In the past, variable speed control of small chemical feed pumps has been done using DC drives. Lately, we're seeing more AFDs used with standard induction motors. Does anyone have any feelings regarding which of these technologies is more appropriate for chemical feed? DC drives required more maintenance with respect to brush replacement and the related need to stock spare DC motors which were more expensive. I'd appreciate any insight on where the technology is headed now in these small drives.
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chemical feed pump drive
- Thread starter tgreif
- Start date
Good day Tgreif!
Motor speed control this these is now becoming simplier by means of Variable Speed Drives (VSD's).
I am not familiar with AFDs but I assumed it means Automatic Frequency Drive. If this is the case it is the same as VSD.
My experience suggest that AC speed control has more advantage than DC speed control.
Besides you can find lots of suppliers offering VSDs for AC motors as low as 1/2 hp.
Regards
Lucino
Motor speed control this these is now becoming simplier by means of Variable Speed Drives (VSD's).
I am not familiar with AFDs but I assumed it means Automatic Frequency Drive. If this is the case it is the same as VSD.
My experience suggest that AC speed control has more advantage than DC speed control.
Besides you can find lots of suppliers offering VSDs for AC motors as low as 1/2 hp.
Regards
Lucino
Hello tgreif
The use of DC drives today is being replaced by the VFD technology in large numbers.Obviously, industry has realized that the VFD technology has made tremendous improvements in cost and reliability.As for your particular application, unless you are using it to pump some exotic qhemical the VFD should not be a problem. Your motor has to be suitable to operate on that environment.The only motor that could be superior to the VFD even a Flux Vector VFD, would be a Brushless DC drive motor.As I understand ,its Speed/torque characteristics
are Excellent and its superior speed regulation will make it a valid option in some applications.
GusD
The use of DC drives today is being replaced by the VFD technology in large numbers.Obviously, industry has realized that the VFD technology has made tremendous improvements in cost and reliability.As for your particular application, unless you are using it to pump some exotic qhemical the VFD should not be a problem. Your motor has to be suitable to operate on that environment.The only motor that could be superior to the VFD even a Flux Vector VFD, would be a Brushless DC drive motor.As I understand ,its Speed/torque characteristics
are Excellent and its superior speed regulation will make it a valid option in some applications.
GusD
tgreif, I suspect everyone responding here is going to say that variable speed AC drives have the edge. Economics is the main factor, the AC induction motor is manufactured in huge quantities over a very wide range of ratings, and even if DC motors were too they would be more expensive because of the extra cost of commutator, brushgear and the extra windings - not to mention increased size and the maintenance costs.
The VFD (variable frequency drive) is also pretty cheap through economy of scale, at say 2.2kW (3hp) a drive + motor probably cost around US$500 just for a 1 off, and for that they are sensorless vector running down to zero speed. They are also easy to install and replace, and are available everywhere. They are also easier to make explosion proof (totally enclosed explosion proof DC motors create more problems due to the internal accumulation of brush dust).
I don't have any knowledge of your application, for instance the typical power and speed ratings. There are potential problems to look out for:
- for VFD use it is better to use an "inverter-rated" motor
- at low speed there can be cooling problems with self-cooling motors, especially with constant torque loads
see also thread237-57745 and no doubt others.
lucino, I think AFD = adjustable frequency drive, which is the same thing as:
VFD = variable frequency drive
VSD = variable speed drive
VVVFD = variable voltage variable frequency drive
and others anyone can think of.
Where there are differences between drives, these are down to modern developments such as sensorless vector (no tacho required), direct torque control. As these are largely control algorithms implemented in drives software, they are effectively free add-ons. Incidentally, for the lower power ratings say up to 3hp, it is possible to get a drive for a 3-phase motor with a single phase feed, these are a bit cheaper.
The VFD (variable frequency drive) is also pretty cheap through economy of scale, at say 2.2kW (3hp) a drive + motor probably cost around US$500 just for a 1 off, and for that they are sensorless vector running down to zero speed. They are also easy to install and replace, and are available everywhere. They are also easier to make explosion proof (totally enclosed explosion proof DC motors create more problems due to the internal accumulation of brush dust).
I don't have any knowledge of your application, for instance the typical power and speed ratings. There are potential problems to look out for:
- for VFD use it is better to use an "inverter-rated" motor
- at low speed there can be cooling problems with self-cooling motors, especially with constant torque loads
see also thread237-57745 and no doubt others.
lucino, I think AFD = adjustable frequency drive, which is the same thing as:
VFD = variable frequency drive
VSD = variable speed drive
VVVFD = variable voltage variable frequency drive
and others anyone can think of.
Where there are differences between drives, these are down to modern developments such as sensorless vector (no tacho required), direct torque control. As these are largely control algorithms implemented in drives software, they are effectively free add-ons. Incidentally, for the lower power ratings say up to 3hp, it is possible to get a drive for a 3-phase motor with a single phase feed, these are a bit cheaper.
jbartos
Electrical
- Jan 15, 2000
- 6,440
Suggestion: Depending how the DC was obtained, there may be now a concern about VFDs, AFDs, etc. with their harmonics on their input and on their output. The harmonic treatment has to be added to the cost of procuring them. Also, the Mean Time Between Failure (MTBF) and Mean Time To Repair (MTTR) of VFDs, etc. needs to be watched. It is a good idea to find it out from the manufacturer, if it happen to be available.
Hello;
One thing you need to look out for is speed regulation. In general a VFD connected to an induction motor without a speed feedback will have 2-3% speed variation with load variation. This may skew your chemical feed process.
In any case check the rated speed regulation vs load.
One thing you need to look out for is speed regulation. In general a VFD connected to an induction motor without a speed feedback will have 2-3% speed variation with load variation. This may skew your chemical feed process.
In any case check the rated speed regulation vs load.
As field experience, we have successfully integrated small chemical dosing pumps into our HRSG chemistry control scheme without any big issue.
Check the pump will run ok on a VSD - pumps can be awkward things to start with a VSD. If you have the choice, a rotary or centrifugal pump is much easier to control. We ended up using ABB's ACS100 drive with a displacement pump![[sad]](/data/assets/smilies/sad.gif "[sad] [sad]")
. The drive is controlled by a 4-20mA signal from our DCS and has proved fairly reliable.
Check the pump will run ok on a VSD - pumps can be awkward things to start with a VSD. If you have the choice, a rotary or centrifugal pump is much easier to control. We ended up using ABB's ACS100 drive with a displacement pump
. The drive is controlled by a 4-20mA signal from our DCS and has proved fairly reliable.- Status
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