Co-Generation Switchgear Main Breaker Protection Scheme

[rockman7892]

I'm looking at a lineup of 13.8kV double ended switchgear that is used as part of a co-generation arrangement. The swichgear has (2) 2000A main breakers which are connected to the utility transformers. The feeder breakers in this lineups serve various plant loads, and one feeder breaker on each side of the lineup is used as a generator bus interface breaker to a generator bus that is used as part of a co-generation scheme. The generators are actually 4.16kV so these 13.8kV interface breakers hit transformers before the 4.16kV generator bus.

In looking at this distribution arrangement I am curious what kind of typical protection schemes are provided for the 13.8kV switchger main breakers (utility interface breakers) and generator interface breakers. From looking at the one-line and control diagram it appears that the generator interface feeder breakers are supposed to have 50/51, 50/51N, 27/59, & 80O/U protection while the main utility interface breakers only appear to call for 67 and 67N direction protection.

My question is wheather or not this is typical for a co-generation arrangment? Do the main breakers only require 67/67N protection and not any 50/51N protection? If this is true I'd be interested in understanding why? There is relay on the main breakers that is capable of providing 50/51 functions, should these be used as backup protection?

I am simply looking at an existing drawing trying to understand the logic behind this type of protection scheme for my own interest. I appreciate any input others can offer.


Also I am curious if anyone has ever seen "CSR" and "TSR" relays in a DC breaker control schematic? I have never seen these before and from what I can tell from searching these appear to be some sort of single shot reclose relay used for the main breakers? Has anyone seen this before? I can post a schematic to further clarify.

Thanks for the help!

 

[davidbeach]

CSR is a Control Switch Relay, a remotely operable control switch. Not sure what a TSR is. Don't know if there is a "typical" protection scheme. I think your 80O/U should really be 81O/U. The 67 on the main is to distinguish between internal faults being fed by the utility vs. external faults being fed by the co-gen. Feeders only don't have a source out on the feeder and don't need directionality. Generator interface breakers look like they have the minimum required by IEEE-1547.

 

[dpc]

There's no real standard for abbreviations like CSR and TSR on schematics. This is why they need legends. You'd have to post the schematic.

The protection sounds reasonable, with David's comments. The utility basically just wants your generation to go away as soon as possible and as reliably as possible in the event of any kind of fault on their system. There are a lot of different ways to achieve this.

 

[slavag]

LOM- loss of main protection or decoupling protection

59, 27, 81U, 810, 81R, 78-Voltage vector jump, 47U ( positive sequence undervoltage ).
in special cases 67 with 27 undervoltage start, direction to grid

 

[rockman7892]

Thank your for the responses!

Attached is the breaker control schematic that I was referencing which has the CSR and TSR relays outlined in red. It appears that these relays are triggered by some sort of remote swich and have contacts in both the close and trip circuits for the breaker however I cant seem to figure out exactly what their purpose is?

The 67 function on the breaker makes sense as described by davidbeach. If there is a fault on the utility system you want to trip the main breaker as soon as possible to remove the generator fault contribution. I'm assuming this 67 setting will have a very fast trip time. For faults occuring in the facility system I'm assuming that you would want to coordinate the 67 setting in that direction to coordinate with the other feeder breakers the same as you would approach normal coordination? So the 67 in the utility direction would have a somewhat instantaneous setting while the 67 in the facility direction would have a time dealy similar to a normal 51 setting on a main breaker. Does this sound right?

I guess you would not want to use the 50/51 settings on the main breaker because the breaker would have no way of knowing what direction the fault was and therefore could not trip as intended and as I described above for the 67 setting? Are there any voltage or frequencly related trip functions that should be set on the main breaker, or should these settings be left to the geneerator interfact feeder breaker as I described in my origonal post?

Lastly are there any sepecial CT or PT considerations for the CT's and PT's on the main breker in terms of location, orientation, and type?

Thanks again for the help!

 

[davidbeach]

The HGA is an aux relay. In this case CSR and TSR are Close S Relay and Open S Relay, not sure what S is. Far more complex that it needs to be, just use an actual 52CSR, which is a 52CS (Breaker Control Switch) with control inputs to move the switch to the close or trip position.

The use of 100A fuses on the DC system is highly suspect; at 100A you will definitely be blowing trip or close coils to protect the fuses instead of the other way around.

 

[Marmite]

It looks to me like CSR and TSR are interposing close and trip relays respectively. The coil operating current is derived from a separate DC source (or separately fused DC source at least). Perhaps this is to avoid exporting the main DC tripping and closing supply beyond the main curtilage of the substation to the point where the remote trip and close switches are located? My guess as to the acronyms could be Close Seal Relay and Trip Seal Relay.

Regards
Marmite

 

[slavag]

Its really standard scheme with NCC/DCS/RTU remote control aux relays.
RTU DC voltage will be 48-60V DC.

 

[oldfieldguy]

The use of the CSR & TSR relays reduces the requirements for conductors to the remote operating station. The relay operating currents are much lower than the current requirements to switch actual close and trip currents.

The use of a high-rated fuse (or in some cases, a brass slug, no fuse at all) in the trip circuit is not unusual in the areas in which I operate. The rationale is that the last thing one wants to happen is for a fuse to open up on a trip circuit.

Note that both these comments are brought forth from the days when trip and close coils drew large amperages to operate. Modern breakers with vacuum or SF6 interrupters generally require much less current, so some of these problems no longer exist.

old field guy

 

[rockman7892]

Thanks for all of the responses! It does appear now that the relays in question are auxilar control relays for remote breaker opening and closing.

I'm assuming that the CS/T contact in the trip circuit and in parallel with the "Red" light is the contact from the local control switch at the breaker.

Does anyone know what the Delta (Triangle Symbol) contact in the trip circuit may represent? I'm thinking this may represent the output contact from a bus differential relay which exists in the switchgear?

Thanks for the help

 

[rockman7892]

One other question that comes to mind is the location of the Pt's in the switchgear. The one-line appears to call for Pt's on the line side of the main utility breaker, on the 13.8kv switchgear bus, and on the load side of the generator feeder breaker. Are all 3 sets of Pt,s required for protection, synchronization, etc....?

I also notice that the main breaker line side Pt's are 3 winding Pt's while the other Pt's are broken delta Pt's. Is there a reason for using one type over the other?

In this application is there an advantage to locating the main breaker ct's on the line side of the main breaker as opposed to the load side?

Thanks!

 

[davidbeach]

With decent relays there is no reason for VTs to be connected in anything other than wye. To do all the necessary synchronization you will need all three sets of VTs, although it might be possible get away with one set being only single phase.

 

[living2learn]

Also I believe IEEE 1547 requires wye-wye PT's which aid in directing fault direction.

Maybe I missed it by why would you still not use the 50/51 protective device on the mains? I guess the only thing it would protect would be the bussing between the mains and the feeder breakers and by the time this engaged, game could be over.

 

[davidbeach]

67 is 50/51 plus direction. If one source is much stronger than the other then you really only need direction toward the strong source and can use non-directional overcurrent toward the weak source. So, if the lowest current fault you want the mains to respond to on the system fed by the utility is larger than the maximum possible fault current that the facility can supply for a fault on the utility, there is no need for directionality for utility sourced faults, but the only way to trip for utility faults without being overly sensitive for internal faults is to use directional elements.