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The HVAC system in our 4 year old vocational school building is supposed to be capable of maximum 15000m3/h to ventilate an area of 2100m2 (approx. 6500m3) occupied by 140-160 students (age 15 up) and teachers from 8:00 to 16:00 and maybe some 10-20 students/staff from 16:00 to 21:00
The system has an air intake with a centifugal blower driven by V-belts from a WEG type 132M-4 motor rated 400/690V, 50Hz, 7.5kW, 14.2/8.23A the blower is running at approx 70% of motor-rpm The motor is connected to a SEW Eurodrive type MC07A055-5A3-4-00 (rated 5.5kW)
(the exhaust blower is similar setup, a bit smaller and has run without trouble)
The maximum motor rpm is set at 1250. the minimum motor rpm is set at 900 Ramp up time is 20s and ramp down is 45s
Now at the time of writing the motor runs at 1210rpm with phase current 8.3A according to the drive display.
The rpm of the system is regulated by a PI temperature regulator. Minimum speed is supposed to be adequate for air supply at all times (I really wonder if that is correct, but that is another story)
The HVAC also slows down to minimum speed at 21:00 and speeds up again at 7:30
The drive has stopped several times with error F-07 = DC overvoltage. I do not know for sure when that happens, just that it on or after 21:00 and before 8:00 The manual suggests that error F-07 indicates bad brake resistor or connections.
The drive does not have a brake resistor installed.
The drive has also failed totally (output transistors) 6 times in the past 4 years.
When the drive failed first time it was replaced by the next larger version (rated 7.5kW) That setup failed also several times and now it has been replaced with the "size that was designed " i. e. 5.5kW type.
The motor has also been replaced once because of "suspected" insulation failure.
Can anyone see a problem(s) with this setup and/or suggest a solution? Is the drive too small or wrong type? Is this type of drive less reliable than some other type? Is the motor unsuitable for the drive? Is a brake resistor needed? Any other remarks?
These repeated failures are getting very tiresome for staff and students, repairs now take ages (last time 4 weeks) while the relevant parties battle over who shall pay for the repair.
I have suggested to the HVAC designer that he might try to add a brake resistor, to absorb any possible overvoltage from regenerative braking. He refused and said "There should be no regeneration, the ramp down time is more than adequate, we do not do such experiments here".
Best regards.
Thor
Þórhallur Ragnarsson Electronics technician/teacher
The system has an air intake with a centifugal blower driven by V-belts from a WEG type 132M-4 motor rated 400/690V, 50Hz, 7.5kW, 14.2/8.23A the blower is running at approx 70% of motor-rpm The motor is connected to a SEW Eurodrive type MC07A055-5A3-4-00 (rated 5.5kW)
(the exhaust blower is similar setup, a bit smaller and has run without trouble)
The maximum motor rpm is set at 1250. the minimum motor rpm is set at 900 Ramp up time is 20s and ramp down is 45s
Now at the time of writing the motor runs at 1210rpm with phase current 8.3A according to the drive display.
The rpm of the system is regulated by a PI temperature regulator. Minimum speed is supposed to be adequate for air supply at all times (I really wonder if that is correct, but that is another story)
The HVAC also slows down to minimum speed at 21:00 and speeds up again at 7:30
The drive has stopped several times with error F-07 = DC overvoltage. I do not know for sure when that happens, just that it on or after 21:00 and before 8:00 The manual suggests that error F-07 indicates bad brake resistor or connections.
The drive does not have a brake resistor installed.
The drive has also failed totally (output transistors) 6 times in the past 4 years.
When the drive failed first time it was replaced by the next larger version (rated 7.5kW) That setup failed also several times and now it has been replaced with the "size that was designed " i. e. 5.5kW type.
The motor has also been replaced once because of "suspected" insulation failure.
Can anyone see a problem(s) with this setup and/or suggest a solution? Is the drive too small or wrong type? Is this type of drive less reliable than some other type? Is the motor unsuitable for the drive? Is a brake resistor needed? Any other remarks?
These repeated failures are getting very tiresome for staff and students, repairs now take ages (last time 4 weeks) while the relevant parties battle over who shall pay for the repair.
I have suggested to the HVAC designer that he might try to add a brake resistor, to absorb any possible overvoltage from regenerative braking. He refused and said "There should be no regeneration, the ramp down time is more than adequate, we do not do such experiments here".
Best regards.
Thor
Þórhallur Ragnarsson Electronics technician/teacher