All last summer, the plant suffered from repeated voltage sags. As cooler weather arrived in September, these tapered off in frequency. Now it’s been several weeks since one has hit.
The plant engineer connected the dots here, and looked at the HVAC system. His suspicion was that the load was too great for the supply. But it turns out that the supply transformers would be only 80% loaded with all loads running.
How can you determine the cause?