The proper grounding and the shielding geometry (e.g equipment chassis earthed, cables shielded) may affect more than the distance itself as well as much as possible not sharing any of the busses, one would expect to have the data center supplied throught a double conversion UPS system and make sure that cabling from both are within not the same metallic ducts, and not close enough to induce noise, particularly if routed in parallel. Anyway, these transformers are presumed to meet electromagnetic emission requirements, correct? BTW, I sympathize with your concern, it do not feel comfortable to place sensitive devices in the vicinity of a power station. Think of shielding the room and the floor of the data center, or at least, enclosure transformers with metal cases (faraday gauge).