Are RTDs really necessary?

[REEngineer]

I want to utilize RTD relays for protection of 3300V motors. The motors are already equipped with overload, earth fault and stalling relays. What is the condition in which RTD relay trips and the others don't?

I need this to justify the installation of RTD relays. If their purpose can be fulfilled by overload and stalling relays, then why should we bother installing them?

[ December 11, 2005, 10:52 PM: Message edited by: REEngineer ]

 

[Nick]

Re: Are RTDs really necessary?

An RTD is there to measure winding and or ambient temperature. You could have high temperatures inside the motor without having an overload or short circuit.If this is a large expensive motor you would be wise to use them. It is, however, a design choice.
Where are you that you have 330V??

 

[Leitmotif]

Re: Are RTDs really necessary?

What is your question --
are you asking
1. if you should connect RTDs already installed in motors.
OR
2 if you should specify motors have RTDs installed
during manufacture
OR
3. if you should rewind motors just to get RTDs

1. Of course -- doubly so if they are on a VFD and will run at slow speed.
2. Good idea
3. Well it is your money I don't see the need to retrofit.

 

[tom baker]

Re: Are RTDs really necessary?

Often the RTD will fail, and will be bypassed. It makes sense on a large expensive motor. But for the smaller motors its not worth it. You'll get good motor protection with quick trip, ambinet compensated overloads, better yet with time delay fuses set at 125 to 140% of the motor FLA.

 

[REEngineer]

Re: Are RTDs really necessary?

There was a mistake in my post. I typed 330V instead of 3300V! Sorry!