Modern protective relays
Modern protective relays
(OP)
This is a general discussion for the fraternity to ponder and put their views.
In the era of digital technology, the development of relays have gone far beyond what is really required. As many features are being added to the relays they are getting too complicated. Some of the relay manuals are now reaching to more than one thousand (1,000) pages! In the internet age where the attention span of the people is getting reduced, it is serving the purpose by publishing such a huge instruction manuals?
The protection relay itself is loosing its focus from the basic functionality. In my opinion the time has come for the relay manufacturers to adapt different strategy. Make the protection relay simple and easy to understand the set. The relays can be handled by an average qualified technician. This would benefit all in the industry.
As the technology is getting cheaper by the day, it has become a trend for the relay manufacturers to make it more fancy and sell with these features.
Any thought on this view or anyone who share these views?
In the era of digital technology, the development of relays have gone far beyond what is really required. As many features are being added to the relays they are getting too complicated. Some of the relay manuals are now reaching to more than one thousand (1,000) pages! In the internet age where the attention span of the people is getting reduced, it is serving the purpose by publishing such a huge instruction manuals?
The protection relay itself is loosing its focus from the basic functionality. In my opinion the time has come for the relay manufacturers to adapt different strategy. Make the protection relay simple and easy to understand the set. The relays can be handled by an average qualified technician. This would benefit all in the industry.
As the technology is getting cheaper by the day, it has become a trend for the relay manufacturers to make it more fancy and sell with these features.
Any thought on this view or anyone who share these views?






RE: Modern protective relays
In some POCOs/substations relays are called to do a number of very complex functions which necessitate a plathora of features and logic sequences being used as offered by modern relays. Add "smart grid" to that equation and the relay is using it all.
On the other hand in most other applications (especially retrofit) I think modern relays are grossly over featured. It is those excessive features and complex user manuals that IMO create reliability risks because the odds of something being set incorrectly increase- not to mention through programmer confusion.
RE: Modern protective relays
There's also something to be said for working with as few different relays as possible. If I use just a handful of functions in a relay I've very familiar with I'm less likely to make mistakes than if I try to "optimize" the relay selection and work with an unfamiliar relay that is a "better" fit for the limited application.
RE: Modern protective relays
If you want simple relays, they can be found, just don't specify the top of the line relays that were made for the EHV applications, which is likely to use more of the relay functions.
Does the quarter or half cycle faster really matter for a 100kV line. Maybe a faster breaker would make up for that (if you can justify that).
And david is right, turn off what you don't need.
Simpler over current relays do exist.
RE: Modern protective relays
RE: Modern protective relays
https://cdn.selinc.com/assets/Literature/Product%2...
RE: Modern protective relays
So it is not the processor speed alone that makes a faster relay, but also how it processes the information.
If you look at the tables on the relay speed, you can see typical times for different faults.
If you want a little faster speed, order the high speed contacts.
It should be possible to setup a speed vs cost chart, but I don't of anyone who has done that.
But some people have turned to line differential because they want to avoid the setting complexity issue.
RE: Modern protective relays
@cranky108, Thanks for elaborating on this. My understanding is that the SEL400 series relays are always faster than 300 series for any given fault, particularly a zone 1 fault, but I could be wrong on that.
Line differential looks good for high speed clearing, but in any case it is always a good idea to set step distance and over current elements into the relay as though you had no differential to begin with. Even redundant fiber optic paths can fail (heck you have people putting the splice boxes near ground level) and Zone 2/3 is needed in the event both relays fail at the remote substation.
RE: Modern protective relays
I have tended to avoid the 400's because of the complexity issues, not just for my self setting them, but also the training of the tech's, and the testing.
As I said, if you don't need the horsepower, don't buy the top of the line relay.
RE: Modern protective relays
It sure is a slow moving industry....
RE: Modern protective relays
RE: Modern protective relays
SEL does not give the processing speeds, that I know of. They do however give the typical speeds for reaction to different types of faults.
This also depends on the fault current of the fault.
The 87L functions do operate faster than the 21 functions.
RE: Modern protective relays
RE: Modern protective relays
RE: Modern protective relays
RE: Modern protective relays
I've always thought that the delay you want to be concerned about with a 311L 'type' device is comm delays, not processing... I believe this is also the reason a Z1 21 trip will go faster than an 87 trip (from a comparable relay.
RE: Modern protective relays
RE: Modern protective relays
RE: Modern protective relays
The problem is that the suppliers are going for "one fit for all" solution. This mind set should be changed. The electrical industry invests lot of money for many unknown future provisions. Majority of the time they will be scrapped untouched along with the one which is in service at the end of the life span.
RE: Modern protective relays
RE: Modern protective relays
RE: Modern protective relays
My position for this, is that we take a step back, and try to simplify. The relay does protection, and the RTU does control. And with help of a RTAC, the relay now also does metering.
The point is if you attempt to cram too many functions into one box, you have problems. So the relay does protection, and the RTU does control. We may revisit the one box approach one day, but not to day.
The other thing is introducing too many new things too fast will cause problems.
You need to determine how much complexity your company can stand, and don't exceed those limits. And those limits will change with time, and you should change at that time.
Most of the complexity limits, and change limits will happen at some retirement party, so you should go to those.
RE: Modern protective relays
The excel spreadsheet I mentioned is the setting calc spreadsheet. There's a bunch of questions about the application that determine the logic that will be needed; lots of fault cases get entered, specific fault cases get selected to drive certain settings, the usual stuff for a setting calc sheet. The spreadsheet addresses the whole gamut of the settings from actual protection settings to display points to SER points to ...; pretty much the whole works. When that's all taken care of and reviewed, the engineer clicks a button and a text file is produced. That text file then gets used twice. One use is that it is imported into AcSELerator, every setting in all settings groups, the whole works. The other use is that it is read by a different VBA script which parses it out and writes a OneLiner RAT file that gets imported into our OneLiner model. This leaves the engineers working on engineering and the computer gets to play the clerk/typist role in getting the settings from the calc sheet and into the relay. The vast majority of the individual relay settings are never touched by the Protection Engineer doing the settings.
RE: Modern protective relays
@David Beach- ok, that makes sense now- and I like your approach btw.
RE: Modern protective relays
And two of four the 421 relays are only being used as over-current relays to backup the 387 relays, as well as the automation.
RE: Modern protective relays
RE: Modern protective relays
RE: Modern protective relays