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Armature Temperature Measurement on DC motor

Armature Temperature Measurement on DC motor

(OP)
Hello guys,

Is anybody saw this kind of armature temperature measurement on DC motor (see attached photo).

We should upgrade drive for this motor with new one, and hopefully we should keep temperature measurement.

Anybody has idea what this resistance frequency converter is doing here ?

Milovan Milosevic

RE: Armature Temperature Measurement on DC motor

My guess would that it's there to get a more noise resistance signal (a frequency) through the slip rings. Small resistance changes might be affected by noise in the transmission path.

RE: Armature Temperature Measurement on DC motor

You might consider a modern wireless transmitter, you may even be able to get something multiplexed.
This would eliminate the sliprings.

RE: Armature Temperature Measurement on DC motor

(OP)
Hello roydm,

But I must supply this trasmitter somehow. Also I would not like to install anything on rotor.

Milovan Milosevic

RE: Armature Temperature Measurement on DC motor

I seem to recall once seeing what was essentially an analog ohmmeter permanently connected to the field circuit of an alternator, calibrated to read in degrees Celcius.

For sure it was technology that Noah threw off the ark, maybe...but would it or a more modern adaptation of the same thing do the job?

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

RE: Armature Temperature Measurement on DC motor

I don't see how this measures armature winding temperature correctly given the brush resistance, contact resistance etc. are all measured together. The normal way is to measure the interpole temperature via RTD and correlate it to the armature temperature since they carry the same current. Since the armature is better cooled, the interpole temperature will be higher than that of armature and thus the temperature limit set for interpole will also protect the armature.

Muthu
www.edison.co.in

RE: Armature Temperature Measurement on DC motor

Hi edison, I never said it was good, just that I'd seen it... smile

The fact that the voltage divided by the current in the above application also measured the slip ring resistance, which might not be consistent, in series with the field rotor resistance was either compensated for or ignored, I was never sure which.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

RE: Armature Temperature Measurement on DC motor

Running in circles here. Frequency isn't affected the least by slip ring resistance. And even if contact is bad, you will still get a reading now and then. Temperature doesn't change very quickly and I think that the slip ring plus R/f converter is a good principle.

To measure surface temperature with an IR thermometer could work. But, given the carbon dust, it will not be a very safe method.

Energy harvesting in a DC armature must be trivial. And simple short-range telemetry is yours for the asking...

But if you do nut want to add anything to the rotor, the solution you already have is as good as anything else,

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Armature Temperature Measurement on DC motor

Quote (OP)

Anybody has idea what this resistance frequency converter is doing here ?
Edison has explained why direct reading of the temperature through the slip rings is a bad idea.
Skogsgurra has explained the reason for converting the temperature to a frequency signal.
If the present installation is contained on the armature it may be difficult to duplicate it without installing anything on the armature.

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

RE: Armature Temperature Measurement on DC motor

(OP)
I just dont understand how frequency signal depent on resistance is "injected" to this 2 wires named as A and B.

Milovan Milosevic

RE: Armature Temperature Measurement on DC motor

A suggestion.
There are temperature sensors embedded in the armature.
There is a transducer which converts the temperature signals to a frequency signal.
As the temperature varies, so the resistance of the temperature sensors varies and so the frequency varies.
The frequency signal is not affected by the possibly varying and possibly non-linear resistance of the slip ring and brush arrangement.
The frequency is displayed in a meter marked in temperature.
Possibly the sgnal is sent to an alarm relay which responds to a changing frequency.

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

RE: Armature Temperature Measurement on DC motor

Milovan,
I do not now what is tip of motor because slip rings and DC motor are different stories .
Looking at power connection assume that this is Siemens equipment where are three PTC resistors and 2 are not in operation.
Maybe pictures of nameplate DC motors and frequency converters should help in analysis .
Good luck !

