Using duplex type RTDs in High Voltage Motor protection


Thread Starter

Kunal S Dabi

1. What is the advantage of using duplex type RTDs in High Voltage Motor protection (Motor stator and winding)?

2. Is it possible to replace Simplex type RTD with Duplex type RTD on site? If yes then which type of implication require in Motor & receiving end of RTDs signals like Motor protection relay, PLC, DCS etc.
Without knowing the application of High Voltage motor protection, let me state some basics of RTDs:

An RTD is a resistor, so it requires an excitation source current to develop a voltage drop that the instrumentation can 'see' or 'read'.

An RTD's 'signal' cannot be paralleled when more than one temperature reading is needed by multiple instruments.

One means of getting multiple readings is to use multiple RTD's in one sheath: dual elements or duplex sensor assemblies. One RTD connects to one instrument, the other RTD connects to the other device.

It is entirely possible to replace a Simplex (single RTD element) with a Duplex (dual RTD elements) as long as the probe physically fits in the same location.

The only implications I can think of involves connecting the 2nd RTD to some instrument which will needs to be RTD input compatible (you can't connect an RTD to a thermocouple or 0-5Vdc analog input) and the RTD element type must match the analog input type: 100 ohm Pt or 120 ohm nickel or whatever.
Kunal... typically, RTD's used to monitor motor temperature are embedded in the winding slot. Thus, they are not replaceable and a duplex arrangement increases monitoring reliability!

Regards, Phil Corso