If your plant is stuck in the loop where the vendor blames the utility and the utility blames you, the way out is not another round of phone calls. It is evidence. The loop only ends when someone produces objective proof of where the problem actually starts, taken inside your facility, on your side of the meter.
What it takes to produce an answer nobody can wave off
Monitoring on your side of the meter
What it is. Temporary power quality monitoring installed on your system, recording voltage, frequency, power factor, harmonic distortion, and current draw over real operating time, timestamped throughout.
The trade-off. It requires access to your electrical system and a monitoring period long enough to capture an event. In exchange, when an event happens the data shows what happened at that moment and where it originated.
An analyst with nothing to defend
What it is. An independent engineer reading the monitoring data, with no equipment in the building and no delivery contract at stake.
The trade-off. It is a separate cost from the vendor and the utility, both of whom will analyze for free. Independence is not a nice extra here. It is what makes the finding credible to everyone who has spent weeks passing the responsibility around.
A willingness to accept an internal answer
What it is. Going into the measurement without a preferred outcome.
The trade-off. More often than people expect, the monitoring shows the cause was internal all along. That is uncomfortable, and it is the useful result, because an internal cause is one you can actually do something about.
What changes once the source is settled
This step turns a question of blame into a question of fact. Nobody has to be talked into anything. The data separates a utility-level problem from a facility-level one, and it does it in a way neither the vendor nor the utility can dismiss.
If the disturbance really did come from the utility, you now have documentation to make them fix it. If a motor start inside your plant sagged the voltage, the conversation with the utility is over and you can target the actual condition instead of replacing more equipment that was never the problem.
Either way the loop is finished, because the question that kept it running finally has a measured answer instead of a stack of competing opinions.