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type of motor and starter? 1
- Thread starter lin111
- Start date
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1
- #2
Hello
the problem is not that simple. It really depends on 2 main things: application and bus strength.
1. Application. You may need a VSD on a small potable water pump that has a 1.5 kW motor, and you may want to DOL a 250 kW exhaust fan or a 400 kW fire pump. The application is an important consideration.
2. Bus strength. You need to model what is happening to the bus voltage during starting. For instance, you can easily DOL a 400 kW motor as long as you have a nice strong system ahead of it. The MVA during starting DOL must be worked out and compared to bus MVA (short circuit fault available) and other running loads need to be considered.
HTH
the problem is not that simple. It really depends on 2 main things: application and bus strength.
1. Application. You may need a VSD on a small potable water pump that has a 1.5 kW motor, and you may want to DOL a 250 kW exhaust fan or a 400 kW fire pump. The application is an important consideration.
2. Bus strength. You need to model what is happening to the bus voltage during starting. For instance, you can easily DOL a 400 kW motor as long as you have a nice strong system ahead of it. The MVA during starting DOL must be worked out and compared to bus MVA (short circuit fault available) and other running loads need to be considered.
HTH
I would suggest you decide whether you will be needing a Nema or IEC rated starter. Select the manufacter which is a matter of your choice. Then visit the website of the manufacture and select your product. Almost all electrical distributor websites are easy to navigate. You will need to know the voltage at which the motor will be running and the full load amps the motor is plated for. This information is located on the data plate on the motor. Also consider service factor of motor when sizing your overload. Also consider if the coil operating the starter is a control voltage or across the line voltage. I am including a link to Allen Bradleys website. Good luck
Hope this helps
Hope this helps
jbartos
Electrical
- Jan 15, 2000
- 6,440
- Thread starter
- #5
thank you for the info.
My problem, I was given 2 tables from 2 different sources for starting method.Both sources are different in rating power for equipments. Source A used <2.238kW for DOL, while source B used <5kW for DOL. Source A used 2.238-7.46 kW for Starr Delta/Auto trans ,while 5-15kW for Star-Delta. For the rest ,source A used Rotor Resistance and source B used Auto trans.
Therefore, I need clarification on both rating,which one to follow.
Thank you
My problem, I was given 2 tables from 2 different sources for starting method.Both sources are different in rating power for equipments. Source A used <2.238kW for DOL, while source B used <5kW for DOL. Source A used 2.238-7.46 kW for Starr Delta/Auto trans ,while 5-15kW for Star-Delta. For the rest ,source A used Rotor Resistance and source B used Auto trans.
Therefore, I need clarification on both rating,which one to follow.
Thank you
As JeepXJ has told Application and Bus strength are the prime consideration. Without these 2 factors we will simply grope in dark only. The following may be useful
-The motor will deliver the power required by the application
- The starting characteristisc depends on the load, motor inherent characteristic, and the type of starter.
- The bus strength decides the capacity of the power that can be delivered especially during starting.
-The motor will deliver the power required by the application
- The starting characteristisc depends on the load, motor inherent characteristic, and the type of starter.
- The bus strength decides the capacity of the power that can be delivered especially during starting.
Hello lin111
The science of motor starting includiong motor selection, and starter selection is not well understood or engineered in most situations that I have come across. You are correct in asking these questions.
Firstly, you need to consider the driven load. The driven load has a minimum torque requirement in order to accelerate to full speed in a reasonable time. This determines your minimum starting torque.
Secondly, the motor acts as a transducer to convert amps into newton meters (torque) and this determines the minimum starting current to achieve the torque required by the load. Please note that motors vary dramatically in their ability to convert current into torque during start!!
Thirdly, the starter can control the current/voltage applied to the motor to limit the starting current to that required by the motor to start the load.
Finally, the supply dertermines the maximum starting current that can be delivered to the motor.
If you follow the sequence above and optimise each component, load, motor, starter and supply, you will get the best results.
In many situations, reliance is made that the starter will eventually end up on full voltage and the motor will start the load at that time. In these cases a simple DOL starter would be cheaper and more effective.
If you look at my site, you will find more information on the science of motor starting.
Best regards,
Mark Empson
The science of motor starting includiong motor selection, and starter selection is not well understood or engineered in most situations that I have come across. You are correct in asking these questions.
Firstly, you need to consider the driven load. The driven load has a minimum torque requirement in order to accelerate to full speed in a reasonable time. This determines your minimum starting torque.
Secondly, the motor acts as a transducer to convert amps into newton meters (torque) and this determines the minimum starting current to achieve the torque required by the load. Please note that motors vary dramatically in their ability to convert current into torque during start!!
Thirdly, the starter can control the current/voltage applied to the motor to limit the starting current to that required by the motor to start the load.
Finally, the supply dertermines the maximum starting current that can be delivered to the motor.
If you follow the sequence above and optimise each component, load, motor, starter and supply, you will get the best results.
In many situations, reliance is made that the starter will eventually end up on full voltage and the motor will start the load at that time. In these cases a simple DOL starter would be cheaper and more effective.
If you look at my site, you will find more information on the science of motor starting.
Best regards,
Mark Empson
jbartos
Electrical
- Jan 15, 2000
- 6,440
Suggestion to lin111 (Electrical) Dec 30, 2003 marked ///\\My problem, I was given 2 tables from 2 different sources for starting method.Both sources are different in rating power for equipments. Source A used <2.238kW for DOL, while source B used <5kW for DOL. Source A used 2.238-7.46 kW for Starr Delta/Auto trans ,while 5-15kW for Star-Delta.
///The source B is providing a larger kW margin. Nature of motor load and motor duty cycles may have influenced that.\\ For the rest ,source A used Rotor Resistance and source B used Auto trans.
///Resistors tend to be more often used. The autotransformers tend to provide smoother start with less energy waste.\\Therefore, I need clarification on both rating,which one to follow.
///The proper recommendation will require additional information, e.g.
1. Describe the motor load nature
2. Describe the motor duty
3. What is the motor rated voltage?
4. Etc.\\\
///The source B is providing a larger kW margin. Nature of motor load and motor duty cycles may have influenced that.\\ For the rest ,source A used Rotor Resistance and source B used Auto trans.
///Resistors tend to be more often used. The autotransformers tend to provide smoother start with less energy waste.\\Therefore, I need clarification on both rating,which one to follow.
///The proper recommendation will require additional information, e.g.
1. Describe the motor load nature
2. Describe the motor duty
3. What is the motor rated voltage?
4. Etc.\\\
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