BradHall
New member
- Location
- Tacoma, WA
I work for a small utility and am the engineering technician. We have a customer who would like three phase power at his property. There are two primary lines that run along his street. We can install two transformers with an open delta (high leg b-phase). One transformer will be larger than the other. The problem is I cannot find a formula for the transformer calculations. I've heard the capacity of the transformers will be 83% of their normal rating. Is that correct? The house is a little over 3,000sq-ft. Assuming a 5-ton heat pump with electric heat, I've estimated the maximum load for the house to be 21.5KVA. The shop will be 1,800sq-ft with three phase shop equipment. Unfortunately, I do not have the load information for this equipment. I?m assuming an air compressor and saws. I will eventually verify the actually equipment loads. So, my question is how to size the transformers? Will the house load and two of the three phases for the shop be on one transformer and the third phase be on the second? For example, 21.5KVA for the house and 9KVA (for math purposes only) for the shop. 21.5KVA + 6KVA (two of the three phase loads) = 27.5KVA If we use a 37.5KVA transformer at 83% = 31.125KVA capacity on the larger transformer. The remaining 3KVA would be on a 10KVA transformer. Is this correct or could somebody please give me an example of how to do the calculation? Thanks.
