I work on very big VGT's

[Wildcard]

(07-05-2021 )Rawze Wrote:  

(07-05-2021 )Wildcard Wrote:  ...
No tach feedback, it's just a WAG from programming motor parameters and motor speed at 60hz.
...

huge mistake with a system like that.. What cheap bas$tard would do such a thing is would I would be asking.

Open loop systems like that are always going to have issues... I would be looking into putting a tach on it and a better VSD instead of chasing surge, load balancing, and all sorts of other issues that can easily be avoided if it had been designed right to begin with.

I have worked with, and have designed from the ground up, drive and control systems far bigger than that in my day.

Better call York, Carrier and Trane cause none of them use a tach. Not that it would be useless but in the VSD Centrifugal chiller world there are far more variables that create a surge, and we are always chasing that surge line regardless of impeller speed, as its where the machine operates the most efficient. The variables of refrigerant gas pressures, variable water flow, variable load through the chiller, maintaining oil pressure all need to be taken into the "math". If the lift gets out of whack from water flow, building load, a cooling tower issue etc, etc these chillers will surge. Unlike a turbo or a Centrifugal air compressor or water pump there are far more variables to cause a surge. Were pumping refrigerant gas and the surge line is always changing.

I have a pretty good set of training slides I could email ya if you would like to view them. I would be interested in your thoughts.