Can someone please explain why you need trip isolation links in protection relay panels

[electrical429]

I understand that you need them to isolate tripping functions, but what would be the reason why you would want to isolate certain trip functions? Looking at attached circuit breaker DC schematic example:

LK10 (light blue) BUS ZONE TRIP ISOLATION - I assume you need to remove this link if you are performing maintenance/testing on busbar protection relay when CB is closed so testing does not trip the breaker?
LK17 (green) and LK18 (turquoise) BUSBAR PROTECTION TRIP ISOLATION and BUSBAR PROTECTION INTERTRIP ISOLATION - why do you need these links when you can isolate busbar protection trip relay via LINK10 (light blue)?
LK4 (orange) TRIP ISOLATION LINK - what would be the scenario/reason when you would have to remove this link?
LK12 (red) INTERTRIP RELAY SUPPLY - what would be the scenario/reason when you would have to remove this link?
LK13 - LK16 (blue) INTERTRIP PILOT ISOLATION - what would be the scenario/reason when you would have to remove this link?

https://files.engineering.com/getfi...-42a8-88c6-e63d8ff9c06e&file=DC_schematic.jpg

 

[bacon4life]

PRC standards require testing that every possible trip path function properly. When there are multiple paths the trip signal could take, being able to open all but one of them is quite helpful.

 

[thermionic1]

Upgrades and maintenance.

I am currently in the process of replacing an entire control building and breakers in a live sub that's carrying about 250 MW. We use the test switches to isolate a breaker or isolate a relay that may initiate a Breaker failure to another relay, as well as other signals. The list goes on. Some test switches are voltage (AC or DC) and some varieties are for current that also short around the relay / meter. This is also a very convenient place to measure current and or phase angle. These were especially useful for electromechanical and static relays and were the only way for these relays to know what the relay was "seeing".

There were many turbine generators that were installed in the 2000's that had multiple digital relays as part of the OEM standard package. Then came NERC requirements and I was paid handsomely in the past to write procedures and then lift wires for testing and re land and document.

 

[electrical429]

Is there any good book that would explain this subject (ideally based on UK, but not essential)? I know "Keith Harker - Power System Commissioning and Maintenance Practice", its quite good but is very broad and covers everything from relay protection to cables, and primary commissioning. I would like one that for starters would explain the topic in this thread about the links and mostly be related to protection and control commissioning. I am a designer, not commissioning engineer so would like to have a bit more understanding why certain things are there in the design standards. For example why aren't there a trip isolation link for TR-2 next to LK18 (turquoise) in the intertripping circuit. Things like that.

 

[thermionic1]

I don't remember if it's covered specifically, but the Alstom (or whoever they are now) has the Network Protection and Automation Guide (or similar?) that is free to download and is certainly IEC based.