Maintenance testing of digital relays

[veritas]

I need to do maintenance testing on digital current differential relay. Besides the current diff function the relay is also used for directional OC & EF as well as reverse busbar blocking (RBBB). It serves an 11kV network. The relay was tested to death with commissioning when every single item was tested down to the last LED. I am now wondering what tests are necessary 8 years down the line? My think is as follows:

For the current diff function:
1. test pickup from both ends.
2. test at one point on each of its dual slopes.

OC & EF
1. IDMT - pickup and one point on curve
2. Def time - pickup and timing test

Logics, inputs, outputs and LED's
I think it vital to prove all logics that will result in trips such as the RBBB.

But do I check every I/O and LED? Comments?

Thanks.

 

[FreddyNurk]

Different context I suspect, but one of the advantages I was aware of regarding periodic testing, is that sometimes it picks up alterations to the recorded settings. The area of the utility I worked for didn't have the best record keeping, along with an occasional penchant for 'updating' the settings if a feeder tripped once too often.

I wouldn't have thought that an exhaustive run of tests would necessarily be required, but it may be easier to carry it all out in the one go if outages have to be planned to access the equipment.

EDMS Australia

 

[JG2828]

You should also check accuracy of the metering, Current, voltage, and angles using a calibrated three phase test set.

 

[veritas]

The client has no ability to alter the settings in any way as the do not have the equipment, software or expertise to alter any settings. He has assured me of this. Access to the equipment is also not that difficult as it is a ring feed which can be opened anywhere.

Yeah I suppose I could add in metering checks. Maybe not a bad idea as the display of these relays are problematic. Of the 20 installed, the display cards of 7 had to be replaced already as they go haywire. Apparently some driver in the relay was corrupt. Didn't think this could happen.

Makes me wonder what else could go corrupt! I thus tend to test a bit more rather than to little. Probably a good idea to check all I/O and LED's.

 

[DTR2011]

In our transmission grid, maintenance testing of SEL relays is limited to meter checks, documenting the relay "STA"tus command, & I/O checks.

Virtual "soft points" are commonly used for SCADA alarms. I've done SCADA projects, where an RTU was changed and alarm points had to be tested with a relay test set. Here we found latent problems with element pickup settings that were not realistic for the desired function (Open Phase & LOP).

Last week we performed a function check on an existing reclosing relay, as part of a construction project. The reclosing never worked (and this was 345kV!!).

I believe with modern relay test sets, it's easy enough to perform a test of each protective element.

If you are providing contracting services, make sure the client understands the small extra effort (and time) could provide substantial benefits. If your competitor is not including this, make sure the client understands this as well.