sparky952

Sorry, I have been all over the place. There is one of me and we have 62 offshore facilities in the Gulf and 200 onshore. Anyway, the motor is a 2300 Volt motor (Medium Voltage), the RTDs are for winding temperature to prevent overheating. The strange thing is that we lost the RTDs that were connected to an NR8. There are 2 RTD's per winding, and we only connected one. I had to replace the NR8 and connect to the unused RTDs. All is working now. I speculated that our DC Power Supply, being ungrounded (or not having the negative bonded to Earth) may have caused some issues. I measured 20 volts to ground from our negative 24 Volt Power supply. Anyway, that is all I can remember. Thanks for your reply. Sorry for not replying back.

I am new to forum posting so be gentle! I have a 2300 V motor. This motor has winding RTDs (Ni 120 Ohm). The RTDs are wired to an NR8 in a SLC 500 rack. When the motor is started the three winding RTD inputs go full scale for a short duration but long enough to cause an alarm. Currently I do not have a time delay on the alarms and I do understand that would solve my problem as a band aid. This motor has been in service longer than I have been in the business (15 years for me). A week ago the motor started going down during start up. We discovered that the RTD inputs for the windings (3 total) where showing full scale during start up. Once the motor has started the RTDs return to normal. Any ideas what could cause this? The motor has 6 winding RTDs, 2 per phase and I did swap to the other "set". I also have some bearing RTDs on the same motor that are unaffected. I set the Hz filter to 800 Hz (well, it was already set up that way). I don't want to time delay the issue, I would like to fix the issue. I speculate that perhaps I have some bleed over from the windings into the RTDs (sounds very uneducated I know). I measured some voltage during start up, but I used a high impedance fluke as I didn't have my Simpson with me so I don't trust the 3 or 4 volts measured. Maybe I should. Well, any suggestions would be awesome. Thanks.