I've recently started to get involved with some transmission scale renewable energy projects and it seems like the design around the 34.5kv system is limited based on what is commercially available for circuit breaker ratings and potentially disconnects.
IEEE C37.04-2018 Table 12 "Preferred Ratings for class S2 (outdoor) circuit breakers" shows the highest rating for a 38kv class breaker as 3000A. The highest rating that I can find for this type of breaker is by Siemens via their SDV7 breaker which appears to have a high limit rating of 2500A at 40kA.
IEEE C37.04-2018 Table 8 "Preferred Ratings for class S1 (indoor) circuit breakers shows the highest rating for a 38kv class breaker as 4000A. The highest rating that I can find for this type of breaker is by Eaton which is a 3000A force air cooled breaker, otherwise it's 2500A as well.
Does anyone know of any other vendors that offer any higher ratings?
The reason why I've been digging into these ratings in the first place is I'm trying to figure out what a realistic limit on transformer sizes should be with a 34.5kv secondary but this all rides on my next question: Is there a limit on how many circuit breakers can be on a 34.5kv bus if there is no low side breaker on a main power transformer? Some folks that I've asked at work keep referencing a 6 breaker rule if there is no main breaker on the 34.5kv bus on the low side of the transformer but I don't believe that rule applies since a generating facility would not apply under Article 230 as a Service. The breaker on the high side of the transformer would be limited to 300% per 450.3(A) so I think we are covered from that regard as I would consider the collector substation to be a supervised location.
One thing that could be an issue is that the highest fault current rating that seems to be available at 34.5kv level equipment is 40kA so if the system strength is high at the transmission side from being near generation sources, that might end up being the limiting factor for the transformer size and 34.5kv system size.
So if the fault current is not an issue then we could use a 4000A+ switch on the secondary of the transformer, (Southern States WAG-A Switch) and then have physical bus on the with 1200A breakers serving the collector circuits this seems like it would be the ideal setup for a collector substation.
I'm interested to see if anyone has a comments on this arrangement or sees any fatal flaws. Thanks all!
IEEE C37.04-2018 Table 12 "Preferred Ratings for class S2 (outdoor) circuit breakers" shows the highest rating for a 38kv class breaker as 3000A. The highest rating that I can find for this type of breaker is by Siemens via their SDV7 breaker which appears to have a high limit rating of 2500A at 40kA.
IEEE C37.04-2018 Table 8 "Preferred Ratings for class S1 (indoor) circuit breakers shows the highest rating for a 38kv class breaker as 4000A. The highest rating that I can find for this type of breaker is by Eaton which is a 3000A force air cooled breaker, otherwise it's 2500A as well.
Does anyone know of any other vendors that offer any higher ratings?
The reason why I've been digging into these ratings in the first place is I'm trying to figure out what a realistic limit on transformer sizes should be with a 34.5kv secondary but this all rides on my next question: Is there a limit on how many circuit breakers can be on a 34.5kv bus if there is no low side breaker on a main power transformer? Some folks that I've asked at work keep referencing a 6 breaker rule if there is no main breaker on the 34.5kv bus on the low side of the transformer but I don't believe that rule applies since a generating facility would not apply under Article 230 as a Service. The breaker on the high side of the transformer would be limited to 300% per 450.3(A) so I think we are covered from that regard as I would consider the collector substation to be a supervised location.
One thing that could be an issue is that the highest fault current rating that seems to be available at 34.5kv level equipment is 40kA so if the system strength is high at the transmission side from being near generation sources, that might end up being the limiting factor for the transformer size and 34.5kv system size.
So if the fault current is not an issue then we could use a 4000A+ switch on the secondary of the transformer, (Southern States WAG-A Switch) and then have physical bus on the with 1200A breakers serving the collector circuits this seems like it would be the ideal setup for a collector substation.
I'm interested to see if anyone has a comments on this arrangement or sees any fatal flaws. Thanks all!
