Motor thermal overload protection, ANSI 49 with Sepam Relays 1

[radug]

Hello,

I already posted this in electric motors forum, but as I have no replies, I post it here in case someone can help me:

I am trying to define protection settings of a Sepam relay for thermal overload protection of an AC motor, ansi 49 function. This relay has 2 curves, cold and hot.

I have the relay manual and do not understand exactly how to define proper settings from ac motor datasheets (sometimes I have cold and hot time constants and with other motors I have the curves).

I have contacted the relay manufacturer (in Spain) and it has been of no help.

I have also read the IEEE AC Motor Protection Standard but still, I do not understand exactly what this relay does and how to select proper settings.

Anyone has experience dealing with this relay?


Thanks.

 

[DanDel]

What are the actual input settings and ranges of the relay?

 

[slavag]

Hi Rdug.
Please send us type of relay.
For the start, see attached thread.
thread238-207119
Regards.
Slava

 

[radug]

Thanks for your prompt answers,

Relay info is in the attached file.

The problem I have is that sometimes I have only hot and cold time constants and no thermal curves of the motors. If I use the hot time constant value and put a similar but lower value in the settings of the relay, when I plot them the cold curve is very high, so I do not see any "purpose" for that curve.

Thanks.

 

[slavag]

Hi Radug.
I have some additional Q's: what is typical size, voltage and type of motors? Maybe we try use some typical curves.
Regards.
Slava

 

[Runsor]

The IEC 60255-8 thermal model is a simple single time constant model.
The two time constants are by no means for hot and cold but for "running" and "stopped" situations. For generators and cables there may not be any difference between the heating and the cooling time constants.
When the motor is running, the measured equivalent current and the time constant T1, are used to model the temperature rise of the motor.

 

[slavag]

Hi Radug.
What I understand from this manual.
1. First of all, Ransor was right: hot and cold time constant is for running and stopping motor.
T2 you need use for the function like to number of starts per hour or close inhibit. and of course T1<T2 for motors, for trafos and cablea are the same, BTW for motors, for my opionin possible use same value too. You don't use T2 for cold curve calculation!!!!!
2. Of course cold curve is higer then hot curve.
Cold curve you can use as simple overload protection .
Hot curve you can use as lock-rotor protection or start up protection.
Please Send some example of motor data and will try calculate something.
Regards.
Slava

 

[veritas]

Hi Radug

Sorry I missed your first posting. Please find attached a write up I did outlining my philosophy applied when I set the M87. The thermal function in the M41 and M87 is the same. If you want I can also send you a little spreadsheet I did to automate the calculations. Helps a great deal with relay testing.

I want to point out most important that a given time constant fixes both the Hot and Cold curves, BUT the cold curves can be moved around relative to the hot curve by use of the Es0 settings.

Let know if anything is still unclear.

Regards.

 

[radug]

Hi all,

Sorry for delaying so much in this reply but I have been on vacation.

I have been using Es0 value to move the "cold" curve relative to the "hot" one as you have suggested. The problem I have is that I do not understand what that curve protects, I think it will never trip because the motor is protected (besides the 49) with the following ansi functions: 37, 46, 50N/51N, 48/51LR, 66 and 51 (by a fuse)

I attach a file where the fuse, locked rotor, and 49 hot and cold curves as well as the locked rotor point of the motor and the motor starting curve.

 

[AMBMI]

I think your setting values are fine.
The purpose of the F49 element is protecting the motor against many small repeated overloads; each of them is increasing the motor temperature but after a while the current goes below the rated current value for few seconds. In this situation the F51 element won't trip because it will reset every time the current goes below the trip threshold but if the following overload is very close the motor doesn't have time to cool down and we risk to reach the motor thermal limit. The F49 element has exactly the purpose to mock up the motor thermal status: when the current goes below the threshold the element doesn't reset suddenly but the thermal status starts decreasing. It increases again as soon the current is above the threshold.
During a short circuit the F50/51 element is tripping without waiting for the longer F49 trip time.

 

[slavag]

Hi Radug.
I think AMBMI are right. Your setting seems fine. please add 50/51 function on the plot.

 

[radug]

Well,

I do use T1 constant for both 49 hot and cold curves, or running and stoppig curves as some of you clarified. If the hot time constant is, let's say 35 minutes, then I use something lower, for example, 30 minutes in both curves. Then I use ES0 value to lower the cold curve as much as possible. But: what is as much as possible? where is the limit? what will this curve protect? when will it trip?
And also, by lowering the curve increasing Es0, is there any danger that ansi 66 function will not work?

The 50/51 function is in the plot as a fuse doing that function. In "small" motors I have fuses and in "large" motors I use the 50/51 function of the Sepam S80 relay together with a ansi 87 function.

For me, it is more a a doubt about motor behaviour than relay setting. I was quite sure about the relay settings I posted in the graph but do not understand well the motor thermal behaviour.

Thanks all again.