×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Sensing Air Temperature Inside 23 KV Generator Housing

Sensing Air Temperature Inside 23 KV Generator Housing

Sensing Air Temperature Inside 23 KV Generator Housing

(OP)
Group:

I have a customer who has been directed to install temperature sensing inside the housing of a large generator at a dam power plant. His chore is to bring the air temperature of the cooling air back to a building automation system (JCI Metasys) for monitoring.

The generator has bearing and stator RTDs that are being used for normal power plant montoring / alarming / etc..., and he can't use them for his purpose anyway.

So he will be penetrating the outer steel enclosure and placing a temperature sensor in the air that blows over the stator conductors.

My question is how to do this safely and mitigate any effects of having the sensor so close to such high voltage (inductive heating of the stainless steel sensor sheath, impressed voltage on the sensing conductors, etc...).

I've never installed such inside an enclosure above 600V.

Can y'all give me pointers or help with a direction to point my customer for expert advice?

The sensor itself can be anything, too -- his system can take 1000 Ohm RTDs directly, or a 4-20 mA transmitter if needed.  If there's a special type of shielded sensor for such an application, that would be excellent.

There will be plenty of experienced folks on site to deal with the actual installation, grounding, and all that.  I just need to help him find what he needs for pricing at this point.

Thanks tons, and good on ya,

Goober Dave

RE: Sensing Air Temperature Inside 23 KV Generator Housing

Why can't they communicate to the same relays/monitor that monitors the stator and bearing temperatures?  

Rafiq Bulsara
http://www.srengineersct.com

RE: Sensing Air Temperature Inside 23 KV Generator Housing

Common sense would dictate monitoring either the discharge or intake air, or both depending on what he is trying to achieve. There is nothing to be obtained by placing the sensors so close to the stator windings and he may be compromising his data. After the air has left the stator, the temperature will not change enough to worry about until it is discharged. Getting close to the stator in the wrong location may result in measuring less than the maximum temperature.  

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Sensing Air Temperature Inside 23 KV Generator Housing

If there is cooling air in and out you should measure the homogenized air at the discharge. As waross suggests, measuring the intake temp would be a great idea too.

Subtracting the two will give you the temperature rise  which is a very useful number on rotating machinery.   It tells how much waste heat is being jettisoned.  Whereas, just the outlet temp does not, it only tells how close to 'too hot' your machine is operating.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Sensing Air Temperature Inside 23 KV Generator Housing

I know pretty much exactly what, where and how I'd configure this on a turbo machine but I'm much less familiar with the internal air paths on big salient pole machines. I'm hoping Wolf might offer some thoughts on the best measurement locations.
  

----------------------------------
  
If we learn from our mistakes I'm getting a great education!
 

RE: Sensing Air Temperature Inside 23 KV Generator Housing


DRWeig:

I can only think of one hydro power plant worldwide where a generator voltage of 23 kV has been selected. But this plant has units installed with direct water-cooled stator and field windings and I therefore don't understand the background of the requirements described. Maybe there is another plant around with units of 23 kV.

Even for air-cooled hydro generators I can't imagine why the knowledge of cooling air temperatures in the vicinity of stator end windings is of importance. It is difficult enough to select a proper location for temperature sensors measuring meaningful generator inlet and outlet cooling air temperatures. End windings have a strong magnetic field environment where not only iron but all other metallic components are subject to eddy-currents. Common resistance temperature sensors of the Pt100 type therefore cannot be used.

If you give us more details about the background of this peculiar requirement we may be able to find a suitable solution.

Why don't you ask the generator OEM for advice?

Regards

Wolf
WWW.HYDROPOWER-CONSULT.COM

 

RE: Sensing Air Temperature Inside 23 KV Generator Housing

(OP)
Hi Guys,

Thanks for the great input -- I'll pass it all along to the customer in our discussions.

I believe the background may very well be that the facility mechanical designer (HVAC guy) made the decision to place this temperature sensor in there -- without knowledge of what might be involved due to the electromagnetic fields. Perhaps he just wanted an interesting data point to display in the maintenance office?

In any event, you've validated my fears (thanks especially Wolf, but all of you too).

I did find a fiber optic sensor to show the fellow too, that appears to be relatively inexpensive:

http://www.neoptix.com/t-guard.asp.

I'm going to point him back to the system designer first, with a summary of the reasons why not and the suggestions for monitoring at intake and discharge instead.  Failing that, I'll ask him to contact the generator manufacturer and perhaps Neoptix for a solution.

I'll post the end result when I found out what it is!

Good on ya'll,

Goober Dave

 

RE: Sensing Air Temperature Inside 23 KV Generator Housing

Thanks for sharing the information on the Neoptic package Dave. What is the approximate cost of the Neoptic system?
Star for the Neoptic info.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Sensing Air Temperature Inside 23 KV Generator Housing

(OP)
Bill --

List prices run about $2000 per point (including approx 50 meters of extension fiber per point and everything) for a 12-point transducer with probes up to maybe $4500 per point for a single channel device.  I'd expect that actual purchase price might be 20% lower, but I can't be sure.  Having a purchase order in hand tends to really make things negotiable in these economic times.

There's also a competitor named Fiso out there making the same stuff -- www.fiso.com.

All --

I won't get to make the sale, but thanks to your help my customer is good to go.  He's taking your advice to locate the sensing at the air intake and exhaust, is planning on using the fiber optic system, and will submit it all to the generator manufacturer for approval before doing any ordering.

I didn't get a chance to ask "why" they're doing this during the conference call, but if I get to talk to him again in a more relaxed atmosphere, I'll find out for all of us and post it here.

Good on ya again,

Goober Dave

RE: Sensing Air Temperature Inside 23 KV Generator Housing

One problem I can see with mounting a (single?) sensor so close to the stator (so as to worry about electric/magnetic field interference) is that the airflow and/or temperature distribution may not be uniform at this point. I'm assuming that there is no duct work into which one can place a sensor at such a distance from the generator so as to ensure proper air mixing.

A suitable solution may entail the use of multiple sensors positioned at several locations in the cooling air flow. Alternately, one can install a small sampling duct (made of non magnetic/non conductive material) having several inlet ports and a small muffin fan to draw in air, mix it and pass it over a single sensor.  

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources