Eeram
19-07-2009, 03:49 PM
Hi Guys and Girls, I need some help on a recently installed ammonia system.
The 3 compressors were running for the last 7 months all the time, eating up some 9000Kw per 24 hour period!
We were asked to step the compressors according to size, so not all run at the same time at only 10% slide valve capacity, in order to save energy.
We change the compressor setpoints with the help of the Installation Company, but now, every night they trip on motor failure. The Danfoss soft starters either show phase imbalance fault or under frequency fault. Danfoss soft starters are set to motor information.
This never happens when they were running all the time.
All three compressors were set to the following set points:
Cut in - 215 Kpa
Control set point - 205 Kpa
Cut out - 150 Kpa
Minimum trim slide valve position - 10%
Minimum pre trim slide - 90%
Pre trim Control setpoint offset - 20 Kpa
Discharge pressure - average 1060 Kpa
Surge Drum pressure - 250 Kpa
Liquid pump pressure - 500 Kpa (2 of 3 pumps are running)
8 Rooms running at 2 deg. Celsius.
We left the Mycom 250 VSD settings as it was and change the other 2.
200 VLD Settings now:
Cut in - 220 Kpa
Control Set Point - 210 Kpa
Cut Out - 160 Kpa
160 VLD Settings now:
Cut in - 225 Kpa
Control Set Point - 215 Kpa
Cut Out - 170 Kpa
The compressors are cycling now, with the 250 VSD doing most of the work. The only problem now is the tripping only at night time. Electricity supply is very reliable.
Anybody with ideas please? I would appreciate it.
The 3 compressors were running for the last 7 months all the time, eating up some 9000Kw per 24 hour period!
We were asked to step the compressors according to size, so not all run at the same time at only 10% slide valve capacity, in order to save energy.
We change the compressor setpoints with the help of the Installation Company, but now, every night they trip on motor failure. The Danfoss soft starters either show phase imbalance fault or under frequency fault. Danfoss soft starters are set to motor information.
This never happens when they were running all the time.
All three compressors were set to the following set points:
Cut in - 215 Kpa
Control set point - 205 Kpa
Cut out - 150 Kpa
Minimum trim slide valve position - 10%
Minimum pre trim slide - 90%
Pre trim Control setpoint offset - 20 Kpa
Discharge pressure - average 1060 Kpa
Surge Drum pressure - 250 Kpa
Liquid pump pressure - 500 Kpa (2 of 3 pumps are running)
8 Rooms running at 2 deg. Celsius.
We left the Mycom 250 VSD settings as it was and change the other 2.
200 VLD Settings now:
Cut in - 220 Kpa
Control Set Point - 210 Kpa
Cut Out - 160 Kpa
160 VLD Settings now:
Cut in - 225 Kpa
Control Set Point - 215 Kpa
Cut Out - 170 Kpa
The compressors are cycling now, with the 250 VSD doing most of the work. The only problem now is the tripping only at night time. Electricity supply is very reliable.
Anybody with ideas please? I would appreciate it.