RE: Armature Temperature Measurement on DC motor

Dear Panter. I think that you need to have a look at that diagram again. The slip rings have nothing with the motor as such to do - they are there only to connect to the temperature transducers (PTC as it happens to be).

The differential transformer secondaries create a "Ghost Channel" (remember old telephone lines?) where the AC components cancel and the frequency information can be read between the transformer secondaries (the now famous A and B connections).

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Armature Temperature Measurement on DC motor

(OP)
I don't have a nameplate photo. It's a normal DC motor somewhere about 5 MW. As Gunnar said this sliprings are only for temperature measurement. Temperature element is most probably PT100. I decided that I will most probably use some converter Hz (kHz) to 4...20 mA signal. I saw that Murr Elektronik have this kind of converter. Now I only don't know what is a voltage range of this signal so maybe I need to use one additional transformer. I must check it on site.

Milovan Milosevic

RE: Armature Temperature Measurement on DC motor

PR Electronics (used to?) made some converters with a very wide supply voltage range, I think a frequency converter was among the range.

RE: Armature Temperature Measurement on DC motor

Have you looked at something like this?

http://www.farsens.com/wp-content/uploads/2016/09/...

I was involved with several generators using a similar technology, that seemed to work quite well.

This article discusses another system in hydro generators,
http://www.hydroworld.com/articles/print/volume-17...

I have used systems from this company for wireless monitoring of engine bearings, not generator rotors, although I'm told they also supply systems for that.
https://www.isa.org/WorkArea/DownloadAsset.aspx?id...


MikeL.

RE: Armature Temperature Measurement on DC motor

If you have an embedded PT 100 RTD connected to the sliprings, wouldn't be easier to just connect it to a standard temp controller or the DCS?

Muthu
www.edison.co.in

RE: Armature Temperature Measurement on DC motor

There are reasons, Muthu. It is not just because it is so beautifully complicated. Or, as the Germans say: "Why keep it simple when it possible to complicate it?"

The only slip rings that would work in this application (and with a direct connection to a Pt100 are mercury ones. And they were banned many years ago.

BTW, the symbol (a plus sign and a Theta) stands for a device with a positive tempco - PTC or Pt100 or whatever. So we don't know about that either.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Armature Temperature Measurement on DC motor

(OP)
I assume it is PT100 not PTC because temperature is measured continual (in degrees) not just as overtemperature signal like PTC do it.

Milovan Milosevic

RE: Armature Temperature Measurement on DC motor

skogs,

There are still liquid metal slip-rings available. They use a gallium (?) alloy which is liquid at room temperature. It is expensive! We used it in the electrode assembly of a seam welder which passed current through rotating electrodes to attach a hermetic lid to a Kovar enclosure for thick film hybrids.

RE: Armature Temperature Measurement on DC motor

Good to know, Scotty!
There's sometimes a need for such a device. Can you remember who makes/sells it?

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Armature Temperature Measurement on DC motor

Ours were proprietary parts on a seam welder made by Solid State Equipment Corp. (SSEC). It was a temperamental machine at best, and most of the time it wasn't at its best. Probably late 1980's / early 1990's vintage. The photo below shows one of the welding electrodes and its slip ring housing above the blue keypad. This one looks like it has been run very hot so the liquid metal has probably failed (like ours did).





From a quick look on Google: http://www.mercotac.com/ for new products.

RE: Armature Temperature Measurement on DC motor

Scotty - That looks like some snake oil to me.

Gunnar - All this electronics stuff is way above my pay grade.

Muthu
www.edison.co.in

RE: Armature Temperature Measurement on DC motor

Muthu - you should discuss that with your employer. It is only us self-employed that can accept such a situation... bigsmile

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Armature Temperature Measurement on DC motor

Edison,

Could be! Maybe we were really handling mercury in 1996, even though we were told it was a safer replacement. The stuff we removed from the electrode was thick and lumpy, while the fresh material looked very like mercury.

I have no knowledge of Mercotac's products - that was from Google - so if it's snake oil then you have my apologies!

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