Transformer Primary Relay Setting

[timm333]

Page 7 of the link below gives rules of thumb for transformerprimary phase settings. Bullets 3 and 5 say that the time dial cannot be morethan 2 sec. The relay that I have (Multilin 735) has 10 time dial settings (1through 10). Does a time dial setting of 1 means 1 sec, and 10 means 10 sec? Soin this case, should the maximum time dial setting for transformer primaryrelay be 2 ?

Also in bullet 4, what is the difference between shortcircuit current and maximum through fault current?

Thanks!

http://www.hv-eng.com/OvercurrentProtectionAnnex.pdf

 

[templdl]

Page 7 of the link below gives rules of thumb for transformerprimary phase settings. Bullets 3 and 5 say that the time dial cannot be morethan 2 sec. The relay that I have (Multilin 735) has 10 time dial settings (1through 10). Does a time dial setting of 1 means 1 sec, and 10 means 10 sec? Soin this case, should the maximum time dial setting for transformer primaryrelay be 2 ?

Also in bullet 4, what is the difference between shortcircuit current and maximum through fault current?

Thanks!

http://www.hv-eng.com/OvercurrentProtectionAnnex.pdf

This is the way that I interpret it:
The 1-10X the pick up amperes and the delay should be from .1 sec to 2.0 seconds.
The pick up setting should be less than 3X (300%) of the self cooled rating or 1.5X (150%) the Max transformer rating.
They recommend a time delay of 1.0 sec. Please note the exception.

Primary ? Phase Settings
?CT Ratio: 200% FLA
?Set pickup to comply with NEC 450-3, but as a rule of thumb setting
should be less than 300% of transformer self cooled rating or 150%
of transformer maximum rating.
?Try to set the time dial such that pickup time for maximum through fault
is in the neighborhood of 1.0 seconds or less. If higher, ensure that ANSI
damage points are not exceeded.
?Set instantaneous at between 160% and 200% of maximum through fault
(assume infinite bus). Ensure that available system short circuit allows this.
?Time Dial set at 1.0 to 1.5 seconds at maximum fault.

 

[timm333]

The time dial setting on relay is 1 thtough 10 (in steps of 1.) Does a time dial setting of 1 mean a time delay of 1 sec?

As the time dial settings are only in steps of 1 (1, 2, 3, etc); so how shall we set the time delay to 1.5 sec?

 

[templdl]

The time dial setting on relay is 1 thtough 10 (in steps of 1.) Does a time dial setting of 1 mean a time delay of 1 sec?

As the time dial settings are only in steps of 1 (1, 2, 3, etc); so how shall we set the time delay to 1.5 sec?

Yes, I see what you mean so I actually looked at the mamual.
Take a look at the actual manual and the settings refer to points on the trip curve where the trip curve itself has the values, time on the left and current across the bottom which you should be familiar with. The following is the link to the manual:
http-://www.gedigitalenergy.com/app/ViewFiles.aspx?prod=735737&type=3

As you will note you will have to determine the settings indirectly with the use of the TC curve as included in 3.2 of the manual.

 

[kingpb]

There is no such thing as "Rule of Thumb" for protective relay settings.

Each device needs to be set based on the actual equipment being protected and the information gathered by performing the system studies. Time coordination curves need to be completed.

I have made this point many times; the allowable settings in the NEC for transformers is baseless and will more than likely lead to an unprotected transformer such that damage will occur to the equipment prior to operation of the protective device.

What are the ratings of your transformer?