high ampere problem in grasso ammonia screw compress0r

[ghanghas85]

Good morning to all my refrigeration engineer fellows,dear friends i have installed 11 no. screw compressor.3 comp. -30 deg c , 2 compressor -38 deg c,3 compressor -10 deg c and 3 compressor on -2 deg c system. but there is some problem in 1 compressor of -10 deg c and 1 compressor on -2 deg c.all the parameters are normal during operation but when capacity reach in AUTO/MANUAL mode 71% to 74 % it draw 460 ampere while on 100 % it draws 430 ampere.Kindly gives your valuable views.

[NH3LVR]

Are these variable VI (Volume Index) machines?

[ghanghas85]

yes sir this is variable vi machine

[NH3LVR]

First, I am not familiar with your machines, so this information is general. I took a quick look at the Grasso website, but did not know which machine you have.
Others on this site certainly know these machines well.

If you have machines working at identical conditions it makes troubleshooting a lot easier.
I have watched the amperage draw go up when I have dropped VI on compressors. The first thing I would do is to check the VI on another machine that is operating correctly, at the same condition. If it is not in the same range, change the VI manually (if that is possible). Be careful. Dropping the VI too low can put a tremendous strain on the motor and compressor.
I think that others on this site can advise you better. I know that Grasso uses a little different control system on their Variable Speed screws.
I assume you have the technical literature on your machines. If you do not have them they are available on the Grasso website.