4160V 2000HP Stator RTD

[kenaslan]

Has anyone ever only used one stator RTD? I have always used all 6, 2 per winding and the 2 on the bearings. However, the controls engineer says only one RTD back to the protective relay is all that is needed. Would it be a warranty issue if not all RTDs were used as specified by the motor manufacture? IMHO there is a reason manufactures have not one, but two RTDs on the windings, and not on just one winding, but all three.

 

[Jraef]

Has anyone ever only used one stator RTD? I have always used all 6, 2 per winding and the 2 on the bearings. However, the controls engineer says only one RTD back to the protective relay is all that is needed. Would it be a warranty issue if not all RTDs were used as specified by the motor manufacture? IMHO there is a reason manufactures have not one, but two RTDs on the windings, and not on just one winding, but all three.

I've seen it done, but not often. The risk is that RTDs are not perfect and don't last forever and when they fail, the RTD relay knows it because it is constantly checking it's health. So in most RTD protection schemes, you use what's called "voting", meaning that before the relay initiates a trip commend, at least two (or 3) of the RTDs must "agree" on the temperature reading. That's why you have 6 RTDs in the windings. That way if a single RTD fails, it doesn't immediately trip and cost you money in unnecessary down time. On something this big, it's likely very important for the operation of the plant, so any unnecessary down time will likely cost them a LOT more than just putting in more RTDs to make sure.

But common sense is rare these days, lots of people only look at the bottom dollar of the initial outlay. Ben Franklin called that "Penny wise, pound foolish".

As to whether or not it's a warranty issue, that can only be answered by the equipment supplier.

 

[Besoeker3]

Has anyone ever only used one stator RTD? I have always used all 6, 2 per winding and the 2 on the bearings. However, the controls engineer says only one RTD back to the protective relay is all that is needed. Would it be a warranty issue if not all RTDs were used as specified by the motor manufacture? IMHO there is a reason manufactures have not one, but two RTDs on the windings, and not on just one winding, but all three.

I'm with you on this. Just a common sense engineering approach.

 

[iceworm]

All of the new bigger* motors I've seen have two, a few with three, RTDs /phase. Bigger defined as 2400V, 4000V, 6500V.
I recall going through the RTDs and picking out the highest reading ones to connect to the protective relay. I also recall a few older (40 years maybe) where the protective relay had only one winding temp input. As I recall that motor had 10 ohm copper RTDs.

After 20 years, a motor could be easily down to a few, to no, RTDs. One I saw had RTDs glued to the end turns. As long as the wedges are tight and windings meg out, the bearings get changed and they get run.

 

[paulengr]

RTDs are a customer decision, nkt warranty. They are cheap so you get however many you want. Some customers use them, some don't. An overload relay is a calculated heat level in a motor. A temperature sensor is a much more accurate way to protect it. Given that 99% of the motors out there only have overload relay protection and don't have much higher failure rates, RTDs are better but not an absolute must.

All RTDs rely on very thin, fragile parts by nature so they are far less reliable than the motor itself. This "voting" logic to try to ignore the failed ones. Thermocouple are much more rugged but less accurate and less common.

Way before a bearing overheats issues show up in vibration data. By the time it is overheating it is already all but destroyed.

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