Multilin Standard Thermal Curve
Multilin Standard Thermal Curve
(OP)
Hi all.
I have a Question regarding the multilin 469 relays which we use for motor protection which protects a 1000HP motor which runs a Crusher.
We do the installation of the multilin protection scheme through the standard way of putting in required input parameters it asks about the motor.
But At this standard thermal curve(which it assume with the motor parameters) we are able to start the motor only 3 times per hour. If we start more than 3 times, the thermal limit exceeds and the multilin dont let us start. But the RTD attached to the motor never heat up. So i want to find out if the standard thermal curve assumed by the multilin is good or whether it needs to be customized according to the application.
If it needs to be customized what we should do.
Hopefully i could get some inputs from you guys.
gokul
I have a Question regarding the multilin 469 relays which we use for motor protection which protects a 1000HP motor which runs a Crusher.
We do the installation of the multilin protection scheme through the standard way of putting in required input parameters it asks about the motor.
But At this standard thermal curve(which it assume with the motor parameters) we are able to start the motor only 3 times per hour. If we start more than 3 times, the thermal limit exceeds and the multilin dont let us start. But the RTD attached to the motor never heat up. So i want to find out if the standard thermal curve assumed by the multilin is good or whether it needs to be customized according to the application.
If it needs to be customized what we should do.
Hopefully i could get some inputs from you guys.
gokul





RE: Multilin Standard Thermal Curve
Three times per hour for 1000 hp motor seems excessive.
I'd check with the motor manufacturer regarding the allowable starts and go with their recommendations.
"The more the universe seems comprehensible, the more it also seems pointless." -- Steven Weinberg
RE: Multilin Standard Thermal Curve
----------------------------------
If we learn from our mistakes I'm getting a great education!
RE: Multilin Standard Thermal Curve
Coming to my question, is it by any chance that the thermal limits of the motor can vary according to the application of to what pupose its used? I personally feel no. but my manager wants me to research about it. So i want to double check and make sure.
gokul
RE: Multilin Standard Thermal Curve
If you can get data from the motor manufacturer related to cooling times, allowable starts, etc, the model the relay uses can be improved a great deal.
Schweitzer has a fairly new motor relay out that claims advanced thermal modeling capabilities. I'm including a link to one of their technical papers on motor modeling. You may need to register with SEL to get access to it.
http://www.selinc.com/sel-710.htm
http:
"The more the universe seems comprehensible, the more it also seems pointless." -- Steven Weinberg
RE: Multilin Standard Thermal Curve
I will go through them and get me informed.
will get back to you guys in case i dont understand something
thank you once again.
gokul
RE: Multilin Standard Thermal Curve
JIM
RE: Multilin Standard Thermal Curve
"The more the universe seems comprehensible, the more it also seems pointless." -- Steven Weinberg
RE: Multilin Standard Thermal Curve
i agree the limit of 3 x per hour is very annoying at times.
Roy
RE: Multilin Standard Thermal Curve
I have seen a system for large motors that has RTDs for the rotor an a wireless communication system back to a protective relay, but the motor must be big enough to house the components in the rotor assembly. Even then, I don't know that I would completely trust direct measurement like that over a very complex tried-and-true thermal modeling systems as is used in the Multilin and SEL relays.
"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies
RE: Multilin Standard Thermal Curve
http://www.accumetrix.com/demo/mgp.html
"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies
RE: Multilin Standard Thermal Curve
I've been trying to figure out a way to use the thermal model and thermal capacity to control this (2) cold (1) hot standard. This would mean that for the two cold starts each start should only use up 50% of the motors thermal capacity. I have heard in some cases that in order to do this you need to set the tric curve somewhere inbetween the hot and cold thermal damage curves for the motor.
Does anyone have any experiene with setting these models to use the thermal capacity to drive the Nema recommended number of starts?
RE: Multilin Standard Thermal Curve
When i requested for the curves the motor manufacturer has provided me with to curves, one for running and one for starting, and both of them are %full load current VS time.
Now i am assuming that all i got to do now is to see that the curve assumed by the multilin is below that so that it gives less space and time or above it right.
Or are there any other curve which actually gives the thermal capacity of the motor.
I am attaching the curves for perusal.
gokul
RE: Multilin Standard Thermal Curve
"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies
RE: Multilin Standard Thermal Curve
Can we move the multilin curve above the "hot" thermal damage curve as long as we stay belwo the cold?
RE: Multilin Standard Thermal Curve
Shouldnt we have to make sure that we have our curve above the motor inrush to avoid false trips.
Where should i look for the motor inrush curve. When asked the motor manufacturer he says he has never heard of that term before.
gokul
RE: Multilin Standard Thermal Curve
You should buy a copy of the IEEE Red Book. This is all covered in there.
"The more the universe seems comprehensible, the more it also seems pointless." -- Steven Weinberg