Dap Plant Dryer Issue

We are Operating a Diammonium Phosphate Fertilizer Plant , which was originally designed by AZF Grande Proiesse. The plant was later on revamped by Jacobs for a capacity increase of 165 %

During the revamp , the dryer was also revamped with some modification in non feed end rotating tyre. The dryer is similar to cement kiln. After two years of sucessful operation we are experiencing problem of current fluctuation in the driver Medium Voltage Motor 450 kW ,2.4 kV,142 A.
Normal running amperes of motor are 90-100 A.
Presently the motor current fluctuate between 46-157 A.Motor No Load Current is 45 A.

The motor is driving DAP product dryer through hydraulic coupling arrangement. We have chekced the motor an no abnormality is observed in the motor. Also, motor has been replaced and chnage in ampares observed . It means that the current fluction is from load end

Have any one observed similar issue and what was the probable cause.

regards