happens VERY often) that the switches which are failing are not suited for the application (temperature range). Despite what the sourcing people are told or believe.

Also, you haven't told us how the switches are failing. Is it the wiring insulation that's melting? The switch internals? This would again point to an improperly sourced switch.

If the switches were purchased from the OEM and it's felt they are the proper switch for the expected temperature range, then it's pretty likely there is some problem with temperature and/or cooling air flows in the compartment.

MANY people have replaced mechanically-actuated limits switches with non-contact proximity switches. They must still be rated for the proper temperature range, and they must have very low leakage current specification (the Speedtronic can sometimes think a proximity switch is always "closed" if the leakage current is excessive, more than a few micro-amperes). And, the proximity switch must also be rated for the voltage of the contact input (usually 125 VDC); but there are definitely proximity switches which will work just fine for the temperature AND the voltage with LOW leakage current specifications.

Hope this helps!

Please write back to let us know what you do to resolve this problem!

 

Thank you CSA for your usual supports as in the past.

Yes there could be issues with poor ventilation because this problem only with the top bleed valve limit switches. I heard this is existing from the commissioning and seen the duct is away from the bleed vale location.

We are using the OEM recommended limit switches as""LIMIT SWITCH FOR VA2, MFR:CROUZET, MODEL:SP 3969 -10"" so believe OEM instruction is followed.

We had read some article about using the micro switch for bleed valve so interested to look the alternative.

If anyone having any details for micro switch/alternative please share with us.

Thanks again for your detailed feedback.

take care
g.rajesh

 

grajesh,

Did the articles you read not provide part numbers?

If I recall correctly, Microswitch is a brand name (manufacturer based in the USA). And I just used my preferred World Wide Web search engine and Crouzet (a French-based manufacturer) also manufactures/sells "microswitches." So, I'm a little confused as to what it is you're looking for.

You need a high temperature switch, capable of 125 VDC, milliamperes of current (or less), which can sense the actuator/arm of the bleed valve.

If you have an electrical/electronic supplier, or World Wide Web access (which you do), you should be able to have your supplier recommend a suitable switch, or find an on/line source who can recommend a suitable switch.

You could also try contacting Crouzet directly with your questions and situation and description of the failure and ask them for help, if you don't want to go to GE or the packager of the units at your site for help. If you have data and feel the failure rate is excessive, you should be contacting the supplier for assistance.

There have been various suppliers of devices and components to GE in the past that don't or won't sell directly the same part they provide to GE because they have an agreement with GE not to sell directly.

Again, gather or take your data (number of failed switches; length of time in use/service; failure mode(s); actual temperatures measured in the area where the failures are occurring; etc.) and work with a supplier or the OEM to find a suitable replacement.

It doesn't seem there are others here who have had similar failures or situations who are willing to provide part numbers and information.

Please write back to let us know what you find!

 

Thanks again for your feedback.

We read the article very long back so unsure about the P/N details.

Yes, we will contact the manufacturer for any new modified switches available with them.

Meanwhile received few feedback from GE control user group as below,
HSI manufactures a high temperature switch. http://www.hsisensing.com/ Part Number ZA11940

GE is an authorized re-seller for HSI.

We will workout and update the outcome.
take care
g.rajesh