Chiller on step-up transformer

[Jraef]

While modifying the settings is a viable option, he should take care to ensure that the frequency and voltage supplied to the motor is still within mfg. specs. OF course, asking the startup tech to make the changes is the right way to go.

Motors that operate outside their design curves don't do so well in the long run. For example, submersible centrifugal pumps typically cannot be operated at less than 30-35 Hz for long periods because the insulation on the windings will eventually break down. One must also consider that loading characteristics as running a motor off it's curve will cause excessive heat and premature wear. This is why the motor guys will load the motor and record work done and current draw during a startup.

A VFD modifies the voltage and frequency together, which makes most of these issues not apply. The reason why centrifugal pumps are usually not operated below 30-35% speed is simply because they usually no longer overcome the static head at some speed, in which case operating the pump becomes pointless. That operating point is totally dependent on the particular pump curve and the static head, but in a lot of cases ends up in the 25-40% speed range.

Insulation breakdown issues using VFDs can happen if precautions are not taken, but are not related to speed. Speed on a centrifugal pump just means flow (after overcoming head) and the motor power consumed varies by the cube of the speed, that's why VFDs save more energy than throttling valves within their effective operating range.

That said, I still totally agree that speed of a chiller using a VFD should only be handled by someone extremely knowledgable about chiller operations under variable speed conditions. There are serious Mechanical repercussions to getting it wrong (ie "surging" and cavitation), that can lead up to and include the destruction of the chiller.

 

[Besoeker]

We will let it go, as you are not likely familiar with NEMA standard transformer sizes, 112.5 kVA is a standard three phase size but not a standard single phase size, at about any standard voltage as well.

Yes, but the voltages should have been a clue...........and it's a pretty basic stuff.
As my late great friend Tommy was fond of saying:
"The man who never made a mistake never made anything."