Calculating 59N pickup for DG PV site

[ItsAllDownhill]

Hello all. I've got a 12.47kV distribution feeder which is connected to a 3MVA PV site. The protection on the feeder side is a SEL-751. The feeder is grounded wye, and the VT is grounded wye at 60:1.
I didn't create these settings but they "rolled down hill" to me. The 59N function in the SEL-751 is currently set to 12 volts, with zero delay. I would be expecting something more like 80-100 volts secondary. The problem I'm facing is that the folks who set it claim that they simulated faults in the field to generate this setting pickup. I've attempted to explain that this is too low but I'm not gaining much traction. Could someone more experienced in this scheme provide a "rule of thumb" settings value? As mentioned, the delay for the pickup is set to zero, and, not surprisingly, the element is picking up often and tripping the site. I'm pushing the utility to allow us a 20-30 cycle delay here. Any thoughts on that are also most welcome.
And this is my first post, although I've been lurking for over a decade. Thanks in advance!

 

[jim dungar]

Without knowing all of the protection scheme settings, it would be difficult to comment. However I would investigate any feeder/main function that does not have a delay in order to coordinate with downstream devices.

Have you looked at any white papers or application notes from Schweitzer? I have found them to be a good place for a quick intro to using their protective functions.

 

[ItsAllDownhill]

Jim, thanks for responding. To clarify a bit, I am working for the owner of the PV installation. We are connecting to the utility feeder in this instance, and have no visibility to any feeder protections. In my experience these would typically be comprised of 51/51N relaying or just coordinated expulsion fuses. My personal experience with 59N functions are using it as a transmission line protection, IE protecting the line from a single line to ground fault being fed from a generator after the line protection clears the remote terminals but the generator islands.
The small DG has experienced frequent (daily) trips from the relayed recloser on the 12.47kV side which interconnects to the utility feeder. Frankly I have some idea what I want to do with these settings, but I have noticed that if I post my personal plan of attack, that is what gets the feedback. I'm trying not to bias any responses with what I want to do, and hope to snag the attention of a more knowledgeable protection engineer without muddying the waters. I am familiar with the traditional application using a broken delta connection into a EM relay or solid state relay. Thanks again!

 

[ItsAllDownhill]

Also yes, I've perused SEL's database.

 

[Hv&Lv]

I didn’t think the 751 had 59N..
are they LEA inputs?
LEA 12V is 450 volts to the relay
LEA .12 is 4.5 volts
Maybe they are on the wrong side of the decimal?

 

[topgone]

Keep in mind that increasing your 59N setting will leave you not covering the whole winding of the equipment you are protecting. 59N coverage is = (rated line-neutral voltage - the pickup setting x turns ratio)/rated line-neutral voltage.
In your case = (7,200-12 x 60)/7,200= 90%.
Also, setting the 59N too low would result in tripping even when in normal service. I recommend to you increase it a bit to keep the nuisance trips out. 5-15V is the figure I always see. Is 87.5% coverage okay with you? (changing to 15V pickup setting).