Circuit Breaker lugs temperature monitoring 1

[newdryno]

Trying to find a suitable way of monitoring the lug temperatures of a ~1000V circuit breaker. I see that infrared pyrometers are quite common but that simply won't work in this case. I'd like direct contact rather than monitoring the air temperature near the lugs however the obvious problem is isolation from high voltage & current. However medium voltage generators and motors monitor winding temperatures with RTDs so I thought this would be a possibility. I see one manufacturer's data sheet for a thin film RTD for slot insertion and it's dielectric strengh is shown as 3200V. Has anyone tried this method of monitoring, say on bus bars? Any suggestions are greatly appreciated.

 

[Zogzog]

Infared sensing is your best solution, it does not monitor air tempature but radiation, you can use small permanatly mounted IR sensors that tie into you SCADA or other comm system to alert you (Via computer or your cell phone) when your connection reaches the pre-determined limit. There are also TC's availble to use is direct sensing is required, all ties into the same system. I have installed this system in several data centers and it works great.

 

[desertfox]

Hi newdryno

I haven't used the method your talking about but here's a site that might give you some more info:-

http://newton.ex.ac.uk/teaching/CDHW/Sensors/an046.pdf

desertfox

 

[newdryno]

As I mentioned, infrared pyrometers won't work. It's too bad; I agree that it would be the best solution. However we need a VERY wide ambient temperature range for the electronics to operate/survive and we cannot install the transmitter outside of the enclosure.

 

[Zogzog]

Then use the thermocouples, the whole system stays internal to your switchgear.

 

[newdryno]

Guess I need to rephrase the question; has anyone installed one of these winding monitoring-type RTDs directly on a 'hot' conductor? In a motor or generator stator, I assume these types of sensors are slipped between windings, of course the windings have insulation if only varnish.

 

[itsmoked]

I'm baffled. There is no good reason that non-contact IR can't be used. It is the standard in assaying switch gear temperature issues. You can get very small IR thermocouples that are very robust and put out a TC signal.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[newdryno]

Ambient temperature range: -20 to +70C

 

[newdryno]

Raytek's MID pyrometer: 0 - 85C ambient (problem on low end.
Infra-View: max. ambient ~50C without cooling
Bridex: 0 - 65C
I don't want to add a jacket to the sensing head - there's no cooling water or air (compressed or fan-driven) supply available.

 

[BJC]

Got room for temperature markers? Pain them on and they change color at a predetermined color. They are made to chang ecolor at various temperatures. You never know how hot somethig got, just that it got hotter than the marker you used. You then have to paint it with the next temperature and od it again. If the lugs are big enough you can use more thna one at once.
There several firms that make them -one is below.

http://www.nissenmarkers.com/catalog/Category/Temperature-Indicating-Sticks

 

[newdryno]

This is in machinery that has no personnel nearby and must be continually monitored by a PLC to ensure that the upper temperature limit is not exceeded.

 

[BJC]

There fiber optics temperature sensors that might work. As I remember they work by changing the reflected light. No electronics ( on the sensor end) and no moving parts.

 

[cgrodzinski]

If the system is important the BJC advise is what you should use. It is dielectric and the information can be transfer over long distances 24/7. Off course all perks of other older type equipment are included. However, it doesn't come cheap but is very reliable in electrical field environment.

 

[Mobius44]

The infrared sensor & the breaker you're measuring would probably prefer a temp controlled environment, but if that's not an option you might check the Omega OS36 series of "infrared thermocouples" rated for -18C to +85C ambient.

 

[jraef]

These are typically less than $100 each, I have seen several SWGR mfrs use them for that purpuse.

http://www.exergen.com/industrl/microirtc/microbrochure.pdf

"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[pwlgal]

Newdryno -

A better solution than infrared, is a fiber-optic temperature sensor for electrical equipment utilizing fiber-optic technology to provide temperature data 24 hours a day, 365 days a year. The fiber is connected via a mounting fixture on bus bars, splices, circuit breaker finger stabs, etc. Attached from an electronics module (mounted in a safe area) directly to your PLC via serial Modbus, you will know exactly when thermal escalation begins.

Perfomance Stats:
Temperature Range: -20°C to +120°C (-4°F to 226°F)
Resolution: 1°C
Accuracy +/- 2°C

more info? email me at OBR@powellind.com

 

[Skogsgurra]

It depends somewhat what accuracy you need. I have put NTC thermistors in isolating tubes and strapped them to bus bars with silicon paste between bus bar and tube and also inside the tube for good thermal contact. I then put mineral wool on top of the assembly to minimise influence from surrounding air.

Those standard NTCs are accurate within a few degrees if you don't care to calibrate them individually and a lot better if you do.

Did a check between 23 and 159 C a few weeks ago and that works quite well. My test set up was with a 10 kohms series resistor at 25 C, so 25 C is in the middle of the measuring range. That means that you could easily go down to -20 C and lower.

One thing: the impedance is around 10 kohms or lower. That means that capacitive pick up could be a problem. But easily overcome if you put a low pass filter on the input of the receiver. Use a time constant around 10 seconds to get very good 50/60 Hz suppression.

Do you need to record temperatures or do you need to sound an alarm or similar?

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[Skogsgurra]

Hmm... Just noted that the OP is from May this year. Probably followed jraef's advice since no posts from him after that.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[gattie]

Google Microtherm
I've used these thermostatic devices successfully for protecting high voltage motor windings from overheating due to impact loading.
They were fixed with epoxy resin to the coil windings close to the exit from the stator slots.
You could strap them to each switch busbar & if required, provide additional insulation resistance with class H glass type material (sleeving) at mating surfaces.
You would have to specify the upper temperature limit required
with your order. Their accuracy/repeatability is excellent.

 

[newdryno]

I thought I should at least tell you guys which solution was implemented. I used a typical motor winding RTD with a 3200V dielectric rating. The RTD was held in place against the lug by a nylon 'holder'. It worked quite well. I also used a typical RTD-input hi-limit relay for shutdown. I would have liked to use a infrared pyrometer but as I mentioned, the ambient conditions were quite wide and none of the pyrometer electronics could meet those requirements. Also the fiber optic devices mentioned above are also pyrometers; the fiber optic cable is only used as the medium to get the infrared 'image' (or photons) to the sensor.