Maximum transformer rating/circuit breakers in parallel configuration
Maximum transformer rating/circuit breakers in parallel configuration
(OP)
Dear all,
all manufacturers has a certain upper limit or maximum rating for the circuit breakers that they manufacturem, i.e. feeder rating. For example some manufacturer would have for 33 kV rated breakers a maximum current rating of 2500 A. In other words if I am to serve a load from a transfomrer with 33 kV at the LV side the maximum rating of the transfomer should be sqrt(3) x 2500 x 33 = 145 MVA.
If i am to use a larger transfomer lets say 200 MVA i would need to install two breakers in parallel since there is no one breaker at the 33 kV level that can take around 3500 A. In this case i came to know that this configuration is problametic and it is recommended to avoid due to possible issues with synchronized openning and so on.
I would like to benefit form your experience concerning this topic and whether this is, i.e. parallerl breakers, an industry normal practice and what are the possible problems and limitations of such a configuration.
Thank you.
Adam
all manufacturers has a certain upper limit or maximum rating for the circuit breakers that they manufacturem, i.e. feeder rating. For example some manufacturer would have for 33 kV rated breakers a maximum current rating of 2500 A. In other words if I am to serve a load from a transfomrer with 33 kV at the LV side the maximum rating of the transfomer should be sqrt(3) x 2500 x 33 = 145 MVA.
If i am to use a larger transfomer lets say 200 MVA i would need to install two breakers in parallel since there is no one breaker at the 33 kV level that can take around 3500 A. In this case i came to know that this configuration is problametic and it is recommended to avoid due to possible issues with synchronized openning and so on.
I would like to benefit form your experience concerning this topic and whether this is, i.e. parallerl breakers, an industry normal practice and what are the possible problems and limitations of such a configuration.
Thank you.
Adam






RE: Maximum transformer rating/circuit breakers in parallel configuration
May you grow up to be righteous, may you grow up to be true...
RE: Maximum transformer rating/circuit breakers in parallel configuration
actually it isnt for distribution but kind of generation. These configuratinos are mainly used in offshore wind farms as i believe using many transformers would take more space than having a big transformers. Splitting the secondary winding to two is also an options which is used sometims. But i saw a lot of configuratinos with parallel breakers at the secondary and was wondering what is the operative limitations or problems with that.
RE: Maximum transformer rating/circuit breakers in parallel configuration
I got a bit confused with your example above and I thought you're talking about distribution, feeding demand.
I looked at two offshore windfarms just now and one of them has 240 MVA transformer offshore 132/33 kV with 2 breakers in parallel, Siemens 8DA10 2500 A and the other one 150/33 kV 180 MVA transformer with two 2500 A breakers in parallel.
With the restriction being the current continuous rating, 1 breaker can cope with the fault break easily (most of the 33 kV breakers are rated for 31.5 kA) on a platform behind a big transformer and next to nothing fault infeed from the mills. Why do you think you would need synchronised opening?
May you grow up to be righteous, may you grow up to be true...
RE: Maximum transformer rating/circuit breakers in parallel configuration
BC Hydro have 460 mva, 16 kv generators.
ABB can parallel some of their breakers to operate in parallel so you can get about 6ka continuous.
Three winding xformer sounds optimum for 2 collector rings as suggested.
RE: Maximum transformer rating/circuit breakers in parallel configuration
For example, suppose impedance of breaker path between the points of paralleling is 0.1ohms. A small resistance increase at a clamp in one of the circuits of say 0.1ohm will have one circuit seeing 66% of the total current, with the balance in the other.
RE: Maximum transformer rating/circuit breakers in parallel configuration
Thanks!
RE: Maximum transformer rating/circuit breakers in parallel configuration