Single-Phase, Three Wire System
Single-Phase, Three Wire System
(OP)
If a single phase transformer primary is connected to L-L voltage, only one half of the three-phase short circuit MVA( GE SC calculation Manual, Page 33).Does anybody have reference to this calculation?
Thank you,
Thank you,






RE: Single-Phase, Three Wire System
What?
RE: Single-Phase, Three Wire System
If a single phase transformer primary is connected to L-L voltage, only one half of the three-phase short circuit MVA will contribute to short circuit amperage on the secondary side.
What I need to know is if the transformer primary is connected to H1-G , what portion of three-phase short circuit MVA will contribute to short circuit from utility.
SKM needs both values for single phase calculation, however I think only L-G MVA is needed .
Regards,
RE: Single-Phase, Three Wire System
RE: Single-Phase, Three Wire System
The in-phase transformer contributes its full capacity. The other two transformers may be considered as an open delta transformer bank. They will create a "virtual" transformer equal to the third transformer.
For example a transformer bank has three 100 KVA transformers. A single phase load is connected to "A" transformer. The transformer will supply 100 KVA. The "B" and "C" transformers together also contribute to the three phase load. If you add the vectors, voltage, current, voltage drop, etc. you will see that they create a "Virtual" transformer identical in phase angle and capacity to the "A" transformer. Together the "B" and "C" transformers will contribute 100 KVA to the load. Hence the three phase 300 KVA transformer bank will supply 200 KVA to a single phase load.
These numbers are familiar to any one who has used the double delta connection to convert a three phase generator to single phase.
respectfully